Development of capacitance type densimeter with high accuracy for slush hydrogen

Slush hydrogen is a mixture of solid hydrogen particles and liquid hydrogen, 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 the fabrication of three variations of capacitance type densimeters using combinations of a flat plate and two cylinders for the electrodes, as well as presenting subsequent measurement of the density of slush hydrogen made using the freeze-thaw method. The density values measured for slush hydrogen with a solid weight % of up to 30% were generally found to correspond to within ±0.5% of the density values estimated from the latent heat of evaporation of liquid hydrogen. Because the flat plate/cylinder electrode type densimeter allowed easy penetration of solid hydrogen particles within the electrodes, highly accurate density measurements were obtained compared to those simultaneously measured using densimeters with parallel flat plate electrodes. The practical applicability of the new type slush hydrogen densimeter was accordingly confirmed.