Sharif Digital Repository

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,... 

In the first work, the method of direct growth was used to grew MOFs based on cobalt, as electroactive centers, for preparing electrochemical sensors for the determination of glucose. In comparison to most of the electrochemical sensing platforms based on MOFs for determining glucose, which suffer from some disadvantages like time-consuming synthesis procedures and using hazardous organic solvents, the proposed in situ growth method is much faster and no need to toxic organic solvents. Herein, cobalt-based MOFs were grown on the surface of the reduced graphene oxide modified glassy carbon electrode by the direct and rapid conversion of cobalt hydroxide nanosheets intermediates. The... 

In the present work, nanocomposites consisting of nickel oxide nanostructures and a hollow carbon substrate were used to modify a glassy carbon electrode's surface for the electrooxidation of hydrazine hydrate. For this purpose, hollow carbon nanospheres were first synthesized using aniline and pyrrole copolymerization process without any template needing. The hollow carbon nanospheres prepared by this method have outstanding features such as high specific surface area and good stability. On the other hand, they did not require toxic and environmentally harmful solvents to remove the template. In this study, after preparing hollow carbon nanospheres as a suitable substrate, different... 

In this article we have investigated an inventory control model with uncertainly in supply and capacity constraints in the volume and variety of goods for supply chain of chain toy stores. The purpose of model is to minimize inventory costs, ordering cost and the cost of shortage to develop an acceptable customer service level. In order to execute replenishment process of goods we propose three periodic review inventory control policies that are implemented automatic, step by step and by using indicators defined in this article. The major difference between the proposed policies and the as-is policy is to use categorization od goods based on specific characteristics. Each of the three... 

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... 

The solid-gas fluidized beds are widely used in the petrochemical, energy, chemical, and metallurgical industries. Because they provide fast heat- and mass-transfer rate along with good mixing behavior of solids. Because of carry over of fine particles in columnar beds, the application of tapered fluidized beds has become widespread in industires due to the variation in axial velocity along the bed height. In this work, a 2D two-fluid model (TFM) incorporating the kinetic theory of granular flow (KTGF) was used to simulate the hydrodynamic behavior of gas bubbles in a tapered fluidized bed. The experimental data obtained in the laboratory were compared with the simulation results and good... 

Bread holds a significant place in the daily lives of Iranians, making the bread supply chain as one of the country's most vital product supply chain. The Iranian government has undertaken the responsibility of supplying the bread chain, and to achieve this, a specialized mother company was established. As a result, this company manages all aspects of this supply chain. Initially, the company's database and macro-policy objectives were examined to provide recommendations that align with its goals. One of the proposed suggestions was to optimize the extra-provincial transportation, which plays a crucial role in the supply chain. This proposal was chosen and thoroughly investigated. By...