Heat Transfer Characteristics Of Liquid Hydrogen Flowing Inside Of A Vertical Heated Pipe Under Quasi-Stationary Heat Input

Heat transfer from inner surface of a vertical heated pipe to subcooled or saturated liquid hydrogen flowing upward was measured for quasi-steadily increasing heat input up to fully developed film boiling regime and decreasing the heat input through the film boiling regime. The experiments were carried out at the inlet pressures of 400, 700 and 1100 kPa and subcoolings from 0 K to 11 K. Three test pipe heaters made of SS310S with inner diameters of 6 and 8 mm and lengths of 100 and 200 mm were used. Experimental data from non-boiling to developed film boiling and developed film boiling down to minimum film boiling was obtained with the record of mass flow rate by continuously increasing and decreasing the heat input. It was observed that though the mass flow rate decreases with the increase of the heat generation rate, the heat transfer coefficient increases. Discussions on heat and mass transfer in inverted annular flow, dispersed droplet flow, single-phase vapor flow regimes and their changing conditions from one by one were carried out to clarify the phenomena. A calculation code of heat transfer characteristics was developed based on the discussions. The calculated results are in good agreement with the experimental results.