Experimental Investigation on the Isobaric Molar Heat Capacities of [EMIM][BF₄] and [HMIM][Tf₂N] with Dissolved R32 or R125

An experimental apparatus based on a flow calorimeter was built for the measurement of the isobaric molar heat capacity (Cp,m) of liquids with dissolved gases. The expanded uncertainties of the temperature, pressure, and isobaric specific heat capacity (cp) of the experimental system are 0.046 K, 5.0 kPa, and 0.032 J g–1 K–1, respectively. The Cp,m of four binary mixtures of ionic liquid and refrigerant ([EMIM][BF4] + R32, [EMIM][BF4] + R125, [HMIM][Tf2N] + R32, and [HMIM][Tf2N] + R125) were measured at 290–343 K and refrigerant molar fractions of 0.1–0.6. Experimental results show that the Cp,m values of such mixtures at the same pressure increase approximately linearly with rising temperature and decreasing refrigerant ratio. The Cp,m is much more sensitive to changes in composition than temperature and pressure. Two correlation equations for the Cp,m as functions of temperature and component proportions were compared, with average absolute relative deviations of 0.66 and 0.53%, respectively. Furthermore, the excess isobaric molar heat capacities of four binary mixtures were analyzed in terms of the pure component properties and molecular interactions in the mixtures.