Optimization of wickless heat pipe heat exchanger using R1234-yf and ethanol as working fluids

This experimental study investigates the use of R1234-yf and ethanol as working fluids in a wickless heat pipe, with air flowing through the heat exchanger ducts. The hot air temperatures were set at 50°C, 55°C and 60°C, while the cold air temperature was fixed at 20°C. Both hot and cold air streams were pumped with Reynolds numbers ranging from 2583 to 20664. The wickless heat pipe was oriented vertically and filled with varying filling ratios of 20%, 40%, 60%, 80% and 100%. The results demonstrate that the wickless heat pipe - heat exchanger achieved the best thermal performance of 0.181 at a filling ratio of 60%, using ethanol as the working fluid and a Reynolds number of 10332. Additionally, a novel approach is proposed to predict the overall thermal performance of the wickless heat pipe - heat exchanger