Pressure drop and heat transfer in the entrance region of microchannels

Abstract

Abstract The entrance region constitutes a considerable fraction of the channel length in micro-sized devices. When the hydrodynamic and thermal development lengths are the same magnitude as the microchannel length, entrance effects have to be taken into account, especially in relatively short channels. This chapter deals with issues of hydrodynamic and thermal development in circular and noncircular microchannels, with particular emphasis on the microchannels of rectangular and elliptical cross sections that are the most useful and common channel shapes in practical applications. Slip flow in the entrance region of circular and parallel plate microchannels is first considered by solving a linearized momentum equation. General correlations are developed for slip flow and continuum flow in the hydrodynamic entrance of circular, parallel plate and rectangular microchannels. Three-dimensional laminar flow and convective heat transfer for various thermal boundary conditions at the entrance region in elliptical microchannels are discussed in detail. Models and corresponding correlations are proposed and developments of the velocity distribution are presented for entrance flows in microchannels of circular and noncircular cross sections. In addition, slip flow and nanofluid flow in short microchannel plate fin heat sinks are demonstrated.