Performance Investigation of Cascade Refrigeration System Using CO2 and Mixtures

This paper presents reports on simulation and comparative analysis of single stage vapor compression refrigeration system and cascade systems using carbon dioxide, hydrocarbons (HCs) and CO2/HCs mixture. Thermodynamic parameters of fluids are given using the software REFPROP 9.0. To select the most suitable HCs, three criteria have been fixed: Tc, Tt and Tb. It is found that the HCs chosen in low-stage are propane, propylene and ethane and those for the high-stage are propane, propylene and isobutane. The fraction mixture in the two loops has been varied and results are compared with single stage and cascade systems using CO2 and R22. The fraction x CO2 is varied in the two loops. Results are compared for single and cascade systems using CO2 and R22. For the single stage system, we find for xCO2 = 0.5, an improvement of COP of 14% for CO2/propane mixture and 36% for the CO2/propylene mixture. It is found that for xCO2 = 0.3, cascade system using propane/CO2 mixtures presents a COP lower than that of cascade system using pure CO2. About of 70% of unfriendly fluids like CFCs and HCFCs can be replaced with CO2, without affecting the performance of cascade refrigeration systems.