Sharif Digital Repository

Tapered-in fluidized beds, have unique dynamic characteristics compared to cylindrical fluidized beds, because of the velocity gradient in the axial direction. Therefore in the recent years, tapered fluidized beds were widely used in various processes such as biochemical reactions, biological, crystallization, gasification, liquefaction, etc. In this study, a two-dimensional gas-solid model using Eulerian-Eulerian approach along with the kinetic theory of granular solid in a tapered-in fluidized bed was applied. Moreover, the tapered-in fluidized beds were compared with the tapered-out fluidized beds and cylindrical fluidized beds in order to investigate the hydrodynamic behavior of the... 

In this work, a numerical investigation on shell side performance of a continuous helical baffle helixchanger along with smooth and helically ribbed tubes using CFD commercial code, Fluent, has been performed. The results of simulation for this type of exchanger were compared to a similar heat exchanger with segmental baffles. The geometries are created and meshed using Solidworks and Ansys Meshing softwares, respectively. Mesh generation is carried out using unstructured tetrahedral type elements. Element size (or number of elements) are chosen in such a manner that maintain accuracy and reliability of results in a reasonable run time. Simulation validation were carried out by comparison of... 

The concurrent flow of oil and water is a common occurrence in the field of multiphase flow in different fields including petroleum industry. In oil and gas, production engineers often face a situation in which more than one phase is flowing through the producers. In such conditions an accurate assessment of pressure loss inside the well plays a vital role in efficient and effective production planning. Changes in well orientation, wellbore diameter, reservoir and fluid properties as well as fluid flow rates are among parameters in which will affect the flow patterns that can occur inside a well during its life time. These flow patterns are created as a result of a competition between... 

This dissertation discusses the development of dimensionless correlations for predicting hydrodynamic parameters and CFD simulation of gas-solid two phase flow in conical fluidized beds. This research mainly focuses on the impact of particle size distribution on hydrodynamic parameters. The first section describes the experiments that were carried out with a number of gas–solid systems in a conical column to study certain important characteristics of the fluidized bed. Generalized empirical correlations, based on dimensionless analysis, have been developed in order to predict minimum fluidization velocity, minimum velocity of full fluidization, maximum pressure drop and bed expansion ratios.... 

A numerical simulation of fluid flow in gas condensate wellbore, which annular flow is dominant, is performed. A three fluid model is used for annular two phase flow. The model is based on conservation equations of mass, momentum and energy for gas phase, dispersed phase (droplets) and the film. The friction between phases and with wellbore wall and also mass transfer between phases, which conservation equations rely on them, are considered. Computer programming of obtained system of equations is performed in Matlab. The Reimann method is used for solving our system of hyperbolic equations and simulation is performed for both steady and unsteady state. Transforming system of nonlinear... 

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... 

Understanding the hydrodynamic and physical chemistry basis of surface phenomena is very important for many branches of basic science like Chemical Engineering, Mechanics, Space Engineering, and Material Engineering in the level of fundamental studies and applications. In addition to the common technologies, the role of surface phenomena in novel technologies is also very essential. For example, nanotechnology, chemical or physical sensors, or micro electrical systems in which surface phenomena is playing a main role. Therefore, understanding the basis of surface science is very important for any development in many industrial and fundamental studies. The main topic of this thesis which is a... 

In this thesis, shell and tube heat exchanger with twisted tube bundle in 5 different twist angles is investigated using CFD commercial software, Fluent. A three dimensional unstructured grid has been employed to simulate the heat exchanger model. Optimum grid size is selected according to the level of accuracy required, optimum run time and the available computational resources. The method and simulation accuracy were verified by comparing simulation result with data from Bell-Delaware method. The RNG-K-ϵ method and second order discretization scheme for all variables are selected to model turbulent flow and solve the governing equations. Overall Heat transfer coefficient and pressure drop... 

packed columns are important in liquid-liquid extraction processes. In most studies, at first, drops are broken to small drops as much as possible and then they contact with packings. But, because of different reasons drops during their moving up coalescence together. So far, there is not serious investigation about hydrodynamics of these large drops and their breakage in packed columns. Thus, breakage of two different sizes of drops while collision to 3 different height of 4 different type of packings with two volumetric flow rates and in 2 cases of straight collision of drops to bed and collision to support plate has been investigated. Then size distribution of produced drops throughout... 

The phenomenon of oil drop detachment from solid surface has great importance in many different industries, such as coating, print, membrane emulsification, detergency, and oil enhancement recovery. In our study, we tried to explore this phenomenon. Therefore, we attempted to employ Young equation as force balance for the discussed system which is comprised of n-Decane as oil droplet, aqueous solution (brine) with SDS (Sodium Dodecyl Sulfate), and glass. Also, in order to find governing factors regarding oil detachment process -such as interfacial tension, contact angle, and line friction coefficient- we used an advanced apparatus equipped with horizontal microscope and digital video camera.... 

Thermodynamic modeling is a useful method for predicting of asphaltene precipitation due to various reasons, such as CO2 injection, mixing of different oils in oil storage and pressure changes. However, the application of solid model and thermodynamic micellization model, for prediction of asphaltene precipitation under gas injection condition, hasnot been improved. In this work, two computer codes which are based on two different asphaltene precipitation thermodynamic models, 1-Thermodynamic Micellization Model and 2- Solid Model, have been developed, and, used for predicting of asphaltene precipitation data reported in the literature as well as the experimental data obtained from high... 

Energy harvesting from wasted environmental energy to power low-power electronic devices has emerged as an enabling technology for wireless applications in the past decade. The purpose of this technology is to provide remote power sources and/or recharge storage devices such as batteries and capacitors. This concept has environmental implications in reducing chemical waste produced by replacing batteries and potential monetary benefits that also reduce maintenance costs.Energy harvesting (EH) from untapped natural energy sources is common nowadays due to the increasing demand for electricity. Sources have the potential to generate micro to milliwatt power, depending on environmental... 

By reducing the size of the transistor, it is possible to implement systems on a chip. For this puspose, these chips require different supply voltage levels. Therefore, two types of linear and switching converters are used to convert DC voltage level. At high convertion ratios, linear regulators have lower efficiencies than switching converters. However, in switching converters, due to their nature of functionality, very high efficiencies (near 100 percent) can be achieved. The advantages of linear regulators include low output voltage ripple, no need for off-chip elements, low noise, and simplicity. For this reason, a linear regulator is usually used in the output of the switching... 

Designing artificial intelligence based arithmetic machines that can intelligently perform human-like task has attracted considerable interest among researchers. The ever-increasing advances in soft-computing algorithms require appropriate hardware platforms for such algorithms. One of the most important problems with these algorithms and their hardware implementation structures is the discrepancy between the hardware and the nature of the problem. It can be argued that paying attention to hardware implementation does not necessarily guarantee an optimal implementation of these algorithms. Most of the proposed hardware implementations have very small resemblance to the biological systems... 

High voltage pulse generators are widely used in the radar systems, laser, medical, food processing and etc. One of the pulse quality criteria that was analysed in this thesis is the pulse to pulse regulation. Pulse to pulse regulation is important in various fields. In the radar applications pulse to pulse instability caused undesired errors in the signal processing and limitations in the tracking of the targets. In Free Electron Lasers (FELs) non identical pulses cause RF phase shift in the each pulsed power supply and creates instabilities in the electron beam. Pulse quality is essential in medical application so that in the treatment of cancer an improved precision in delivering the... 

Research on how the human brain processes information leading to the creation of two major groups in the field of soft computing. The first group believes that information is being processed based on linguistic concepts and if-Then rules. Fuzzy logic is based on this idea and tries to avoid exact calculations in information processing tasks. Second group believes that the power of human brain in processing is because of a large network of neurons with small abilities. These studies led to the presentation of artificial neural networks algorithms. Spiking neural network is known as third generation of artificial neural networks and tries for processing information using a real model of brain... 

Cooperative communications have been introduced to combat degrading effects of fading in wireless networks and attracted much attention recently. This technique provides distributed spatial diversity that enables energy-efficient transmission of information from source nodes to destination nodes via intermediate relay nodes. Most existing protocols, detection techniques and optimization methods in cooperative networks assume that perfect channel state information is available. While in practical situations, the estimates of the channels may only be known and for acquiring such knowledge, a fraction of power and bandwidth have to be spent for channel estimation using pilot symbols. In this... 

Human brain is one of the most wonderful complex machine which is designed for ever. A huge complex network, composed of neurons as tiny biological and chemical processors which are distributed and work together as a super parallel system to do control and vital activities of human body. Today the main secrecies of operation mechanism in individual neurons as fundamental elements of brain are reasonably understood, but network interactions of this wonderful processors and full understanding of information coding in brain seems elusive and remains as a big challenge in many interdisciplinary fields of science, from biology to cognitive science and engineering.
Thus human brain learning... 

ALM (Active Learning Method) is based on fuzzy concepts, striving for human-like information processing. Typical fuzzy methods for control and modeling applications rely on linguistic processing with membership functions of the kind in fuzzy rules. ALM, however, processes multiple features of a target by converting each into patterns. This simulates the human approach to the acquisition of knowledge from complex source targets in that it focuses on each feature of the target and processes that information in pattern-like images rather than utilizing numerical interpretations. In ALM, the ink drop spread (IDS) method has been proposed as a means of obtaining useful information... 

OFDMA multi-hop cellular network (MCN) is the topic of a wide range of research today. In this thesis, we analyse this type of networks, regarding shadowing status, mobility patterns and different service requirements. In the multi-hop (MH) scenario, six fixed relays are set up in each cell, which split the cell into seven subcells. For mobility modeling, each subcell is split into several sub-regions. Mobile nodes are able to maintain at each sub-region with a random time distribution and migrate from it to one of its neighboring sub-regions. We also consider three types of services requiring specific number of subcarriers with specific BERs. The set of subcarriers is distributed among...