Study on nucleate boiling heat transfer to slush hydrogen and slush nitrogen

Slush hydrogen is a mixture of liquid hydrogen and solid hydrogen particles, and is being considered as a spaceplane fuel or as a means of transport for hydrogen used as a source of clean energy. This paper describes nucleate boiling heat transfer characteristics to slush hydrogen and slush nitrogen. For visual observation of heat transfer states, a heat transfer unit was placed in a glass dewar designed to minimize the heat leak from atmospheric environment. The heat transfer unit used was a circular flat 'plate 0.025 m diameter made of electrolytic tough pitch copper. For orientations of the heat transfer surface during testing, three different orientations were used; horizontal facing up, vertical, and horizontal facing down. In addition to that for slush hydrogen and nitrogen, heat transfer data for normal boiling point (NBP) liquid hydrogen, triple point (TP) liquid hydrogen, NBP liquid nitrogen and TP liquid nitrogen was obtained up to the critical heat flux (burnout). Comparison of these data with the slush hydrogen and nitrogen data, including the results of observation of the heat transfer surface, clarified nuclear boiling heat transfer characteristics to slush hydrogen and slush nitrogen, which have hardly ever been investigated.