Comparative evaluation of dielectric liquids for single-phase immersion cooling of electronics

Rising heat fluxes in wide-bandgap power electronics and data center hardware have renewed interest in single-phase immersion cooling (SPIC) as a simple, scalable alternative to indirect liquid cooling as well as two-phase immersion cooling systems. However, the lack of standardized, property-based liquid coolant benchmarks has complicated engineering decisions. This study offers a comprehensive evaluation of the thermal and electrical performance of various dielectric liquids for SPIC of electronic devices. An analysis framework was developed using a figure of merit (FOM) based on natural convection correlations, allowing for property sensitivity and weight-factor assessments across different operating liquid temperatures. A buoyancy-driven SPIC experimental platform, featuring a commercial super junction (SJ) silicon MOSFET (drain tab size 10 mm × 12 mm), was built to measure the cooling and electrical insulation performance of 10 commercial dielectric liquids and 5 candidate chemistries not yet available commercially. Results reveal that high fluid thermal conductivity and density strongly improve cooling performance, while dynamic viscosity primarily limits it. Experimental data categorize the tested liquids into three tiers of cooling effectiveness: four commercial liquids in tier 3 with lowest junction-to-coolant thermal resistances of 7.0 – 7.8 K/W (3.27 – 3.75 (cm 2 ˑK)/W), seven in tier 2 with thermal resistances of 5.9 - 6.4 K/W (2.82 – 3.08 (cm 2 ˑK)/W), and four candidate liquids in tier 1 achieving the lowest resistances of 4.9 - 5.4 K/W (2.32 – 2.56 (cm 2 ˑK)/W). Electrical insulation tests show most liquids maintain leakage currents below 5 nA at 550 V. These findings offer clear guidelines for dielectric liquid selection, supporting SPIC deployment in data centers, battery thermal management systems, and power electronics applications.