Abstract
In this article, a novel cascade refrigeration system is proposed for moderately low temperature applications. An ejector expansion vapor compression cycle (EEVCC) and a vapor injection cycle with the flash tank (VICFT) are coupled together through a cascade heat exchanger to develop the novel ejector injection cascade refrigeration system. The goal of this study is to investigate the potential improvement scope of a conventional cascade refrigeration system by integrating EEVCC and VICFT. A detailed energy and exergy balance analysis are conducted on the novel proposed system by considering the following three design parameters: (1) evaporator temperature; (2) pressure drop at the ejector; and (3) lower circuit condensation temperature. The results reveal that the performance of the proposed system is sensitive to pressure drop at the ejector and lower circuit condensation temperature for each evaporator temperature. Therefore, it is necessary to determine the optimal values of these factors in order to conduct an accurate performance analysis. Furthermore, a comparative study between the proposed system and the conventional system is conducted based on the first and second laws of thermodynamics. The results show that at -60 degrees C of evaporator temperature, the proposed system has 8.571 % COP improvement and 7.241 % exergy efficiency improvement over conventional cascade refrigeration system. This study also explores the suitable pair of refrigerants for this proposed system to minimize environmental impact. Among seven pairs of refrigerants investigated, R170 and R601 at LTC and HTC respectively shows the best performance. The proposed system was found to be more sensitive to change of LTC refrigerant than HTC.