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... 

Because of the importance of gas-solid fluidized beds in chemical industrial plants, many experimental and modeling efforts have been conducted the prediction of their behaviors up to now. Gas bubbles have a pivotal role in the hydrodynamics of bubbling gas-solid fluidized beds; so, fundamental understanding of the bubbling behavior of fluidized beds is required to describe bubble-related phenomena such as solids mixing and segregation, reaction conversion, heat and mass transfer, erosion of heat-transfer tubes and particle entrainment. In this work, the effects of different parameters such as bed aspect ratio, bed width, superficial gas velocity, and particle size distribution on the... 

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... 

Silver chloride nanoparticles (AgCl NPs) have been widely used in various areas such as medicine industry, photographic materials, catalytic materials, pigments, and photochromic materials. Therefore, various studies were conducted for their synthesizes. In the present work, precipitation or reactive crystallization method was used for the synthesis of AgCl NPs. In this regard, silver nitrate and sodium chloride as reactants and gelatin as a surfactant were used in a continuous spinning disk reactor (SDR) at the ambient temperature and pressure. The influences of various parameters such as initial supersaturation , free ion ratio, dilution with water , disk diameter , disk rotation speed,... 

Because of the importance of gas-solid fluidized beds in industrial plants, many efforts have been done for predicting their behavior up to now. Generally, there are two major attitudes for describing and simulating the hydrodynamics of fluidized beds, Eulerian-Eulerian methods and Eulerian-Lagrangian metods. Both of these approaches have their own advantages and disadvantages and a lot of studies have been done to understand the nature of gas-solid fluidized beds with aid of these models. Due to fewer presumptions in the basic structure of Eulerian-Lagrangian methods such as DEM in comparison with Eulerian-Eulerian methods like TFM, these models can predict the hydrodynamics of fluidized... 

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 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... 

Because of unique features and numerous advantages, the fluidized bed has been considered as one of the most widely used process equipment in various industries. However, many aspects of the hydrodynamic behavior of the equipment are unknown. In this study, using simulation tool, hydrodynamic behavior and mixing process of binary solids particle mixture in the tapered fluidized bed with a jet at the entrance were studied. Eulerian – Eulerian multifluid model incorporating the kinetic theory of granular flow is used to simulate the gas-solid multiphase flow with open-source MFIX software. To increase the accuracy of the results standard k-ε turbulence model was used. Validation of results was... 

Increasing need for energy, non-renewable fossil resources and environmental pollution persuaded investigators to offer hydrogen as a clean alternative fuel. One of efficient methods for producing hydrogen is the ammonia catalytic cracking reaction. The present work the most to caused on the simulation of both 1D and 2D in an assisted-membrane tapered fluidized bed reactor. In 1D simulation several tubes of membrane placed inside the reactor, but in the case of 2D simulation two membrane tubes on the reactor walls were used. In 1D and 2D simulations the compartmental and Eulerian-Eulerian approach were used, respectively. The simulation results indicate that in a constant static bed height,... 

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... 

Numerous experimental and modeling efforts have been paid done to investigate the behavior of gas-solid fluidized beds. Existence of a velocity gradient in the axial direction in tapered fluidized beds causes unique dynamic characteristics of this type of beds relative to cylindrical fluidized beds. Because of these characteristics, fluidized beds with inclined walls have found wide applications in industrial processes. Gas bubbles play an important role in the hydrodynamics of bubbling gas-solid fluidized beds; so, fundamental understanding of the bubbling behavior of fluidized beds is required to describe bubble-related phenomena such as solids mixing, segregation, reaction conversion,... 

In this study, the mixing and segregation of different mixtures of solid particles with various density or size in gas-solid fluidized beds have been investigated. In this regard, the integrated model of computational fluid dynamics and discrete particle method (CFD-DPM) were used. The soft sphere contact scheme and the linear dashpot-spring model were applied for to evaluate the contact forces. After validating the simulation results with experimental data from the literature, effects of an inlet gas jet were investigated by using some quantitative and qualitative mixing indexes. Effects of gas velocity, percentage of heavy particles, density and particle size ratio, initial arrangement of... 

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,... 

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 this study, mixing of binary solids in Tapered beds with inlet jet using solid particle particle techniques was investigated. A two-dimensional model in which the motion of solid particles and gas in two dimensions is studied is used to simulate the conical beds. For the particle phase by solving the equations obtained with the gas phase equations simultaneously considering the equations and collisions between particles and the gas with the particle is simulated using DEM model. In this study, mixing of binary solids with two different sizes and the influence of simulation parameters such as inlet jet velocity, jet position, using multiple jets instead of single jet with same inlet flow,... 

Simulation runs have been conducted to predict the evolution of sand drying in conical spouted beds with a non-porous draft tube. In the simulation runs, the moisture content of the solid phase was assumed to be 7 % (kg water/kg sand). The simulation results were validated against experimental results reported by Olazar et al. and good agreement was obtained.Influences of various physical and geometrical parameters such as superficial gas velocity, inlet temperature, length and diameter of draft tube and initial moisture content on the sand drying were investigated. Temperature and gas velocity are the most important parameters for improving the drying process and reduce the drying time of... 

Gas–liquid–solid fluidized beds are widely used in the petrochemical, biochemical, biotechnology, and wastewater treatment industries. These beds have the advantage of appropriate mass and heat transfer, better temperature control, and more solid content. In the present work, computational studies have been conducted on two-dimensional tapered fluidized beds to characterize their hydrodynamic behaviour. The presence of two dispersed phases in these beds results in difference in interphase interactions compared to two-phase fluidized beds. Generally, the three phase fluidized beds create a more complex flow pattern than the conventional type of fluidized beds. Three-phase flow in these beds... 

There is extensive use of solid-gas fluidized beds in the petrochemical, energy, chemical, and metallurgical industries. They provide fast heat- and mass-transfer because of the good mixing of solids. Tapered fluidized beds (TFBR) are more appropriate for this type of particle because they have axial velocity changes. This feature allows large particles to remain at the bottom of the bed and fine particles near the bed surface. In this work, the process of the solids mixing in a two-dimensional tapered fluidized bed with a bottom diameter of0/07 m and a height of 0.7 m was studied using computational fluid dynamics (CFD) techniques and applying a two-fluid model approach. The solids mixing...