Pool Boiling Experiment of Dielectric Liquids and Numerical Study for Cooling a Microprocessor

Two-phase liquid immersion cooling has not yet reached its full potential because of two technological issues. The first issue is the boiling crisis and the second is the reliability risk caused by the immersed components, which are designed to work in air cooling applications. Experimental and numerical studies were performed to find the heat transfer limits of immersion cooling of microprocessor and new heat transfer design parameters are proposed. Pool boiling experiments were performed on bare copper surfaces for two dielectric fluids, Novec 649 and Novec 7100, and the critical heat fluxes were found to be 19.5 W/cm
²
and 23.8 W/cm
²
, respectively. Three-dimensional conduction models of a microprocessor were built to predict the junction temperature and junction-to-ambient thermal resistance. Effect of the integrated heatsink (IHS) thickness at different heat transfer coefficients have been investigated and the optimal thickness for the IHS is predicted to be around 4 mm while the heat transfer coefficient is less than 20 000 W/m
²
K on the IHS. Boiling directly on the silicon die has been studied, in order to examine the effect of a decreased thermal resistance by removing the thermal interface material and IHS. In this case, the heat transfer coefficient is predicted to be more than 20 000 W/m
²
K and to have better heat dissipation.