On the three exponents of the isentropic change of the refrigerant R22

The differential isentropic change of real gases is usually calculated by using the corresponding equation of ideal gases, with the isentropic exponent taken as the ratio of the specific heats at constant pressure and constant volume. A closer examination shows that there exist three isentropic exponents, having different values, corresponding to the three possible pairs of variables selected among temperature, pressure and volume. The numerical values of these exponents were calculated for the refrigerant R22. It was found that calculations performed with the conventional isentropic exponent can show significant deviations from the real values.