Experimental Research to Compare the Effect of Varying Inlet and Outlet Temperatures of a Heat Exchanger on the Performance of A Cascade Cooling System

Abstract

Heat exchangers are not merely cooling devices that transfer heat between fluids; they are an effective way to conserve resources, save money, and contribute to global efforts to reduce energy waste, with positive implications for economic security and resource sustainability. Good design and the selection of the best materials for heat exchanger manufacturing ensure optimal exchange. The heat exchanger capacity required for a refrigeration system must achieve the smallest possible difference between the inlet temperature of the heat exchanger evaporator and the outlet temperature of the heat exchanger condenser. The overall system capacity depends on the temperature difference within the heat exchanger to minimize energy consumption. This study demonstrates the importance of the difference between the inlet temperature of the heat exchanger evaporator and the outlet temperature of the heat exchanger condenser, as this difference has a specific value for each main evaporator temperature. For every main evaporator temperature (T_e), there is a corresponding outlet temperature (T_3) in a low-pressure refrigeration cycle (LPC). The operation of heat exchangers is crucial in all refrigeration and air conditioning systems; therefore, careful selection of the heat exchanger type and the materials used in its manufacture is essential. Taking into account several factors to ensure accurate and reliable results, and using the specialized REFPRO refrigeration software, a 24-layer plate heat exchanger was selected to achieve optimal heat exchange between the two refrigeration circuits in this research. To reduce energy consumption in the cascade refrigeration system, the efficiency of the heat exchangers must be improved, pressure loss minimized, and refrigerants selected for the required temperature range must be chosen. Advanced control strategies must be employed to optimize system performance under varying operating conditions, and ambient conditions must be considered during the design and operation of the cascade refrigeration system due to its heavy reliance on the heat exchanger. When using R407C with R32, the refrigerant temperature upon exiting the heat exchanger two hours after system startup is 1.25°C. However, when using R407C with a mixture (90%/10% R32/R600A by mass), the temperature is 0.8°C, a difference of 0.45°C compared to the mixture. The highest temperature recorded for the heat exchanger evaporator in this study was -2.6°C, followed by a low temperature of -5.2°C, which was the lowest temperature recorded for the evaporator in both experiments. The mixture and R32 gas had the same values at the condenser outlet in the low-pressure cycle at the end of the system's operation. The compressor outlet temperature curve in the low-pressure cycle shows that, two hours after startup, the mixture exits the discharge line at a lower temperature than R32 gas. The temperatures of both the mixture and R32 gas allow for determining the optimal compressor outlet temperature, which in turn determines the appropriate compressor size, condenser pipe capacity, and pipe thickness. The compressor inlet temperature in the low-pressure cycle reaches a maximum of 13°C, which is the highest temperature the mixture can reach.