Heat Transfer in Microchannels

Abstract

The use of microchannels in order to cool modern high speed electronic circuits is one of the techniques frequently adopted in current practice. A burst of publications in this area has been observed in the last decade. However, modeling of fluid flow and heat transfer in microchannels is still an open problem. In fact, many deviations have been experimentally observed between well established correlations used for conventional normally sized channels and the behavior of microchannels. These deviations increase as the channel size decreases. Observed experimental deviations will first be listed, followed by a critical review of different hypotheses advanced in the litemture to explain them. One of these hypotheses will be thoroughly studied in order to build a model that explains both the orders of magnitudes and the trends of observed phenomena. In this work, detailed analysis of fluid flow and heat transfer over three subsequent roughness elements• is made. Incompressible unsteady state continuity, Navier-Stokes, and energy equations are solved using the finite element method and assuming that the fluid flow is two-dimensional for simplicity. The effect of roughness on the flow and heat transfer is studied in details for different Reynolds numbers. The results show that the tendency to separation and formation of a low pressure zone between roughness elements take place at relatively low Reynolds numbers and small hydraulic diameters. This gives a better estimate of fluid flow and heat transfer in microchannels including the dependence of flow characteristics on the Reynolds number in laminar flow as well as the early transition to turbulence.