Comparison of near source two-phase flow cooling of power electronics in thermosiphon and forced convection modes

In this paper, we present results of utilization of our patented technology, the force-fed cooling heat sink, to substantially improve the cooling performance of power electronics. In this microchannel heat sink, the heat sink is directly integrated with the substrate, thus reducing the total thermal resistance. The heat sink is tested in two different configurations, the first of which is a passive loop. The cooling process is possible due to the thermosiphon principle, in which thermal or liquid-vapor fluid density difference generate the fluid flow. In order to get the best performance, the effect of varying different parameters was examined, such as the filling ratio, the length of the pipes of the thermosiphon and the introduction of a reservoir to avoid the presence of non-condensable gas that can adversely affect the performance. With the thermosiphon loop, operation for heat fluxes around 230–240 W/cm2 with moderate fluctuation in temperature was demonstrated. In the second test configuration, we introduced a pump in the loop to activate forced convection mode and avoid gravity dependence, and eventually ensuring less flow fluctuations while improving the heat removal performance. The result was a cooling capacity up to 500 W/cm2, with a thermal resistance of 0.125 (K cm2)/W. The detailed characterization leading to these significant results and the comparison of the performance between the two modes is discussed throughout this paper.