Thermal-Hydraulic Characterisation of Electronics Cooling Liquids: A Case Study of Jet Impingement Coldplate on Emulated CPU

Practical considerations such as corrosion, biological growth and expansion due to freezing may require that additives be mixed with water to inhibit these detrimental occurrences. The addition of additives to water generally deteriorates the thermophysical properties that govern the flow and heat transfer behavior (thermal conductivity, viscosity, specific heat capacity). This work aims to gain a more practical understanding of the thermal-hydraulic behavior of water-based engineered fluids for liquid cooling of high-powered CPUs. To achieve this, different commercial coolants, from a graphene-based nanofluid to ethalyne-glycol mixtures, have been tested in a specialised experimental facility that can monitor flow and heat transfer parameters in a scenario that closely matches a liquid-cooled CPU. Importantly, the Thermal Test Vehicle used includes the contribution of the emulated CPU's heat spreader and Thermal interface Material, so as to better gauge the overall contribution to the die temperature, opposed to simply monitoring the change in the convective heat transfer coefficient. Tests were performed with a commercial CPU coldplate for a 20×20 mm2 heat source with power of 250 W (62.5 W/cm2). The results show that fluids that minimise the addition of additives achieve very similar performance to that of the pure water baseline, and this is due to the low influence on the thermophysical properties. For liquids that offer high levels of freeze protection, both heat transfer and pressure drop performance deteriorates significantly, indicating that the choice of coolant should be considered very carefully, and in the context of the environment within which it is to be deployed.