Single Phase Passive Hydrocarbon Immersion Cooling of High-power ICs

Immersion cooling of data-center boards in dielectric fluid is replacing forced air cooling in view of increased power dissipations and growing environmental concerns. The choice of the dielectric fluid presents as a conflict between environmental and heat transfer properties. Hydrocarbon fluids have good environmental properties, but high viscosity, which is unfavorable for flow. This paper investigates passive single phase hydrocarbon immersion cooling as a substitute for forced air cooling on boards with high-power ICs. An analytical flat plate model is used for first estimations followed by CFD simulations on a state-of-the-art 500 W high-power IC, board and heatsink assembly in a 2U (90 mm) immersion cassette. A virtual response surface Design Of Experiments is used to optimize the fin configuration of the heatsink for 300 – 700 W IC dissipations in a 1U (45 mm) immersion cassette. In addition, the effect of position and the effect of multiple boards is investigated for the optimal heatsink configuration. Single phase passive hydrocarbon immersion cooling is shown to have better cooling performance on the existing design, and the optimized fin geometry demonstrates close to a factor 3 better volumetric cooling performance compared to 3 m/s forced air cooling.