Thermodynamic Comparison Analysis on CO_2 Transcritical Reverse Cycles with IHX or Expander

摘要

To improve the coefficient of performance ( COP) of CO_2 transcritical reverse cycle and determine the most efficient cycle, comparison analysis on single-and two-stage CO_2 transcritical cycles with internal heat exchanger (IHX) or expander is presented adopting the principle of thermodynamics. Results indicate that the COP of four cycles, namely single-stage compression with IHX (SI), single-stage compression with expander ( SE). two-stage compression with IHX (Tl) and two-stage compression with expander (TE), can be ranged as TE > SE >TI >SI. It presents that adopting an expander to recover expansion power is the primary method to improve the COP of CO, transcritical reverse cycle if the efficiency of the expander is up to a certain value. Under supposed operating condition, where the outlet temperature of gas cooler is 35 deg C and the evaporating temperature is 5 deg C the COP of TE cycle is about 42 percent higher than that of SI cycle when the expander efficiency is 0. 6 and the degree of superheat of IHX is 15 deg C, Therefore TE cycle is the most recommendatory one and it is better to adopt TE in those high-cooling capacity systems because its technology cost will be higher.