Sharif Digital Repository

Use of micro/nanoelectromechanical systems has become increasingly prevalent in recent years. Therefore, the development of technologies and understanding of fundamental physics associated with them is necessary.In micro-and nano-scale different behavior is often observed and it is due to Knudsen number that forms different types of flow regimes. When the flow is considered to be continuum; for it is in the slip-flow regime, for it is called the transition-flow regime. When , the flow is considered to be free molecular and is sufficiently rarefied to allow molecular collisions to be completely neglected in analysis. For continuum and slip flow regime the Navier-Stokes equations with... 

With a fast progress in nanotechnology devices and components, e.g., MEMS/NEMS, heat transfer study in micro/nanoscales has become so critical for the systematic design and precise control of such miniaturized devices towards the integration and automation of Lab-on-a-chip devices. Demands in high heat transfer rates have returned the concerns to impinging jet cooling systems. However, studying impinging jets in the micro/nano scales is requires the molecular dynamics knowledge to analyze the true micro/nanoscale flow behavior accurately. According to the importance of this subject, we use direct simulation Monte Carlo (DSMC) method to simulate nano impinging jet gas flows. The thesis is... 

With the rapid development in the application of nano-micro systems in space propulsion systems, it is necessary to obtain accurate analysis of flow field in these devices. New generation of space missions are usually performed by using a network of small-scale satellites. The mission control of such small-scale satellites requires specialized propulsion systems than produce small propulsive forces of about 1 micro-Newton. The main purpose of the current PhD thesis is analysing the flow field in different nano/micro propulsion systems by using a hybrid Navier-Stokes (NS)-direct simulation Monte Carlo (DSMC) method. Nano/micro propulsion systems experience different rarefaction regimes from... 

Developing new micro and nano devices, help us instruction micro and nano devices in very small scales. Also nano technology improved in recent decades especially in century 21th. These devices contained many important members, such as micro and nano filters, micro channels, sensors, and electrical chipsets. Navier-Stockes equations with slip and no-slip conditions can not used in transition and free molecular regimes. Since most of the MEMS and NEMS devices working in slip and transition regimes, then we must using DSMC for simulation these devices. DSMC is a physically method and working on the physics bases. Also it was derived from Boltzmann equations by Bird. In this study, we want... 

Progress of technology and the ability of construction of devices in micro and nano scales, have developed a new field of science that the classical laws of fluid dynamics can not be analyzed in by the well known Navier-Stokes Model. So, research fields in micro and nano scales have been paid attention more. In micro and nano scales, due to small size of characteristic length, the fluid is rarefied and the behavior of the fluid and its interaction with surfaces and walls in such scales is very different from those in large-scale systems. So, the particle-based-methods like Direct Simulation Monte-Carlo (DSMC) method have been considered one of the most interesting fields of researches for... 

The co-existance of rarefied and near-continuum flow regimes is widelyencountered in analyzing the multiscale flow problems, e.g., micro-and nanoflows. Previous investigations have revealed that the continuum-based simulation methods would suffer from the lack of accuracy to predict the rarefied flow regimes. On the other hand, the molecular simulation methods are not computationally efficient in simulating the near-continuum flow regimes. Therefore, the use of hybrid simulation methods has been recommended as a serious alternative to simulate the multiscale flow problems. These methods apply the molecular methods in solving the rarefied flow regions and the continuum methods in solving the...