Sharif Digital Repository

In this thesis the steady state convective heat transfer for turbulent, two-dimensional, incompressible gas flow in a circular microchannel under slip flow and temperature jump conditions is numerically investigated by means of finite volume scheme. The low Reynolds number k-ε turbulence model is employed using a new boundary condition for turbulent kinetic energy at solid surface. To calculate variables at control volume surfaces in the axial direction upwind differencing scheme and in the radial direction central differencing scheme are used. Rhie-Chow interpolation technique is used to prevent pressure field oscillations. The set of discrete equations are solved using SIMPLE Algorithm. In... 

Novel manufacturing technologies in micro scales, such as micro machining, guide us through constructing micro scale systems known as MEMS. These systems have a wide range of applications, from fabrication of electrostatic, magnetic, pneumatic sensors and actuators to micro mechanical gears and motors. Also, MEMS applications involve the manipulation of one or more fluids, known as microfluids. Simulation of flow through microchannels over nano particles has important applications in solid particles transport. In this flow, the rarefaction phenomenon will affect the flow behavior and its subsequent impacts such as aerodynamic drag forces. In this work, we use the Lattice Boltzmann method... 

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... 

Fully developed fluid flow and heat transfer is numerically investigated in micro-channels. There are many techniques to intensify heat transfer for internal flows, such as: increasing Reynolds number, extending surface area of channel wall and also disrupting the boundary layer thickness on the wall. Among these, extension wall surface area is a common technique. There are several ways to extend surface area including finned, slotted, chemically etched, grooved as well as porous media adhered wall surface. One other method that we work on it is modifying wall cross-section and usage of uniform suction porous media. The governing equations include the momentum equation of the core region... 

The present paper is an attempt to critically measure interfacial tension with microchannels and achieve the quantity of adsorption in the liquid – liquid interfaces and comparing the adsorption of surfactants and nanoparticles surface modificated as well. At this point we need to make emulsion and it is necessary for droplets to be monodispersed due to analyze these droplets in this paper. According to this condition for our droplets microsystems are the best options. As we know surfactants were already known as a stabilizing emulsion agent and in this paper nanoparticles are suggested as suitable alternatives for surfactants which can be absorbed as if they are in the water / oil... 

In medical science, preparing a high purity sample of certain kinds of cells plays an important role in studying the characteristics and functionality of cells, detecting in vitro harmful pathogens and helping to find ways of preventing and treating diseases that cause cellular disorders in the human body. The goal of this research is to improve the spiral microchannel with stair-like cross section in order to separate white blood cells from whole blood. First, the efficiency of this method was evaluated numerically, using a developed finite element model. Then, the desired microchannel mold was made using the micromiling method, and we fabricated the chip using soft lithography and pasting... 

In the present study, a high-order accurate numerical solution of steady incompressible slip flow and heat transfer in 2D microchannels is presented. The numerical method used is an alternating direction implicit operator scheme which is efficiently implemented to solve the incompressible Navier-Stokes equations in the primitive variables formulation using the artificial compressibility method. To stabilize the numerical solution, numerical filters are used. The present methodology considers the solution of the Navier-Stokes equations with¬ employing different slip boundary condition¬¬ (Maxwell,¬ ¬¬Hyperbolic tangent function of Knudsen number¬ and Beskok slip models)¬ ¬¬on the wall to model... 

In this study, the simulation of two-dimensional supersonic flows through microchannels in slip flow regime is performed using a lattice Boltzmann model (LBM). Traditional LB models have been used to simulate incompressible fluid flows and there are not suitable for modeling compressible or thermo-fluid flows. Herein, a recently developed LB model, namely, the finite difference lattice Boltzmann method (FDLBM), is employed to simulate compressible flows with embedded shocks. In this model, one can select particle velocities independently from the lattice configuration, and therefore, a correct and numerically stable multispeed thermal model by adopting more isotropic particle velocities can... 

The effects of gravity and inertia dominate our experiences of the physical world. But as systems are reduced in size, phenomena such as diffusion, surface tension and viscosity become ever more important; at the microscale they can dominate and result in a world that operates very differently from the macroscopic world. Kidney is one of the vital organs in which fluid and mass transfer occur between blood flow in microvessels and urine in microchannels called nephron. The present work is aimed at applying microchannel theory to study renal system. First, a n efficient numerical orthogonal collocation method has been employed to solve the steady-state formulation of electrolyte transport in...