Synergistic enhancement of pool boiling heat transfer by micro-pin-fins and an external electric field at different gravity levels: An experimental study during the parabolic flight campaign

Pool boiling of FC-72 on a smooth silicon surface (SS) and two micro-pin-fin surfaces (PF30–60 and PF50–120) was investigated during the 81st ESA parabolic flight campaign to characterize heat transfer under Lunar (0.16 g 0 ) and Martian (0.38 g 0 ) gravity. Tests covered nominal liquid subcoolings of 5–35 K and applied voltages of 0 and 15 kV; data at 1 g 0 and 0.01 g 0 were included for comparison. The highest heat flux sustaining quasi-steady boiling is reported as the approximate critical heat flux (CHF). At 5 K subcooling and without an electric field, approximate CHF decreased with gravity, but the measured CHF recovery ratios generally remained close to or above the classical g 0.25 scaling. Both micro-pin-fin surfaces exhibited higher approximate CHF than SS, and PF30–60 showed better CHF retention at 0.16 g 0 and 0.38 g 0 . Increasing subcooling increased approximate CHF and extended the stable high-heat-flux range. Applying 15 kV increased approximate CHF for all surfaces, with a generally greater relative response on the micro-pin-fin surfaces, and improved their high-heat-flux HTC response. For heat-flux-matched PF30–60 conditions, the projected vapor area fraction decreased by 6.76% at 0.16 g 0 and 6.43% at 0.38 g 0 under the electric field. These direct observations show that microstructures and the electric field provide combined enhancement under partial gravity. Together with capillary-wicking measurements, the results suggest that the enhancement depends on the matching of structure-dependent liquid transport and electric-field-induced interfacial regulation, rather than on a single dominant mechanism. The findings provide experimental evidence for designing enhanced two-phase thermal-management systems under partial gravity.