Flow and heat transfer characteristics in convergent-divergent shaped microchannel with ribs and cavities

A computational study has been carried out to examine the effects of ribs and cavities on flow and heat transfer in a convergent-divergent shaped microchannel heat sink with constant heat flux for Reynolds number (Re) ranging from 120 to 900. Three-dimensional governing equations were discretized using the finite-volume method. The computational domain included solid silicon and fluid regions. A significant amount of work has been reported in the literature on the individual effects of channel shape and flow disruption using obstacles on thermal performance of microchannels. In the present study convergent-divergent (CD) shaped microchannel with and without ribs and cavities (RC) are considered and their friction coefficient, thermal resistance and maximum substrate temperature are investigated in detail. The present results show that the usage of CD shape with ribs and cavities can reduce the overall thermal resistance up to 40% and make the bottom surface temperature quite uniform. This heat transfer enhancement is mainly due to interruption and redevelopment of boundary-layers along with recirculation zone. The results also show that increasing Re leads to an enhanced heat transfer in terms of increased averaged Nusselt number from 15% to 46%. The combined effect of CD shape with RC is quite effective in heat transfer augmentation but it gradually loses its effectiveness at large values of Re due to a high pressure drop penalty.