Active Heat Transfer Fluids (AHTF): Enhancement of Convective Heat Transfer by Bubble-Driven Self-Propelled Microparticles

Abstract: Liquid coolants containing conductive nanoparticles (nanofluids) have been widely studied over the past 30 years but have seen limited adoption in real-world cooling applications. The ability of passive nanoparticles to enhance heat transfer in liquids is fundamentally limited because the nanoparticles cannot move on their own relative to the bulk fluid, and thus generate negligible convective enhancements in heat transport. In this work, we present experimental evidence that micron-scale self-propelled particles, which convert chemical energy into autonomous motion, enhance convective heat transfer in liquids. We quantified this enhancement by measuring the convective heat transfer coefficient in a pool of suspension heated from below. The enhancements associated with self-propulsion are most pronounced at low heating powers (Rayleigh number of 10,000), in which case the heat transfer coefficient can be over 100 percent higher in the self-propelled case compared to the same particles without propulsion. This work provides a proof-of-concept demonstration that active particles can enhance heat transfer in liquids, motivating the development of "Active Heat Transfer Fluids" for various cooling applications.