Ultra-Low Global Warming Potential Heat Transfer Fluids for Pumped Two-Phase Cooling in HPC Data Centers

The increasing heat dissipation from microprocessors and power density of racks in high performance computing (HPC) applications necessitates liquid cooling of the microprocessors in the servers. Currently, water and aqueous glycol are primarily used as coolants. The need to sustain ever-increasing power density, inherent risks and inefficiencies with water cooling, and the push towards lower global warming potential dielectric fluids, has motivated a search for suitable two-phase heat transfer fluids. This study presents evaluation of pumped single-phase water cooling and two-phase cooling in microchannel cold plate. The water cooling was tested at mass flow rate of up to 125 kg/h. Two-phase cooling with R134a and ultra-low Global Warming Potential (GWP) dielectric fluids R1233zd(E) and R1234ze(E) was tested at mass flow rates of up to 30 kg/h and heat fluxes up to 640 kW/m
²
. Compared to water cooling, two-phase cooling achieves lower junction temperatures and more uniform cooling for the same flow rates. When compared at equal junction temperature, two-phase cooling requires an order of magnitude lower pumping power than water cooling. This study demonstrates that two-phase cooling with R1233zd(E) and R1234ze(E) can be feasible options compared to water cooling in HPC data centers.