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Experimental Study on Behavior of Particle-Laden Density Current over Obstacles
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Co-Advisor)
Abstract
Density currents, caused by the intrusion of dense fluids under lighter ambient fluids, frequently occur in both natural and industrial situations. As a result of the density differences, the driving force can arise from soluble substances, temperature differences, etc. If the driving force comes from suspended particles including silt and mud, the currents are called turbidity currents. Due to the variation in concentration and the consequent driving force along the flow path, turbidity currents are significantly more complicated than saline currents. These currents play the most important role in sedimentation in lakes, seas and oceans. In addition, turbidity currents are the main factor...
Invetigation of Dynamic and Noise of Subsonic Jets Using Stability Analysis
, Ph.D. Dissertation Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Co-Supervisor)
Abstract
With the growing development of the aviation industry, the emitted jet noise from civil and military aircraft has become a challenging issue in the development of this industry. Despite recent advances in simulation methods using for fluid phenomena, understanding the nature and physics of noise generated by jet flows has been a complex puzzle for the last decades. Although numerical methods are currently able to predict the jet noise, it is still not possible to fully understand the physics of this phenomenon and subsequently use it to control the emitted sound. In this research, with the purpose of studying the pressure fluctuation caused by large-scale coherent turbulence structures in...
Numerical Simulation of Saccardo Ventilation System in Tunnel Fire Scenarios
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Farhanieh, Bijan (Supervisor)
Abstract
While the population of the cities all over the world is increasing, more and more tunnels and underground transportation passages are being constructed. So, there is an urgent need for designing an appropriate ventilation system for these passages, not only in normal conditions but also for emergency scenarios especially in fire incidents.In the present research, the operation of Saccardo ventilation system, especially in emergency fire scenarios is investigated using computational fluid dynamics methods. Studies conducted in this research are classified into five parts.In the first part, the effect of tunnel ventilation flow rate (due to Saccardo system operation) and its interaction with...
Numerical Modeling of Reformer in Direct Reduction Plants
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Farhanieh, Bijan (Supervisor)
Abstract
Direct reduction of iron is a process to reduce iron in solid phase. The output of this procedure is direct reduced iron (DRI) that can be used in electric arc furnacewithout further changes. Midrex technology, which is the most important one among direct reduction of iron processes, provides 60% of DRI.
Required synthesis gas for reduction process is gained from reforming of the natural gas,with the major proportion of methane, with water steam and carbon dioxide in a piece of equipment called “reformer”. As a matter of fact, reformer is a type of plug chemical reactors. Input materials (natural gas, water steam and carbon dioxide) enter from the bottom section to the prepared pipes in...
Required synthesis gas for reduction process is gained from reforming of the natural gas,with the major proportion of methane, with water steam and carbon dioxide in a piece of equipment called “reformer”. As a matter of fact, reformer is a type of plug chemical reactors. Input materials (natural gas, water steam and carbon dioxide) enter from the bottom section to the prepared pipes in...
Numerical Investigation of Different Ventilation Systems in Coal Mines Effects on the Fire Extinguishing
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Farhanieh, Bijan (Co-Supervisor)
Abstract
In recent years, due to fires in mines around the world, the need to study the dynamic behavior of fire to understand how it spreads and design an appropriate fire extinguishing system to reduce damage to people and underground facilities has been felt. Mine fires are usually caused by external sources such as cable connections, methane gas explosions, or coal self-ignition due to oxygen uptake and rising temperatures.In this research, using Fire Dynamic Simulator (FDS) software, after drawing the geometry of a coal tunnel corridor in progress and creating a fire model through pyrolysis of PVC, fire extinguishing was performed by nozzles. If the nozzle does not succeed in extinguishing the...
Numerical Investigation of Fire Characteristics and Behavior in Confined Spaces; Near-Field and Far-Field Phenomena
, Ph.D. Dissertation Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
Safety against fire and its potential destructions is provided by detection, protection and ventilation methods. Knowledge on fire behavior such as ignition and propagation along with heat and smoke release is essential for implementing these methods. Having such deep information, the fire can be detected at the correct time and be controlled or suppressed, with its heat and smoke removed efficiently, so that rescue services will be enhanced and fatalities and damages will be reduced.Numerical simulation of fire requires deep understanding of multiple phenomena including turbulent flows, conductive, convective and radiative heat transfer, large buoyancy forces, chemical reactions and...
The Study of the Effect of Surfactant on the Liquid Drop Motion In Fluid
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Supervisor)
Abstract
The drop motion in fluid and the mass transfer is one of the most interesting and favorite topics that has attracted the attention of many researchers. Knowing the functions of the factors affecting the deformation and the process of mass transfer and the effects of the addition of the surfactant, improve the efficiency of the related industrial processes.In this regard, the present study examines how the shape and speed of a moving Newtonian drop in a Newtonian fluid, the mass transfer of soluble material from inside the drop to the surrounding fluid and also the study of the effect of surfactant on the dynamics of moving droplet is studied numerically. During the drop movement, the...
Study on Motion of Electrical Conductor Fluid Plug Actuated Electromagnetically in Microsystems
, Ph.D. Dissertation Sharif University of Technology ; Shafii, Mohmmad Behshad (Supervisor) ; Afshin, Hossein (Supervisor)
Abstract
Micropumps are regarded as one of the devices used in microsystems, which are responsible for pumping working fluid. The Mercury Magneto Reciprocating (MMR) micropump, which has been introduced for less than a decade, is an innovative kind of micropumps which the pumping agent includes three liquid metal droplets (LMD) placed inside lateral chambers and reciprocated by the electromagnetic force inside the chambers. The working fluid located inside the main channel is pumped through due to the movement of these three LMDs. The equations governing this micropump are complex and their numerical solution is a time-consuming process, due to electromagnetic, hydrodynamic, and unsteady effects. The...
Experimental Investigation of Mass Transfer by Droplet Using Image Processing
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein ($item.subfieldsMap.e)
Abstract
Wide and varied aspects of droplet motion due to its increasing application in various fields has attracted much attention. Analysis of mass transfer from the liquid drop into the other fluid, such as complex and intriguing problems in fluid mechanics, which is very important. Many experimental and numerical studies have been carried out in this case that the evelopment of laboratory equipment and software, are rapidly growing.
In this study, given the importance of this issue, experimental study on mass transfer in fluid systems solution droplet liquid - liquid extraction, have been considered. Different methods have been discussed to date. In the present study, using image processing...
In this study, given the importance of this issue, experimental study on mass transfer in fluid systems solution droplet liquid - liquid extraction, have been considered. Different methods have been discussed to date. In the present study, using image processing...
Numerical Study and Optimization of Effective Parameters in Freeze Desalination
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor)
Abstract
Freeze desalination as a water refining method has attracted a lot of attention due to its potential in lowering process energy consumption compared to other methods. This method is based on the fact that the dissolved salt is drained from the saline water during its freezing. The current study conducts a parametric study on freezing saline water in a cylindrical container to investigate the impact of geometric and functional factors affecting the desalination quality. This has been done by examining the aforesaid factors in the form of dimensionless parameters such as thermal Grashof number, solutal Grashof number, and Jacob number. In addition, in order to improve the desalination, a novel...
Experimental Study of Droplet Formation in Surfactant Solution
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
Surfactants are materials that reduces surface tension, and this property has provided a wide range of applications for them. Most of the surfactants reduce surface tensions at the interface of two fluids. The pharmaceutical and food industries, detergents, cosmetics, agricultural pesticides, dye production and oil extraction are among these applications.In this study, the formation of droplets in the presence of three types of surfactants SDS, CTAB and Tween 20 has been investigated. To evaluate the droplet behavior in the presence of specific surfactants, various parameters such as formation time of the droplet, the diameter and length of the droplet formed, the diameter and length of the...
Numerical Investigation of the Effects of Environmental Parameters on the Simulation of Spread of Fire in Grasslands
, M.Sc. Thesis Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Co-Supervisor)
Abstract
Fire in Grasslands is one of the most dangerous natural disasters that is uncontrollable at the time of its occurrence and will continue until there is a fundamental change in the conditions of the fire. Fire in Grasslands due to the high density of vegetation can produce a large amount of heat energy in a short time and in a very large area, which alone can cause the spread of fire in Grasslands. Today, numerical studies of fire behaviour and propagation are given more attention than experimental studies due to their lower costs and limitations. In the present study, the numerical simulation of the fire spread with the influence of climate parameters such as humidity, rainfall during fire...
Harness Aquatic Clean Energy from Vortex Induced Vibration
, M.Sc. Thesis Sharif University of Technology ; Abbaspour, Madjid (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
Transverse Vortex-Induced Vibration(VIV) and Flow-Induced Vibration(FIV) of a rigid, circular, elastically mounted single degree of freedom cylinder is scrutinized in range 3×104≤ Re ≤12×104 by means of Computational Fluid Dynamics(CFD). ANSYS CFX, based on FV, is employed to simulate VIV and FIV in different system parameters such as stiffness and mass ratio. Firstly, the minimum structured, hexahedron computational cell required to simulate VIV and FIV by means of Finite Volume (FV) method is provided. Then, the appropriate size for computational domain to simulate VIV and FIV accurately is discussed concisely. Approximated amplitude and frequency ratio are compared to experimental data...
Numerical Simulation of the Air Pollution Dispersion to the Neighboring Regions of Traffic Tunnel Portals
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Hosseini, Vahid (Co-Advisor)
Abstract
By expansion of urban areas and increasing in number of vehicles commuting, tunnels are one of the most inevitable part for developing urban areas. Nevertheless, one of the important topics about tunnels is exhaustion of polluted air into its surroundings. Tohid Tunnel, stretching about 2136 meter, is currently the longest urban tunnel in Iran, connecting Chamran and Navvab Highway from north of Fatemi street, to the Shokufeh street. Now, exhausting pollutants is done only by north and south portals beside a middle shaft. The purpose of this project is to analyze pollutant dispersion from south portal of Tohid tunnel which is located in Navvab residential region. This is done by considering...
Development and Assessment of a Numerical Model for Investigation of Regional Dust Distribution
, Ph.D. Dissertation Sharif University of Technology ; Afshin, Hossein (Supervisor) ; Firoozabadi, Bahar (Co-Supervisor)
Abstract
In recent years, dust storms have been recognized as one of the most crucial problems for people worldwide. Provided that the dust masses transport mechanisms are properly known, the main dust sources can be identified, and therefore, appropriate actions can be taken. Therefore, the main goals of the present study are estimating dust concentration, determination of dust distribution with an emphasis on Iran (especially Tehran), and finding the main dust sources which will be followed in five steps. In the first step, by analyzing the measured data during dust observations in Tehran through 2013-2016, several simple and multivariate nonlinear regression models have been established in order...
Three-Dimensional Large Eddy Simulation of Continuous Density Currents
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
When a fluid moves inside another fluid while they have unequal density, a phenomena occurs which is called density (or gravity) current. Therefore density difference and gravity are key factors of density current generation. Due to application in engineering and geology, it is essential to investigate and analyze the above mentioned phenomena. Dam reservoirs, sandstorm in deserts, snow slide onset and falling, ash clouds produced during eruption of a volcano, and spreading of density current due to the collapsing of reservoirs are some examples of gravity current. There are lots of methods to simulate the turbulence of density current like DNS or RANS. But DNS has high computational cost...
Numerical Modeling of Flow and Heat Transfer Inside Helical Tubes for Cryogenic Temperature Ranges
, M.Sc. Thesis Sharif University of Technology ; Afshin, Hossein (Supervisor)
Abstract
Spiral-wound heat exchangers have special applications in industry due to their high efficiency, especially in low temperature ranges (cryogenic) such as gas liquefaction cycles; However, due to drastic changes in properties, the mechanism of flow and heat transfer in this type of exchangers has not been fully studied yet. Therefore, accurate modeling of fluid flow on both sides of tubes and shells as well as heat transfer between them can be very important in analyzing and designing this type of exchangers and optimizing them to increase the efficiency of the exchanger and the cycle. In this study, the focus is on the flow and heat transfer of supercritical fluid inside helical tubes of...
Numerical Solution of Flow and Heat Transfer in Micro Heat Pipes
, M.Sc. Thesis Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
One of the important issues that increasing development of electronic systems has caused is how to transfer the generated heat out of the system. Heat pipes can transfer large amount of heat because of using latent heat of evaporation and condensation. In micro scales using micro heat pipes is popular that in this instrument liquid returns to evaporator by means of surface tension force. So numerical solution is essential for verifying experimental results and increasing performance of this instrument. In this research has been planned to develop a comprehensive model for numerical solution of flow and heat transfer in micro heat pipes. For this reason surface evaporation and …,...
Experimental Investigation and Calculation of Drag Coefficient of Secondary Bag Breakup Regime
, M.Sc. Thesis Sharif University of Technology ; Firoozabadi, Bahar (Supervisor) ; Afshin, Hossein (Co-Advisor)
Abstract
In the present study, we are to investigate and calculate the drag coefficient in the secondary bag breakup regime in droplet experiment in which the liquid droplet falls into continuous air jet flow. A high speed camera is hired to record the pictures of this process. With the help of image processing techniques, parameters such as dimensionless diameter, growth of droplet, drag coefficient and etc. in secondary bag breakup regime are investigated. The liquid used in this experiments are water, gasoline and diesel fuel. Dimensionless number influencing the result of the experiment are weber and Ohnesorge numbers, with weber number ranging from 6.86 to 20.31 and Ohnesorge number ranging from...
Investigation of Water Mist Performance on Firefighting in Underground Parking Lots
, M.Sc. Thesis Sharif University of Technology ; Farhanieh, Bijan (Supervisor) ; Afshin, Hossein (Supervisor)
Abstract
Fire is an undesirable phenomenon that causes human and financial losses. This in itself is a dangerous event that becomes even more dangerous in closed spaces. Car fires in underground car parks are no exception. In this research, the fire caused by burning flammable materials inside the car cabin located in a closed underground parking environment and the performance of sprinkler and water mist nozzles in controlling and extinguishing it have been investigated. Based on the broad foundations of various phenomena affecting this problem, including the separation of solid fuels under the influence of heat and oxygen, chemical reactions, radiant heat transfer and change of liquid phase to...