Research on high injection superheat cycle for R290 low pressure ratio heat pump

The natural working fluid propane (R290) has a GWP close to zero. It is environmentally friendly, has excellent thermophysical properties, and has good application prospects. The discharge temperature of R290 high-pressure rotary compressor is low due to the low adiabatic index of R290, especially in the small pressure ratio condition. The high solubility of R290 leads to the low viscosity of R290/lubricant mixture in the oil sump of high-pressure rotary compressor, which may be difficult to meet the crankshaft/bearings system lubrication and affect compressor reliability. This paper analyzes the relationship between R290 solubility in lubricant and viscosity of R290/lubricant mixture with mixture superheat in low pressure ratio condition. The high injection superheat cycle (HISC) is proposed that it takes advantage of the available energy in the condenser outlet to improve the injection superheat controlling the discharge superheat and the viscosity of R290/lubricant mixture. Meanwhile, HISC can effectively improve the system performance with 11.4% improvement in COP and 23.4% improvement in volumetric heating capacity compared with the single-stage cycle at evaporation temperature -2.89℃ and condensation temperature 51.5℃. © 2023 Chemical Industry Press. All rights reserved.