Experimental Investigation on the Thermal Performance of a Novel Embedded Heat Pipe

An experimental investigation was conducted on a novel embedded gravity heat pipe (EGHP) to evaluate the effects of working fluid, filling ratio (FR), and inclination angle on its thermal performance under various heating powers, aiming to explore its potential for thermal energy storage and building heating applications. The results indicate that, compared to Novec 7000, anhydrous ethanol with a 10% FR reduced the startup temperature by 18.79 °C at 10 W and thermal resistance by 54.67% at 70 W. Among the tested conditions, the EGHP exhibited optimal performance at an FR of 10%, achieving a minimum thermal resistance of 0.07 °C/W, a maximum effective thermal conductivity of 24.27 kW/m·°C, and the lowest temperature uniformity coefficient of 0.34. Moreover, the EGHP demonstrated stable operation across a range of heating powers and inclination angles. In practical applications, a 10% FR and a 45° inclination angle are recommended, under which thermal resistance decreased by 17.27%, effective thermal conductivity increased by 20.87%, and temperature uniformity improved by 10.77% compared to vertical installation. This study highlights the critical roles of working fluid selection, FR, and installation angle in optimizing EGHP performance, providing a pathway toward rapid-response and high-efficiency thermal energy storage and heating systems.