Sharif Digital Repository

The widespread use of internet systems and their popularity have led to an increase in the need for recommender systems, and extensive research has been done to address this need. Systems that suggest desirable options to users based on available information are recognized as recommender systems. Important examples of these systems exist in online stores and social networks. In online shops, data specific to each user is very limited and there are limited connections between users and products, which poses challenges for recommender systems. Incomplete or incorrect data may also cause errors in the system, such that the system performs the recommendation process based on wrong information.... 

Given the necessity of energy storage in today's world, various technologies have been developed to expand energy storage systems on a large scale. Electrochemical-based technologies, due to their high efficiency, are among the most suitable energy storage systems that have attracted the attention of scientists and researchers. Rechargeable zinc bromine flow batteries are one of the most powerful candidates for next-generation energy storage due to their high energy density, lower material costs, deep discharge capability, non-flammable electrolytes, relatively long lifespan, and good reversibility. However, there are many challenges to improving the efficiency and stability of these... 

Titanium dioxide has covered a wide range of applications as a semiconductor photocatalyst. TiO2 is an indirect, 3.2 eV band gap semiconductor which can be stimulated using UV light. Improving the quick electron-hole recombination rate, we can enhance the photocatalytic efficiency of this semiconductor. One of the approaches in hand is to use noble metals in connection to TiO2. Among noble metals, due to its plasmonic and anti-bacterial properties and ease of preparation, silver would serve as a perfect candidate. The mechanism for photocatalytic enhancement in Ag-TiO2 structures lies behind the fact that silver can trap the photogenerated electron of TiO2 and inhibit the electron-hole... 

Fast and accurate fault diagnosis has a significant role in the power system operation. For a power system to come back to the normal state, the precise fault diagnosis is necessary. The current practice in power system fault diagnosis needs operators in the control center to use data of PR and CB in order to infer the faulted section based on their experiences. Expert systems and artificial intelligence have been suggested as alternatives to the human expert experience and inference. Other model- and optimization-based methods have also been reported for fault diagnosis, provided that similar data is available from the SCADA system.Nevertheless, in large disturbances resulting in partial or... 

In this study, deactivation of Midrex reforming catalysts is evaluated kinetically by 3.5-year data of Mobarakeh Steel Company direct reduction site. The variation of Midrex catalyst’s structure is characterized by XRD and BET test. Two deactivation mechanism are characterized, methane cracking carbone deposition and sintering. The project results demonstrate that victorious mechanism is carbon deposition. The methane cracking carbone cause layer by layer deactivation of catalyst during 5.5 months. Although, XRD and BET showed pore volume and radius reduction and Ni crystal increasing, approximated constant activity of catalyst were approved by kinetic evaluation  

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... 

In the recent year, there has been a rising interest in producing functional foods containing encapsulated probiotic bacteria according to their perceived health benefits. Probiotics are feed and food supplements that beneficially affect the host’s health. The term “probiotic” includes a large range of microorganisms, mainly lactic acid bacteria. Because they can stay alive until the intestine and provide health beneficial effects like lowering cholesterol, improving lactose tolerance and preventing some cancers like colon cancer on the host health. It has been recommended that the viability of probiotics should be at least 107 CFU/ml of product at time of consumptions to provide selective... 

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... 

Existence of a velocity gradient in the axial direction in tapered fluidized beds causes unique dynamic characteristics of this kind of beds relative to cylindrical fluidized beds. Due to this characteristic, fluidized bed reactors with inclined walls have found a wide application in many industrial processes. In this study, tapered-¬in and tapered-¬out fluidized bed reactors have been simulated using Eulerian-¬Eulerian approach and applying the Kinetic Theory of Granular Flows (KTGF) for solid particles to investigate the bed behavior in the presence of two kinds of chemical reaction with gas volume reduction and gas volume increase. The results of hydrodynamic simulations show that the... 

In this work solid circulation pattern in 2-D gas-solid fluidized beds has been investigated carefully. In this regard TFM approach was used. In addition KTGF was applied along with Gidaspow drag model. A commercial CFD software (ANSYS FLUENT 15.0) was used to simulate the hydrodynamics of the bed. Effects of a number of operating and design parameters on the solid circulation pattern were examined in detail. These parameters were gas velocity, restitution coefficient, pressure, solid density, temperature and vertical plates. The simulation results were validated against experimental data reported in the literature. Furthermore, the solid vertical velocity was investigated carefully  

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...