Sharif Digital Repository

These days, according to increasing requirement to the applications of clean rooms in industries in and within the developing industry of computer, positive indicators that show a real need to a compere comprehensive study and research about the Clean rooms, in oder to predict the distribution and dispersal of the particles. Correct determination of indoor airflow and particle concentration distribution results in new standard development for Clean rooms. As computational fluid dynamics has become a powerful tool for indoor airflow studies, in this research, influence of effective parameters on the flow and concentration distribution in clean rooms has been... 

Heat pipe is a device with several applications in various industries such as electronics cooling, nuclear and renewable technologies. This apparatus transfers heat from a hot source to a cold one. Thermosyphon is a special type of heat pipe that transmits heat using gravitational forces. Although scholars have performed many experiments on thermosyphon, mostly they were about the thermal characteristics of thermosyphon and rarely the hydraulic specifications of thermosyphon have been investigated. But it is clear that these two specifications (thermal, hydraulic) relate to each other closely and detailed study about their interaction may bring out better results. In this thesis, initially a... 

Two phase cross flows around a body have seldom been studied until now and considering these flows can play a significant role in long-term reliability and safety of industrial systems. In this paper flow regimes, drag coefficient and void fraction around different cross-section prisms were considered. To achieve this aim, main equations of flow have been developed for investigation of drag coefficient in air-water two phase. Our numerical analyses were performed by a designed and written CFD package which is based on Eulerian-Eulerian approach. Geometries, which have been studied in this article, are: circle, rectangle and triangle, for different aspect ratio and leading edge angle,... 

Pipe freezing has become well established in industry as a method of short-termisolation in order to carry out maintenance or repairs. It is often necessary to repair system components without plant shutdown or drainage of system having many piping structures which may have hazardous or expensive fluid. Therefore, a series of tests has been arranged to investigate the ice plug formation in two standard pipes with different diameter size. The freeze zone on the pipe has been created by means of an aluminum jacket which liquid nitrogen flows in it. In the tests the freezing time, amount of liquid nitrogen usage andthe pressure tolerance of ice plug have been determined. Moreover, the numerical... 

Today, the importance of transportation and motor vehicles is crystal clear for everyone. On the other hand, energy crisis and the emissions of these vehicles are two fundamental problems of internal combustion motors. On account of this, the diesel vehicles have absorbed researchers’ attentions due to their higher efficiency and low fuel consumption.Due to high diesel vehicle efficiency, it is tried to substitute gasoline vehicles with these vehicles. In addition, the unrecyclable nature of fossil fuels has led to more attention to renewable energies such as biofuels. A lot of kinds of herbal oils have identical characteristics with diesel fuel.In this research, the combustion of Rapeseed... 

There are different flow regimes in multiphase flows through the pipes, which affect the flow structure and other important fluid parameters. Each of these flow regimes are considered to be suitable or not in different industries. So it is needed to provide the situation of suitable flow regimes formation and to prevent the others from development. One of the main parameters affecting the flow regimes development is considered to be the passing flow’s channel section are or the pipe diameter. This project is defined to investigate the effect of changing pipe diameter on the formation of flow regimes in an air-water upward two-phase flow, experimentally. Therefore, a vertical pipe of 6 meters... 

Airlift pumps are widely used in numerous industries for different applications such as transmission of viscous fluids (heavy hydrocarbons of oil), pumping of corrosive liquids and so on. In general, parameters which affect the efficiency of an airlift pump can be classified into two major groups. The first group is the designing parameters such as the diameter of the upriser pipe or the submergence ratio. The second group is the operation parameters such as diameter of the bubble, inlet pressure of the gas and so on. One of the designing parameters which can have an effective influence on the performance of an airlift pump is the non-constant diameter of the upriser pipe, which can be... 

Pulse Tube Refrigerator (PTR) has an exceptional feature among all similar refrigerators, because of its unique characteristics such as long lifetime, compact size and no moving parts in low temperature. Despite of all these advantages because of its low efficiency, many researchers are trying to optimize performance of this refrigerator. Most of these efforts are based on one-dimensional simulation of the system. In this thesis, a two-dimensional analysis is performed to study the nature of flow field in an Inertance Tube Pulse Tube Refrigerator (ITPTR). This analysis is based on a numerical modeling of an entire ITPTR. To reach this purpose the two-dimensional form of mass, momentum and... 

Double channel and coreless induction furnaces are used extensively in many processing industries due mainly to their good heating efficiency, high production rate, clean working environments and relatively low operating costs. The study of heat transfer treatment and evaluation of the heat losses of these furnaces becomes an important issue in melting industries. In this dissertation, a heat transfer analysis will be performed for an induction furnace and heat losses by conduction, convection, Eddy-Current and Hysteresis in a furnace structure, and radiation from the body of a specific induction furnace will be modeled considering the symmetry of the furnace chamber. The models presented in... 

Nowadays, cleanrooms have a growing application in a broad range of industries, e.g. pharmacy, aerospace, nuclear energy and electronics. So, it seems that numerical modeling of airflow in such spaces becomes more essential. As computational fluid dynamics has become a powerful tool for indoor airflow studies, in this research, influence of effective parameters on the flow and concentration distribution in cleanrooms has been investigated by the use of CFD. To do so, aerosol flow in a 3-D cleanroom has been numerically modeled by Fluent 6.3, using Euler-Euler approach and standard k- turbulence model. Comparison between numerical results and experimental data shows a considerably good... 

With the increasing number of applications in internal combustion engines, environmental impact and air pollution caused by emissions has been much attention. Natural gas is a promising fuel for limiting pollution laws in many countries. The use of fuel with a higher ratio of hydrogen gas to carbon pollution reduction motor. In this context and with regard to development policy and also due to the diversity basket NGV fuel, fuel injection, has been modeled analytically and numerically in a direct injection engine. In this study, an analytical model for spray injection fuel delivery and is dissolved. The resolution of the method of separation of variables is taken. The effect of the nozzle... 

Pulsating heat pipe (PHP) is a type of wickless heat pipe that has a simple structure and an outstanding thermal performance. Nanofluid is a type of fluifid in which nanoparticles are dispersed in a base fluid and has a better thermal conductivity in comparison with its base fluid. In this article, the performance of a nanofluid PHP is investigated. In order to simultaneously investigate the thermal performance and flow regimes in the PHP, a one-turn copper PHP with a Pyrex glass attached to its adiabatic section was used. A one-turn Pyrex PHP was also used to fully visualize flow patterns in the PHP. Our results showed that the material that a PHP made of and temperature of working fluid... 

The lab-on-a-chip (LOC) devices utilizing electroosmosis for flow actuation are usually encountered with non-Newtonian behavior of working fluids. Hence, studying the flow of non-Newtonian fluids under an electroosmotic body force is of high importance for accurate design and active control of these devices. In this thesis, mixed electroosmotically and pressure driven flow of salivathrough a rectangular microchannel is examined utilizing two viscoelastic constitutive equations, namely PTT and FENE-P models. Since the hydrodynamic entry length is usually negligible for microflows, a hydrodynamically developed flow is considered in the analysis. The governing equations in dimensionless form... 

Pulse tube refrigerator due to the relatively high efficiency, high reliability of linear compressor and the absence of moving parts in the cold area is known as one of the best options to generate up to one kW of cooling power at temperatures from 4 to 123 K. More recently, the use of the device at a temperature of about 150 K, makes use of it even outside of cryogenic temperature. The most important part of the device is regenerator, so understanding the nature of the flow and interaction of gas and solid network in the retrievers is necessary. In this study, Inertance pulse tube refrigerator (IPTR) is simulated using Ansys Fluent in two different conditions. In the first condition the... 

The advances of technology of microelectrical devices and their computational capacity and so, their heat rates, make the thermal control of them more complex. Utilizing nanopfluids is one of proposing options. The current research investigates the effectiveness of using nanoparticles on the heat transfer rate of fluids in the natural convection. A two-component two-phase lattice Boltzmann method (LBM) has been implemented for this purpose. A wide range of Rayleigh number (Ra), namely 103 to 109, 0 to 0.05 volume fraction s of nanoparticles and nanoparticle diameters below 100 nm has been investigated in this research. The method is optimized for complex geometries. Two and three dimensional... 

In order to safe design and optimize performance of industrial systems which work under two phase flow conditions, it’s often needed to categorize flow into different regimes. In present work the experiments of two phase flow were done in a large scale test facility with length of 6m and 5cm diameter. Four main flow regimes were observed in vertical air-water two phase flows at moderate superficial velocities of gas and water: Bubbly, Slug, Churn and Annular. Some image processing techniques were used to extract information from each picture. This information includes number of bubbles or objects, area, perimeter, height and width of objects (second phase). Also a texture feature extraction... 

In solar systems, the required space and cost, the impossibility of continuous access to energy, energy storage and optimal use of the received energy are the basic parameters and issues. Therefore, with the knowledge of these cases, proposing ideas and approaches to study the possibility of reducing the above mentioned issues are of the main objectives of this research. In solar thermal systems and solar electrical systems, the collector and photovoltaic panels are the main components, respectively. However, the studies show that there are issues regarding the existing collectors and photovoltaic panels, e.g. the flat-plate type which is most used in solar systems, and the basis is not... 

Today, oscillating heat pipes play an undeniable role in energy recovery due to their high thermal capacity. Studies show that the working fluid plays a more effective role in improving the performance of the oscillating heat pipes. In this study, a model is proposed to determine the optimal concentrations of Fe3O4-MWCNT/DI Water hybrid nanofluid based on NSGA-II multi-objective optimization algorithm. The Thermophysical properties of the fluid have been optimized to obtain the concentrations that provide the highest thermal conductivity and specific heat capacity and the lowest dynamic viscosity and density for hybrid nanofluids. Then a number of these concentrations¬ have ¬been selected... 

Duo to the strictly pollution legislation in the last decade and increasing demand of lightweight internal combustion engines with rated power , turbocharging of the spark ignition engines become more interested. Therefore the turbocharging of M15GS engine was studied in both gasoline and natural gas fuels with purpose of enhancement of performance characteristic of engine. According to this approach 0-D turbocharger matching performed for gasoline and natural gas fueled M15GS engine. Also an innovative 1-D turbocharger matching performed for gasoline fueled engine. Then engine equipped with SJ50 turbocharger and dynamometer and combustion development tests performed on gasoline fueled... 

Due to the wide application of plate-fin heat exchangers in various industries such as the petrochemical industry, aerospace industry, air conditioning systems, separation and liquefaction of gases, especially natural gas, boiling, condensation, and transportation industries, proper design of these heat exchangers is necessary. Most of the previous researches in the field of heat exchanger modeling has been done in single-phase mode. The two-phase modeling has been performed, often thermodynamically, and the effects of turbulence and surface tension have been ignored. Thus, in the present study, numerical modeling of the two-phase plate-fin heat exchanger is presented. In this project,...