Sharif Digital Repository

Reactive crystallization or precipitation is an important industrial process. Many chemicals and biochemicals such as catalysts and pigments are produced by precipitation. Because of the advantages of impinging jets in chemical engineering processes, the main aim of this research was to investigate the application of this method in precipitation and to study the effects of different operating and design parameters on the product’s quality and properties. Two chemical models of barium sulfate and copper oxalate were used as main products. Each of these chemicals was produced by a liquid-liquid reaction of two aqueous solutions, which were fed to an impinging-jets reactor. Effects of... 

In this work the transesterification reaction of waste cooking oil in the present of solid catalyst as a type of solid-liquid catalytic reaction, has been studied. For this purpose, two types of alkali solid catalysts were synthesized. CaO-ZrO2 and KOH/γ-Al2O3 catalysts were prepared by co-precipitation and impregnation method, respectively. These catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF), BET surface area, and temperature programmed desorption of CO2 (TPD-CO2). The obtained results for the CaO-ZrO2 catalysts indicate that with increasing Ca/Zr atomic ratio, the activity of catalysts increases, but the stability... 

In this work, a comprehensive survey on the different methods of modeling fluidized beds was done. Finally, the discrete particle method with soft particle approach was selected as the method of modeling the solid phase. For the gas phase, computational fluid dynamics (CFD) as the method of modeling is used. In order to verify our simulation results for the solid phase, a simulation of a bed with many particles distributed all around the bed was done. At the first second of the simulation, the gas phase flow was truned off and the particles were falling down. The results obtained with this method were verified with the references. For verification of the gas phase, a 2D bed with the gas... 

Vortex flow reactor (VFR) is used for biochemical reactions and separation applications. By using the second flow regime, called Taylor-Couette flow, VFR provides high amounts of mass transfer and mixing for biological components sensitive to shear stress. Mass transfer in a bench-scale Taylor-Couette contactor with a radius ratio, equal to 0.77 and an aspect ratio, equal to 30.7 was studied for solid particles dissolution. The working fluid was water and the suspended particles were benzoic acid. In this project the concentration of fluid phase was measured by injection of definite amount of the solid particles in to the contactor and sampling in different time intervals and the effects of... 

The aim of this work was to investigate the performance of different kinds of Linde type A zeolite (LTA) for the dehydration of Tetrahydrofuran (THF)-water solution. Batch experiments were carried out to evaluate the effect of various operating parameters such as contact time, initial concentration, mixing temperature (10, 15,and 25 C), amount of adsorbent, and zeolite type(3A, 4A, and 5A zeolites). In theoretical studies, we took the advantage of several types of equilibrium model isotherms such as Langmuir, Freundlich, Dubin-Kaganer-Radushkevich (DKR) to describe the experimental adsorption data. Besides, three adsorption kinetic models including pseudo-first-order, pseudo-second-order,... 

Xylene isomers have similar boiling points and, therefore, their separation by conventional distillation is not practical. The industrial separation of these isomers is generally performed by adsorption or crystallization processes, which are very energy consuming. In this work, the various methods of the separation of these isomers have been reviewed and the equilibrium adsorption of these components in liquid phase using two commercial types of zeolite including Z-700 and Na-BETA as adsorbent at 15, 25, and 35 oC and an initial concentration range of up to 50 wt% as well as in single and binary solutions was investigated. It was found that Z-700 adsorbent has no selectivity for the binary... 

In the present study a novel phenomenological discrete bubble model (DBM) has been developed for freely bubbling gas-solid fluidized bed simulation. In this model the path of each bubble was tracked through the bed. The model can predict the bubble and emulsion phase dynamic behavior very well. At the first stage the model was developed for a pseudo 2-D gas-solid fluidized bed, and then it was adapted for 3-D beds. The emulsion phase assumed to be as an incompressible fluid and the potential flow assumption has been used to find the velocity flow-field around a single isolated bubble. For a swarm of bubbles the superposition rule has been used to find the velocity vector field. In... 

The theory of mass transfer accompanied by chemical reaction for gas-liquid systems was used to measure the specific interfacial area and mass transfer coefficient in a two impinging jets reactor (TIJR) in the presence of γ-Al_2 O_3 nanoparticles.The absorption of oxygen in sulfite solutions used for the determination of mass transfer characteristics. First 3 liters of nanofluids were prepared at concentration of 1 w% then diluted To produce 10 Liters of nanofluids containing 0.3 w%. The stability of this nanofluid was determined using uv-vis to be less more than 95% in the first 3 hours. The influence of weight percent of nanoparticles (0, 0.05, 0.1, 0.15, 0.2, 0.3) on the specific... 

Fluidized bed spray granulation is an important powder production process with several key advantages compared to other powder production processes, such as spray drying. Moreover, in fluidized bed granulators, whole process takes place in just one apparatus and there is no need to side processing. Most important characteristics and essential part of fluidized bed granulation is the wetting of primary particles by atomized liquid binder to coating the primary particles and producing granules. To date, a lot of research has focused on modeling and understanding of the separate particle growth mechanisms which have been integrated into the population balance models. Although, these concepts... 

In this thesis, the momentum and heat transfer of a ferrofluid in a partially filled vertical porous channel under the influence of nonuniform magnetic field has been investigated. In this magneto-thermo-echanical problem, our objective was to enhance the heat transfer which is attributable to both ferrofluid and porous medium unique characteristics. Accordingly, this problem is twofold and their relevant aspects would be discussed respectively. The ferrofluid flows upward, in the channel and a gradient magnetic field is generated by a permanent magnet in the vicinity of the channel. To solve the system of govering equations,COMSOL Multiphysics software has been used. The results shows that... 

The good performance in cooling, especially in systems with small dimensions, is one of the critical needs of many industries. Heat transfer around sphere in all systems that contain particles, is important. Many methods have been proposed to improve the heat transfer rate but using nanofluids is one of the ways that has attracted more attention than others. Ferrofluids have magnetic properties in addition to nanofluids properties and this has a significant impact in increasing the heat transfer rate. Controlling heat transfer by magnetic field is one of the unique characteristics of this fluid. The project aim is to investigate the effect of magnetic field on heat transfer around sphere in... 

Magnetite (Fe3O4) nanoparticles were synthesized and coated with Oleic Acid using the co-precipitation method. The particles were characterized using DLS, FT-IR, SEM, XRD, VSM and UV-Vis spectrophotometry analysis. The mean size of particles was 28.8 nm and the FT-IR analysis indicated that Oleic Acid was coated suitably on the nanoparticles. The vsm test indicated no hysteresis loop for the particles, defining the superparamagnetism of them. A nanofluid containing nanoparticles in 5wt% Acetic Acid in Toluene as the base fliud was prepared. The stability of this nanofluid was determined using UV-Vis spectrophotometry to be less more then 95% in the first two hours. This nanofluid is used as... 

In this research work, a two-impinging-jets reactor (TIJR) has been designed and tested to synthesis calcium carbonate nanoparticles. The application of calcium carbonate nanoparticles in various industries including health, food industry, pharmacy, etc., and the dependence of product quality on properties such as morphology and particle size distribution, persuaded us to study the synthesis of calcium carbonate nanoparticles in the designed TIJR. The precipitation processes are fast chemical processes and mixing plays an important role in the final product quality. TIJR have come to the attention of researchers because of the low micromixing time in recent years. In this research work,... 

Porous media have many applications including heat exchangers, single-phase flow and multi-phase flow packed beds and reactors with different flow patterns, aquifers, and oil and gas reservoirs. To evaluate the behavior of porous media there is need to understand transport phenomena. In this work, we focused on metal foam porous media as an advanced porous media. The effective thermal conductivity of solid matrix, heat transfer in the presence of fluid flow, and pressure drop were investigated using CFD techniques in micro-scale supposing that the solid foam structure consisted of connected kelvin cells. The comparison of simulation results with experimental data reported in literature shows... 

High mixing efficiency and high liquid-liquid mass transfer rate are two key features of spinning disk contactors. This work presents the experimental investigation of mixing and liquid-liquid mass transfer characteristics in a new double coaxial spinning disks contactor. The micromixing efficiency was investigated using a standard system of competitive parallel reaction known as iodide/iodate test reaction. The influences of various operating conditions such as the rotational speed of the disks, the direction of rotation, the feed radial location, the feed distribution pattern, the distance between the disks, and the feed flow rate on the mixing quality were examined carefully. The obtained... 

It has been shown that absorption of carbon dioxide can be enhanced using nanoparticles and in the presence of magnetic field. In the present work, the influences of ferrofluids and magnetic fields on the absorption of CO2 in packed-bed contactors have been investigated carefully. In this regard, multi-tube approach has been applied to model the contactor. The simulation results were validated against experimental data reported in the literature in the absence of nanoparticles and magnetic fields and good agreement was obtained. The influences of variable operating conditions on the contactor performance were carefully investigated. It was found that for 3.4% volume percent of magnetic... 

The importance of gases and liquids absorption in the liquid falling film is mostly due to the wide applications of liquid falling film reactors in the chemical industries. In such a reactor the mass and heat transfer occur simultaneously, but in most cases, the importance of mass transfer is predominant. Therefore, the study of heat transfer in this kind of reactor is neglected. In order to improve the efficiency of absorption, different methods have been employed by researchers. Owing to the rapid growth of nanotechnology, nanofluids have widely been used for increasing the absorption of solution, recently. Magnetic fluids due to their unique combination, among different kinds of... 

Spouted beds are widely used in various process industries as an appropriate gas-solid contacting device. Thus, it is of great importance to study their hydrodynamics as a way of improving their design and efficiency. Furthermore, adding a draft tube to spouted beds considerably changes their hydrodynamic behavior. In this research work, the influences of different parameters involved in the simulation of spouted beds were examined to choose the appropriate ones that can reproduce the experimental data reported in the literature. In this regard, Wen and Yu drag model, Lun et al. radial distribution function, a restitution coefficient of 0.95, and a specularity coefficient of 0.02 were chosen... 

Today, the usage of hollow membrane contactors is considered by the researchers as a novel solution in the separation and purification industry, including the sweetening of gas. Improving the performance of these devices requires a more detailed study of the process factors and changes in its chemistry. Hence, providing a suitable mathematical model by examining the details of the flow pattern within the contactor is based on the computational fluid dynamics technique in the agenda. Also, improving the absorption of components such as carbon dioxide and hydrogen sulfide from the gas mixture using chemical absorbents such as monoethanolamine will be investigated. The change in the mass... 

In the present study, mixed-convective heat transfer of nanofluids in a vertical rectangular channel partially filled with open-cell metal foam has been investigated experimentally and numerically. Al2O3–H2O nanofluids with different concentrations were synthesized and their stability was inspected with UV-Vis spectroscopy. The outlet temperature and pressure drop were measured for different nanofluid flow rates (i.e., Reynolds number values). In the numerical section, a two-dimensional volume-averaged form of the governing equations was used. The velocity and temperature profiles were obtained using finite difference method. The Brinkman–Forchheimer extended Darcy model and the...