This experimental study was conducted to investigate the refrigeration cycle performance of a 10kW refrigerator unit using R404A refrigerant. The capacity, COP, and refrigeration cycle of the refrigerator unit were confirmed by changes in refrigerant charging amount and degree of superheat. The cooling capacity and COP of the refrigerator unit showed different tendency according to changes in refrigerant charging amount and degree of superheat. It was confirmed that the performance changes of the refrigerator unit were more dependent on the change in degree of superheat than the refrigerant charging amount. From the capacity, COP, pressure, and p-h diagram, the refrigeration cycle of the refrigerator unit showed the greatest capacity and COP at 4℃ for degree of superheat and 7,400g for the refrigerant charging amount.

Abstract The cascade refrigeration cycle system has been used mainly to obtain the ultra-low temperature. In this study, the effects of internal and outdoor temperatures at chamber on the heat capacity of fin-tube heat exchangers were examined. In addition, refrigerant line patterns as well as refrigerant type for cascade cycle were optimized. The results in this study show that the refrigerant line patterns have greater effect on the sensible capacity than the total capacity. Also, the condenser heat release rate for R717-R744 cycle varies the ratio of 46 % with outdoor temperature by comparing with that of 24% for R134a-R410a cycle.

The LNG carriers have been propelled by steam turbines and the LNG boil-off(BOG) has been used as fuel or vented. However, as the alternative propulsion systems such as diesel engines are being equipped on the LNG carriers for better fuel efficiency, a need for the LNG BOG re-liquefaction system that liquefies the BOG and sends the liquid BOG back to the LNG cargo has arisen in recent years. This study investigates the design of the BOG re-liquefaction system based on the reverse Brayton refrigeration cycle. The thermodynamic and heat exchanger analysis are carried out and the limitations to the system performance are discussed.