Energetic and exergetic analyses of a transcritical N_2O heat pump system

摘要

In the present study, energetic and exergetic analyses of a transcritical nitrous oxide (N_2O) 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 'N_2OPROP' to estimate the thermodynamic properties of N_2O in subcritical and supercritical regions. Variation trends of optimal parameters for an N_2O system are similar to those of a CO_2 system. However, the N_2O cycle exhibits higher cooling COP, lower compressor pressure ratio and lower discharge pressure and temperature, and higher second-law efficiency than those of CO_2-based systems. An N_2O system is inferior in terms of volumetric cooling capacity compared with a transcritical CO_2 system. The maximum exergy loss is observed in the throttle valve (expansion valve) as in the case of a CO_2 transcritical system due to low critical temperature.