The Effects of R1234ze(E) Replacing R134a on the Two-Stage Compression Cycle Centrifugal Compressor and Refrigeration Performance

To investigate the changes in the performance of centrifugal compressors and refrigeration efficiency after the replacement of refrigerant R134a with R1234ze(E), this study establishes a mathematical model of the refrigeration cycle and a flow model of a two-stage series centrifugal compressor based on a two-stage vapor compression refrigeration cycle with incomplete cooling between two throttling processes (VCS-TS-FT). The influence of the replacement of R134a with R1234ze(E) on compressor and system performance is analyzed in detail. Numerical results show that, after replacing R134a, under the same condensing temperature and unchanged rotational speed, R1234ze(E) achieves 83.7% of R134a's cooling capacity, with a 2% higher pressure ratio, nearly unchanged efficiency, 0.5% lower discharge temperature, 11.6% lower shaft power, and a decrease in coefficient of performance (ξ_cop) from 6.83 to 6.59. Adjusting the compressor speed significantly alters the performance of the compressor and refrigeration cycle. A 7% increase in speed results in a refrigeration capacity of R1234ze(E) equal to that of R134a at the designed speed, but the compressor efficiency decreases by 5.9%, and the system ξ_copdrops to 6.15. Conversely, a 3.4% decrease in speed with unchanged compressor volumetric flow results in the refrigeration capacity of R1234ze(E) being reduced to 76% of that of R134a at the designed speed, while the system ξ_coprises to 6.87. Therefore, the direct replacement of R134a with R1234ze(E) without redesigning the compressor cannot achieve equivalent levels of both ξ_copand refrigeration capacity compared to R134a. Additionally, improvements to the condenser and evaporator are required to achieve the same refrigeration capacity.