Thermodynamic Analysis of Vapor Injection Heat Pump Cycle with Dry Working Fluid

The use of high-temperature heat pumps to recover industrial waste heat has a high potential for energy conservation. High-temperature heat pumps require high critical temperatures, and the majority of the available working fluids are dry. However, when the dry working fluid is compressed from the saturated vapor phase, the compression process enters the two-phase region, resulting in a risk of liquid slugging that is detrimental to the operation of the compressor and high-temperature heat pump. Two improved vapor injection heat pump cycles (Cycle A and Cycle B) using isohexane, R1336mzz (Z), and R1233zd (E) as working fluids are proposed. The effects of compressor isentropic efficiency, evaporating temperature, and condensing temperature on the minimum superheating degree and heat pump performance are analyzed. The results indicate that, for cycle B, the evaporation temperature increases from 50 ℃ to 80 ℃. For R1336mzz(Z), the maximum COP (coefficient of performance) can be increased by 2.56%, and the maximum volumetric heating capacity (VHC) can be increased by 3.18%. For R1233zd(E), the maximum COP can be increased by 0.44%, and the maximum VHC can be increased by 0.54%. Cycle A has good adaptability to the isentropic efficiency. For cycle B, when the isentropic efficiency is higher than 0.6, isohexane is not suitable as a working fluid. When the isentropic efficiency is higher than 0.95, R1336mzz (Z) is also not suitable.