Thermal design exploration of a swirl flow microchannel heat sink for high heat flux applications based on numerical simulations

Numerical simulations of velocity and temperature fields to explore the design of a single phase microchannel cooling system with spiraling radial inflow for high heat flux applications are presented. Total pressure drop and average wall heat flux are calculated for different flow rates and the effects of changing the microchannel height, flow inlet angle, and working fluid are investigated. Rotation of the fluid induces a crossflow and entrainment, this is found to enhance convective heat transfer considerably due to motion of fluid towards the heat exchange surface. The strength of this effect depends on the structure of hydrodynamic boundary layers, which is characterized by the Reynolds number and the flow inlet angle. The effect of reducing the Prandtl number is evaluated changing the working fluid from water to a 2 vol% and a 4 vol% water-Cu nanofluid suspension. For the cases studied, it is found that heat transfer enhancement by increasing the inlet swirl is greater than that of decreasing the Prandtl number using a nanofluid, though at a much higher pumping cost. In order to improve the performance of the device for high heat flux applications, admission of the flow should be as tangential as practically possible. It is found that, when reducing the microchannel height, boundary layers may merge and the entrainment effect is lost, therefore the total heat flux may not always increase with a decrease of the flow passage area, as opposed to conventional microchannels. The swirl flow microchannel heat sink showed promising cooling characteristics for applications such as thermal management of electronics or concentrated photovoltaics, with a ratio of pumping cost to heat rate of 0.02% for the base design studied.