Correlations for calculating heat transfer of hydrogen pool boiling

Understanding the heat transfer characteristics of hydrogen pool boiling as well as constructing reliable correlations to guide the boiling heat transfer analysis is of significance to the applications of liquid hydrogen (LH2). In the present paper, the available hydrogen experimental data in literature are summarized and analyzed. Based on these data, several existing correlations aiming at different boiling regimes are evaluated or modified in order to realize the quantitative analysis of hydrogen boiling heat transfer. After sufficient comparison studies, several improved correlations for nucleate boiling, critical heat flux (CHF) and minimum heat flux (MHF) are proposed. Moreover, a complete set of correlations for hydrogen boiling heat transfer are summarized and subsequently a predicted hydrogen boiling curve is constructed. The results show that heat flux in the nucleate boiling regime is approximately a function of Delta T-2.5. For the calculation of hydrogen film boiling, Breen & Westwater correlation seems to be appropriate for revealing the heat transfer characteristics no matter what heater geometry is used. For the hydrogen boiling under 0.1 MPa condition, heat fluxes at onset of nucleate boiling (ONB), CHF and MHF are in the order of 10 W/m(2), 10(5) W/m(2) and 10(3) W/m(2), respectively, and the corresponding wall superheats are approximately 0.1 K, 3 K and 4 K. In addition, pressure effect on hydrogen boiling heat transfer is investigated, and it shows pressure has a significant influence on MHF while a little effect on the heat fluxes in liquid natural convection and film boiling regimes. CHF of hydrogen increases with the increase of system pressure firstly and then decreased with further pressure increase. The maximum of CHF locates at about P/P-c = 0.35. Generally, the present study is beneficial to understand the boiling heat transfer characteristics of hydrogen, and the summarized correlations could provide researchers with reliable mathematical tools to conduct the boiling heat transfer analysis of hydrogen systems. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.