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 (C_p,m) of liquids with dissolved gases. The expanded uncertainties of the temperature, pressure, and isobaric specific heat capacity (c_p) of the experimental system are 0.046 K, 5.0 kPa, and 0.032 J g^-1 K^-1, respectively. The C_p,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 C_p,m values of such mixtures at the same pressure increase approximately linearly with rising temperature and decreasing refrigerant ratio. The C_p,m is much more sensitive to changes in composition than temperature and pressure. Two correlation equations for the C_p,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.