| Along with the growing attention paid on the environment problems, more restricts are imposed on the environmental performance of refrigerants. Different regulations have been proposed these years all over the world, in order to limit the usage of refrigerants with high Global Warming Potential (GWP). At the same time, HFCs refrigerants with low GWP and unsaturated HFCs (also as HFOs) refrigerants with extremely low GWP have drawn more and more focus and been regarded as the most promising candidates as new generation refrigerants.Isobaric heat capacity of liquid refrigerants is one of most important thermodynamic properties which directly associates with energy functions. It plays an essential role in the thermodynamic calculation for refrigeration cycles and in the establishment of highly accurate fundamental equations of state for refrigerants. Experiment is always the most direct way to know the isobaric heat capacity information of liquid refrigerants. However, subject to constrains of experiment system and method, experimental data for these liquids are limited in a certain temperature and pressure range. On the other hand, as a fundamental thermodynamic property, isobaric heat capacity could be derived from equation of state or other theoretical ways. Nevertheless, the fact is that none of the available theories could be used to predict the isobaric heat capacity of HFCs liquids with a satisfactory accuracy level.In this work, the isobaric heat capacities of several commonly used or promising HFCs (HFOs included) refrigerants were investigated experimentally and theoretically. A measuring system with inert gas as pressure source was developed. The system mainly consisted of a Calvet calorimeter and a customized pressure balance unit. It was qualified for isobaric heat capacity measurements of liquid refrigerants above room temperature and at a wide range of pressure. Tests with different standard liquids confirmed its reliability and accuracy.On the measuring system, experimental heat capacity data of liquid HFC-161, HFC-152a, HFC-143a, HFC-245fa, HFC-236fa, HFC-227ea, HFO-1234yf and HFO-1234ze(E) were obtained at temperatures ranged from 305.15 K to 365.15 K and pressures up to 5.54 MPa. Most of these data were reported for the first time. For engineering applications, empirical equations for the experimental data were correlated by a stepwise statistical method for different refrigerants. The equations were properly structured with high accuracy. By extrapolating the equations to saturation lines, the isobaric heat capacities of saturated liquid refrigerants were also obtained.Starting from the experimental data and based on the corresponding state method, a semi-empirical equation was proposed for the calculation of isobaric heat capacity of liquid HFCs refrigerants. A comprehensive comparison with available experimental data indicated that the equation had an overall correlating accuracy of 1.07% and a predicting accuracy as high as 1.78%, which showed its outstanding application potential.At last, isobaric heat capacity of a typical binary mixture consisting of HFC-32 and HFO-1234ze(E) was measured at different temperatures and compositions. Then the proposed corresponding state equation was applied to the mixture and a best mixing rule was selected. The average predicting accuracy was 1.39% and the maximum deviation was no more than 5%. Furthermore, the corresponding state equation and the selected mixing rule were applied to four commonly used HFCs refrigerant mixtures, and the calculation results were compared to those calculated by their own fundamental equations of state. The final results agreed well with each other with an average deviation of 0.87% and maximum deviations less than 1.90%, which further confirmed the reliability for the corresponding state equation to be used to predict the isobaric heat capacity of HFCs refrigerant mixtures. |
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