Nucleate boiling of liquid oxygen under a magnetically compensated reduced-gravity environment

The nucleate boiling heat transfer behavior of liquid oxygen (LOX) under reduced gravity is critical for assessing the reliability of multiple ignition cycles in orbiting liquid rocket engines. However, existing experimental data and theoretical correlations are insufficient for accurately predicting the associated heat transfer processes. In this study, pool boiling experiments of LOX were performed at three gravity levels ($g_0$, $0.24g_0$, and $0.13g_0$) on an 18 mm diameter circular heating surface at 0.1 MPa, using a magnetically compensated microgravity platform. Boiling curves of LOX and bubble visualization results were obtained under all three gravity conditions. A discrete numerical method based on transient heat conduction along the copper rod was proposed to determine the temperature and heat flux at the heating surface. Results show that decreasing gravity suppresses both single-phase natural convection and nucleate boiling heat transfer while lowering the superheat required for the onset of nucleate boiling. Under reduced gravity, larger bubble volumes and enhanced coalescence and accumulation behavior were observed. Additionally, the empirical coefficient $c_R=0.01993$ for LOX in the Rohsenow correlation was determined. These findings provide an improved basis for predicting cryogenic heat transfer performance under reduced-gravity conditions.