Energetic and exergetic analyses of a transcritical N2O heat pump system

摘要

In the present study, energetic and exergetic analyses of a transcritical nitrous oxide (N₂O) heat pump cycle are carried out on the basis of the optimization of discharge pressure. A simulation code was developed to study cycle performances for the given design and operating parameters. This code was integrated with the thermodynamic property subroutine ‘N₂OPROP' to estimate the thermodynamic properties of N₂O in subcritical and supercritical regions. Variation trends of optimal parameters for an N₂O system are similar to those of a CO₂ system. However, the N₂O cycle exhibits higher cooling COP, lower compressor pressure ratio and lower discharge pressure and temperature, and higher second-law efficiency than those of CO₂-based systems. An N₂O system is inferior in terms of volumetric cooling capacity compared with a transcritical CO₂ system. The maximum exergy loss is observed in the throttle valve (expansion valve) as in the case of a CO₂ transcritical system due to low critical temperature.