Experimental Investigation of Circumferential Temperature Variation in Large-Diameter Wickless Glass Heat Pipes

This study investigates the circumferential temperature distribution in large-diameter wickless glass heat pipes under different inclination angles and heat loads. The experimental analysis was carried out on borosilicate glass heat pipes using ethanol as the working fluid. Surface temperatures were recorded at several axial and circumferential positions under heat loads ranging from 25 W to 100 W and inclination angles of 30°, 60°, and 90°. The results showed that heat transfer efficiency and thermal resistance varied significantly with inclination angle. The system showed optimum performance with lower thermal resistance and higher heat transfer efficiency at 30° and 60° inclination angles. However, increased surface temperatures and dry-out zones at 90° inclination negatively affected the heat transfer efficiency. The results highlight the importance of the use of wicks in the design of glass heat pipes for solar energy applications.