Heat capacity, Cp, of fluids from transient hot wire measurements

We report here the first thermal diffusivity measurements that cover a wide range of thermodynamic states including the dilute gas, the dense gas, the compressed liquid, and conditions close to the critical point. The heat capacity is obtained from simultaneous measurements of thermal conductivity and thermal diffusivity in a transient hot wire instrument, while the density is obtained from an equation of state. Values for the heat capacity, C p, of argon were obtained at two temperatures, 172 and 275 K, with pressures up to 70 MPa. For these temperatures the densities range from that of the dilute gas to 2.2 times critical density while the heat capacity varies by a factor of seven from the dilute gas value.