Comparative study on the heat transfer performance of micro-grooved anodized thermosyphon with R134a, R600a and R717 for low-temperature applications

A comparative heat transfer performance of an internally grooved anodized thermosyphon with eco-friendly refrigerants is presented in this study. Thermosiphons are fabricated with 50 numbers of axial micro-grooves having a width of 500 μm and a depth of 550 μm that is formed using an electrical discharge machining process. The micro-grooved surface was then anodized and characterized using SEM as well as DSA 25 drop shape analyzer. Later, the heat transfer performance of non-anodized grooved thermosyphon is studied by varying fill ratio (20-80 %), inclination angle (0-90°), and heat inputs (5-50 W). The heat transfer coefficient of the thermosyphon is improved by anodization by 20.9 %, 17.2 %, and 18.1 %, respectively, with R717, R134a, and R600a at optimum circumstances (30 % fill ratio and 60° inclination angle). Due to the performance enhancement and zero global warming potential of R717, an anodized surface with the same is recommended for a wide range of heat transfer applications.