Experimental Determination of Isobaric Heat Capacities of R227 (CF3CHFCF3) from 223 to 283 K at Pressures up to 20 MPa.

A new experimental method for measuring isobaric heat capacity cp down to 223K at pressures up to 30MPa was developed with the aim to study alternative refrigerants at sub-ambient temperatures and elevated pressures. The experiments are carried out in a batch mode, using a differential fluxmetric calorimeter Setaram BT-215, equipped with a customized high-pressure unit. The measurements are performed at constant pressure with a continuous scan of temperature. First, the method was tested at atmospheric pressure with methanol in the temperature range 223–283 K. The relative deviation from recommended isobaric heat capacity data in the literature is about 0.5%. Second, the measurements were performed at pressure up to 18.2MPa with an alternative refrigerant R134a (1,1,1,2-tetrafluoroethane) of well-known heat capacity. Our results agree with representative literature values within 0.4%. New original results were obtained for refrigerant R227 (1,1,1,2,3,3,3-heptafluoropropane) in the temperature range from 223 to 283K and at pressures of 1.1, 5, 10, 15, and 20MPa. The consistency of our isobaric heat capacities with calorimetric values above 273K and with pV T data reported in the literature is discussed.