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

Abstract

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 of slush hydrogen and slush nitrogen. For the visual observation of heat transfer states, a heat transfer unit was placed in a glass Dewar designed to minimize the heat loss from an atmospheric environment. The heat transfer unit used was a circular flat plate 0.025 m in diameter made of electrolytic tough pitch copper. During testing, three different orientations of the heat transfer surface were used: horizontal facing up, vertical, and horizontal facing down. Heat transfer data for the normal boiling point (NBP) of liquid hydrogen, the triple point (TP) of liquid hydrogen, the NBP of liquid nitrogen, and the TP of liquid nitrogen were obtained up to the critical heat flux (burnout). These data for slush hydrogen and nitrogen, including the results of observation of the heat transfer surface were compared. This clarified the nucleate boiling heat transfer characteristics of slush hydrogen and slush nitrogen, which have rarely been investigated.