Coolant Considerations for Liquid-Cooling

Liquid-cooling provides an efficient method to cool high power ASICs and CPUs that are tightly packaged on a chassis. The ideal coolant would have desirable properties such as electrically insulating, non-toxic, low viscosity, low freezing point, good thermophysical properties and is thermally stable over time. The select fluid for the coolant would meet most of these desirable properties.The most widely used coolant for single-phase liquid-cooling is aqueous glycol, typically ethylene or propylene glycol. Glycols possess good thermophysical properties, but since they contain water, they are electrically conducting. A leak can pose a potential hazard, even leading to catastrophic system failure. One focus of this work is on characterizing a glycol coolant that has very low ionic conductance. Such a coolant can limit the damage caused by a leak, so there is time for personnel in the datacenter to react to the leak. An example is provided to illustrate how the method is used to estimate potential issue caused by coolant leak.Besides system failure due to a leak event, other considerations for the coolant include: (1) change in thermophysical properties with glycol concentration and temperature, (2) effect of glycol concentration on freezing point, and (3) inhibition of microbial growth. These additional considerations are briefly covered in this study.