Experimental study on the heat transfer characteristics of an immersed wickless heat pipe cooler

In recent years, the power density of electronic devices has surged, leading to increasing attention to phase-change cooling technologies due to their high effective heat transfer coefficients. However, traditional heat pipes face challenges such as high interfacial thermal resistance and poor temperature uniformity, while immersion phase-change cooling systems are hindered by complex structures and high costs. This study proposed an Immersed Wickless Heat Pipe (IWHP) cooler that immerses the heating element directly in the working fluid inside the evaporator chamber, aiming to reduce interfacial thermal resistance and improve surface temperature uniformity, while utilizing gravity for condensate return. Using R-1233ZD(E) as the primary working fluid, this work systematically investigated the dynamic and steady-state thermal performance of the IWHP under forced air cooling, and compared its thermal performance with that of R-1233ZD(Z), a structural isomer with a higher boiling point and lower vapor pressure. Within the tested range of 200–1200 W heating power and 20%–72% filling ratio, the heat pipe thermal resistance of the IWHP remained in the range of 0.0111–0.0194 °C/W, and the temperature uniformity coefficient decreased from 0.014 to 0.007 with increasing power, indicating consistent temperature uniformity. No performance degradation was observed at the upper test limit, suggesting a broad effective operating range. The IWHP provides a structurally simple thermal management configuration for high heat flux electronic devices.