Development of Measurement Facility for Sound Speed of Hydrogen with a Spherical Acoustic Resonator ～Theory of Measurement and Calibration for

Thermophysical properties of hydrogen are needed to design equipments associated with hydrogen. The speed of sound is one of thermophysical properties itself and includes the important information of thermophysical properties, such as specific heat at ideal gas. In this paper, the measurement facility for sound speed of hydrogen with spherical acoustic resonator which we made and the theory of acoustic measurement are explained. We have calibrated the radius of the spherical cavity in this apparatus with high purity helium as reference gas at 100～1000 kPa and 40～100℃, and obtained the average radius of 25.016±0.014mm(±0.055%)