Sharif Digital Repository

In this study, the numerical investigation of the plasma actuator has been discussed on the combustion within a channel by FLUENT software. For this purpose, the empirical and analytical force is applied as a source term in the momentum equations in a certain area of the channel. The empirical force is obtained from experimental data and the analytical force is obtained by simplification of Maxwell equations. These equations include electrical potential and density of charge particle equations. In order to validation of UDF code, the analytical force is applied to air flow and the results are compared with other numerical simulation. Then, we discussed the results of combustion without... 

Nematic liquid crystal shells (droplets) containing cores have attracted considerable attention in recent years. Defect structures that form in such systems do not emerge in the bulk.These shells which could be created using double emulsion techniques in the laboratory have provided applications in microscale optical structures.In the past just boundary conditions and bulk parameters were noticed but recently the geometry of the core is considered likewise.In this work oblate ellipsoid cores are examined numerically using finite-element method. The boundary conditions in studied systems are perpendicular in outer surface of droplet and planar in the vicinity of the core. First by minimizing... 

The advent and advancement of technology through the conversion of Gas-Synthesis (a mixture of CO and H) into liquid hydrocarbons, by Fischer- Tropsch synthesis (FTS) gives more promising future in this field. Metals such as cobalt, nickel, zinc and iron are used as catalysts for FTS. Studies have shown that the surface structure of metal catalyst has a great influence on the process, and leads to different products and transition states. Iron has been known the most used and the most cost-effective metal catalyst in FTS. Different surfaces of Iron have different catalytic roles. In our work, Fe(100) -that is the most stable after Fe(110) and is known as the most active iron’s surface in... 

In the present thesis we will design and study some rendezvous algorithms for cognitive radio networks. In cognitive radio networks, secondary users try to access the spectrum of primary users in an opportunistic manner. Each secondary user constructs a channel list of accessible resources by channel sensing. These resources are not necessarily the same for different users; therefore, in order to make a connection in absence of a fixed control channel, different secondary users should find each other properly and quickly after entering the network. This is known as the blind rendezvous problem. We will develop and examine a new sequence based algorithm for blind rendezvous. Moreover, some... 

Generally, virtual loads is used to test all AC power and energy meters and are usually passive. To prevent possible damage of this heat and to control the temperature, cooling blowers are used which increases the volume and weight. So, recycling the power delivered from the grid causes a small amount of power to be converted to heat in proportion to the load efficiency. The purpose of this study is design, predictive controller model for programmable electronic regenerative AC load. The structure used is a back-to-back converter consisting of an AC-DC converter and a DC-AC converter, which according to existence of capacitance between these two structures, two converters can be controlled... 

The Weil group WF is assigne to every local field F. Langlands Correspondence is a bijetion between semisimple two-dimensional Deligne representations of Weil Group WF and irreducible representations of GL2(F) which fixes assigned L-functions and local constants. In this thesis we have classified an important class of irreducible representations of GL(2) over local fields called Principal Series. We also tried to give a taste of Langlands Correspondence to the reader. First we explain preliminaries and introduce locally profinite groups and their smooth representations. Then we classify representations of GL2(F) when F is finite. Then we study GL2(F) when F is a local field. Finally we... 

This project shows the flow of implementing a 5s Program into a factory. From it’s first step by studying current situation until the last step implementing and monitoring the results. Manufacturing companies have a growing, market-driven need to adopt World Class operating technologies, including lean manufacturing 5S principles. Understanding the program's importance and knowing how to get started are the most important steps. In Iranian economic environment it is always hard to convince any top management to invest on methodologies like TPM. The reason behind this is that there are very few examples of companies with successful implementation of these methodologies. Since management... 

Machining of Aluminum Metal Matrix Composites faces different problems including adhesive wear, large machining forces, chatter, poor surface quality and therefore low geometric accuracy etc. due to the fact that a ductile matrix is supporting brittle particles. On of the methods used to reduce such difficulties is vibration assisted machining in which a 10 to 20 micron displacement stimulation is applied to the workpiece or tool during machining process. The effect of this method on the milling of the Al/Sic composite is studied through two separate experiments including one and two dimentional vibration assisted milling respectively. Milling forces, tool wear and surface quality are... 

Tin Oxide Nanoparticle (SnO2) with the band gap of around 3.6 eV is one of the promising materials in various fields such as photocatalysis water splitting, pollutant removal and also biotechnology. Inorder to use this material in a visible-light rang, some promotions should be conducted.By combining SnO2 nanoparticles with the non-metalic graphitic carbon nitride (g-C3N4), a proper nanocomposite with wide range of application can be obtained. But, in order to industrialize this material, the cost of the final product is an imperative issue to consider.Here we have introduced a novel and low-cost method for synthesis of g-C3N4/SnO2 nanocomposite by using urea as a precursor for g-C3N4 and... 

Best way to extinguish one kind of species is targeting their habitat instead targeting the species directly. Targeting tumor microenvironment is source of several methods of cancer immunotherapy attending to the effective factor at microenvironment appears as main spot in designing immunotherapy protocols. Cells compete in an atmosphere in which they create different mechanisms in tumor microinvronment. Now, we can make abstract models of these cellular mechanism using accurate mathematical instruments, this is theoretical biology which is as subset in the field of mathematical biology. In these models, we can identify parameters that has more therapeutic value in the microenvironment.... 

In this thesis, elliptical liquid jet breakup in crossflow has been investigated. To do this, two elliptical nozzle with different aspect ratio were built. First, the effective and important dimensionless numbers were extracted. Then, the physical aspect of the question was analyzed. All the experiments have been done in atmospheric conditions with water fluid, air as the liquid jet, and gas crossflow respectively.To create crossflow, a square cross section channel and one blower which are set in the beginning of the channel were made use of. Water is injected into air crossflow by the injector installed under the channel. The system used in revealing the crossflow is shadowgraphy system.... 

With increasing demand for more efficient combustion processes, alternative processes like application of magnetic and electric fields for modification of combustion have offered possible solutions. In the recent years, liquid electro-spraying has been a hot topic with growing interest due to its wide applications in such area as fuel atomization in combustion systems, which has been investigated in this project. Notice that in this method the liquid fuel in the high voltage electric field between electrodes will be broken into small droplets. In this thesis diffusion combustion of two alcoholic liquid fuels of ethanol and butanol at the exit of a small-scale combustor of vertical Pyrex... 

Electrospray is an interesting method to produce spray. This study has an insight on electrospraying phenomenon and its effective parameters. All modes, the forces and the situation to establish has been investigated for ethanol. Suitable configuration is introduced and for different flow rates and voltages the phenomenon is studied. Images are captured by two camera (high speed camera and high resolution camera) by using two method (shadowgraphy and light scattering). In the respect of producing fine and monodisperse droplets in cone-jet mode the stability of this mode is imported to enlarge. The special nozzle is design to increase stability of cone-jet mode even 70 times of using... 

Flow analysis in and out of the pressure-swirl injector in supercritical condition is investigated in this thesis. These injectors widely are used in different industries such gas turbine combustion chamber and liquid fuel rockets. Flow simulation in these injectors is so complex because of existence of gas core in axial region and high swirl and axial speeds in injectors. Unlike subcritical condition, droplet and ligament don’t form in supercritical condition so injector performance represents with two parameters including liquid film thickness in vortex chamber and liquid spreading angle. Mass flow, geometric constant, length and the distance between tangential inlet and injector head, are... 

In the present study liquid thermophysical properties in electrospray has been studied. Other parameters such as electrical configuration do not change during this study. For this purpose Alcoholic fuels have been chosen because of their high energy density and their polarity that make them suitable for electrospraying. Electrical conductivity, surface tension, viscosity, density and permittivity are the most effective liquid properties in the electrospraying. The visualization method used for this study is shadowgraphy and light scattering method. In this study the range of flow rate and voltage is acquired for each operational mode and Q-V diagram has been obtained for all liquids... 

The purpose of this project is investigating the effect of cross flow and electric field on a liquid simple-jet experimentally. In this research the effect of parameters such as liquid to air momentum ratio, electric field on jet trajectory, penetration and the lenght of breakup point with respect to the jet outlet were studied. The air was produced by a blower in a duct with square test section of 8 cm sides. The air velocity varied from 1 m/s to 11 m/s. Liquid ethanol was injected into the duct with a needle with outer diameter of 0/62 mm and inner diameter of 0.4 mm and 28 mm length. The velocity of jet was 0/62 m/s while the change of liquid to air momentum ratio was from 3 to 260 The... 

Direct steam generation (DSG) process using linear FRESNEL collectors has been developed widely in recent years and is one of the most promising solar technologies for thermal power generation, Industrial processes and domestic usage. In this process water as heat transfer fluid (HTF) is heated through a solar field. Continuous breakthroughs are being achieved on improvement of these collectors. A multi-phase CFD model is developed to calculate the wall temperature of linear Fresnel absorber tubes and fluid properties including temperature, velocity, and pressure. In order to design the collector field and identify the critical condition such as overheating of the absorber tubes, modeling of...