Measurement of the speed of sound of gases.

The knowledge of the ideal-gas heat capacities is essential for the calculation of the caloric properties of fluids. It can be determined most precisely by measuring the speed of sound with a spherical resonator. Starting from the speed of sound data, also other thermodynamic gas properties can be determined, e.g. second virial coefficients. An apparatus for the measurement of speeds of sound of gases within -60 and 150°C and up to 15 MPa was developed and constructed in our group. It is used for the investigation of working fluids as, e.g., refrigerants or humid air.