Evaluation of R404a single loop thermosyphon for shaft cooling in motorized spindle

In this study, a single loop thermosyphon charged with refrigerant R404a was investigated for shaft cooling in a motorized spindle. Tests were performed for a heating power range of 20–200 W, evaporation temperatures between 20 °C and 72 °C, and filling ratio (FR) of 30–80%. Effects of zeotropic mixed refrigerant R404a on heat transfer performance and optimal FR were analyzed and compared with those of pure refrigerants R134a and R600a. Results indicated that R404a single loop thermosyphon has a higher heat transfer efficiency and smaller thermal resistance than those charged with R134a and R600a when the temperature of evaporation is below 57 °C. Due to changes in R404a components during the injection process, the minimum average thermal resistance of R404a single loop thermosyphon (0.41 °C/W) appears at 50% < FR < 60%, compared to 30% < FR < 50% for pure refrigerant.