Sharif Digital Repository

Numerical investigation of flow field and determination of velocity components in swirl flow are novel and important subjects in combustion chamber of swirl flow. The exact understanding of vortex phenomena and flow structures in vortex engine results in better design and control in terms of stability, geometry, cooling, and combustion efficiency. Although, numerical approaches are computationally complex, they are worthwhile and efficient. The aim of this work is to study the velocity field in a bidirectional swirl flow within the combustion chamber using numerical approaches. The investigation of flow field has been performed in the cold chamber. Four different models (RSM and LES) have... 

One of the most important equipment in a power station is desuperheater which its operation has effect on power station performance and efficiency.It is necessary to identify and evaluate the most important factors that have effect on its performance. Using desuperheater cause that the temperature of exhausting superheat steam of boiler decreases to the desired quantity. If the temperature of superheat steam is very high, it will cause burning of superheater pipes that is very dangerous.Steam is used for two purpose of power generating and operational process. Unfortunately these applications have different requirement. In power generating for maximizing efficiency, turbine needs high... 

The air distribution is the main factor of contaminant transportation in cleanrooms. The experimental method is the most reliable one for investigation of flow field, which the difficulties associated with it, has limited not only the examination of the flow field in cleanrooms, but also the improvement of their qualities. Most of the experimental researches in indoor air quality concern conventional rooms and do not take into account specific supply-exhaust diffuser configurations, which are used in cleanrooms. Using small-scale models can reduce the complexity and the cost of measurements. In this research, the 3D velocity field of a small-scale cleanroom is measured in three different... 

In this paper, a one-dimensional and two-dimensional numerical approach is used to study the effect of various parameters such as micro combustor height, mass flow rate and external convection heat transfer coefficient on the temperature and species mass fraction profiles. A premixed mixture of H2-Air with a multi-step chemistry (9 species and 19 reactions) is used. The transient gas phase energy and species conservation equations result in an Advection-Diffusion-Reaction system (A-D-R) that leads to two stiff systems of PDEs, which can not be solved by conventional Computational Fluid Dynamics (CFD) methods. In the present work, Strang splitting method, which is suitable for nonlinear stiff... 

Designers consider formation of slug flow in pressurized pipes because of hazardous effects of this flow pattern. Therefore, researchers, using different methods, attempt to study formation of slug flow and its effects. For numerical simulation of this phenomenon, In spite of existence of commercial 2D or 3D two-phase models, numerical models used for the slug flow modeling are 1D. In this thesis, a 2D model has been developed to simulate the initiation and formation of slug flow and estimation of the effects in pressurized pipes. Most important assumptions used in this model are existence of turbulence, surface tension and air compressibility. Isothermal condition has been supposed for... 

Recent stringent HC and CO emission regulations are because of increasing consciousness of the perilous influences of exhaust emissions. The chief attempt to pass the standards is to decrease the emissions during cold-start, due to catalytic converters are not efficient until they arrive a light-off temperature. It has been discovered that 50% to 80% of the controlled HC and CO emissions are sent out from tailpipe of automotive during the cold-start. Therefore, in order to minimize the cold-start emissions and fast light-off of catalytic converters, it is important to understand the catalytic converter characteristics and techniques for rapid warm-up catalyst. This thesis describes a... 

Due to increasing of internal combustion engine applications in metropolitan, reduction of emission is one of the challenging issues for engine companies. Natural gas is a promising fuel for the strict legislation of emission in many countries. Vast variety of natural gas sources in Iran and also lower carbon to hydrogen content of natural gas motivates us to use this fuel for engine application. Using natural gas also helps to increase the variety of fuel basket in Iran. Present research has focused on mixture formation and injection characteristics of natural gas direct injection engine. Injection and mixture formation in direct injection engines is very important for good combustion and... 

Employing array of antennas in amny signal processing application has received considerable attention in recent years due to major advances in design and implementation of large dimentional antennas. In many applications we deal with such large dimentional antennas which challenge the traditional signal processing algorithms. Since most of traditional signal processing algorithms assume that the number of samples is much more than the number of array elements while it is not possible to collect so many samples due to hardware and time constraints.
In this thesis we exploit new results in random matrix theory to charachterize and describe the properties of Sample Covariance Matrices... 

Adaptive beamforming performance is very sensitive to any mismatch between actual and presumed steering vectors of desired signal. In addition to this sensitivity, presence of desired signal in training snapshots dramatically reduces the convergence rate, as compared to the case that signal-free training snapshots are available.
The present work is aimed at proposing a new adaptive beamformer that is robust against direction-of-arrival (DOA) mismatch and has high convergence rate. This method is based on desired signal elimination from training snapshots and sub-array beamforming technique. To this end, a Blocking matrix that converts primary data to desired signal free data is... 

A Synthetic Aperture Radar (SAR) is a system which collects the received signal from a ground target area along linear motion of a flying vehicle carrying it, in order to provide a very high resolution 2D image of it. In Inverse SAR (ISAR), the radar is fixed on the ground and the data collection is performed along the linear motion of the aerial target. Using a second receiver antenna close to the main transceiver antenna of ISAR, it is possible to make a three-dimensional (3D) image of the target, or equivalently find the 3D coordinates of the target scattering points. Such system is called bistatic, monopulse or interferometric ISAR (InISAR). In the conventional model of ISAR, the flying... 

Considering the undeniable role of technology in modern era, we investigate both the concept of technology as well as its relation as a tool with human beings. Modern technologies have had both positive and negative impact on human individual and social lives. In particular, the labor problems, environmental problems, distortion of the classic human perception of the world, and many other problems provide a very disparate perspective compare with the notion of techno-utopianism. Therefore, many contemporary philosophers such as Andrew Feinberg have made serious criticisms of technology and its consequences. Feinberg states that there is a possibility in reforming the currently derailed role... 

In this project, two Ferrofluidic micropumps that do not need any mechanical moving parts are presented. These micropumps are including simple microchannels containing magnetic fluid plugs that are used as flow actuator and the on/off valve. Using external magnetic field actuation in this type of micropumps, the magnetic fluid would have continuous motion in a channel with micrometer dimensions that would provide the main fluid to be pumped. Although the plug of magnetic fluid has surface contact with operative fluid, but considering its specific features, it would not compine with the pumping fluid. These micropumps may be used to pump the fluids or gases. The outcomes of the investigation... 

Dissipative particle dynamics (DPD) is an emerging mesoscopic computational method in which the interparticle forces arise because of coarse-graining at the molecular level. In the asymptotic limit of large length scales, the governing equations of continuum are reproduced, as demonstrated in this work. This method of simulation has the capability of simulating larger order of time and space in compare with dynamic molecular method. One of the important applications of DPD is simulating the dilute polymer solution. In this project, we developed a general code to simulate dilute polymer behavior which consists of polymeric forces and different types of usual DPD boundary conditions. This code... 

There are a wide variety of radar systems that one of them is MIMO Radars. After a spark in communication in 1998 that developed MIMO communication, recently there has been a great attention towards MIMO radar systems. MIMO radars divided into co-located and widely separated branch. In this thesis, the spatial diversity and multiplexing gain and the tradeoff between them in MIMO communication and MIMO radar systems investigated. Diversity and multiplexing gains in communication defined analytically, so diversity and multiplexing gain presented as detection probability improvement and throughput or capacity improvement respectively. Also tradeoff between these two gains investigated... 

Various application of polyethylene material in different industries caused to modern techniques for controlling and measuring specifications of micro-particle suspension. Many industries try to increase stability of suspensions in front of their phase separation.
Because of the consequences of suspension homogeneity, at first, we measured this property. Then, the stability was tested by three different methods. In the first method, the transmitted laser light was measured to assay the suspensions stability. In the second, number of sediments of particles was counted. Sedimentation velocity of particles was measured directly by using a horizontal microscope as the third method. The... 

There are numerous ways available to achieve low temperatures that cryocoolers might be among the most important of them. In the meantime, the pulse tube refrigerator has a special place due to its simple geometry and not be using any moving parts. This simple property make the pulse tube refrigerator one of the most popular methods to achieve low temperatures. Nowadays, a pulse tube refrigerator is used for cooling in the range of 4 to 123 Kelvin in two form of one-stage and two-stage and up to an approximate power of 1 KW. Today, due to the temperature and the amount of power required for cooling, as well as the time it takes to reach that temperature, this chiller is used in medical,... 

Knock is an abnormal phenomena in combustion engines and one the main limiter elements in increasing engine efficiency. From years ago, recognition and elimination of this phenomenon had studied by investigators and various approaches to anticipation had presented. One of the newest methods is using of property variety in air and fuel mixture with using technologies like Variable Valve Timing (VVT) system.
The purpose of this work is development a simple model in basis physics of 3 zone, homogeneous, ignition combustion with a partial kinetics model that this model can predict the knock phenomenon onset with good precision for various qualities of mixture. This study survey effect of... 

Recent developments in MEMS related areas have increased the demand for practical and novel pumping methods. Utilizing Electroosmotic force for flow generation in microchannels has become really popular recently, because of its reliable operation and control. One of potential applications of MEMS devices is biological and medical analysis which most samples are considered to be non-Newtonian; consequently, thermal transport characteristics of non-Newtonian electroosmotic flow of power-law fluids is investigated in this paper. In this study, thermal and hydrodynamic behavior of non-Newtonian electroosmotic flow of power-law model in a slit microchannel is analyzed. It is assumed that the flow... 

In recent two decades, with developments in micro and nano scale fabricating techniques, use of microfluidic systems is increasing in different fields. How to drive fluid is a hard question because of high pressure drop in micro scale. Different methods has been suggested to solve this problem, among which, electroosmotic pump is preferred because of its advantages. One of the main applications of microsystems is in biomechanical devices like microreactors which are usually working with non-Newtonian fluids. The cross section of these devices are most often close to rectangular shape.Therefor, in this study,Hydrodynamic charactristics and mass transport of non-Newtonian fluids under... 

In the study of heat transfer in micro-channels, free and force convections are two limit cases and these two methods of heat transfer are combined together generally, so to achieve the most accurate informations about the flow field they should be considered in combination. In the first part of the thesis the fully developed slip flow mixed convection in vertical micro-ducts of arbitrary shapes is investigated.Uniform axial heat flux and uniform peripheral wall temperature (H1) is considered. The method considered is analytical-numerical in which the governing equations and three of the boundary conditions are exactly satisfied but the remaining slip boundary condition on the duct wall...