Film boiling heat transfer properties of liquid hydrogen flowing inside of heated pipe

The knowledge of heat transfer properties of liquid hydrogen is important for designing and developing superconducting devices. In this study, film boiling heat transfers of liquid hydrogen flowing inside of heated pipe were measured under saturated conditions at the absolute pressures of 700 kPa for various mass flow rates. Test pipe heater made of SS310S with a diameter of 8 mm and a length of 200 mm was used. The test heater was once heated up to the film boiling regime with exponential heat generation rate. And then, while the heat generation rate was decreased exponentially down to the minimum heat flux, the film boiling heat transfer coefficient, mass flow rate per unit area and the degree of superheat of pipe length direction were measured. It was observed that though the mass flow rate decreased according to increase of the heat generation rate, the heat transfer coefficient increased. Discussions on the experimental results of various conditions were carried out to clarify the phenomenon of film boiling of liquid hydrogen flowing inside of heated pipe. It was considered that since the void fraction in the flow path was high, the effect of improving the heat transfer rate was also observed in the film boiling region due to the acceleration of the liquid phase.