Sharif Digital Repository

Many studies have been conducted in plate heat exchangers. However, some effective parameters on the performance have been less considered. It has been demonstrated that heat exchanger performance increases with more uniform flow distribution. It is possible to make the flow distribution more uniform by installing a baffle inside the header. The ‘gap’ or the distance between this baffle and the inlet is one of the important parameters in determining performance but is has been mostly overlooked by previous studies. This study investigates the effects of inlet baffle place on heat exchanger performance. Another important factor is the header geometry. Elongation and reduction in header... 

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... 

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... 

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... 

Turbidity currents are one of the more frequently observed types of stratified flows. In these currents, the density difference is created as a result of particles. Hydrodynamic instabilities at the interface of these currents could occur in various modes and have an important role in the mixing process. The main goal of this study is to investigate the interfacial stability of turbidity current, theoretical and experimentally. The linear stability analysis in temporal and spatial framework are used for studying the stability characteristics of a particle-laden stratified two-layer flow for two different background density profiles: smooth (hyperbolic tangent) and piecewise linear. The... 

Improving efficiency of heat exchangers has always been an important concern for the industry. Pulsating heat pipes are novel and efficient technology in the field of heat transfer. Pulsating heat pipes are widely used in solar water heaters, solar desalination systems, air conditioning systems, cooling of electronical boards, etc. these applications explain the necessity of performing this study in our country. In this research, thermal performance of open loop pulsating heat pipes using two operating fluids (ferrofluid with surfactant and aluminum microfluid) is experimentally investigated. Start-up and steady thermal performance of pulsating heat pipes charged with these two operating... 

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... 

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 …,... 

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... 

Acoustic noise from turbulent jet flow discharged to the einvironment is called turbulent jet noise which is a problem for turbojets, turbofans, missiles, rockets and everywhere the discharge of a jet at high speed exists. In order to achieve the jet noise reduction methods, understanding this phenomenon with modeling on a detailed theory for the future developments in this field is required. In this study the noise generation from coherent large scale structures for a subsonic jet with acoustic Mach number of 0.5 is studied using linear stability analysis. To get the base flow used in instability analysis, the jet flow is modeled using different two equation k-ε models and after... 

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... 

Gas liquefication in low temperatures is one of the most challenging fields in engineering due to complexity of its thermodynamic analisys and fabrication of equipments. Heat Exchangers are one of the most important equipments in these prosseces. High prices of Heat Exchangers in these facilities makes their Optimal and cost effective design, of crucial importance. In this thesis three dimensional model of a Plate Fin Heat Exchanger is thoroughly investigated. Fistly, by means of Aspen Heat Exchanger design Software a counter flow Heat Exchanger is designed. This HX is to be placed in Collins cycle, so, working fluid in both hot and cold streams is Helium Gas. The HX then by means of ANSYS... 

Heat transfer enhancement in heat transfer equipment, such as heat exchangers, has been widely studied. There are plenty of techniques to increase heat transfer in tubular heat exchangers. One of these techniques is applying a porous medium. These media have a great interface with fluids which can enhance the heat transfer rate. Meanwhile, the thermal conductivity of these media is usually greater than that of the studied fluid. Thus, by adding a kind of highly conductive porous insert to a heat exchanger, we are able to save the material used to construct the device and the space occupied by it.
Shell-and-tube heat exchangers are one of the most widely-used types of exchangers in... 

In the present study, hydrodynamics and particle sedimentation of a rectangular basin is studied numerically. Results are also validated with experimental data. Two major goals are perused in this work: First comparing LES and RNG k-ϵ turbulence models and second, investigating the accuracy of simulation of particle sedimentation by solving the concentration formula.
In order to achieve these goals, a 2D sedimentation tank is simulated using the RNG k-ϵ model. Velocity and concentration profiles are also plotted. Comparing the results with experimental data reveals that simulating sedimentation by the mentioned method has acceptable accuracy and can be used to predict sedimentation. In... 

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... 

Drop deformation and breakup are of great importance in a wide variety of applications, from fuel combustion to agriculture, pharmaceutical processes, and coating. In this experimental study, droplet secondary bag breakup has been investigated. By conducting experiments on different fluids with a wide range of properties and in different conditions, the effects of different parameters on secondary bag breakup have been addressed. For this purpose, the breakup of these fluids, water, ethanol, glycerin, and SDS solution were scrutinized and by comparing their trajectory and morphological parameters, results are driven. Experimental conditions were such that the Weber number are from 11 to 17... 

Due to its unique properties, helium has extensive applications in various fields such as medicine, life sciences, electronic industries, welding, meteorology, and the industries which require low-temperature cooling. Also, designing the cryogenic distillation columns is one of the complex aspects of these plants. In the present study, the distillation column of a helium extraction plant from natural gas has been simulated by means of theta method of convergence. The required thermodynamic properties were determined from the Enhanced Predictive Peng-Robinson (E-PPR 78) equation of state, which has high accuracy in predicting the thermodynamic properties of natural gas componens. The... 

Bubble growth and formation is used in many of the two-component processes including gas and liquid such as extracting pure metal from ore, separation of water from oil, distillation and absorption. The regime of bubble formation determines the main characteristics of the mentioned process like bubble shape and volume, its formation time and the interaction of the successive bubbles such as collision or coalescence. So predicting the regime of bubble formation and its characteristics helps the engineers to control the process. In this presented research, through doing experiments, different regimes of air bubble formation in water and Aqueous glycerol i.e. single, double, multiplex and... 

Heat exchangers are one of the most important components used in liquefaction cycles and overall efficiency of the cycle mainly depends on the heat exchangers effectiveness. It has been shown that the effectiveness of these equipments should be high enough to be able to liquefy a gas. Spiral heat exchangers are used frequently in cryogenic industry and specially in Helium liquefaction industry due to their specific characteristics, however according to literature review it turns out that little study is done in the field of simulation and geometrical parameter investigation of these kind of heat exchangers, so in this study the design and simulation of these cryogenics heat exchangers are... 

Cryogenic is the study of physical phenomena at temperatures below 123 Kelvin. One of the applications of cryogenic science is the liquefaction of gases. In the liquefaction cycles of gases, such as helium liquefaction, fluidization occurs in the pressure reducing valve but temperature of the gas should be greatly reduced before it enters the pressure reducing valve. For this purpose, high-performance heat exchangers should be used. Spiral Wound is one of the heat exchangers that has ability to achieve over 90% efficiency due to its structure. Researchs in the field of design and simulation of spiral heat exchangers are limited and are done with a lot of simple assumptions such as constant...