상용탑차용 냉동사이클의 성능특성에 관한 실험적 연구

Abstract

Recently, the eating out culture has been developed due to the living level and quality elevation. Home-delivery service is increasing by demand of the refrigerated food. Accordingly, the freezing conveyance becomes the essential things all over the world, and it is rapidly increasing by actual demanding in the present-day life every year. However, the research is insufficient for the performance of refrigerating system in commercial refrigerator truck. In this study, the performance of refrigerating system was measured by changing from the TXV(thermal expansion valve) to EEV(electronic expansion valve) in order to improve responsiveness of expansion device. As a result, the optimal refrigerant charging amount was determined by 1700 g for both system with TXV and EEV. In addition, COP of EEV system is a 1.61% higher than that of TXV system when the EEV opening is 75% which is optimal EEV opening. Besides, the performance of EEV system is higher than system of TXV system for variable driving conditions. The performance variation of EEV system with the operation condition is larger than that of EEV system. Under this condition, the optimal EEV opening was investigated and the correlations of system COP and mass flow rate verses EEV opening was developed , The regulation of the CFC, HCFC refrigerant was initiated due to the global warming problem. Hence, the natural refrigerant, CO2, is in the spotlight as the ultimate solution. The simulation modeling was developed based on the commercial refrigeration truck using CO2 in order to determine the applicability and consider the system performance characteristic according to driving conditions. In addition, the frost growth was considered to investigate the effect of frost on the system performance. The system capacity of non-frost condition was determined by compressor volume which have the cooling capacity of 2.3 kW like that of refrigeration experimental condition. Besides, the system performance analysis was performed with indoor air temperature, outdoor air temperature, front air velocity and compressor speed in order to compared the system performance of non-frost condition. The system performance analysis was carried out with frost thickness so as to the investigate the effect of frost growth on the evaporator. The cooling capacity was analyzed every 5% decrease according to operating conditions. As a result, it confirmed that the simulation results shows the similar tendency of experiment test. The cooling capacity was decreased by 33% when the frost thickness was 2 mm. The performance of CO2 refrigerating system showed similar trends compared with experiment results. As the frost thickness increased, the cooling capacity and compressor work was decreased simultaneously due to the reduction of heat transfer in the evaporator. Therefore, the system COP was decreased with frost growth.