Prediction of pool boiling heat transfer for hydrogen in microgravity

Pool boiling heat transfer of hydrogen frequently occurs in microgravity. Understanding the heat transfer characteristics of liquid hydrogen (LH2) in low gravity condition is of importance to its space application. In this paper, an existing gravity scaling analysis, proposed based on the experimental data of non-cryogenic fluids, is assessed using the boiling heat transfer data of hydrogen under different gravities. Validation study shows that this scaling analysis is also acceptable in predicting the nucleate boiling heat transfer of hydrogen in low gravity condition. Through this analysis, the heat flux at any gravity level can be obtained if the data in the similar condition are available at a reference gravity. Moreover, another scaling analysis aiming at the film boiling regime is proposed, and its predictive accuracy is validated by comparing with the hydrogen experimental data. The comparison study shows that an excellent agreement is obtained and the deviation is within 15%. Furthermore, the hydrogen boiling curves under normal gravity and microgravity conditions are constructed. It exhibits that microgravity yields lower heat flux throughout the overall boiling range, and the influence of gravity on heat flux is most significant in the film boiling regime. Generally, the validated and the proposed scaling analysis can provide researchers with reliable mathematical tools to perform a preliminary investigation of hydrogen heat transfer system in microgravity.