Immersion cooling technology of SiC-based on-vehicle inverter by anti-freezing liquid with subcooled boiling

Subcooled pool boiling heat transfer is evaluated for Long Life Coolant (LLC) that is a binary mixture of water and ethylene-glycol (EG). The experiments are conducted at the concentration of 30 vol.% solution of EG in water and 30 vol% solution of LLC in water under the atmospheric pressure. The liquid subcooling is 50 K. Although the boiling curve for the EG solution shows the same tendency as that for distilled water, the boiling curve especially in the nucleate boiling regime for the LLC solution shifts on higher wall-superheat side. The critical heat flux for the LLC solution is also suppressed and its value is much lower than that of distilled water. In addition, MEB-like phenomenon (Microbubble Emission Boiling) that emits microbubbles from the heat transfer surface is visualized also for the LLC solution, but the boiling curve doesn't show the steep increase in the heat flux that is unique for MEB for water. In addition, it is confirmed that a large amount of fluff is floating inside the LLC solution and some of it deposit on the copper heat exchanger. These results clarify some engineering issues that should be solved for the practical use of the LLC solution for the cooling with the subcooled boiling heat transfer.