Research On New Working Fluids And Their Thermodynamic Properties For Moderate-high-temperature Heat Pumps

The lack of suitable working fluids with both excellent thermal and environmental performances is one of important factors constraining the wide application and development of moderate-high-temperature heat pumps. In order to find out new working fluids with excellent comprehensive performance, in this paper, the study on the theoretical thermodynamic performance and the comprehensive cycle performance for new working fluids developed were carried out, and relevant experimental tests were conducted.Firstly, the excellent comprehensive cycle performance was took as starting point, according to the gas state equation and mixing rules, the theoretical performance analysis and calculation of some non-ozone-depleting pure working fluids selected have been carried out at different working temperatures. According to theoretical calculation results, three mixtures Z1-Z3 with excellent environmental performances and six mixtures M1-M6 with higher condensing temperature of 60-90℃have been developed and studied. The thermodynamic properties of the Z1-Z3 and M1-M6 had been analyzed. It was found that Z1-Z3 could be used as new alternatives for refrigerant R134A.Secondly, the selection for new working fluids is generally based on single or several cycle performance indecis so that the theoretical and real performance of new working fluids could not be accurately evaluated. In order to compare the working fluids in a more fair and reasonable way, nine common and important performance indecis of working fluid was selected as variables and the principal component analysis was used to evaluate the working fluids'comprehensive cycle performance.Lastly, the experimental study for working fluids of R134A, R417A and M5 has been done using a test rig specifically built for water-to-water moderate-high-temperature heat pumps. The experimental results showed that the M5 had higher thermal efficiency than other two working fluids under same working conditions. At the ambient temperature respectively of 30℃and 40℃, 70 and 65 minutes were correspondingly taken by the heat pump test rig charged with M5 as working fluid to heat 100L of water from 30℃to 80℃, meanwhile the system's COP was respectively 2.9 and 3.0. Hence, M5 was considered to be the suitable fluid for moderate-high-temperature heat pumps. According to the results of theoretical thermodynamic performance analysis, comprehensive cycle performance evaluation and experimental tests, it was found that the thermodynamic performances of Z1-Z3 were closed to R134A. Since Z1-Z3 had excellent environmental performance, they then could be the alternative of R134A. Because the new working fluids M1-M6 had excellent cycle performance across wide temperature range, they should have the great potentials to become the working fluids for moderate-high-temperature heat pump at condensing temperature from 60℃to 90℃. Keywords: moderate-high-temperature heat pump, new working fluids, thermodynamic...