HFE-7100 spray cooling under microgravity: Liquid film dynamics and heat transfer

Spray cooling under microgravity is not only motivated by space applications but also by the essential pursuit of the exploration spirit facing the unknown. This study was the first series of scientific experiments conducted at the China New Microgravity Experiment Facility with Electromagnetic Launch. In this study, the liquid film dynamics and heat transfer characteristics of HFE-7100 spray, including liquid film morphology, wetted area, equivalent diameter, and velocity under different inlet pressures and heat fluxes, were quantitatively captured on smooth and rough silicon surfaces under microgravity. Several classic scenarios of liquid films, including spreading, bifurcating, bridging, fusiform, tadpole-shaped, and isolated liquid film, were recognized for the first time. The morphologies of the liquid films and the heat transfer performance under smooth and rough surfaces showed insignificant differences under normal and microgravity conditions. In addition, the dimensionless groups (Weber number and Reynolds number) were updated corresponding to approximately 92.4% of the total We samples and approximately 96.4 % of the total Re samples ranging from 0.01 to 1 and 10 to 300, respectively, regardless of the different coolants (HFE-7100 and HFE-7000), pressures, nozzle-to-surface heights, heat fluxes, surface conditions, orientations, and gravities (1 g and mu g).