Influence of the thermophysical properties of working liquids on heat transfer performance during flow boiling in microchannels

A thorough understanding of the governing interfacial interactions during flow boiling in a microchannel would provide important insights into the underlying physics of fluid dynamics and heat transfer mechanisms. In this study, flow-boiling experiments were performed in a single rectangular microchannel with hydraulic diameter of 0.18 mm. Three working fluids (water, ethanol, and HFE7100) with significantly different thermo-physical properties were tested under an inlet subcooling of 25°C, mass flux of 50–330 kg·m−2·s−1, and effective heat fluxes up to 400 kW·m−2. Non-dimensional groups were used to quantify the relative effects of the forces governing the liquid–vapor interface. The bubble dynamics, flow pattern transition, heat transfer, and pressure drop were compared for the three different working fluids, and a mechanistic explanation of the flow boiling performance was proposed based on a force scaling analysis. Meanwhile, through investigating the influence of dimensionless parameters on heat transfer coefficient, a new basic heat transfer correlation that applies to a wide range of working fluids was developed, with 92.5% of data points falling within ±30% error bands and with a mean absolute error of 14.7%. HFE7100 exhibited the minimum increase in pressure drop with heat flux owing to its smallest liquid-to-vapor density ratio, low viscosity, and lowest interfacial tension effect. This study lays the foundation for the development of more reliable theoretical correlations and provides important insights into optimal design principles.