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: 2021
Renewable Energy (0960-1481)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
Madadi avargani, V.,
Norton, B.,
Rahimi, A.,
Karimi, H. Publication Date: 2021
Sustainable Energy Technologies and Assessments (2213-1388)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
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: 2020
Sustainable Energy Technologies and Assessments (2213-1388)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
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: 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.
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.
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.
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
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.
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
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
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.
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.
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
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.
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.
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.
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: 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.
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
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
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 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.
