Paper Title
Preliminary Investigation of the Experimental CO2 Cascade Heat Pump System from Exergetic Point of View

Abstract
Thermodynamic properties and heat transfer characteristics of CO2 is important to investigate for new refrigeration systems. This study presents a preliminary investigation of a CO2 cascade heat pump system which can achieve the ultra-low temperature below the CO2triple-point temperature of -56°C and a thermal energy above 100.0℃. It is known that the system performance of this heat pump system can be optimized by an exergy analysis of the system. Exergy can be considered as an indicator to measure how nearly the efficiency of a process approaches the ideal condition. Therefore, this study has pointed out the specific weakness of the heat pump with meaningful method over the system to evaluate the inefficiencies. The main purpose of this study is to apply the conventional exergy analysis to the CO2 cascade heat pump system in order to improve our understanding of the system components and to provide useful information for optimizing the heat pump performance. The results show that the exergy efficiency of the Cool Water Gas Cooler is very low in both high-pressure and low-pressure side. However, it has seen that the efficiency of the Cool Water Gas Cooler increase when the inlet water temperature increase. Therefore, the performance of this CO2 cascade heat pump system can be optimized with appropriate inlet water temperature of the cool water gas cooler. Keywords - Carbon Dioxide, Exergy Analysis, Heat Pump, System Performance