Sharif Digital Repository

The purpose of the current study is the thermodynamic, economic and environmental analysis of a cogeneration system capable of generating power, freshwater and/or air conditioning (AC) used in buildings. A photovoltaic-thermal system was used in conjunction with a concentrated reflector in order to generate power and heat. Photovoltaic cells and the cogeneration cycle turbine were tasked with generating electric power. In addition, a portion of the heat generated by the thermal collector was used to preheat the working fluid of the third-generation cogeneration cycle and another portion was used to produce freshwater. In order to provide the AC needed during summer, the cogeneration cycle... 

Helium gas is the working fluid in common Pulse Tube Refrigerators (PTRs) due to its brilliant properties in reaching cryogenics temperature as low as 4 K. Generally ideal gas equation of state has been used to evaluate thermodynamic performance of He. However using ideal gas equation of state for He in 10 bar and 5 K causes considerable error on estimation of density. The objective is to use real gas equation of state for temperatures near zero Kelvin. This approach makes an accurate prediction of PT cooling capacity and COP. In this thesis the objective is to realize the most relevant equations of state describing the proper behavior of He in the regions of operating point of PTR. Later on... 

In order to promote the efficiency of fossil fuel power stations, rotary air preheaters are used to warm the air entering the boiler. So, knowing the essential parameters of such exchangers and their effect on the efficiency is the primary objective and choosing the appropriate parameters and the dimensions reducing the liquid pressure, weight of exchangers and subsequently the maintenance expenses would be the secondary objective.
In this research we tried to know the principles of regenerative convertors introducing the tentative air preheaters and their functional characteristics .We also assessed the factors in designing the ideal tentative air preheaters including the type of... 

In the recent decades, cleanrooms have found growing applications in broad range of industries such as pharmacy and microelectronics. Concerns about negative effects of the contaminant exposure on the human health and product quality motivate many researchers towards understanding of the airflow and contaminant distribution through these environments. With an improvement in computational capacity of the computers, computational fluid dynamics (CFD) technique has become a powerful tool to study the engineering problems including indoor air quality (IAQ). In this research, indoor airflow in a full-scale cleanroom is investigated numerically using Eulerian–Eulerian approachand the results are... 

Modern microelectronic systems generate a large amount of heat which must be transferred out of the system without excessive temperature rise. Conventional forced air convection and microchannel cooling plates have reached their performance limits Nanofiuids are proposed as an innovative way to solve the problem. A nanofiuid is nanoscale solid particles dispersed in a traditional heat transfer liquid. Some studies show an anomalous increase in the thermal conductivity for stationary nanofiuids. However, there are only few previous studies on the convection heat transfer rate and viscosity of nanofiuids. Both convection and stationary measurements of the thermal conductivity are widely... 

A new experimental setup was fabricated; equipped with an adjustable chamber’s length, with air tangentially flowing through the wall of vortex engine. In a vortex combustion chamber, the tangential inlet fuel or oxidizer creates both inner and outer vortices which are rotating in the same angular direction. Indeed, inner vortex moves from head to the end of engine in the axial direction; however, outer vortex moves in the opposite direction. This setup was fabricated to see the effect of fuel nozzle characteristics on the wall temperature of the chamber. In a vortex engine, vortices affect spray droplets and force them to have a spiral path. Moreover, relative velocity of droplets and flow... 

Vortex engine has shown to be a credible substitute in thermal power and aerospace industries mainly due to their advantages such as better mixing, improved combustion, and considerable cooled walls of combustion chamber. The engine geometry and tangential inlet oxidizer create inner and outer vortices rotating in the same angular direction. The inner vortex moves from head to the end of engine in the axial direction and outer vortex moves in the opposite direction. In the vortex engine, vortices affect spray droplets and force them to have a spiral path and apply a centrifugal force on the droplets to push them towards sidewall. Also axial relative velocity of droplets and flow filed act as... 

Vortex flow is one of the most sophisticated fluid movements in nature which has great industrial and scientific importance. In this dissertation, in order to study the combustion process due to a vortex flow, a new experimental model of a cold wall vortex engine, was designed, fabricated and tested with oxidizer issuing tangentially toward the end of the chamber. The cold wall effect in these chambers is a result of the cool layer of oxidizer which significantly reduces the amount of heat transfer to the chamber’s wall. This experimental model was designed to withstand the massive temperature rise resulting from the usage of Polyethylene as fuel and Nitrous oxide as oxidizer. In a series of... 

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... 

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... 

Cancer is one of the most causes of mortality in the world. Leukemia is a type of cancer initiated by the rapid proliferation of blood cells including WBCs, RBCs, and Platelets, that classified into four general types of AML, ALL, CML, and CLL. The main treatment of leukemia is chemotherapy. Because of many problems that patients have with this treatment and not so good results of chemotherapy, we design a microfluidic chip that can perform personalized medicine treatment for leukemia patients.This microchip consists of two main parts, Concentration Gradient Generator (CGG), and cell culture. CGG system is a tree CGG with two inlets and four outlets, which makes a linear concentration of... 

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... 

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... 

A bioreactor can refer to any device or system constructed on engineering basis and has an active biological medium. This medium includes aerobic and non-aerobic reactions in which organisms and the theire produced substances have the main role. One of the applications of bioreactors is to provide an appropriate medium for animal and plant cell culture and growth. Nowadays many biological processes in high volume scales are carried out in stirred tank bioreactors. In these bioreactors oxygen transfer is usually increased by increasing turbulence which is necessary for mixing nutrients and keeping the homogeneity of the medium. However, there are some limitations for increasing the stirring... 

In the present thesis, intracellular fluid flows have investigated for study cell motions. It is due to firmly relation between the cell motion and these flows. Generally, the cell firstly adheres to a surface, then, moves forward with the effects of the internal fluid flows. In this study, the cell structure is invided to two general parts; the front part of the cell and the cell body. The front part of the cell plays a essential roles in the cell motion, however, the cell body is considered as a extra cargo that is carried by the front of the cell. Therefor, in the present modellings, the front part is only considered. Here, using four different models for the front part of the cell, many... 

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...