Transport Phenomena,
S. Amirzadeh; J.S Moghaddas
Abstract
Most industrial operating units are basically in contact with two gas and liquid phases. Bubble characteristics over the last years have been determined through different methods. In this project a mass transfer system has been designed for absorbing gas bubbles by liquid phase. The mass transfer and ...
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Most industrial operating units are basically in contact with two gas and liquid phases. Bubble characteristics over the last years have been determined through different methods. In this project a mass transfer system has been designed for absorbing gas bubbles by liquid phase. The mass transfer and hydrodynamic behavior in the wake of single rising air bubbles were investigated by using an image analysis method and empirical relations. By considering these methods, the overall bubble properties including the size of single bubble, shape, path, rising velocity and mass transfer coefficient were studied and measured. The investigation was developed with 0.15×0.15×0.35 m3 bubble column and nozzle diameter (0.5, 1, 1.5, 2, 2.5 mm) in different liquids considering viscose changes. Moreover, from the results obtained, it can be concluded that the increase of nozzle diameter increases the bubble diameter which results in reduction of velocity and mass transfer coefficient. This is a fact that, by raising the viscosity of liquid phase the bubble diameter stands at the highest level and on the contrary velocity and mass transfer coefficient stand at the lowest level. So according to these outcomes we can conclude that, the diameter of bubble depends on physical properties of fluids and has a direct relation with nozzle diameter.
E. Tohfegar; J.S. Moghaddas; E. Sharifzadeh; S. Esmaeilzadeh-Dilmaghani
Abstract
In this work, hydrophobic silica aerogels were synthesized using sol-gel method and drying at ambient pressure. The surface morphology, pore size, and the presence of functional groups on the surface of the nanoparticles were analyzed using FE-SEM, TGA, FT-IR, and EDX, respectively. After calcination ...
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In this work, hydrophobic silica aerogels were synthesized using sol-gel method and drying at ambient pressure. The surface morphology, pore size, and the presence of functional groups on the surface of the nanoparticles were analyzed using FE-SEM, TGA, FT-IR, and EDX, respectively. After calcination at 500 °C, the hydrophilic property of the adsorbents was evaluated by water contact angle measurements. The calcinated silica aerogels were used for adsorption of nitrate from aqueous solution in both batch and continuous processes. In the batch process, the effect of initial nitrate concentration, contact time, pH level, and adsorbent dosage were investigated. Results showed that the nitrate removal percentage increased with the decrement of the pH level and the initial nitrate concentration. On the other hand, increasing the contact time and the adsorbent dosage resulted in higher removal percentage. Accordingly, process optimization resulted in a nitrate removal of 92.2 %. Furthermore, it was found that the equilibrium results were in agreement with the Langmuir isotherm model better than with the Freundlich model and also the adsorption kinetics followed the pseudo-second-order model. In the continuous process, the effects of the input flow rate, the bed height, and the initial nitrate concentration were investigated.
A. Mohammadi; J. Moghaddas
Volume 16, Issue 3 , September 2019, , Pages 3-22
Abstract
Although not listed on the United States Pharmacopeia (USP), like standard USP 2, small volume USP 2 dissolution apparatus has gained a great deal of attention, especially for cases where small amount of drug product is available for testing in research and design step or evaluations are to be made on ...
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Although not listed on the United States Pharmacopeia (USP), like standard USP 2, small volume USP 2 dissolution apparatus has gained a great deal of attention, especially for cases where small amount of drug product is available for testing in research and design step or evaluations are to be made on a tablet containing trace amounts of the active pharmaceutical ingredient. In this work, firstly, small volume USP 2 apparatus was designed and manufactured using downscaling rules and considering standard USP 2 as a reference. Then, velocity profile, flow patterns, and shear rate were obtained by PIV and COMSOL simulation software at paddle speeds of 66 and 133 rpm, corresponding to agitation speed of 50 and 100 rpm, respectively, in the standard USP 2. Comparison between experimental and computational results showed acceptable adaptation. Instantaneous velocity data showed eddies and secondary flows in different zones of the vessel, which is desirable for micro-mixing but undesirable in terms of system consistency and reproducibility, as sampling from these zones are known to lead to inconsistent data. Furthermore, increased agitation rate led to the disappearance of rotational zones around the paddle. The magnitude of velocity and shear rate increased by 35% with an increment of paddle stirring from 66 to 133 rpm.
Transport Phenomena,
A. Mohammadi; J. Moghaddas
Volume 16, Issue 1 , March 2019, , Pages 1-21
Abstract
In this study, nanoporous silica aerogel and silica aerogel-activated carbon composites have been synthesized using a water glass precursor by cost effective ambient pressure drying method. Equilibrium and kinetics of benzene and ethyl benzene adsorption on silica aerogel and its composites have been ...
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In this study, nanoporous silica aerogel and silica aerogel-activated carbon composites have been synthesized using a water glass precursor by cost effective ambient pressure drying method. Equilibrium and kinetics of benzene and ethyl benzene adsorption on silica aerogel and its composites have been measured in a batch mode at tree weights of adsorbent. For the first time, the experimental data have been fitted with intra-particle diffusion model for determining of diffusion coefficients. The saturation adsorption capacity of benzene and ethyl benzene vapours was 2033 mg.g-1 and 458 mg.g-1 respectively. The components uptake curves have been described by mathematical models of pseudo first order and pseudo second order models. It has been found that the pseudo first order model fits the experimental data better than the pseudo second order model. Also, the pseudo-second order model could be used for modeling of benzene adsorption over silica aerogel and silica aerogel-2% wt. activated carbon composite at the beginning of adsorption process. The diffusion coefficients of benzene and ethyl benzene within the silica aerogel were in the range of 〖2.16×10〗^(-14) - 〖6.66×10〗^(-13) m2.s-1 and 〖3.65×10〗^(-13) - 〖1.95×10〗^(-12) m2.s-1, respectively.
Separation Technology,
Jafarsadegh Moghaddas; Leila Amirkhani; Hoda Jafarizadeh- Malmiri
Volume 13, Issue 3 , July 2016, , Pages 19-31
Abstract
Magnetic silica aerogel in hydrophobic and hydrophilic forms were used as support to immobilize Candida rugosa lipase by adsorption method. Response surface methodology (RSM) was employed to study the effects of the three most important immobilization parameters, namely enzyme/support ratio (0.3-0.5, ...
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Magnetic silica aerogel in hydrophobic and hydrophilic forms were used as support to immobilize Candida rugosa lipase by adsorption method. Response surface methodology (RSM) was employed to study the effects of the three most important immobilization parameters, namely enzyme/support ratio (0.3-0.5, w/w), immobilization time (60-120 min) and alcohol percentage (20-40, %v/v) on the specific activity of immobilized lipase on the hydrophobic supports. For hydrophilic supports, alcohol percentage was removed as there was no need for pre-wetting step in enzyme immobilization process. Second order regression models with high coefficient determination (R2) values of higher than 0.98 were fitted to predict the response as function of immobilization parameters. The results indicated that for hydrophobic supports, optimum values for enzyme/support ratio, immobilization time and alcohol percentage were obtained at 0.45 (w/w), 94.27 min and 38.81 %, respectively, in which specific activity were predicted at 15.32 U/mg-protein. For hydrophilic supports, the optimum enzyme/support ratio and immobilization time were predicted at 0.47 (w/w) and 83.47 min, respectively. Specific activity in these conditions were obtained 11.21 U/mg-protein. As the difference between the experimental and predicted values was showed as non-significant, the response surface models employed could be considered as adequate.
Process Control and Engineering, Process Safety, HSE
N. Yasrebi; J. Moghaddas
Volume 12, Issue 2 , April 2015, , Pages 3-12
Abstract
> Copper-silica aerogel was synthesized by the sol-gel method and was heated at 400, 500 and 600°C for 3 h in the air. The gained materials were named as sample (a), (b) and (c) respectively. Then all samples were characterized by FE-SEM, EDX and FTIR spectroscopy. For resistance measurements ...
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> Copper-silica aerogel was synthesized by the sol-gel method and was heated at 400, 500 and 600°C for 3 h in the air. The gained materials were named as sample (a), (b) and (c) respectively. Then all samples were characterized by FE-SEM, EDX and FTIR spectroscopy. For resistance measurements the pulverized material was pressed to form a disk-type sensor. The measurements of resistance in the relative humidity range of 11.3-84.3% were performed for all samples. For the following experiments sample (a) was chosen. Then the response time and stability properties were examined. The response time of 7.5 minutes was obtained and the stability graphs showed that in the higher RH the sensor was more stable.