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Harandizadeh a.h., A.H.,
Aghamiri, S.,
Hojjat, M.,
Ranjbar-Mohammadi M.,
Talaie m.r., M.R. Nanomaterials (20794991)(3)
Among the new adsorbent forms, nanofiber structures have attracted extra attention be-cause of features such as high surface area, controllable properties, and fast kinetics. The objective of this study is to produce the polyacrylonitrile (PAN) electrospun nanofibers loaded with Ni-MOF-74/MWCNT to obtain maximum CO2 adsorption. The prepared PAN/MWCNT/MOF nanofiber based on the Box–Behnken design (BBD) model suggests the CO2 adsorption of about 1.68 mmol/g (at 25◦C and 7 bar) includes 14.61 w/v%, 1.43 w/w%, and 11.9 w/w% for PAN, MWCNT, and MOF, respec-tively. The results showed the effective CO2 adsorption of about 1.65 ± 0.03 mmol/g (BET = 65 m2/g, pore volume = 0.08 cm3/g), which proves the logical outcomes of the chosen model. The prepared PAN/MWCNT/MOF nanofiber was characterized using different analyzes such as SEM, TEM, TG, XRD, FTIR, and N2 adsorption–desorption isotherms. More MOF mass loading on the nanofiber surface via secondary growth method resulted in 2.83 mmol/g (BET = 353 m2/g, pore volume = 0.22 cm3/g, 43% MOF mass loading) and 4.35 mmol/g (BET = 493 m2/g, pore volume = 0.27 cm3/g, 65% MOF mass loading) CO2 adsorption at 7 bar for the first and second growth cycles, respectively. This indicates that secondary growth is more effective in the MOF loading amount and, consequently, adsorption capacity compared to the MOF loading during electrospinning. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.
International Journal of Thermal Sciences (12900729)
Laminar flow of Al2O3/water nanofluids in rectangular ducts with different aspect ratios (AR) were simulated numerically. Both heat transfer coefficient and pressure drop of nanofluids are higher than the base fluid and increase with nanofluid concentration in ducts of all aspect ratios. For a duct with AR = 2, the heat transfer coefficient of nanofluids with a concentration of 5% vol. is on average 22% higher than the base fluid. Its pressure drop is about 2.5 times of the base fluids. The effect of nanofluid concentration on the heat transfer coefficient is more significant in ducts with a lower aspect ratio. The heat transfer coefficient of a 5% vol. nanofluid in a duct with AR = 1 is about 24% larger than the base fluid; this value is about 18% for a duct with AR = 6. The effect of nanofluid concentration on the pressure drop of all ducts is identical. The results of the numerical simulation were used for training a multi-Layer perceptron artificial neural network (MLP-ANN) model. The ANN model predicts the pressure drop and heat transfer coefficient of nanofluids in rectangular ducts very accurately. The maximum differences between the values of heat transfer coefficient predicted by the ANN and those obtained from the numerical simulation is about 0.11%, and that of the pressure drop is about 0.65%. Multi-objective NSGA-II optimization algorithm was applied to optimize the nanofluid flow in rectangular ducts. In optimization, the goal was to maximize the heat transfer coefficient and minimize the pressure drop. The values of objective functions were evaluated by the resulting ANN model. Optimization for ducts with each aspect ratio was performed. Optimization was also done for all channels. Pareto fronts were obtained from optimization. The best solution for each optimization is determined by two decision-making methods. For the overall optimal solution, nanofluid concentration, Reynolds number, and the duct aspect ratio are 2.28% vol., 400, and 6, respectively which are the same as the optimal solution of the duct with an aspect ratio of six. © 2021 Elsevier Masson SAS
Esmaeili F.,
Hojjat, M.,
Denayer, J.F.,
Gholami, M. Industrial and Engineering Chemistry Research (08885885)(12)
The reduction of cycle time is crucial to obtain viable adsorptive CO2 capture processes. In thermal swing adsorption processes, heating and cooling of the adsorbent result in long cycle times. In the present paper, the adsorbent was coated on a finned heat exchanger tube to reduce the heating and cooling times. The effect of the adsorbent/exchanger mass ratio on the regeneration time and energy efficiency of CO2 adsorption and desorption were investigated. To do so, finned tubes were coated by three different masses of 13X powder and were used in an indirect-heating system for CO2 sorption. Increasing the loaded adsorbent mass density from 58.5 to 215.7 g/m2 did not affect the CO2 sorption rate. This is because of the short characteristic time of heat diffusion due to the limited spacing between the adjacent fins. Energy analysis of the system shows that the energy consumed per mole of desorbed CO2 decreases with increasing adsorbent mass. The maximum energy efficiency is less than 3%. ©
Journal Of Thermal Analysis And Calorimetry (13886150)(6)
The cooling performance of Newtonian and non-Newtonian nanofluids in a square duct was identified experimentally. The flow regime was laminar. Two-step method was used to prepare stable dispersions of γ-Al2O3 and TiO2 nanoparticles. Water and ethylene glycol were used as the base fluids of Newtonian, and a 0.5 mass% carboxymethyl cellulose in water was used as the base fluid of the non-Newtonian nanofluids. Nanoparticle concentration was in the range of 0.1–1.5% by volume. Heat transfer coefficient of nanofluids enhances significantly relative to the base fluids. The enhancement of heat transfer coefficient of nanofluids is proportional to the Peclet number and nanofluid concentration. Nanoparticles type and the base fluid affected the Newtonian nanofluids performance, while for non-Newtonian nanofluids this is not the case. The improvement in nanofluids heat transfer coefficient is more than just related to their thermal conductivity enhancement. The obtained experimental data were modeled by the artificial neural network (ANN). Two empirical correlations were also fitted on the data. The experimental data are well predicted by the ANN models and empirical correlations. Statistical criteria show that the ANN models are more accurate. © 2020, Akadémiai Kiadó, Budapest, Hungary.
Waste and Biomass Valorization (18772641)(5)
The effect of loading alkaline earth metal oxides on sulfated alumina-zirconia (S/AZ), as a nanocatalyst in esterification of oleic acid (OA) and transesterification of waste cooking oil (WCO) was experimentally investigated. S/AZ modified by calcium (S/Ca–AZ), magnesium (S/Mg–AZ), strontium (S/Sr–AZ) and barium oxides (S/Ba–AZ) were synthesized by solvent-free method and characterized by various methods. Based on the results, zirconia (Z) and S/AZ exhibited less activity in biodiesel production due to their low acidity and basicity while their activities were clearly increased by loading alkaline earth metal oxides. Among the samples, S/Ba–AZ shows the highest activity in both esterification and transesterification reactions, followed by S/Mg–AZ, S/Ca–AZ, and S/Sr–AZ, respectively. However, evaluating the activity of catalysts in second uses as an important factor for industrial application of a catalyst shows that, although the activity of all samples decreases, S/Ca–AZ has the least deterioration in activity. This can be related to its small particle size (below 15 nm), and well bonding of the calcium oxides with other metal oxides and sulfate groups which eliminates the leaching of active phases. Results confirm that S/Ca–AZ can be chosen as the most appropriate nanocatalyst with high activity and stability for biodiesel production from low-cost feedstock. © 2018, Springer Nature B.V.
Applied Mathematics and Computation (00963003)
In the present study, an artificial neural network (ANN) was developed to predict the thermal and hydrodynamic behavior of two types of Newtonian nanofluids used as coolants in a shell and tube heat exchanger (STHE). Inputs of the ANN model are nanoparticle volume concentration, Reynolds number, nanoparticle thermal conductivity, and Prandtl number. Results indicate that the ANN model predicts the experimental data with very high accuracy. Values of Nusselt number resulted from experiments and those obtained from the ANN have at most 9% difference, this value is 9.6% for the pressure drop. Multi-objective optimization was implemented with the aim of minimizing the total pressure drop and maximizing the nanofluids Nusselt number in the STHE according to NSGA-II algorithm. In optimization procedure nanofluids pressure drop and the Nusselt number (tube-side) was evaluated by the ANN model. To find the shell-side pressure drop method of Delaware was employed. Nanofluids concentration and Reynolds number were selected as decision parameters. The Pareto front was obtained. The best solution adopted from points on the Pareto front by two well-known decision-making methods LINMAP and TOPSIS. The Nusselt number of optimal solutions are about 30% greater than the base fluid and pressure drop of optimal solutions are about 10% lower than the base fluid. © 2019 Elsevier Inc.
In this study, the external surface of a finned tube was coated by 13X zeolite powder, and the CO2 adsorption equilibrium and dynamics were investigated experimentally. A slurry consisting of dionized water, 13X zeolite powder, and Acrylic latex emulsion (ALE) was used to coat the finned tube. The finned tube was coated by deep coating method. The equilibrium isotherms were measured at the range of 20–90 °C and fitted well by the dual-site Langmuir model. The average difference between the model and the results obtained from the experiments is about 2.5%. The nitrogen adsorption/desorption at 77 K was used for characterization of adsorbents. A 11% reduction was observed in pore volume and surface area. The dynamic test showed that the desorption of adsorbed CO2 takes place in about 14 s which is an order of magnitude faster than the fastest developed method. A conservative criterion was developed for estimating adsorbent working capacity. This criterion showed that the working capacities of the adsorbent are about 80% of its ideal values. © 2019
Shakouri, Abolfazl,
Ahmari, Hadi,
Hojjat, M.,
Zeinali Heris, Saeed Journal of Vinyl and Additive Technology (10835601)(3)
In recent years, addition of nanoparticles to fluids and polymers has been used as a way of modifying rheological properties. Poly(vinyl alcohol) (PVA) and titanium dioxide (TiO2) nanoparticles aqueous composite nanofluids were prepared through the use of ultrasonic vibration. In fact, ultrasonic vibration is an advantageous method for nanoparticle dispersion. The preparation method prevents reduction of the polymer's molecular weight. TiO2 nanoparticles with different concentrations were employed to investigate the rheological characteristics of composite nanofluids. Rheological characteristics of base fluids and composite nanofluids were measured at different temperatures. Based on the results, all composite nanofluids, as well as base fluids, exhibited non-Newtonian behavior and rheological characteristics of composite nanofluids, following the Herschel-Bulkley model. In addition, model parameters are functions of temperature, PVA, and TiO2 nanoparticle concentrations. Also, two-way interactions among temperature, PVA, and TiO2 nanoparticle concentrations affect flow index and consistency index of the Herschel-Bulkley model. J. VINYL ADDIT. TECHNOL., 23:234–240, 2017. © 2015 Society of Plastics Engineers. © 2015 Society of Plastics Engineers
Hojjat, M.,
Nayebzadeh H.,
Khadangi-Mahrood, Mahmoodreza,
Rahmani-Vahid, Behgam Chemical Papers (03666352)(3)
CaO-Al2O3/ZrO2 mixed oxide catalyst was prepared using free-solvent method. The catalyst was characterized using X-ray diffraction, BET surface area, acidity index (obtained by titration method), and scanning electron microscopy (SEM). With calcium aluminate and calcium zirconate been successfully formed, the mix exhibited small crystal size, high acidity, and large surface area, pore size, and pore volume, making it a catalyst of choice for biodiesel production. The activity of catalyst was evaluated in the course of esterification of oleic acid as well as transesterification of waste cooking oil (WCO) into biodiesel. Based on a four-variable central composite design (CCD), response surface methodology (RSM) was used to optimize effective variables on oleic acid conversion. The optimum yield of 94.68% was obtained at the following set of optimum conditions: reaction temperature of 120 °C, methanol/oleic acid molar ratio of 15.64, catalyst concentration of 2.94 wt%, and reaction time of 4 h; the result was in excellent agreement with the predicted values. Furthermore, under the optimum conditions, the catalyst succeeded to convert 93.48% of WCO into biodiesel. © 2016 Institute of Chemistry, Slovak Academy of Sciences.
Mousazadeh, S.,
Shakouri, Abolfazl,
Hojjat, M.,
Etemad S.G.,
Zeinali Heris, Saeed Journal of Applied Polymer Science (00218995)(41)
In this study, an investigation of the rheological behavior of starch/poly(vinyl alcohol) (PVA)/titanium oxide (TiO2) nanofluids was performed. It revealed that the rheological behavior of starch suspensions displays a particular change due to the presence of PVA and TiO2. All examined fluids demonstrated non-Newtonian behavior and followed the Power law model. The main and interacting effects of starch, PVA, and TiO2 nanoparticles concentrations were studied using the analysis of variance. The results indicated that the flow behavior index (n), as well as the consistency index (K) of suspensions, is influenced by the PVA and TiO2 contents. The flow behavior index (n) decreased and consistency index (K) increased by an increase in PVA concentration. A reverse trend is observed by the addition of TiO2 nanoparticles to starch and PVA blend suspensions. The difference in rheological behaviors was ascribed to the presence of binary and triplet interactions between starch, PVA, and TiO2 nanoparticles. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44062. © 2016 Wiley Periodicals, Inc.
Journal of Dispersion Science and Technology (15322351)(7)
In this article, frictional pressure drop of non-Newtonian nanofluids flowing through a horizontal circular tube was investigated experimentally in both the laminar and the turbulent regimes. Three different types of oxide nanoparticles, γ-Al 2O 3, CuO, and TiO 2, were used for the preparation of nanofluids. A 0.5 wt% aqueous solution of carboxymethyl cellulose (CMC) was used as the base fluid. Pressure drop were measured for a wide range of nanoparticle concentrations. The dimensionless pressure drop for all nanofluids in both the laminar and the turbulent flow regimes as a function of the Reynolds number follows the same trend of the pressure drop observed with the base fluid. Results presented in this investigation are significant because better heat transfer coefficients prevail for nanofluids and yet without an increase in the pressure drop. © 2012 Copyright Taylor and Francis Group, LLC.
International Journal of Thermal Sciences (12900729)(4)
Three kinds of nanofluids were prepared by dispersing γ-Al 2O3, CuO, and TiO2 nanoparticles in an aqueous solution of carboxymethyl cellulose (CMC). The forced convective heat transfer of these nanofluids through a uniformly heated circular tube under turbulent flow conditions was investigated experimentally. The base fluid and all nanofluids show pseudoplastic (shear-thinning) rheological behavior. Results reveal that the local and average heat transfer coefficients of nanofluids are larger than that of the base fluid. Heat transfer enhancement of nanofluids increases with an increase in nanoparticle concentration. Similar trend are demonstrated for Nusselt number of nanofluids. For a given nanoparticle concentration and Peclet number, the local heat transfer coefficient of the base fluid and that of the nanofluids decreases with the axial distance from the tube inlet. A new correlation is proposed to predict successfully the Nusselt number of non-Newtonian nanofluids as a function of the Reynolds and the Prandtl numbers. © 2010 Elsevier Masson SAS. All rights reserved.
Heat and Mass Transfer/Waerme- und Stoffuebertragung (14321181)(2)
Nanofluids are obtained by dispersing homogeneously nanoparticles into a base fluid. Nanofluids often exhibit higher heat transfer rate in comparison with the base fluid. In the present study, forced convection heat transfer under laminar flow conditions was investigated experimentally for three types of non-Newtonian nanofluids in a circular tube with constant wall temperature. CMC solution was used as the base fluid and γ-Al2O3, TiO2 and CuO nanoparticles were homogeneously dispersed to create nanodispersions of different concentrations. Nanofluids as well as the base fluid show shear thinning (pseudoplastic) rheological behavior. Results show that the presence of nanoparticles increases the convective heat transfer of the nanodispersions in comparison with the base fluid. The convective heat transfer enhancement is more significant when both the Peclet number and the nanoparticle concentration are increased. The increase in convective heat transfer is higher than the increase caused by the augmentation of the effective thermal conductivity. © 2010 Springer-Verlag.
International Communications in Heat and Mass Transfer (07351933)(2)
γ-Al2O3, TiO2 and CuO nanoparticles were dispersed in a 0.5wt.%. aqueous solution of carboxymethyl cellulose (CMC) to prepare three types of non-Newtonian nanofluids. Rheological characteristics of the base fluid and nanofluids with various nanoparticle concentrations at different temperatures were measured. Results show that all nanofluids as well as the base fluid exhibit pseudoplastic (shear thinning) behavior. The rheological characteristics of nanofluids and those of the base fluid are functions of temperature and particle concentrations. © 2010 Elsevier Ltd.
International Journal of Heat and Mass Transfer (00179310)(5-6)
Three different types of nanofluids were prepared by dispersing γ-Al2O3, TiO2 and CuO nanoparticles in a 0.5 wt% of carboxymethyl cellulose (CMC) aqueous solution. Thermal conductivity of the base fluid and nanofluids with various nanoparticle loadings at different temperatures were measured experimentally. Results show that the thermal conductivity of nanofluids is higher than the one of the base fluid and the increase in the thermal conductivity varies exponentially with the nanoparticle concentration. In addition to increase with the nanoparticle concentration, the thermal conductivity of nanofluids increases with the temperature. Neural network models were proposed to represent the thermal conductivity as a function of the temperature, nanoparticle concentration and the thermal conductivity of the nanoparticles. These models were in good agreement with the experimental data. On the other hand, the Hamilton Crosser model was only satisfactory for low nanoparticle concentrations. © 2010 Elsevier Ltd. All rights reserved.
Experimental Thermal and Fluid Science (08941777)(7)
Forced convection heat transfer of non-Newtonian nanofluids in a circular tube with constant wall temperature under turbulent flow conditions was investigated experimentally. Three types of nanofluids were prepared by dispersing homogeneously γ-Al2O3, TiO2 and CuO nanoparticles into the base fluid. An aqueous solution of carboxymethyl cellulose (CMC) was used as the base fluid. Nanofluids as well as the base fluid show shear-thinning (pseudoplastic) rheological behavior. Results indicate that the convective heat transfer coefficient of nanofluids is higher than that of the base fluid. The enhancement of the convective heat transfer coefficient increases with an increase in the Peclet number and the nanoparticle concentration. The increase in the convective heat transfer coefficient of nanofluids is greater than the increase that would be observed considering strictly the increase in the effective thermal conductivity of nanofluids. Experimental data were compared to heat transfer coefficients predicted using available correlations for purely viscous non-Newtonian fluids. Results show poor agreement between experimental and predicted values. New correlation was proposed to predict successfully Nusselt numbers of non-Newtonian nanofluids as a function of Reynolds and Prandtl numbers. © 2011 Elsevier Inc.
International Journal of Heat and Mass Transfer (00179310)(1-3)
Heat transfer characteristics of γ-Al2O3/water and TiO2/water nanofluids were measured in a shell and tube heat exchanger under turbulent flow condition. The effects of Peclet number, volume concentration of suspended nanoparticles, and particle type on the heat characteristics were investigated. Based on the results, adding of naoparticles to the base fluid causes the significant enhancement of heat transfer characteristics. For both nanofluids, two different optimum nanoparticle concentrations exist. Comparison of the heat transfer behavior of two nanofluids indicates that at a certain Peclet number, heat transfer characteristics of TiO2/water nanofluid at its optimum nanoparticle concentration are greater than those of γ-Al2O3/water nanofluid while γ-Al2O3/water nanofluid possesses better heat transfer behavior at higher nanoparticle concentrations. © 2009 Elsevier Ltd. All rights reserved.
Korean Journal of Chemical Engineering (02561115)(5)
Forced convection heat transfer behavior of three different types of nanofluids flowing through a uniformly heated horizontal tube under laminar regime has been investigated experimentally. Nanofluids were made by dispersion of γ-Al2O3, CuO, and TiO2 nanoparticles in an aqueous solution of carboxymethyl cellulose (CMC). All nanofluids as well as the base fluid exhibit shear-thinning behavior. Results of heat transfer experiments indicate that both average and the local heat transfer coefficients of nanofluids are larger than that of the base fluid. The enhancement of heat transfer coefficient increases by increasing nanoparticle loading. At a given Peclet number and nanoparticle concentration the local heat transfer coefficient decreases by axial distance from the test section inlet. It seems that the thermal entry length of nanofluids is greater than the base fluid and becomes longer as nanoparticle concentration increases. © 2010 Korean Institute of Chemical Engineers, Seoul, Korea.