Effect of wick use on heat pipe efficiency in all-glass heat pipes

In this study, the use of wick in large diameter glass heat pipes used in solar collectors was experimentally investigated. Studies on heat pipes are mostly focused on small diameter and metal pipes. In the study, glass heat pipes without and with wick were tested at different inclination angles and heat loads and the effect of wick on heat pipe efficiency and thermal resistance was investigated. In the study, it was understood that the fluid returning from the condenser to the evaporator wetted the surface more homogeneously due to the temperature decrease on the evaporator surface with the use of wick. At an inclination angle of 60°, the temperature difference between the top and bottom of the heat pipe was 46°C in the pipe without wick, while this difference decreased to 15°C in the pipe using 50 mesh wick. It was observed that the thermal resistance decreased with the decrease in surface temperature and the efficiency increased. While the thermal resistance at 90° inclination angle was 0.92 in the heat pipe without wick, this value was 0.43 in the heat pipe with 50 mesh wick. At 90° inclination angle, the average efficiency increased from 55% in the heat pipe without wick to 75% in the heat pipe with wick. The use of the wick increased the efficiency of the heat pipe at each inclination angle and provided a more constant efficiency at all heat loads. This study shows that the use of roving in large diameter heat pipes significantly reduces the negative effect of gravity, reduces the radial temperature difference and reduces the thermal resistance.