Flow boiling heat transfer with self-rewetting fluids*

Self-rewetting fluids offer a promising solution in boiling compared to conventional fluids by delaying surface dry-out regions through their unique surface tension characteristics. However, questions remain on the heat transfer capabilities of these fluids in microchannel flow boiling applications. Studies so far rely primarily on experiments which are limited by the data acquisition and, in particular, key information such as dynamic variation of heat-transfer coefficients as a function of flow-regime transition cannot be captured.

In this study, we perform a comprehensive numerical investigation to explore the flow boiling heat transfer characteristics of water (as the conventional fluid) and a 5% v-v butanol-water mixture (as the self-rewetting fluid) in microchannels. To accurately capture the intricacies of flow boiling at the microscale, we employ the Volume of Fluid (VOF) method along with the modified Schrage evaporation model by Hardt and Wondra (2008).

Our Nusselt number predictions have been validated against our experimental data by Venter et al (2023). Also, the bubble shapes are qualitatively similar to those found in our experiments. Our simulations further analyse heat transfer capabilities and surface dry-out region formation rates as a function of flow-rates. This is important given surface tension effects are more dominant at low Reynolds numbers. This analysis aims to deepen our understanding of the potential of self-rewetting fluids under flow boiling conditions, at low Reynolds numbers.