Thermal analysis on optimizing the capillary tube length of a milk chiller using DC compressor operated with HFC-134a and environment-friendly HC-600a refrigerants

In this work, the thermal analysis on optimizing the capillary tube lengths of a dual circuit refrigeration system was carried out experimentally. Two refrigeration circuits were individually operated using two DC powered compressors (HFC-134a and HC-600a) instead of conventional AC powered compressors. The capillary tube optimization was done to maximize the coefficient of performance and exergy efficiency. From the results, it was found that the power consumption and the refrigerant mass flow rate decreases with the increase of capillary tube length for both the HFC-134a and HC-600a circuits, while the refrigeration capacity and coefficient of performance increased up to the capillary tube length of 4.57 m and then decreased. The maximum refrigeration capacity, ice formed, power consumption, and coefficient of performance experienced in the HC-600a circuit were 9.65%, 19.03%, 3.53%, and 7.34% lower than those of the HFC-134a circuit at the optimum capillary tube length. It was also found that at the optimum capillary length, the COP was maximum for the HFC-134a circuit while the exergy efficiency was maximum for the HC-600a circuit. The exergy efficiency of the HC-600a circuit was 11.13% higher than that of the HFC-134a circuit. At the optimum capillary tube length, the total equivalent warming impact values of the HFC-134a and HC-600a circuits were 961.13 kg CO2-eq and 785.77 kg CO2-eq, respectively.