Thermodynamic Studies of Transcritical CO 2 and N 2 O Combined Power Refrigeration Cycles

Objective: Researchers have started proposing the use of natural refrigerants like CO₂ and N₂O in place of CFCs and HCFCs. The cycles using these refrigerants operate in transcritical region. Thus, there is a scope of combined power generation with cooling. This has been analyzed in this work. Methods: The energetic and exergetic analysis are carried out on transcritical CO₂ and N₂O combined power and refrigeration cycles. The equations thus generated for COP and exergetic efficiency are studied for their behavioral dependence on various influencing parameters like evaporator temperature, gas cooler outlet temperature, gas heater pressure and turbine inlet temperature. In the entire analysis the standard property code is used in the program for evaluation of properties. Findings: For a comparison, the Grassmann diagrams for both CO₂ based and N₂O based combined power and refrigeration cycles have been presented at a given operating condition. It is noticed that the performances of transcritical N₂O combined power cycle is better than transcritical CO₂ combined power cycle as it has higher COP and exergetic efficiency under all operating conditions. It is also found that there exists an optimum evaporator temperature at which the exergetic efficiency attains maximum value. Specific exergy loss is found more for throttle valve and compressor. Application: The natural gas based combined power and refrigeration cycle can be used in large applications like cooling and heating in ships or large ice plants etc.