Novel method of measuring heat capacity of supercritical fluid using Peltier elements

We present a simple and convenient method of measuring the heat capacity of a fluid sample at a high pressure. A heat-flux-type calorimeter containing a sample cell with a thin wall and small holes is placed in a high-pressure vessel filled with the fluid sample itself. A thermoelectric module serves as the heat pump and heat flow sensor by taking advantage of the Peltier and Seebeck effects, respectively. To obtain the total heat transferred from the measured raw data, we employ a new estimation technique with a least-squares method. The performance of the method is examined by the measurement of supercritical CO2. The temperature increase necessary for the measurement can be suppressed to less than 40 mK; such a small amount scarcely disturbs the state for a temperature- sensitive sample. This method is suitable for determining the heat capacities of supercritical fluids including the states relatively close to a critical point.