In the present dissertation, fluid flow and heat transfer in microfluidic systems is investigated numerically. Fluid flow in most applications of microfluidic systems is in the slip flow regime, which is characterized by the slip flow and the jump temperature at the wall. Flow in microfluidic devices shows significant slip since the characteristic length is in the order of the mean free path of the fluid or gas molecules. The slip velocity and the jump temperature at the wall is the most important feature in the micro- or nano scale that differs from conventional internal flow. The slip flow and heat transfer in microchannels are simulated. Microfluidic systems are separated into straight and curved microchannels. A good understanding of fluid flow in microfluidic systems can be obtained when the results of straight and curved channels are considered together. Effects of rarefaction on forced convection heat transfer of laminar, steady and incompressible slip flow in straight and curved microchannels with uniform heat flux are investigated. The slip velocity and the jump temperature boundary conditions at the wall are employed. Effects of centrifugal force in the curved microchannels on the hydraulic and thermal behaviors of fluid flow are studied. The Navier-Stokes and energy equations are discretized using the Finite Volume technique. The calculated results show good agreement with previous numerical data and analytical solutions. The calculated results show that the entrance length and the curvature effects can be neglected, when the Reynolds number is less than 100. As a result, microfluidic systems are simulated with considering a very long straight microchannel, which can be modeled as totally fully developed region. The fully developed equations are obtained with considering the Navier-Stokes equations at the fully developed conditions. The analytical solution, which is an eigenvalue problem, is presented. The calculated results for two- and three-dimensional straight microchannels are presented. Flow velocity and temperature fields are calculated with very low computational time. Employing nanofluids is one of the best and practical methods for increasing heat transfer in microchannels. Thermal and hydraulic behaviors of nanofluid flow in microchannels with consideration of the slip velocity and the jump temperature conditions are investigated. Forced convection nanofluid flow in microchannels is simulated to study effects of rarefaction and Al2O3 nanoparticles concentration on the slip flow regimes. The Brownian motions of nanoparticles are considered to determine the thermal conductivity of nanofluid
