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Conference: 1 December 2014
Chemical Engineering and Technology (09307516) 37(12)pp. 2175-2184
A rate-based mathematical model was developed for the reactive absorption of H2S in NaOH, with NaOCl or H2O2 as the chemical oxidant solutions in a packed column. A modified mass transfer coefficient in the gas phase was obtained by genetic algorithm and implemented in the model to correct the assumption of instantaneous reactions. The effects of different operating variables including the inlet H2S concentration, inlet gas mass flux, initial NaOH, concentrations of the chemical oxidants in the scrubbing solutions, and liquid-to-gas ratio on the H2S removal efficiency were studied. A genetic algorithm was employed to optimize the operating variables in order to obtain maximum removal efficiency of H2S. The model results were in good agreement with the experimental data. A modified rate-based mathematical model was developed and evaluated in order to predict the removal efficiency of H2S in a packed-bed column with NaOH and chemical oxidant solutions as absorbents. Results of the validated model were adapted to a genetic algorithm to calculate optimal operating variables. Among the most effective operation parameters the initial pH of the alkaline solution was determined. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2026
Renewable Energy (09601481) 256
This study presents the development of a mathematical model to accurately predict the dynamics of salt and water transport in a batch electrodialysis system used for either NaCl desalination or LiCl brine concentration. The primary aim of the model is to simulate the desalination of high-salinity water under specified current density conditions. The governing equations for the electrodialysis stack and associated tanks were formulated and solved using numerical methods. Model predictions were validated against experimental data, demonstrating high accuracy: the deviation between measured and predicted tank concentrations was within ±2 % for both NaCl and LiCl systems. In addition, the study investigated how initial salt concentration, current density, and flow rate influence system performance. The results show that system efficiency is significantly affected by the initial brine concentration. Increasing the salt concentration from 5 wt% to 10 wt% and 20 wt% reduced desalination efficiencies by approximately 67 % and 93 %, respectively. Moreover, salt flux improved with higher current density, with a 71 % increase in desalination observed when current density was raised from 100 A/m2 to 400 A/m2. © 2025 Elsevier Ltd
Publication Date: 2025
Journal of Environmental Chemical Engineering (22133437) 13(6)
In this study, we have developed a two-dimensional (2D), time-dependent mathematical model focusing on the desalination chamber (DC) of CPDCs. The model simulates ion transport mechanisms, including diffusion and migration, under laminar flow with recirculation between the DC and a well-mixed recirculation tank (RT). Governing equations for mass transfer were solved numerically in MATLAB, and the model was validated against lab-scale experimental data, demonstrating good agreement. The model enables detailed analysis of ion concentration profiles and salinity reduction within the DC, offering predictive insights into system optimization and scale-up. Key operational parameters, such as brackish water flow rate, cell height, intermembrane spacing, and electric potential difference (EPD), were systematically investigated through sensitivity analysis. The results highlight the nonlinear effects of design and operating conditions on desalination efficiency and help define optimal ranges for system configuration. Furthermore, by calculating ion-specific mass transfer coefficient, Sherwood–Reynolds (Sh–Re) correlations were derived for Na⁺ and Cl⁻. These correlations serve as engineering tools for scaling up CPDC modules and optimizing design without full-scale experimentation. In overall, this modeling framework serves as a foundation for future expansion to multi-chamber, fully coupled models that can capture bioelectrochemical dynamics and power generation, ultimately enabling integrated and scalable design of next-generation CPDC systems. © 2025 Elsevier Ltd.
Publication Date: 2025
Chemical Engineering Journal (13858947) 510
The most cost-effective way to produce hydrogen is by steam reforming of methane. Traditionally, conventional fired burners were used for this purpose, despite their drawback of large volumes. The present study modeled an industrial convection reformer integrated into a bayonet tube used for methane steam reforming. The key feature of this compact design is that the furnace and reactor tube remain separate and do not make direct contact with each other. This type of reactor has many complexities from various aspects, including multilayer structure, heat transfer mechanisms, and reactions. A multi-scale one-dimensional model is developed to model the reactor, considering the effects of radiative heat transfer based on fundamental principles. A creative approach is employed to calculate the radiation view factor. A hybrid approach is employed to solve the equations, combining the shooting method with the method of lines to optimize CPU time and ensure equation convergence. The results agree well with plant data across various capacities and operating conditions, achieving 86 % methane conversion while maintaining the fixed bed temperature below 830 °C. Notably, neglecting radiation effects can lead to a 16.2 % error in methane conversion predictions and a 6.5 % error in the estimated reformed gas outlet temperature. Sensitivity analysis reveals that increasing flue temperature from 950 °C to 1300 °C increases methane conversion from 55 % to 95 %, while raising feedstock temperature from 380 °C to 500 °C has a smaller effect, increasing conversion from 83 % to 86 %. These findings highlight the model's potential for accurately predicting the performance of an industrial-scale convective reformer. © 2025 Elsevier B.V.
Publication Date: 2025
Heat Transfer (26884534)
This study explores the experimental and mathematical modeling of energy recovery from hot exhaust gases using a finned tube heat exchanger filled with paraffin. The experimental setup employs air as the heating fluid, water as the cooling fluid, and paraffin with a melting point of 68°C as the phase change material. Key parameters investigated include inlet air temperature, air mass flux during heating, and water mass during cooling. The system's thermal behavior is modeled mathematically by assuming heat accumulation in the paraffin-filled finned tubes. Numerical solutions of the equations are compared with experimental data, and dimensionless parameters are used to evaluate system performance under varying conditions. The model also examines the effects of structural features, such as fin height and the number of fins per unit tube length. The results show that increasing inlet air temperature and reducing air mass flux improve the heating and cooling efficiencies and overall system performance. Enhancing fin height from 0 to 1.5 cm and the number of fins from 0 to 20 within a 10 cm tube length leads to heating efficiency gains of 10.88% and 15%, respectively. © 2025 Wiley Periodicals LLC.
Publication Date: 2024
Chemical Engineering Research and Design (17443563) 212pp. 121-133
Catalytic dehydrogenation of long-chain normal paraffins is the most attractive route for producing of linear alkyl benzene. To make this happen, the radial-flow packed-bed reactors are employed as one of the most efficient currently available technologies. Simplifying assumptions that are sometimes imposed on reactor models to reduce the computational cost may also significantly decrease the accuracy of simulations. Here, it is decided to shed light on this matter by assessing the effect of typical model-simplifying assumptions on simulation results. To this end, one- and two-dimensional semi-homogeneous models are used to simulate an industrial-scale radial-flow packed-bed dehydrogenation reactor under isothermal and adiabatic conditions. Simulations are designed in four 1D isothermal, 1D adiabatic, 2D isothermal, and 2D adiabatic modes to compare different modeling strategies and investigate the effect of flow distribution on the reactor performance. An appropriate LHHW kinetics model is considered for paraffin dehydrogenation and the main associated side reactions over a commercial Pt-Sn-K-Mg/γ-Al2O3 catalyst. The model equations are solved numerically using the finite element method by COMSOL Multiphysics CFD software. The results show a 1–3 % discrepancy between the predictions of one- and two-dimensional models for feed conversion under isothermal and adiabatic conditions. In contrast, the comparison of isothermal and adiabatic results for each one- and two-dimensional models indicate a discrepancy of 33–36 %. Furthermore, the two-dimensional model shows a low non-uniformity in flow distribution under reaction conditions (∼ 0.175), which has a trivial negative effect on paraffin conversion. © 2024 Institution of Chemical Engineers
Madadi avargani, V. ,
Zendehboudi, S. ,
Rahimi, A. ,
Soltani, S. Publication Date: 2022
Applied Thermal Engineering (13594311) 203
Although obstacles on the absorber surface of a solar air heater (SAH) can increase the thermal efficiency by creating turbulent conditions, they might reduce the system's exergy efficiency due to an increase in the pressure drop. In the present work, a 3-dimensional computational fluid dynamics (3D CFD) model is first developed to simulate conical obstacles, and the developed model is then validated using the available experimental data. To find optimal design features, obstacles with various shapes/geometries such as cylindrical, spherical, hemispherical, pyramidal, and cubical are investigated. To attain this goal, a comprehensive study is conducted by including energy, exergy, enviro-exergy, and thermo-hydraulic analyses. The results reveal that vertical cylindrical obstacles have better performance than other geometries as well as a flat absorber without obstacles. The average daily thermal efficiency of the system is increased by 69.16%, and the exergy efficiency of the system is increased by 103.16%. The relative CO2 reduction potential (RCDRP) for a SAH with vertical cylinders is improved up to 168.7%. In addition, the vertical cylinder with a daily average thermo-hydraulic performance parameter of 1.2 shows the greatest thermo-hydraulic performance parameter (THPP) among other geometries, and the pyramidal obstacle with the THPP of 0.66 has the minimum performance. © 2021 Elsevier Ltd
Joulazadeh, M. ,
Rahimi, A. ,
Mirmohammadi, S.J. ,
Kanani, M. ,
Dadkhah, S. ,
Zarean, M. Publication Date: 2022
Industrial and Engineering Chemistry Research (15205045) 61(2)pp. 1179-1191
The benzene dehydration process is of vital significance in the industrial scale especially in linear alkyl benzene production plants. In the present work, different zeolites were utilized for elimination of water from benzene, and their water removal efficiencies were compared. The type of adsorption isotherm for the selected adsorbent (4A zeolite) was examined, and the experimental data were well-fitted with the Langmuir isotherm. The obtained results in kinetics studies suggested that the external and overall mass transfer coefficients are improved when the stirring rate was increased up to 100 rpm and remained constant with further increase in the agitation speed. Furthermore, a continuous setup was designed for investigating the effect of operational parameters on the breakthrough curve characteristics. The highest break time (612 min) was achieved when benzene’s superficial velocity and adsorption bed’s length were set at 0.002 m/s and 30 cm, respectively. The practicability of the 4A zeolite for commercial benzene dehydration applications was verified by its acceptable performance in the reusability study with slight efficiency reduction after four adsorption/desorption cycles. According to the obtained results from breakthrough curves, the internal and external mass transfer coefficients were estimated to be of the same order of magnitude, suggesting that both mass transfer mechanisms are important. Two well-known theoretical breakthrough models including Thomas and Adams–Bohart models were employed to describe the normalized concentration profiles and the predictions of the Thomas model fitted appropriately with the experimental results. © 2021 American Chemical Society
Publication Date: 2022
Journal of Energy Storage (2352152X) 54
A considerable amount of industrial heat is wasted to the atmosphere. This valuable energy could be recovered through fixed bed systems by sensible or latent heat. Mathematical modeling and experimental study of a fixed bed thermal energy recovery system by sensible heat are presented in this paper. An experimental setup was constructed in which air and water were utilized as the charging and discharging process heat transfer fluids, respectively. Three different materials including silica-ceramic, alumina-ceramic, and metal with different sizes were used as the energy storage material. Mathematical modeling was performed at three different levels to analyze the system behavior. The difference among the various modeling levels was in their simplifying assumptions. The resulting equations in each level of modeling were numerically solved. Validation of the modeling results against the experimental data was performed to evaluate the capability of the developed models in prediction of the system actual behavior. Level I model with an average error of 24 % in the charging process and 11 % in discharging process showed unsuitable results, while level II and level III models showed approximately the same and acceptable results with 5 % and 9 % average errors in charging and discharging processes, respectively. Then level II model was selected for prediction of the system performance due to its less complexity compared to level III model. Finally, the influence of the packings material, packing size, and inlet air velocity and temperature on the system performance was predicted using level II model. The system yield had the highest value for all packings at the entering air highest temperature and lowest superficial velocity examined. Metal packings showed better performance and had an experimental system yield of 54 % and 67 % at the entering air highest temperature and lowest superficial velocity, respectively. It was also observed that metal packings outperformed other packings and had the highest experimental yield of 58 % at the same operating conditions. Besides, the highest experimental yield of 61 % was achieved by packings with the smallest size (13 mm) at the highest entering air temperature (140 °C). Based on the findings of this study it can be concluded that lower inlet air velocity and higher inlet air temperature enhanced the recovery efficiency. Besides, the smaller metal packings size showed higher recovery efficiency. © 2022 Elsevier Ltd
Publication Date: 2021
Renewable Energy (09601481) 176pp. 11-24
Trough reflectors can produce a reflected solar flux density that is highly concentrated in specific regions of the receiver surface causing higher thermal losses as well as increasing the likelihood of mechanical damage to the receiver. Time-dependent three-dimensional computational fluid dynamics models were developed and used to compare optical and thermal performances of unglazed tubular, evacuated tubular, and open-aperture evacuated receivers for air heating applications. An evacuated partial-annulus receiver with a non-evacuated open-aperture in the high-density solar flux area produced a more uniform concentrated solar flux distribution. With an open aperture to high-density solar flux, an open-aperture evacuated receiver (i) avoids a dense distribution of reflected solar flux in a specific area of an absorber surface thereby contributing to realizing long-term mechanical integrity, (ii) gives a greater optical performance in all types of trough reflector than an evacuated tubular receiver, (iii) tolerates optical mispositioning and (iv) is particularly suited for use with circular trough reflectors. © 2021 Elsevier Ltd
Publication Date: 2021
Chinese Journal of Chemical Engineering (10049541) 34pp. 61-67
The hydrodynamics and mass transfer characteristics of a lab-scale jet bubbling reactor (JBR) including the gas holdup, volumetric mass transfer coefficient and specific interfacial area were assessed experimentally investigating the influence of temperature, pH and superficial gas velocity. The reactor diameter and height were 11 and 30 cm, respectively. It was equipped with a single sparger, operating at atmospheric pressure, 20 and 40 °C, and two pH values of 3 and 6. The height of the liquid was 23 cm, while the superficial gas velocity changed within 0.010–0.040 m·s−1 range. Experiments were conducted with pure oxygen as the gas phase and saturated lime solution as the liquid phase. The liquid-side volumetric mass transfer coefficient was determined under unsteady-state oxygen absorption in a saturated lime solution. The gas holdup was calculated based on the liquid height change, while the specific interfacial area was obtained by a physical method based on the bubble size distribution (BSD) in different superficial gas velocities. The results indicated that at the same temperature but different pH, the gas holdup variation was negligible, while the liquid-side volumetric mass transfer coefficient at the pH value of 6 was higher than that at the pH = 3. At a constant pH but different temperatures, the gas holdup and the liquid-side volumetric mass transfer coefficients at 40 °C were higher than that of the same at 20 °C. A reasonable and appropriate estimation of the liquid-side volumetric mass transfer coefficient (kla) in a pilot-scale JBR was provided which can be applied to the design and scale-up of JBRs. © 2020 Elsevier B.V.
Madadi avargani, V. ,
Norton, B. ,
Rahimi, A. ,
Karimi, H. Publication Date: 2021
Sustainable Energy Technologies and Assessments (22131388) 47
The temperature of the hot water withdrawn for a solar water heater varies throughout a day. However, for process heat applications, constant temperature water can be required from a solar water heater. This is usually achieved by providing additional auxiliary heat input. Disadvantageously, such extra water heating incurs additional cost and, if met from fossil fuels, produces greenhouse gas emissions. An alternative approach of using a phase change material to moderate variations in the outlet temperature of hot water from the store is examined in this paper using an experimentally-validated CFD model of a solar water heater with a phase change material thermal energy storage in the hot water tank. The CFD model was solved by COMSOL Multiphysics. For a particular solar water heating system, incorporating an encapsulated paraffin wax phase change material has been shown to able to deliver up to 1200 L of hot water at a temperature of 60 °C ± 2 °C for more than 8 h. © 2021 Elsevier Ltd
Publication Date: 2021
Chemical Engineering and Technology (09307516) 44(3)pp. 417-430
A mathematical model entitled varying-bubble model (V-BM) was adapted to simulate a slurry bubble-column reactor, operating in a churn-turbulent regime, based on an axial-dispersion model. This model was theoretically able to estimate the size of forming bubbles at the sparger, variations of each chemical species and catalyst concentration, pressure drop in both gas and liquid phases, change in size and rising velocity of bubbles, as well as gas holdup and specific gas-liquid interfacial area along the reactor axis. A comparison between the V-BM and single-bubble model (S-BM) indicates that the V-BM is better compatible with the experimental data. The results demonstrate that the contribution of mass transfer is much more than the pressure drop in increasing the size of the bubble along the reactor. © 2021 Wiley-VCH GmbH
Publication Date: 2020
Sustainable Energy Technologies and Assessments (22131388) 40
A new type of solar water heating system using an array of parabolic trough collectors (PTCs) was investigated. A coupled simulation technique was used to solve the complex radiation, convection, and conduction heat transfer problem inside the system. The realistic non-uniform heat flux at the walls of the receiver pipe was obtained by optical analysis and was used simultaneously in thermal modeling. A comprehensive model by considering thermal losses under the non-uniformity of heat flux was proposed and verified with experimental data. In the experiments, the water with different inlet temperatures and flow rates was tested. The obtained results demonstrate that the location of the receiver pipe relative to the PTCs significantly affects the system's thermal efficiency. For the system under study, the best position of the absorber pipe was found at the d/f ratio of 0.8. At the optimal position of absorber pipe, the average daily system's thermal efficiency is about 70%, and for an absorber pipe located at the focal line of the collectors, it is less than 60%. It can be concluded that the thermal efficiency of the current system is higher than that of conventional systems under the same conditions. © 2020 Elsevier Ltd
Publication Date: 2020
Industrial and Engineering Chemistry Research (15205045) 59(19)pp. 8984-8994
The reactive absorption kinetics for SO2 removal from flue gas was studied by the use of a saturated solution of Ca(OH)2 in a bench-scale jet bubbling reactor (JBR). Gas- and liquid-side mass transfer coefficients were determined using suitable chemical and physical absorption methods in the JBR. The influences of main parameters, such as the gas flowrate, concentration of inlet SO2, slurry pH, slurry temperature, and sparger submergence depth, were investigated on the rate of SO2 absorption in the JBR. The results obtained from the kinetic study of SO2 absorption by Ca(OH)2 solution showed that the reaction was empirically a pseudo-first-order fast reaction concerning SO2. The mass transfer rate in this process was much lower than the chemical reaction rate; therefore, the mass transfer was the main controlling step. Moreover, a model was proposed and validated for the absorption rate of SO2 into Ca(OH)2 in the JBR. The validation results showed that the calculated values were in good agreement with experimental data. Copyright © 2020 American Chemical Society.
Publication Date: 2020
International Journal of Heat and Mass Transfer (00179310) 159
This paper presents the results of experimental study and mathematical modeling of thermal energy recovery from the flue gases in a packed bed using phase change materials (PCMs). Air and water were used as the heat transfer fluids (HTFs) in the heating and cooling periods, respectively. Paraffin wax was used as the PCM which was encapsulated within polyethylene spheres of 40 mm diameter. The effect of temperature and velocity of the entering air to the bed on the system performance was investigated. In addition, mathematical modeling was conducted, and its numerical results were compared with experimental data. Moreover, two dimensionless parameters (i.e. efficiency and yield) were defined to evaluate the system performance under various operating conditions. The results of this study showed that the efficiency of energy recovery in the considered system could be increased by increasing the inlet gas temperature and decreasing the inlet gas velocity. A 40% increase in inlet gas temperature at constant gas velocity increases the system efficiency by up to 44%. Besides, the mathematical modeling results showed a good agreement with the experimental data. © 2020
Publication Date: 2020
Applied Thermal Engineering (13594311) 170
In this study, a pilot plant of a triangular channel solar air heater with a U-turn airflow pattern was constructed and its performance was investigated using a developed model and experimental data under different operating conditions. A new equivalent radiation-convection circuit was developed as the most sophisticated part of the model. Based on the circuit, a mathematical model with minimal simplifying assumptions was developed to predict the performance of the heater. Compared with the results of an integral model of overall energy balance equations, the developed model showed a 50% reduction of error in prediction of thermal efficiency and outlet air temperature. The maximum thermal efficiency of the system could be obtained at an air mass flow rate of 0.045 kg/s (i.e. mass flux of 8.18 kg/m2.s). Considering the air pressure drop (as the most important penalty) and outlet air temperature, the highest thermohydraulic performance was obtained at a channel internal peak angle of 60°. Besides, the results indicated that to achieve a certain thermal efficiency, the presented solar air heater requires less surface area than that of a flat plate solar air heater for the same input solar radiation. © 2020 Elsevier Ltd
Madadi avargani, V. ,
Rahimi, A. ,
Divband, M. ,
Zamani, M.A. Publication Date: 2020
Thermal Science and Engineering Progress (24519049) 20
Optical and thermal analyses of a parabolic dish collector (PDC) with spiral baffles embedded in the annular space of a cylindrical cavity receiver was studied in windy conditions under realistic non-uniform solar flux distribution. The asymmetric distribution of solar flux on the cavity walls was obtained by a nonsequential ray tracing and finite element (FEM) coupled simulation technique. The performance of the system was analyzed in windy conditions, for two different wind directions of inward and outward of the receiver aperture. The slope error of the dish surface has a significant effect on the distribution of reflected rays on the receiver walls. For higher slope errors, the dishes that are more concave and for smaller slope errors more flat dishes give higher thermal efficiency and have better performance. For a dish collector with a focal point of 1.5 m, when the slope error of the dish surface is only 10 mrad, about 13% of the total solar flux received by the dish is lost. When the slope error of the dish surface increases, the system thermal efficiency decreases, and this reduction is more severe for larger focal points and more flat dishes. The effect of wind direction on the system performance for inward aperture mode is more than that of outward mode, and by increasing the wind speed from 1 to 10 m/s, the system thermal efficiency is reduced up to 50%. © 2020 Elsevier Ltd
Publication Date: 2019
Environmental Engineering Research (2005968X) 24(3)pp. 389-396
The electrical energy consumption (EEC) in removal of NO by a UV/H2O2 oxidation process was introduced and related to removal efficiency of this gas. The absorption-reaction of NO was conducted in a bubble column reactor in the presence of SO2. The variation in NO removal efficiency was investigated for various process parameters including NO and SO2 inlet concentrations, initial concentration of H2O2 solution and gas flow rate. EEC values were obtained in these different conditions. The removal efficiency was increased from about 22% to 54.7% when H2O2 concentration increased from 0.1 to 1.5 M, while EEC decreased by about 70%. However, further increase in H2O2 concentration, from 1.5 to 2, had no significant effect on NO absorption and EEC. An increase in NO inlet concentration, from 200 to 500 ppm, decreased its removal efficiency by about 10%. However, EEC increased from 2.9 × 10-2 to 3.9 × 10-2 kWh/m3. Results also revealed that the presence of SO2 had negative effect on NO removal percentage and EEC values. Some experiments were conducted to investigate the effect of H2O2 solution pH. The changing of pH of oxidation-absorption medium in the ranges between 3 to 10, had positive and negative effects on removal efficiency depending on pH value. © 2019 Korean Society of Environmental Engineers.
Heidari, M. ,
Rahimi, A. ,
Amin, M.M. ,
Bina, B. ,
Sami, S. ,
Nourmoradi, H. ,
Mohammadi-moghadam, F. ,
Norouzi, S. Publication Date: 2019
Environmental Progress and Sustainable Energy (19447450) 38(6)
Mathematical modeling of biofiltration systems improves our understanding and design of such complex systems. This study focused on the theoretical and technical aspects of the modeling of xylene biofiltration in the absence and presence of a nonionic surfactant. In this regard, a mathematical model was developed based on mass balance principles in gas and biofilm phases. The developed model was calibrated and validated using the experimental data obtained from a lab-scale scoria-compost biofilter, which operated for 151 days in the absence and presence of Tween-20, a nonionic surfactant. First, the model was calibrated using the experimental data obtained at empty bed retention time (EBRT) of 90 s and then validated with the data obtained at two other EBRTs. The biofilter provided maximum elimination capacities (ECmax) of 97.5 and 93.6 g m−3 hr−1, respectively, in the absence and presence of the surfactant at EBRT of 90 s. The corresponding predicted ECmax values were 99.9 and 95.7 g m−3 hr−1, respectively. Both model output and experimental data revealed that the nonionic surfactant improved the performance of the biofilter at moderate inlet loading rates. Various statistical measures, including fractional bias, average absolute relative error, and coefficient of determination (R2), showed good agreement between experimental data and estimated model predictions. Sensitivity analysis of the model showed that the specific surface area and bioreactor length affected strongly the results of the model. In general, the results of this study would in turn form the design basis for engineering purposes. © 2019 American Institute of Chemical Engineers
Publication Date: 2018
Desalination (00119164) 433pp. 48-55
The performance of humidifier was studied in a solar humidification-dehumidification desalination in which dehumidification is carried out by compression. The modified mathematical models were developed to investigate the effect of operating condition on humidifier performance. The modeling results were evaluated by experimental data and compared with those of another mathematical modeling. The results showed, in the mathematical model with insulation effect the model precision increases compared to the model without insulation effect and the absolute error is decreased up to 2.4% based on experimental data. © 2017
Publication Date: 2018
Chemical Engineering and Processing - Process Intensification (02552701) 133pp. 303-311
An experimental investigation is performed for the desulfurization of model and real fuel oil samples through one-pot extraction combined with oxidation method with an acid catalyst under UV-irradiation. The kinetics of desulfurization process is obtained by fitting the data taken from a pilot-scale reactor. The effects of various operating parameters on the desulfurization efficiency and the optimal process condition were statistically analyzed using Taguchi experimental approach. The most important parameters affecting the desulfurization efficiency are temperature and the amount of acid catalyst. The obtained optimum conditions are applied to the three real fuel samples. The results of applying UV assisted and ultrasound assisted desulfurization are compared. Both methods have high desulfurization efficiencies about 90% for kerosene fuel. The desulfurization efficiency of about 75% for high sulfur diesel is obtained after a two-stage UV assisted desulfurization process. The results show that in the same conditions UV assisted process consumed ten times less energy than ultrasound assisted desulfurization. © 2018 Elsevier B.V.
Amin, M.M. ,
Rahimi, A. ,
Bina, B. ,
Nourmoradi, H. ,
Hassanvand, M.S. ,
Mohammadi-moghadam, F. ,
Norouzi, S. ,
Heidari, M. Publication Date: 2017
Process Safety and Environmental Protection (17443598) 107pp. 508-517
This study evaluated the biodegradation of n-hexane as single pollutant, and in a mixture with benzene, toluene, ethylbenzene, and xylenes (BTEX) in a scoria/compost-based biofilter. Initially, the biofilter was fed with n-hexane and maximum elimination capacities (ECmax) of 10.7 and 8.1 g m−3 h−1 were obtained for inlet loading rates (ILR) of 14.0 and 11.6 g m−3 h−1 at empty bed retention times (EBRT) of 138 and 108 s, respectively. Michaelis–Menten kinetic model was well fitted to the experimental EC of n-hexane in the single pollutant condition. In the presence of BTEX, the removal efficiency of n-hexane dramatically decreased from 76 to 21% at EBRT of 108 s. In this condition, BTEX was easily degraded with an ECmax of 110.6 g m−3 h−1 for ILR of 119.1 g m−3 h−1. A competitive inhibition kinetic well described the n-hexane removal in the presence of BTEX with an inhibition constant of 0.151 g m−3. Moreover, the interaction index of benzene with the addition of BTEX was −0.702, indicating the significant inhibitory effect of BTEX on n-hexane biodegradation. This study revealed that, in the biofiltration of n-hexane/BTEX mixture, a significant decrease in BTEX concentration is a prerequisite for the efficient removal of n-hexane. © 2017 Institution of Chemical Engineers
Bashipour, F. ,
Rahimi, A. ,
Nouri khorasani, S. ,
Naderinik, A. Publication Date: 2017
Oil and Gas Science and Technology (12944475) 72(2)
The gas effluents of oil gas and petrochemical industries called off-gas have high H2S concentration that causes environmental pollution and equipment corrosion. Using a spray column the production of sodium sulfide (Na2S) by H2S reactive absorption was studied using Response Surface Methodology to design and optimize the process based on Central Composite Design. An Artificial Neural Network model was used to predict Na2S production. The maximum weight of 15.5% Na2S was achieved at optimum operational of conditions by a numerical and graphical analysis at an initial 19.3% w/w NaOH concentration scrubbing solution temperature of 40°C and liquid-to-gas volumetric ratio of 24.6 x 10-3 v/v. The results show that Na2S production from H2S-rich off-gas is a suitable and reasonable way to achieve Na2S besides removing the principal portion of H2S from off-gas.
Publication Date: 2017
Chemical Engineering and Technology (09307516) 40(6)pp. 1149-1157
An experimental study on NO removal via UV/H2O2 process was conducted in a semi-continuous bubble-column reactor and the effect of some operation parameters including NO initial concentration and gas flow rates on removal efficiency was investigated. Applying UV light increased the efficiency significantly. The steady-state removal efficiency was found to be higher at the lower gas flow rates. The bubble size as an important factor in mass transfer calculations and modeling procedure was determined at different gas flow rates using bubble photographs and image processing technique. In the ranges of flow rates studied here, the gas flow rate had no significant effect on the bubble diameter. A mathematical model was developed to describe the NO removal process. The model predictions were compared with existing experimental data, confirming a good agreement of the data. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2017
Canadian Journal of Chemical Engineering (00084034) 95(6)pp. 1150-1155
Simultaneous absorption of CO2 and SO2 was analyzed using the Taguchi method for NaOH solution in a powder particle spouted bed reactor. Experimental results revealed that CO2 removal efficiency increased as the inlet CO2 concentration inlet gas temperature and Na/C molar ratio increases and decreases as the inlet SO2 concentration and gas flow rate decreases. A 68.564% maximum CO2 removal efficiency was achieved under optimal conditions of 13.55 m3/h gas flow rate 1400 Μg/g of flue gas for inlet CO2 concentration 0.0 Μg/g of flue gas for inlet SO2 concentration 200 °C and 2.4 Na/C molar ratio.
Publication Date: 2017
Journal of Environmental Chemical Engineering (22133437) 5(1)pp. 1244-1251
A mathematical model is introduced for the extractive separation of aromatic from aliphatic hydrocarbons in a counter current rotating disc contactor (RDC). The Mass conservation law is applied for toluene/n-heptane/solvent system to predict the concentration variation of toluene in continuous and dispersed phases along the column length. The obtained results are compared with the available experimental data of a pilot-scale contactor. This model is developed with two perspectives: with plug flow approach and with back mixing effects. The effect of parameters, like inlet solvent flow rate, rotor speed and extraction temperature on the contactor performance is studied. Disregarding back mixing effects for solvents with low viscosity leads to enormous errors in prediction of concentration profiles. An increase in the solvent flow rate and extraction temperature results in higher de-aromatization efficiency of extraction process while the rotor speed does not have noticeable consequence on the final performance of extraction column. © 2017 Elsevier Ltd. All rights reserved.
Publication Date: 2017
Case Studies in Thermal Engineering (2214157X) 10pp. 413-422
This work applies the method of energy and exergy analysis over first step of linear alkyl benzene (LAB) production namely kerosene pre fraction plant, to determine unit energy and exergy performance and loss, besides of opportunities for improvement based on operational data. For this purpose macroscopic energy and exergy balance was developed over main equipment including electro pumps, heat exchangers, air coolers, and distillation columns. The results shows that total energy performance of plant is 92.62% by 19.76 MW energy lost, while from exergy perspective, unit performance is 78.08% by 17.92 MW exergy lost. Maximum local exergy lost occurs in the feed pre heater exchanger by 27% performance which is designed to recover energy from top product of second column, furthermore results shows that upgrading low quality energy in air coolers based on heat pump concept would protect energy and exergy emission to the environment and reduce 40% of total lost energy and 16% of total lost exergy in plant. © 2017 The Authors.
Amin, M.M. ,
Rahimi, A. ,
Bina, B. ,
Mohammadi-moghadam, F. ,
Nourmoradi, H. ,
Heidari, M. Publication Date: 2016
Clean - Soil, Air, Water (18630650) 44(12)pp. 1759-1765
The effect of a non-ionic surfactant, Tween-20, on xylene removal performance of a previously acclimated scoria-compost-based biofilter was evaluated. In the presence of the surfactant, the maximum elimination capacities (ECmax) of 71.0, 84.1, and 93.6 g m−3 h−1 were obtained for xylene inlet loading rates (ILRs) of 114.9, 124.1, and 197.1 g m−3 h−1 at empty bed residence times (EBRTs) of 40, 60, and 90 s, respectively. When the biofilter was fed the nutrient solution with Tween-20, the average removal efficiency (REavg) was increased approximately 13 and 14% at EBRTs of 40 s (ILRavg of 43–47 g m−3 h−1) and 60 s (ILRavg of 61 g m−3 h−1), respectively. This indicates that the surfactant improved the performance of the biofilter at moderate ILRs. However, the removal of xylene was not significantly affected by the surfactant at high ILRs, around which ECmax was achieved. This means that the non-ionic surfactant probably had a positive effect on the biofiltration of xylene when the diffusion through the biofilm, rather than biodegradation rates, appears to be the main process governing the performance of biofilter. Overall, this study showed that Tween-20, in terms of xylene removal efficiency, may not have similar effects on the performance of biofilter at various loading conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Publication Date: 2016
Journal of Energy Engineering (19437897) 142(4)
An exergy and energy analysis on a solar parabolic dish collector (PDC) is carried out. In the experimental conditions the destructed exergy due to solar energy absorption by receiver and heat losses from the receiver end up being approximately 60% waste of total exergy in some cases. The maximum exergy efficiency in the experiments is less than 10%. An objective function for maximizing the exergy efficiency is developed mainly based on heat transfer fluid (HTF) inlet temperature and mass flow rate. Optimization results indicate that the HTF outlet temperature as design parameter can be specified based on the given system application. At optimum values of operating parameters, the maximum destructed exergy due to solar absorption and heat losses from the receiver are less than 45 and 15%, respectively. A parametric study based on the developed objective function shows that exergy efficiency greater than 20% is attainable. In this condition an optimum HTF inlet temperature to the receiver is found to be approximately 310 K. The intensity of solar irradiation has significant effect on the optimum HTF mass flow rate. To achieve the maximum exergy efficiency, depending on solar intensity, the optimum HTF mass flow rate must be selected from optimization results. © 2015 American Society of Civil Engineers.
Publication Date: 2016
International Journal of Environmental Health Engineering (22779183) 5(1)
Aims: In present study, the mass transfer-reaction kinetic parameters of nitric oxide (NO) removal by ultraviolet (UV)/H2O2 process in a bubble column reactor in the presence of SO2 are calculated. Materials and Methods: The mass balance equation for NO through a layer thickness of δ, under the steady state condition is solved, and NO absorption rate is calculated. The value of rate constants and Ha numbers are obtained based on experimental data under different conditions. Results: The calculations indicate that the values of Ha number are >3. The values of rate constants (kobs) are fitted to some empirical equations for different operating conditions. It is observed that the value of kobs increases with an increase in H2O2 concentration and UV radiation intensity while it decreases with an increase in NO and SO2 inlet concentrations. The values of rate constants are in order of 10−5, expect for SO2, which are in order of 10−7. The results reveal that there is a good agreement between calculated and experimental values where the maximum absolute error is 16.18% related to UV light intensities between 0 and 0.012 W/m3. Conclusion: The obtained values of Ha numbers under different condition confirm that the absorption process of gas in the liquid phase is a fast reaction. The maximum error values resulted from a comparison between the calculated NO absorption rates and the experimental ones are acceptable. © 2016 Medknow. All rights reserved.
Naghavi z., ,
Ghoreishi s.m., ,
Rahimi, A. ,
Hadadzadeh h., H. Publication Date: 2016
International Journal of Chemical Reactor Engineering (15426580) 14(1)pp. 143-154
In this research, the kinetics of platinum extraction from a selective linear paraffin dehydrogenation spent catalyst in cyanide solutions at high pressure and temperature was experimentally studied. Three variables, including reaction temperature, initial sodium cyanide concentration in solution and liquid to solid weight ratio were investigated. Based on the design of experiments via response surface methodology (RSM) by computer simulating software "Minitab 16", experiments were carried out at operating conditions including five solution temperatures, five initial concentrations of cyanide solution and five liquid/solid weight ratios. The effects of these operating conditions on the reaction kinetics and extraction time were determined. The obtained kinetics data were fitted into an empirical power-law rate equation. The kinetics model parameters were evaluated by using experimental data via non-linear regression analysis. It was found that the platinum extraction from a selective linear paraffin dehydrogenation spent catalyst in cyanide solution at high pressure and temperature can be appropriately modeled by the proposed correlation in the selected range of operating conditions. © 2016 by De Gruyter 2016.
Publication Date: 2016
Desalination and Water Treatment (19443994) 57(33)pp. 15285-15292
The performance of humidification-dehumidification desalination, in which dehumidification is carried out by compression, was studied experimentally. A test rig was designed and assembled based on a new idea. In this system, the carrier gas is humidified through direct contact with hot water; and after humidification, the humid air is compressed by a compressor and cooled in a heat exchanger to recover the humidity as desalinated water. The effects of water-to-air ratio, water and air inlet temperatures, operating pressure, and condenser temperature on desalination performance were examined. It was found that the increase in temperature of the feed water and/or inlet air to the humidifier increased the water production rate and gain output ratio (GOR) of the system. The water-to-air ratio showed an increasing-decreasing trend in relation to the water production rate and GOR of the system; the best water-to-air ratio was found to be 2. © 2015 Balaban Desalination Publications. All rights reserved.
Publication Date: 2016
Chemical Engineering Research and Design (17443563) 109pp. 180-189
In this article, the reactive absorption of SO2 by seawater is studied in a spray tower experimentally and mathematically. The liquid film formation on the tower wall is implemented in the model and measured experimentally at different operating conditions. The effect of liquid to gas flow rate, initial SO2 concentration in gas phase and initial gas temperature on SO2 removal efficiency is examined. Regarding the importance of liquid droplets hydrodynamics and its effect on the performance of the equipment, the required differential equations for predicting the trajectory and local velocity of droplets are also developed based on the nozzle and spray characteristics and solved simultaneously with other governing equations. In order to survey the effect of nozzle type on removal efficiency, two different types of nozzles are examined. Semi-empirical correlations are proposed for two different nozzles by using experimental data and droplets hydrodynamics model, to predict the amount and the variation of liquid film mass flow rate on the spray tower wall. Results indicate that neglecting the liquid film formation leads to an average of 23% error in predicting the removal efficiency when nozzle type 1 is used, while the calculated error of model by considering the film formation is reduced to 4%. By implementation of droplets hydrodynamics model and applying a modified thermodynamics model for predicting the behavior of the existing chemical reactions, the capability of the spray tower model in predicting the SO2 removal efficiency is enhanced. © 2016 The Institution of Chemical Engineers.
Publication Date: 2015
Desalination and Water Treatment (19443994) 54(6)pp. 1526-1541
The technologies that are used mainly in the seawater desalination industry are reviewed and evaluated in this article. The utilization principles, applications, and problems of these processes are summarized and discussed. The desalination methods are compared with each other for performance ratio (PR), gain output ratio (GOR), unit energy consumption (kWh/m3), or unit operating cost ($/m3) and afterward the preferred method is identified. © 2014, © 2014 Balaban Desalination Publications. All rights reserved.
Publication Date: 2015
International Journal of Environmental Health Engineering (22779183) 4(2)pp. 1-8
Aims: In this study, the potential capability of compost in the simultaneous adsorption of gas-phase n-hexane and benzene, toluene, ethyl benzene, and xylene (BTEX) was studied. Materials and Methods: Batch adsorption technique was used to assess the adsorption properties of compost. The pseudo-first and pseudo-second order kinetics were considered in order to identify the possible mechanism of the adsorption process. Moreover, the suitability of the adsorbent was evaluated using Langmuir, Freundlich and The Dubinin-Radushkevich isotherm models. Results: After 24 h contact time, the adsorption capacity of one g compost was 1.42 mg n-hexane and BTEX for initial concentration of 7.74 mg/l. The adsorption capacities were in order of n-hexane < benzene < toluene < ethylbenzene < xylene. This order is in accordance to the ascending octanol-air partitioning coefficient (KOA) order of the compounds (the lowest for n-hexane and the highest for xylene). The kinetics data proved a closer fit to the pseudo-second order model, while the isotherm experimental data were a good correlation to both Freundlich and Langmuir models. Conclusion: The experimental data show that a material with an organic matrix, that is, raw compost, has a higher adsorption capacity for the gaseous compounds with higher KOA. Overall look to the results of this study indicates that although the raw compost could adsorb gaseous n-hexane and BTEX, its capacity may not be sufficient for the continuous removal of VOCs from the air in the compost-based biofilters, in which biodegradation play a key role. © 2015 Authors. All rights reserved.
Publication Date: 2015
Chemical Engineering Research and Design (17443563) 98pp. 157-167
In a co-current lab-scale spray dryer absorber fitted with a two-fluid nozzle, the removal of carbon dioxide through chemical absorption with NaOH solution as absorbent was investigated experimentally and theoretically. Experimental results showed that in selected ranges of operating parameters, increasing the inlet gas temperature and absorbent concentration has the increasing-decreasing effect on the overall removal efficiency. Also increasing L/G ratio (liquid to gas flow rate), decreasing inlet CO2 concentration and decreasing the droplet mean diameter had favorable effects on overall removal efficiency. Process modeling was done through Computational Fluid Dynamics (CFD) method and using Ansys Fluent 13.0 software. In the three dimensional model of the process the gas phase was modeled as a continuum using the Euler approach and the droplet/particle phase was modeled by the Lagrange approach. An empirical correlation for reaction rate was obtained through experimental data and added to the CFD model of the process as a surface reaction via a user defined function. Predictions of the CFD model were compared to the experimental data. The model prediction in comparison to the experimental trends is fair. © 2015 The Institution of Chemical Engineers.
Publication Date: 2015
Journal of Non-Equilibrium Thermodynamics (03400204) 40(1)pp. 49-61
This study undertakes the experimental and theoretical investigation of heat losses from a cylindrical cavity receiver employed in a solar parabolic dish collector. Simultaneous energy and exergy equations are used for a thermal performance analysis of the system. The effects of wind speed and its direction on convection loss has also been investigated. The effects of operational parameters, such as heat transfer fluid mass flow rate and wind speed, and structural parameters, such as receiver geometry and inclination, are investigated. The portion of radiative heat loss is less than 10%. An empirical and simplified correlation for estimating the dimensionless convective heat transfer coefficient in terms of the Re number and the average receiver wall temperature is proposed. This correlation is applicable for a wind speed range of 0.1 to 10 m/s. Moreover, the proposed correlation for Nu number is validated using experimental data obtained through the experiments carried out with a conical receiver with two aperture diameters. The coefficient of determination R2 and the normalized root mean square error (NRMSE) parameters were calculated, and the results show that there is a good agreement between predicted results and experimental data. R2 is greater than 0.95 and the NRMSE parameters is less than 0.06 in this analysis.
Publication Date: 2015
Energy (18736785) 91pp. 1049-1056
An industrial process is synthesized and developed for decoking of de-hydrogenation catalyst, used in LAB (Linear Alkyl Benzene) production. A multi-tube fixed bed reactor, with short length tubes is designed for decoking of catalyst as the main equipment of the process. This study provides a microscopic exergy analysis for decoking reactor and a macroscopic exergy analysis for synthesized regeneration process. The dynamic mathematical modeling technique and the simulation of process by a commercial software are applied simultaneously. The used model was previously developed for performance analysis of decoking reactor. An appropriate exergy model is developed and adopted to estimate the enthalpy, exergetic efficiency and irreversibility. The model is validated with respect to some operating data measured in a commercial regeneration unit for variations in gas and particle characteristics along the reactor. In coke-combustion period, in spite of high reaction rate, the reactor has low exergetic efficiency due to entropy production during heat and mass transfer processes. The effects of inlet gas flow rate, temperature and oxygen concentration are investigated on the exergetic efficiency and irreversibilities. Macroscopic results indicate that the fan has the highest irreversibilities among the other equipment. Applying proper operating variables reduces the cycle irreversibilities at least by 20%. © 2015 Elsevier Ltd.
Publication Date: 2015
Journal of Non-Equilibrium Thermodynamics (03400204) 40(3)pp. 171-183
The performance of a pilot scale flat plate solar water heater system is investigated theoretically and experimentally. The effect of the operating conditions and characteristic factors of the collector on the system efficiency is studied. A conceptual mathematical model is developed in order to analyze the system behavior in different operating conditions by considering the physical and constructive aspects of the system. The accuracy of the model result is estimated by comparing the model results with the existing experimental data. The highest obtained system thermal efficiency is 45%, and the optimum local values for surface azimuth and tilt angles are obtained at 180 degrees from north and 33 degrees, respectively, for the constructed solar water heater in Isfahan, Iran, with the local latitude of 32.6333°N. © 2015 by De Gruyter 2015.
Publication Date: 2015
Bulletin Of Chemical Reaction Engineering And Catalysis (19782993) 10(2)pp. 155-161
The Pt/γ-Al2O3 catalyst life time was limited by the formation of coke on the external and internal sur-faces of catalyst in dehydrogenation reactors. The kinetics of decoking of dehydrogenation catalyst was studied in a pilot scale fixed bed reactor experimentally. The effects of temperature, oxygen concentra-tion and other operating conditions on decoking process were investigated. A kinetic model was deve-loped to describe the decoking of mentioned catalyst. An objective function was defined as the sum of squares of the deviations among the calculated and plant data. Accordingly the appropriate values were found in order to minimize this function. It was concluded that there was a good agreement be-tween simulation results and experimental data. © 2015 BCREC UNDIP. All rights reserved.
Publication Date: 2015
Chemical Engineering and Technology (09307516) 38(12)pp. 2137-2145
H2S removal from an off-gas stream was performed in a spray column by H2S reactive absorption into a NaOH solution. The individual and interactive effects of three independent operating variables on the percentage of absorbed H2S were investigated: the initial pH of the scrubbing solution, the initial scrubbing solution temperature, and the volumetric liquid-to-gas ratio. The optimum operating variables were determined by response surface methodology (RSM) attaining a percentage of absorbed H2S of 98.7±0.2%. Additionally, the process performance was modeled by an artificial neural network (ANN) to predict the percentage of absorbed H2S. The results showed that the experimental data agreed better with the ANN model than with the RSM results. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2015
Applied Catalysis A: General (0926860X) 489pp. 226-234
The present study provides a dynamic mathematical model for a regeneration process of coked catalysts in a multi-tube fixed-bed reactor. Mass and energy conservation laws are applied to predict the temperature variation of gas and solid phases along the reactor length in two main stages: heating and coke burning. The kinetics of decoking is obtained by fitting the data taken from a pilot-scale reactor. The model results are compared with the experimental data taken from both a pilot-scale and a commercial-scale plant. The effect of operating parameters, including inlet gas flow rate, temperature, and composition on the reactor performance is studied. Controlling the O2 concentration is the best strategy to prevent the catalyst sintering. In order to reduce the regeneration process duration, two strategies are examined: constant and stepwise rising trend of inlet O2 concentration. Using the inlet O2molar-fraction of 5.5% reduces the regeneration duration by about 4 h. © 2014 Elsevier B.V. All rights reserved.
Rezazadeh, M. ,
Esfahani, M.S. ,
Rahimi, A. ,
Ehsani, M.R. Publication Date: 2015
Chemical Engineering and Technology (09307516) 38(5)pp. 759-768
A simplified dynamic mathematical model for a simulated moving-bed adsorption process is presented. The model is adopted to simulate the separation process of p-xylene from the other 8-carbon aromatics by means of the Parex™ technology. Operating conditions and the moving-bed structure for a commercial plant were used and the performance of the unit was simulated. The model results are in good agreement with the findings of similar existing studies. Comparison of the results of this simplified model with those obtained by other researches indicates a considerable decrease in central processing unit (CPU) time. A simple but efficient mathematical model is proposed for performance evaluation of a simulated moving-bed adsorption unit. The proposed model is capable for analyzing the adsorption unit with acceptable accuracy and a lower central processing unit time. It can contribute to the optimization of operating conditions, trouble shooting, and enhancement of productivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2015
Process Safety and Environmental Protection (17443598) 98pp. 342-353
In the present study, a comprehensive non-isothermal model is developed to study the performance of a spouted bed reactor (SBR), in which CO2 is removed at the presence of SO2 by using NaOH solution. For this aim, the stream-tube model is applied for hydrodynamics of solid and gas phases, and then by using the conservation laws of mass and energy, the governing equations for gas and solid phases are derived and solved numerically. The effects of variation of different operating parameters and process conditions are evaluated, and by comparing the model results with the gathered experimental data, the maximum, minimum and average error are obtained. The results indicate that the CO2 removal efficiency increases by increasing the inlet CO2 concentration and by decreasing the inlet SO2 concentration, ratio of superficial gas velocity to minimum spouting velocity and inlet gas temperature. Also, the modeling overall results indicate that by increasing the bed diameter and static bed height, CO2 absorption efficiency increases. © 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Montazerolghaem, M. ,
Seyedeyn-azad, F. ,
Rahimi, A. Publication Date: 2015
Korean Journal of Chemical Engineering (19757220) 32(2)pp. 328-334
H-Y zeolite was prepared with Na-Y zeolite via ion-exchange method. Ni-Y and Ce-Y zeolites were then prepared with H-Y zeolite via solid-state ion-exchange (SSIE) method. The pellet form of the zeolites was employed for removal of thiophene from samples containing 194, 116 and 72 ppmw sulfur in a batch system at ambient condition. The removal of sulfur over the three types of the adsorbents decreased according to the following order: Ce-Y (81.7%) >Ni-Y (75.2%)>Na-Y (51.7%), indicating that the Ce-Y zeolite was the most effective adsorbent for removing of sulfur compounds from gasoline. Adsorption isotherms of thiophene on Ni-Y and Ce-Y zeolites were obtained and correlated with six well-known isotherms. The equilibrium data of thiophene adsorption were well fitted to the isotherms and the corresponding parameters and fitting error criteria of the isotherm equations were obtained. © 2014, Korean Institute of Chemical Engineers, Seoul, Korea.
Montazerolghaem, M. ,
Rahimi, A. ,
Seyedeyn-azad, F. Publication Date: 2014
Chemical Product and Process Modeling (21946159) 9(2)pp. 155-164
In this study, Ni-Y and Ce-Y zeolites are prepared using synthesized Na-Y zeolite through solid-state ion-exchange method. The adsorptive desulfurization of a model gasoline containing 194, 116 and 72 ppmw sulfur is evaluated in a batch system under ambient conditions. A dynamic model is established in order to investigate the performance of the adsorption process. The model predictions are compared with the obtained experimental results for thiophene adsorption on Ni-Y and Ce-Y zeolites from model solution containing different concentrations of thiophene, and a good agreement is observed. The model parameters: diffusivity and mass transfer coefficient are estimated by comparing the model predictions and experimental data. © by De Gruyter 2014.
Publication Date: 2014
Polish Journal of Chemical Technology (18994741) 16(4)pp. 60-65
In this study, the thin-layer drying characteristics of Figs (Ficus carica) are investigated in a pilot scale forced convective dryer. Experiments carried out under various operating conditions including air temperature (40, 50, 60, 70°C), air velocity (0.65, 2.1, 3.45, 4.85 m/s) and air humidity (0.005, 0.010, 0.015 kg/kg) and the effects of these operating conditions on the drying kinetics and the drying time determined. The obtained kinetics data are fitted into a conceptually developed model. The equilibrium moisture content of the dried figs is determined at different values of temperature and relative humidity of air. The values of effective moisture diffusivity (Deff) are obtained from the Fick's second law and a temperature-dependent relation is proposed for this parameter. © by A. Rahimi 2014.
Publication Date: 2014
Chemical Product and Process Modeling (21946159) 9(1)pp. 15-24
The performance of a pilot-scale spray dryer is investigated experimentally and theoretically. The governing equations for flow field, heat and mass transfer, and particle trajectory are solved by applying computational fluid dynamics (CFD). The effects of inlet air temperature and initial particle diameter on the outlet humidity and particle residence time are examined. These parameters should be considered carefully in proper designing of spray dryers especially for the heatsensitive products. The model is validated with an error of 5.5%. Copyright © 2011-2014 by Walter de Gruyter GmbH.
Publication Date: 2014
Heat and Mass Transfer (09477411) 50(9)pp. 1291-1300
An unsteady-state model is developed for primary and secondary stages of freeze drying process of skim milk. The results are compared with those obtained from a quasi-steady-state (QSS) formulation. The QSS formulation is not valid where the applied heat load is high. The applied heat load affects on the drying time the most compared to other parameters like chamber pressure and the radiation surface temperature. © 2014 Springer-Verlag Berlin Heidelberg.
Publication Date: 2014
Petroleum Science and Technology (15322459) 32(11)pp. 1318-1326
A 3D computational fluid dynamics (CFD) model is developed to predict the dispersion of gaseous pollutants released from different stacks in Isfahan refinery in Iran. Three types of turbulent models including the standard k-ε, the RNG k-ε, and the realizable k-ε models are compared and considered. The results of model are compared with the experimental data obtained by measuring the CO2 concentration inside and close to the refinery boundaries. The comparison shows the sufficient precision of model predictions. By using the design of experiment (DOE) technique, the effects of model parameters are investigated on the results. The results of standard k-ε model for Sc t = 0.5 and hr = 2 m, the realizable k-ε model for hr = 2 m, and the RNG.k-ε model for hr = 2.5 m provide more acceptable results when these results are compared with the models responses with ideal values of these parameters. The latter gives some better results for the case of Isfahan refinery. © 2014 Taylor & Francis Group, LLC.
Publication Date: 2014
Environmental Engineering and Management Journal (15829596) 13(10)pp. 2615-2623
This paper presents an optimization procedure to minimize the cost of drying in a solar cabinet dryer based on the results of a mathematical model. The model has been developed previously for performance analysis of a solar cabinet dryer. The optimal values for geometry of the solar collector, mass flux of air through the collector, and initial moisture content are obtained in a way that the drying cost is minimized. The results indicate that to optimize the drying cost, the best values of initial moisture content, air mass flux, the length and the surface area of collector are 9–10 kg/kg (dry basis), 0.03–0.045 kg/m2.s, longer than 2.5 m, and 2.5–3 m2, respectively. The results can help the designers to choose the optimum drying conditions for small scale industrial applications. © 2014, Gh. Asachi Technical University of Iasi. All rights reserved.
Publication Date: 2014
Environmental Engineering Research (2005968X) 19(4)pp. 299-308
This study presents a review on Chemical looping combustion (CLC) development, design aspects and modeling. The CLC is in fact an unmixed combustion based on the transfer of oxygen to the fuel by a solid oxygen carrier material avoiding the direct contact between air and fuel. The CLC process is considered as a very promising combustion technology for power plants and chemical industries due to its inherent capability of CO2capturing, which avoids extra separation costs of the of CO2from the rest of flue gases. This review covers the issues related to oxygen carrier materials. The modeling works are reviewed and different aspects of modeling are considered, as well. The main drawbacks and future research and prospects are remarked. © 2014 Korean Society of Environmental Engineers.
Publication Date: 2014
Journal of Non-Equilibrium Thermodynamics (03400204) 39(4)pp. 183-197
The energy and exergy performance of a parabolic dish collector is investigated experimentally and theoretically. The effect of receiver type, inlet temperature and mass flow rate of heat transfer fluid (HTF), receiver temperature, receiver aspect ratio and solar radiation are investigated. To evaluate the effect of the receiver aperture area on the system performance, three aperture diameters are considered. It is deduced that the fully opened receivers have the greatest exergy and thermal efficiency. The cylindrical receiver has greater energy and exergy efficiency than the conical one due to less exergy destruction. It is found that the highest exergy destruction is due to heat transfer between the sun and the receivers and counts for 35 % to 60 % of the total wasted exergy. For three selected receiver aperture diameters, the exergy efficiency is minimum for a specified HTF mass flow rate. High solar radiation allows the system to work at higher HTF inlet temperatures. To use this system in applications that need high temperatures, in cylindrical and conical receivers, the HTF mass flow rates lower than 0.05 and 0.09 kg/s are suggested, respectively. For applications that need higher amounts of energy content, higher HTF mass flow rates than the above mentioned values are recommended. © 2014 by De Gruyter 2014.
Publication Date: 2014
Desalination (00119164) 341(1)pp. 120-125
In this communication, a new Humidification De-Humidification process desalination technology is identified which has some advantages (such as: high energy performance, high recovery flow rate, energy recovery and so on) in comparison with other similar methods; this technology is named "Humidification Compression". This method is simulated by a commercial process simulation software and the results are compared with two conventional methods. It is seen that, gain output ratio (GOR) for proposed method is higher than conventional methods; also capital cost per product for proposed method is lower than two others. © 2014 Elsevier B.V.
Publication Date: 2014
Separation Science and Technology (15205754) 49(3)pp. 317-328
Absorption of CO2 by monoethanolamine, diethanolamine, and triethanolamine solutions in a lab-scale packed bed tower was investigated. A model for analyzing the heat and mass transfer mechanism in the presence of reaction was developed and validated using the measured data for MEA and TEA solutions and the results were compared with the others' experimental data. The well-known correlations for determining Henry's constant, as a critical parameter in the presented model, were evaluated and it was shown that the available correlations are often limited to a narrow range of operating conditions which could limit the applicability of the available models. © 2014 Copyright Taylor and Francis Group, LLC.
Amin, M.M. ,
Rahimi, A. ,
Bina, B. ,
Heidari, M. ,
Mohammadi-moghadam, F. Publication Date: 2014
Journal Of Environmental Health Science And Engineering (2052336X) 12(1)
The removal of xylene vapors was studied in a biofilter packed with a new hybrid (scoria/compost) packing material at various inlet loads (IL) and empty bed residence times (EBRT) of 90, 60, and 40s. The best performance was observed for EBRT of 90s, where a removal efficiency of 98% was obtained under steady state condition for inlet xylene concentration of 1.34 g m-3, while a maximum elimination capacity of 97.5 g m-3h-1was observed for IL of 199.5 g m-3h-1. Carbon dioxide production rates and the microbial counts for xylene-degraders followed xylene elimination capacities. Overall look to the results of this study indicates that the scoria/compost mixture could be considered as a potential biofilter carrier, with low pressure drop (here <4 mm H2O), to treat air streams containing VOCs. © 2014 Amin et al.
Publication Date: 2014
Drying Technology (15322300) 32(14)pp. 1655-1663
An image processing technique was used to predict the size distribution of the high speed, fine droplets at downstream of an air blast atomizer. The spray visualization setup consisted of UV lamps as light source, a stroboscope for slowing down the droplet motion, and a digital camera to capture the droplet images. The experiments were carried out at different liquid flow rates with various nozzle diameters. Two key unknown parameters (spray half angle and dispersion angle) of the air blast atomizer model in Fluent were obtained from these experiments. Using the obtained parameters and other structural parameters, the spray modeling was performed, and the Rosin–Rammler distribution was obtained and compared with those obtained from image processing technique through a diagnostic matrix. Regarding the kappa value, the agreement between predictions of the Fluent model and the image processing technique was moderate. © 2014, Copyright Taylor & Francis Group, LLC.
Publication Date: 2014
Separation Science and Technology (15205754) 49(7)pp. 988-998
Flue gas desulfurization of industrial plants using seawater is studied experimentally and theoretically in a counter-current packed-bed tower. Experiments are carried out based on a 16-run orthogonal array of the Taguchi method (five factors, four levels) and ANOVA table created to determine the most significant controlling factors on SO2 removal efficiency. Liquid flow rate (1.5-4 l/min), gas temperature (50-350°C), gas flow rate (8-20 m3/h), and SO2 concentration (500-2000 ppmv) are revealed as important factors, while the pH of seawater (8-9.5) is not significant. Experimental results show that an increase in gas temperature causes a decrease in the removal efficiency. A mathematical model is developed for the removal of SO2 by seawater for non-isothermal operating conditions. In the modeling procedure the equilibrium reactions of eight dissolved species within the liquid phase are considered to calculate the kinetic of reaction correctly. The results of this study confirm the capability of seawater for SO2 removal in packed-bed towers. Copyright © Taylor & Francis Group, LLC.
Publication Date: 2013
Chemical Engineering and Processing - Process Intensification (02552701) 70pp. 289-291
A one-dimensional model published previously for spouted beds is evaluated. Certain errors exist in the governing equations which are modified and corrected in this Letter to Editor. It is confirmed that this is an efficient model as it needs few number of empirical correlations to solve. © 2013 Elsevier B.V.
Publication Date: 2013
Journal of Analytical and Applied Pyrolysis (01652370) 104pp. 707-709
A kinetic model published previously for pyrolysis of tyre in conical spouted beds is evaluated. Certain errors exist in the model constants which are modified and corrected. © 2013 Elsevier B.V. All rights reserved.
Publication Date: 2013
International Journal of Mineral Processing (03017516) 124pp. 58-66
A general model is developed for moving-bed reactors where multiple non-catalytic gas-solid reactions and multiple gas-phase reactions take place. The grain model is adopted and modified as the kinetics model for multiple non-catalytic gas-solid reactions case. The proposed model covers the modified grain model and provides the local degree knowledge of the origin solid reactant along with the intermediate solids within the porous pellets. The heat transfer by convection, conduction and radiation in the gas bulk and the radial temperature distribution of the pellet are considered. The model predictions for solid conversion, gas temperature, and gas concentrations are obtained for an industrial moving-bed reactor for Fe2O3 pellets reduction. This proposed model well simulates the experimental data with an average 1.2% error. © 2013 Elsevier B.V.
Publication Date: 2013
International Journal of Mineral Processing (03017516) 124pp. 67-74
The general model developed in the first part of this study is based on the grain model. In order to determine the overlapping range of this kinetic model and the unreacted shrinking core model the attempt is made in this part of the article to identify the simplest and most accurate model. Although under certain circumstances the found results in both the models are almost similar, the developed model based on grain model predicts the experimental data much better than the shrinking core model. The simplicity of the model's results in the outcome is due the predominant diffusional regime. This regime is revealed where the pellet size is big; nevertheless, the results of two models are not similar even in small values of pellet porosity. Two correlations for determining effective diffusivity are tested and it shows a direct effect on the overlapping range of both the models. © 2013 Elsevier B.V.
Publication Date: 2013
Drying Technology (15322300) 31(3)pp. 295-307
A mathematical model has been developed for unsteady-state operations in spouted bed dryers based on a streamtube concept. This model predicts radial distributions of heat and mass inside the bed using a set of simple plug-flow stream tubes. The model's predicted results for moisture content and air temperature have been compared with the experimental data for drying of green peas in a spouted bed and a good agreement has been observed with a mean relative deviation of 4.4%. When significant radial distributions exist inside the bed, large discrepancies are observed between the streamtube and plug flow models predictions. The discrepancies become wider when lower air temperature and higher air humidity are applied, whereas particle diameter and air flow rate are not effective in a pilot-scale dryer. © 2013 Copyright Taylor and Francis Group, LLC.
Publication Date: 2013
Drying Technology (15322300) 31(9)pp. 975-989
Spouted bed technology is highly dependent upon empirical correlations for design and modeling purposes. In order to carry out a state-of-the-art review on the hydrodynamic parameters needed for design and performance evaluation of spouted beds, a detailed analysis is made regarding the reliability of various hydrodynamic correlations of spouted beds reported in the literature. Spout diameter, maximum spoutable height, and minimum spouting velocity as critical hydrodynamic parameters are evaluated. Many correlations show poor predictions for calculating these parameters in certain operating conditions. Cecen's equation[ 1 ] successfully predicts the maximum spoutable bed height for fine particles. For large particle diameters, the equation of Morgan and Littman[ 2 ] is valid. The equations of McNab[ 3 ] and Malek et al.[ 4 ] for determining spout diameter and the equations of Grbavcic et al.[ 5 ] and Mathur and Gishler[ 6 ] for calculating the minimum spouting velocity are recommended. Although some researchers have tried to modify the old equation of Mathur and Gishler[ 6 ] to improve its predictions of minimum spouting velocity, this equation is more successful than any other equation proposed yet for a wide range of operating conditions. © 2013 Copyright Taylor and Francis Group, LLC.
Publication Date: 2013
International Journal of Refrigeration (01407007) 36(4)pp. 1233-1242
Exergy analysis was applied to investigate the performance of a domestic refrigerator originally manufactured to use 145 g of R134a. It was found that the highest exergy destruction occurred in the compressor followed by the condenser, capillary tube, evaporator, and superheating coil. Taguchi method was applied to design experiments to minimize exergy destruction while using R600a. Taguchi parameters were selected by the obtained results from R134a and an experiment using 60 g of R600a, which indicated similar results as R134a. Based on the outcomes, R600a charge amount, condenser fan rotational velocity and compressor coefficient of performance were selected for the design. The analysis of variance results indicated that R600a charge amount was the most effective parameter. At the optimum condition, the amount of charge required for R600a was 50 g, 66% lower than R134a one, which not only brings economic advantages, but also significantly reduces the risk of flammability of the hydrocarbon refrigerant. © 2013 Elsevier Ltd and IIR. All rights reserved.
Publication Date: 2013
Desalination (00119164) 317pp. 23-31
This study presents an experimental and theoretical energy and exergy analysis for a solar desalination system consisting of a solar collector and a humidification tower. A mathematical model is developed and the air and water characteristics across the collector and the humidification tower are predicted. The model is verified against measured data for air temperature, water temperature, and air humidity. The results indicate the high exergy efficiency of the solar desalination system. The overall exergy efficiency increases by a decrease in humidification tower length, a decrease in inlet air temperature, and an increase in tower diameter. •The model presented here well predicts the predictions of a solar desalination system.•Large exergy efficiency is observed for the solar desalination system.•The overall exergy efficiency is decreased with an increasing length of the humidification tower.•Higher than a certain value for length tower, there is no further decrease in exergy efficiency.•Exergy efficiency increases by decreasing inlet air temperature, and increasing tower diameter. © 2013 Elsevier B.V..
Publication Date: 2013
Korean Journal of Chemical Engineering (19757220) 30(6)pp. 1201-1206
Drying kinetics of quince (Cydonia oblonga) in mashed form was investigated in a pilot scale freeze dryer. Experiments were conducted in various operating conditions, and the effects of initial moisture content, heat load power and the initiation time of heat application were investigated on drying rate and performance of the dryer. The experimental data of the moisture changes were correlated through non-linear regression and an appropriate mathematical model was obtained. The drying kinetics of the sample was determined on the basis of the pre-identified mathematical models as a function of operating parameters. The obtained values of mean relative percent deviation for the kinetics models of the primary and secondary drying stages are 7.47% and 5.94%, respectively. It is revealed that by applying a high heat load power at the beginning of the process the drying time is reduced significantly. © 2013 Korean Institute of Chemical Engineers, Seoul, Korea.
Publication Date: 2013
Chemical Engineering and Technology (09307516) 36(3)pp. 500-506
A semi-empirical kinetic correlation was obtained through a shrinking core model assumption for reactive absorption of CO2 with NaOH solution by applying response surface method analogy in a laboratory-scale spray-dryer absorber. The effect of approach temperature, absorbent concentration, nozzle diameter, and L/G ratio on the kinetic coefficient was studied and the optimum operating conditions to reach the maximum absorption were determined. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2013
Journal of Solar Energy Engineering (15288986) 135(3)
A mathematical model is presented to analyze the performance of a counter-current solar desalination system. Besides, the heat transfer equations, the mass transfer is also considered to improve the model precision. A new approach is used for analyzing the radiative heat transfer in these systems. A low enough value for feed flow rate, a moderate value for glass temperature, taking the advantage of high flux at the appropriate time and appropriate insulation of the floor could effectively increase productivity. The system length is also a significant parameter. The model can be sufficiently extended for other continuous solar desalination systems. Copyright © 2013 by ASME.
Publication Date: 2013
Journal of Petroleum Science and Engineering (09204105) 108pp. 222-229
Applying empirical correlations to estimate various parameters used in a mathematical model is inevitable. In this study, a mathematical model is developed for a packed-bed air dehumidifier and the impact of some well-known empirical correlations available in literature is evaluated on the model's predictions and accuracy. The results reveal that in designing an air dehumidifier, using different empirical correlations may lead to very different predictions for the required bed height. The equations of Onda et al. (1968) and Rocha et al. (1996) to calculate the effective interfacial area, the equation of Treybal (1981) to calculate the heat transfer coefficient, and the equations of Chung et al. (1996) to calculate the mass transfer coefficient show precise results and increase the reliability of the mathematical models.© 2013.
Publication Date: 2012
Drying Technology (15322300) 30(6)pp. 574-582
The wall deposition phenomenon in a pilot-scale spray dryer was investigated based on mathematical modeling and experimental trials. For this purpose, the governing equations were obtained and solved numerically by applying a mathematical modeling technique and an open-source computational fluid dynamics (CFD) software. The wall deposition, velocity distribution of the existing phases, and droplet trajectory in the drying chamber were determined. The effect of the operating parameters including the feed flow rate, inlet concentration of dissolved solid, and initial droplet diameter on the air flow pattern, droplet trajectory, and wall deposition was investigated. Through the experiments, the wall deposition of powder product in different positions of the drying chamber was measured. In modeling part of this study, we attempted to determine the effect of particle diameter on the percentage of wall deposition and the position where it occurred.The model results obtained for wall deposition were compared with collected experimental data and good agreement was observed. © 2012 Copyright Taylor and Francis Group, LLC.
Publication Date: 2012
Drying Technology (15322300) 30(2)pp. 128-137
In this study, green pea drying is investigated experimentally in a laboratory-scale spouted bed dryer. A mathematical model is also developed to investigate the effect of operating conditions on the performance of the system. The effect of operating parameters such as inlet air temperature, particle size, and flow rate of the drying air on the performance of the dryer are studied experimentally. In order to build the process model, it is necessary to analyze the transport in both solid and gas phases. A complete set of equations with no adjustable parameters is derived for existing zones in the spouted bed dryer in order to predict variations in the temperature and moisture content of the solid and gas phases with time for batch drying conditions. Model results are compared with corresponding experimental data. Agreement between the model results and experimental data is good. © 2012 Copyright Taylor and Francis Group, LLC.
Publication Date: 2012
Computers and Chemical Engineering (00981354) 38pp. 44-51
A mathematical model is developed for simulation of dynamic behavior of coke-burning process in a hydrocracker reactor with an array of 4 fixed beds. The model is used for parametric study of the coke burning process. Results show that the effective parameters are inlet oxygen concentration, the flow rate of carrier gas and temperature within the beds. The effect of referred parameters on performance of regeneration of an industrial hydrocracker reactor is investigated for a real case and the optimum values of operating conditions are predicted. The optimum value for oxygen concentration during regeneration obtained as 0.85. mol%, with a predicted regeneration time of around 76. h. © 2011 Elsevier Ltd.
Publication Date: 2012
International Journal of Modelling and Simulation (02286203) 32(1)pp. 49-56
The performance of a cylindrical packed bed waste heat recovery system was analyzed using different mathematical models. The models were compared in terms of accuracy, precision and computational cost. Then, the best model was used to calculate the heat recovery yield and the thermal efficiency of system. The results show that the yield of heat recovery for packed bed increases when the diameter of the particles and the temperature of the inlet gas decreases. Moreover, by increasing the velocity of the inlet gas and time of heating period the yield of the system increases. The efficiency of apparatus increases by decreasing particle diameter, decreasing inlet gas velocity and increasing the inlet gas temperature.
Publication Date: 2011
Applied Thermal Engineering (13594311) 31(5)pp. 670-673
Maryam Moradi, Amir Rahimi, and Mohammad Sadegh Hatamipour from Department of Chemical Engineering, Faculty of Engineering, University of Isfahan, Iran, critically analyze an article titled 'Experimental and numerical investigation of solid particles thermal energy storage unit' by A. Benmansour, M.A. Hamdan, and A. Bengeuddach. Similar boundary and initial conditions are used for comparison of the two referred models. Both of the models have been developed with the assumption that when the temperature of PCM reaches to its melting point, the phase change period begins and the PCM temperature during this period remains constant. After this process is finished and all of the solid paraffin wax melted the temperature begins to rise. In the next section the results of the present model are presented and compared with the results of Benmansour and colleagues, model and also with corresponding experimental data. Unfortunately, the mathematical model results which were reported by Benmansour are not in agreement with this theory.
A note on the article titled: Unsteady-state operation of trickle-bed reactors, by: Lange, R., Schubert, M., Dietrich, W., Grunewald, Published in Chemical Engineering Science, 59, 5355-5361 (2004)
( Article . )
Publication Date: 2011
CHEMICAL ENGINEERING SCIENCE (00092509) 66(1)pp. 115-116
Publication Date: 2011
Chemical Engineering Research and Design (17443563) 89(6)pp. 616-620
In the present study, the carbonation reaction of hydrated lime in semi-dry condition is investigated experimentally in a laboratory-scale spouted bed reactor. Results show that for operating conditions where the concentration of CO2 is low, the capture efficiency is raised by increasing the inlet CO2 concentration. Additionally, because of the inconsistency between the experimental reaction rate and the calculated values based on the previous proposed equations, a new rate equation is introduced that considers the dependency of CO2 concentration too. To validate the proposed equation, its predictions were compared with another set of experimental data. © 2010 The Institution of Chemical Engineers.
Publication Date: 2011
Separation Science and Technology (15205754) 46(1)pp. 105-118
This study presents mathematical modeling of non-isothermal gas absorption in a coaxial two impinging streams absorber (TISA). The governing equations on the performance of these ideal systems for three different models including the plug flow model, the tanks-in-series model, and Markov-Chain analysis are used to model the real system behavior. In order to approach a realistic model, the size distribution of the liquid droplets also is implemented in the models. The comparison between the results of the models with corresponding reported experimental data shows the desirable accuracy of the suggested models. Also, the effects of some operational variables on the average absorption rate and final removal efficiency of TISA are investigated. Results show that for similar operating conditions the removal efficiency of impinging streams absorber is higher than the conventional systems. © Taylor & Francis Group, LLC.
Publication Date: 2011
Chemical Engineering and Processing - Process Intensification (02552701) 50(1)pp. 104-112
In this paper, the shortage effect of neglecting heat and mass transfer phenomena in mathematical descriptions of pressure drop through venturi scrubbers is studied. For this purpose, a descriptive model is presented with particular emphasis on the mass and energy equations. There is a correction factor introduced, for the first time, and correlated to improve the model predictions in the divergent section. The results indicate that pressure drop prediction is greatly affected by the simplified assumptions of the existing models. In fact, the occurrence of heat and mass transfer phenomena between two phases decreases the pressure drop intensively. Therefore, neglecting the undeniable effects of these phenomena will lead to some large errors. These errors are enhanced in higher gas temperatures, liquid, and gas flow rates, but the gas humidity has a negligible effect. © 2010 Elsevier B.V.
Publication Date: 2011
Drying Technology (15322300) 29(7)pp. 825-835
A dynamic mathematical model for drying of agricultural products in an indirect cabinet solar dryer is presented. This model describes the heat and mass transfer in the drying chamber and also considers the heat transfer and temperature distribution in a solar collector under transient conditions. For this purpose, using conservation laws of heat and mass transfer and considering the physical phenomena occurring in a solar dryer, the governing equations are derived and solved numerically. The model solution provides an effective tool to study the variation of temperature and humidity of the drying air, drying material temperature, and its moisture content on each tray. The predicted results are compared with available experimental data. It is shown that the model can predict the performance of the cabinet solar dryer in unsteady-state operating conditions well. Furthermore, the effect of some operating parameters on the performance and efficiency of dryer is investigated and compared with selected published data. © 2011 Taylor & Francis Group, LLC.
Publication Date: 2011
Energy (18736785) 36(5)pp. 2847-2855
In the present study, using a previously developed dynamic mathematical model for performance analysis of an indirect cabinet solar dryer [1], a microscopic energy and exergy analysis for an indirect solar cabinet dryer is carried out. To this end, appropriate energy and exergy models are developed and using the predicted values for temperature and enthalpy of gas stream and the temperature, enthalpy and moisture content of the drying solid, the energy and exergy efficiencies are estimated. The validity of the model for predicting variations in gas and solid characteristics along the time and the length of the solar collector and/or dryer length was examined against some existing experimental data. The results show that in spite of high energy efficiency, the indirect solar cabinet dryer has relatively low exergy efficiency. Results show that the maximum exergy losses are in midday. Also the minimums of total exergy efficiency are 32.3% and 47.2% on the first and second days, respectively. Furthermore, the effect of some operating parameters, including length of the collector, its surface, and air flow rate was investigated on the exergy destruction and efficiency. © 2011 Elsevier Ltd.
Publication Date: 2011
International Journal of Chemical Reactor Engineering (15426580) 9
Reactive absorption of CO2 with NaOH as absorbent was evaluated experimentally in a lab scale spray dryer. Taguchi method was used for design of experiments. Results showed that the most important factors are inlet CO2 concentration, nozzle size, absorbent concentration and temperature, respectively. The optimum conditions are 150°C for temperature, 10% (w/w) for NaOH concentration, 10% for CO2 concentration, and 0.5 mm for nozzle diameter. By conducting experiments under the optimum conditions, the removal efficiency was obtained as 69.4%. Copyright © 2011 The Berkeley Electronic Press. All rights reserved.
Publication Date: 2011
Drying Technology (15322300) 29(14)pp. 1648-1655
In this study, a drying kinetics model for predicting the drying of green pea particles using a bench-scale spouted bed with heat carriers is investigated. The experiments were carried out under different operating conditions. The effect of inert particle diameter, inert particle type, and the mass ratio of inert particles to green peas was examined based on the performance of the dryer and the rate of drying. As expected, the rate of drying increased with increased mass ratio of inert particles to green peas and thermal diffusivity of inert particles. © 2011 Taylor & Francis Group, LLC.
Publication Date: 2011
Separation and Purification Technology (13835866) 80(3)pp. 509-518
In present study, a non-isothermal comprehensive mathematical model is developed for performance analysis of a spouted bed reactor in which CO 2 is removed by using a semi-dry chemical absorption process. For this aim, based on the hydrodynamic model of streamtube and equations of mass and energy balances for a reactive absorption process, the governing equations for gas and solid phases in three different regions of the bed are derived and solved numerically. The effects of variation of different operating parameters and process conditions are investigated and corresponding maximum, minimum and average values of errors are obtained by comparison of the model results with existing experimental ones. Results show that the superficial gas velocity and the approach to saturation temperature have considerable effects on CO 2 removal efficiency, while Ca/C molar ratio, inlet concentration of CO2 and static bed height of reactor do not influence performance of the reactor significantly. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011
Chemical Engineering Research and Design (17443563) 89(6)pp. 777-784
A mathematical model is developed for investigation of SO2 removal in a powder particle spouted bed (PPSB) for non-isothermal operating condition. For this aim, the stream-tube model which was already validated for such systems is applied for hydrodynamics of solid and gas phases, and then by using the conservation laws of mass and energy, the governing equations for gas and solid phases are derived and solved numerically. The published experimental data in the literature are used to validate the accuracy of the proposed model. The results show that the model is capable of predicting the behaviour of this system properly. Also the optimum performance of this system is investigated by studying the effects of different parameters such as bed height, molar ratio of sorbent to acid gas (Ca/S) and inlet concentration of SO2. © 2010 The Institution of Chemical Engineers.
Publication Date: 2011
Environmental Technology (United Kingdom) (1479487X) 32(4)pp. 373-381
In this study the biodegradation of H2S in the air in a biofilter is modelled in the non-isothermal operating condition. For this purpose, using conservation laws of heat and mass transfer and considering the physical and chemical phenomena occurring in a biofilter, the governing equations in non-isothermal, isothermal, steady, and unsteady-state operations are obtained and solved numerically. The model results are compared with the available experimental data and also with the results of the isothermal model. The comparisons are made both in steady and unsteady-state situations. The results show that considering the heat effects on the modelling of a biofilter improves the accuracy of the model results. Furthermore, the effects of some operating parameters on the removal efficiency of biofilter are investigated. © 2011 Taylor &Francis.
Publication Date: 2010
Chemical Engineering Science (00092509) 65(10)pp. 3147-3157
A new model has been developed to analyze the performance of a moving bed reactor producing uranium tetrafluoride. The model includes the solid and gas flow rates, heat transfer by convection, conduction and radiation between gas and solid streams and by the external surrounding. A kinetics model has been also developed for the gas-solid reactions on the basis of the grain model in which, the different resistances are taken into account to determine the overall reaction rates. This study provides an initial and theoretical basis for optimum design of the moving bed on the basis of the kinetics models. The optimum design is carried out from the viewpoint of required length of the reactor and the maximum conversion. According to the primary expectations which are provided by the kinetics models, the feed temperature seems not to have any effective influence on the reactor performance. On the other hand, it is predicted that the inlet gas flow rate contributes an important role. The investigations show that although the kinetics models are rather useful in primary estimations, the strong interdependence between different zones of the reactor may prevent general expressions. © 2010 Elsevier Ltd. All rights reserved.
Ni, Z. ,
Sunderrajan, S. ,
Rahimi, A. ,
Manjunath b.s., Publication Date: 2010
Proceedings - International Conference on Image Processing, ICIP (15224880) pp. 37-40
This paper proposes a distributed algorithm for object tracking in a camera sensor network. At each camera node, an efficient online multiple instance learning algorithm is used to model object's appearance. This is integrated with particle filter for camera's image plane tracking. To improve the tracking accuracy, each camera node shares its particle states with others and fuses multi-camera information locally. In particular, particle weights are updated according to the fused information. Then, appearance model is updated with the reweighted particles. The effectiveness of the proposed algorithm is demonstrated on human tracking in challenging environments. © 2010 IEEE.
Montazerolghaem, M. ,
Rahimi, A. ,
Seyedeyn-azad, F. Publication Date: 2010
Applied Surface Science (01694332) 257(2)pp. 603-609
In this research, the adsorption of a model sulfur compound, thiophene, from a simulated gasoline onto Ce-Y zeolite in pellet and powder forms was investigated. For this purpose, zeolite Na-Y was synthesized, and Ce-Y zeolite was prepared via solid-state ion-exchanged (SSIE) method. Adsorptive desulfurization of model gasoline was conducted in a batch reactor at ambient conditions to evaluate the equilibrium and kinetics of thiophene adsorption onto Ce-Y zeolite. The equilibrium data were fitted to Langmuire and Toth models. Pseudo-n-order and modified n-order models, LDF-base model, and intra-particle diffusion model were evaluated to fit the kinetic of the adsorption process and to determine the mechanism of it. The corresponding parameters and/or correlation coefficients of each model were reported. The LDF-base model was used also to fit the mass transfer coefficient for both powder and pellet forms of the adsorbent. The best fit estimates for the mass transfer coefficient were obtained 4 × 10 -11 m/s and k = 3.1 × 10 -12 [exp (- t/τ) + 1/(t + 10 -4 )], for powder and pellet form adsorbents, respectively. © 2010 Elsevier B.V.
Publication Date: 2010
International Journal of Food Science and Technology (09505423) 45(12)pp. 2546-2552
Drying of Green Peas (Pisum sativum) was studied experimentally in a lab-scale spouted bed. Experiments were carried out at different operating conditions, and the effect of inlet air temperature and its flow rate, bed height (initial mass of wet particles) and average diameter of particles were examined on performance of dryer and rate of drying. The obtained experimental results were fitted by an exponential form equation to model the drying kinetic behaviour of green peas in a spouted bed. The fitting parameters are presented in the form of mathematical correlations as a function of operating parameters. As expected, it was found that by increasing inlet air temperature and air-flow rate, the rate of drying increases, but by increasing the bed height and diameter of particles, the rate of drying decreases. The results can help the design engineers to choose the optimum drying conditions for industrial applications. © 2010 The Authors. International Journal of Food Science and Technology © 2010 Institute of Food Science and Technology.
Publication Date: 2010
Journal of Industrial and Engineering Chemistry (1226086X) 16(1)pp. 147-151
In uranium conversion industry, the fluorine is used as chemical raw material gas to produce UF4 and UF6 while its purity is very important. In this study, the adsorption process of hydrogen fluoride, as an impurity in the process of fluorine production, on sodium fluoride pellets is experimentally studied in a lab-scale fixed bed adsorbent. Also, the effects of some operating parameters including inlet concentration and inlet temperature of hydrogen fluoride are precisely investigated on the adsorption process. The data of adsorption are analyzed and correlated by Langmuir, Freundlich and Temkin isotherms. The adsorption capacity is found to be 1.908 and 0.750 g HF/g NaF by the Langmuir isotherm at 22 and 54 °C, respectively. The favorability nature of adsorption which is expressed in terms of a dimensionless separation factor (RL) is found to be more than 1 which indicates an unfavorable adsorption. In addition, the data analysis shows that the Langmuir and Temkin isotherms correlate the equilibrium isotherms better than that of Freundlich. © 2010 The Korean Society of Industrial and Engineering Chemistry.
Publication Date: 2010
Chemical Engineering Communications (00986445) 197(5)pp. 692-708
In this study two simple mathematical models are proposed to describe the drying process of wet particles in a coaxial impinging stream dryer. The models represent the particles in two conditions, surface and internal moisture, which are solved numerically. The effect of various parameters including particle diameter, air velocity, and air temperature are investigated on the final moisture content of the product. In addition, drying intensity of the coaxial impinging stream dryer is compared with the other common dryers. This comparison leads to the conclusion of the high efficiency of impinging stream dryers at higher air velocity and smaller particles. Comparing the results of the models with available experimental data shows that the numerical predications are in good agreement with the experimental ones. © Taylor & Francis Group, LLC.
Publication Date: 2010
Journal of Industrial and Engineering Chemistry (1226086X) 16(6)pp. 978-985
In the current study, hydrogen fluoride (HF) adsorption onto the sodium fluoride pellets is modeled. For this purpose a two-dimensional, non-isothermal model was developed and the governing equations were solved numerically. The contributions of diffusion transport in axial and radial directions also were considered in mathematical formulations. The model results of effluent concentration and breakthrough curves of HF were compared with the experimental data obtained in a lab-scale adsorption unit, reported in our previous work [1]. The results indicate while the feed gas velocity decreases, the HF adsorption capacity on NaF is significantly enhanced and there is a delay in breakthrough time. The adsorption capacity of HF on NaF decreases slightly when inlet HF concentration increases. Moreover, the model results were compared with the obtained results from a one-dimension model. This comparison indicates that one-dimensional model can well predict the HF dynamic adsorption behavior for lab-scale fixed beds. Comparing the experimental breakthrough curves of HF adsorption on NaF pellets with the model results shows the ability and accuracy of the model with maximum 7.82% errors. © 2010 The Korean Society of Industrial and Engineering Chemistry.
Publication Date: 2010
Separation and Purification Technology (13835866) 72(3)pp. 288-293
The performance of a powder-particle spouted bed (PPSB) on the removal of CO2 is investigated. A laboratory scale PPSB is employed to investigate the effects of operating parameters such as approach to saturation temperature, static bed height, Ca/C molar ratio, inlet CO2 concentration and type of sorbent on CO2 removal efficiency. The experimental results show that the CO2 removal efficiency increases by increasing the static bed height, Ca/C molar ratio and inlet CO2 concentration, and decreases by increasing the approach to saturation temperature and superficial gas velocity. Also it is concluded that maximum CO2 removal efficiency could be up to 50% when approach to saturation temperature is 8 K, Ca/C molar ratio is 1.4 and the static bed height is 0.225 m. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2010
Special Topics and Reviews in Porous Media (21514798) 1(3)pp. 231-241
Using the mathematical modeling technique, the reaction rate constant for high temperature and pressure coke-burning processes was obtained by considering a simple reaction rate equation; while in accordance with the industrial operating conditions the feed rate and inlet oxygen concentration were changed continuously with time. Using the precise data of a real regeneration process and adjusting the reaction's rate constant for matching the results of the model with the experimental data, the rate of reaction was estimated. The precision of the method and the reaction rate is validated by using another set of experimental data. The obtained kinetics along with the mathematical model is able to predict the behavior of the coke-burning process with an acceptable error for applied aims. © 2010 by Begell House, Inc.
Publication Date: 2009
Powder Technology (1873328X) 193(1)pp. 101-109
In this study a common type noncatalytic gas-solid reaction is modeled based on some well-known, previously presented mathematical models, including grain, modified grain and additive reaction times models. In order to approach more realistic models, the heat effects and the changing of solid structure effects are considered in the above named mathematical models. The governing equations are developed and solved numerically. Then, the predicted results are compared with available experimental data presented for some important industrial gas-solid reactions. The results reveal shortage of the simplifying assumptions of the referred models to predict solid conversion, as a result of neglecting heat effects and structural changes of solid reactant. In this study, for the first time, the process of the change in the different reaction controlling steps is considered during the reaction time. The results also show that the main rate-limiting resistances convert to each other during the reaction progress. It reveals that the undesirable heat and structural changing effects decrease with decreasing the particle diameter, increasing the convective heat transfer coefficient, and taking appropriate gas temperature. This study shows that considering heat effects and changing of solid structure improve the abilities of previous mathematical models to predict the behavior of noncatalytic gas-solid reactions. © 2009 Elsevier B.V. All rights reserved.
Publication Date: 2009
Drying Technology (15322300) 27(1)pp. 30-39
In spite of the fact that the principles of impinging stream reactors have been developed for more than half a century, the performance analysis of such devices, from a viewpoint of the mathematical modeling, has not been investigated extensively. In this study two models are proposed to describe the drying performance of particulate materials in two-impinging stream dryers. The models are developed based on the Markov chain analysis and the tanks-in-series model. The required parameters for each model are determined by using RTD data obtained in a two-impinging stream dryer and the governing equations are solved numerically. Comparison of the results of the models with available experimental data shows that the stirred tanks-in-series model successfully explains the drying behavior in impinging stream dryers. Nevertheless, the results of the model that is developed based on the Markov chain analysis are not in exact agreement with corresponding experimental data because of the extremely short residence time of the particles inside the dryer. Also, the effects of some operating parameters on the performance of such dryers are investigated. The results indicate that the drying efficiency of the dryer increases when solid-to-gas flow rate ratio, initial moisture content, and diameter of the particles decrease and when the temperature of the carrier gas increases.
Publication Date: 2009
Energy (18736785) 34(1)pp. 14-21
The present study provides a descriptive mathematical model for energy and exergy analysis for a cocurrent gas spray cooling system. Conservation laws of mass, energy and momentum are used to predict the variation of temperature and enthalpy of gas and liquid streams along the tower length. The same procedure is also used to calculate the energy and exergy efficiencies. The validity of the model for predicting variations in gas and liquid characteristics along the tower length was examined against some operating data measured in a commercial cement plant. The results show that in spite of high energy efficiency, the gas spray cooling systems have relatively low exergy efficiency. This was due to thermodynamic irreversibilities and entropy production during heat and mass transfer processes. Also the effect of some operating parameters, including tower diameter, tower length, liquid drop size distribution and water flow rate was investigated, on the amount of exergy destruction. This study also concluded that the exergy of water is not completely absorbed by gas and a remarkable portion of exergy is destroyed. Results of such investigations may provide us with the true energy potential carried by fluids. © 2008 Elsevier Ltd. All rights reserved.
Publication Date: 2009
Chemical Engineering Science (00092509) 64(3)pp. 618-619
Publication Date: 2006
Canadian Journal of Chemical Engineering (00084034) 84(3)pp. 310-315
An analytical model using eddy diffusivity is applied for predicting droplet concentration distribution and liquid film formation in a Venturi scrubber. By comparing experimental data of film formation reported in literature (Viswanathan et al., 1984) and the results obtained from this model, a semi-empirical correlation for liquid droplets eddy diffusivity is obtained. The validity of this correlation is confirmed by obtaining good agreement between theoretical and experimental data of droplet concentration distribution and film formation in a Venturi scrubber (Viswanathan, 1998; Viswanathan et al., 1984).
Publication Date: 2005
Canadian Journal of Chemical Engineering (00084034) 83(3)pp. 401-408
A mathematical model consisting of differential equations for energy, momentum and material exchange is developed for a non-isothermal Venturi-type scrubber. By this model, the effects of heat and mass transfer on droplets concentration distribution and removal efficiency of particulate in a non-isothermal Venturi scrubber can be investigated. In order to approach a realistic model, the liquid film flow on the walls and droplet size distribution are considered. The model is validated by comparing the results of mathematical model by plant and experimental data reported in the literature. The Results section of this work reveals that the inlet humidity and temperature of the gas can affect the removal efficiency of the scrubber.
Publication Date: 2004
Chemical Engineering Communications (00986445) 191(3)pp. 315-334
A mathematical model has been developed for prediction of pressure drop in a Venturi scrubber. This model includes the effect of the amount of liquid film and re-entrainment of liquid droplets from liquid film. The result of the present model is compared with experimental data of Viswanathan et al. (1985) as well as with the other models (Viswanathan et al., 1985; Boll, 1973). Results of this study indicate that at high liquid to gas ratios prediction of pressure drop can be improved by considering re-entrainment and liquid film effects. Also the effects of gas velocity and liquid to gas ratio were investigated on the rate of droplet re-entrainment and pressure drop. © Taylor and Francis Inc.
Publication Date: 2004
2025 29th International Computer Conference, Computer Society of Iran, CSICC 2025 pp. 203-207
The role of diffusion in reducing the saturation pressure of oil in blocks located at different depths of fractured oil reservoirs has been studied. A model to describe unsteady state diffusion in a matrix block with a given geometry in fractured oil reservoirs has been developed and the results have been compared with the analytical solution. The delay time for solution gas drive due to diffusion in a block with a given shape has been calculated by using the data of Haft kel field. Copyright 2004, Society of Petroleum Engineers Inc.
Publication Date: 2002
Chemical Engineering Communications (00986445) 189(7)pp. 959-973
A mathematical model is developed to study simultaneous heat and mass transfer in hot gas spray systems. The model is obtained by writing mass, energy, and momentum balances for both continuous and discontinuous phases. Governing equations along with suitable correlations for heat and mass transfer coefficients have been solved numerically. In order to develop a realistic model for such complicated systems, a droplet size distribution was implemented in the model instead of using an average size. A steady state spray-cooling problem is analyzed to illustrate the applicability of the model. To validate the mathematical model for this case, necessary data was collected and measured in commercial cement plants. A good agreement between plant data and the model was noticed in general, and results obtained from the model indicate that size distribution of water droplets and physical dimensions of the spray-cooling system are important parameters. This model is very useful in determining the so-called "critical operation condition" at which sludge formation at the bottom of spray-cooling systems will happen. The predicted parameters in spray-cooling systems both for droplet phase and gas phase aptly illustrate the ability of the model to treat the complex phenomena associated with two-phase flows.
University of Isfahan
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