Experimental Study of Speed of Sound in Gaseous Refrigerant $\mathrm{R}$–$507a$

The speed of sound in gaseous refrigerants $\mathrm{R}$–$134a$ and $\mathrm{R}$–$507a$ is measured by the method of ultrasonic interferometer in a temperature interval from $293$ to $373$ K and pressure values from $0.01$ to $0.5$–$2.9$ MPa. The errors in measurement of the temperature, pressure, and speed of sound are $\pm20$ mK, $\pm4$ kPa, and $\pm$($0.1$–$0.2$)%, respectively. On the basis of the data obtained, the temperature dependence of the ideal-gas heat capacity is calculated. The results obtained are compared with calculation of speed of sound from the fundamental state equation for Helmholtz free energy.