Thermodynamic analysis and comparison study of two novel combined cooling and power systems with separators using CO₂-based mixture for low grade heat source recovery

Transcritical CO₂ power cycle is an available technology for low grade heat source recovery, but the low critical temperature (about 31℃) of CO₂ working fluid restricts its practical application because it is hard to ensure the condensation for CO₂ working fluid under the environmental temperature. In this paper, two novel combined cooling and power (CCP) systems with separators are proposed, namely the HCO₂R (High concentration CO₂ mixture Refrigeration) CCP system and LCO₂R (Low concentration CO₂ mixture Refrigeration) CCP system, which integrate a transcritical CO₂ power cycle with an ejector refrigeration cycle. For ensuring the working fluid condensation under environmental temperature, CO₂-based mixtures (i.e. the mixture of CO₂/R32) are using as the working fluid in the proposed systems. Because of the composition separation characteristic of the CO₂-based mixtures, a separator is introduced into the novel system and placed at the ejector outlet. And the two parts of CO₂-based mixture working fluid from separator with different mass concentrations respectively enter the turbine and evaporator for generating power and refrigeration capacity. The system mathematical model is established, the parametric studies and comparison between novel systems and conventional ejector-CCP system are implemented. The results reveal that the novel systems have better thermal performance. The HCO₂R-CCP system presents higher thermal efficiency and the LCO₂R-CCP system presents higher net power output. In most cases, the LCO₂R-CCP system presents higher the exergy efficiency compared to the conventional ejector-CCP system.