Experimental study on the reinforcement of a gravity heat pipe based on a latent thermal functionally fluid

In order to promote the efficient use of solar energy, improve the heat collection efficiency of “gravity heat pipe (GHP) type” solar water heater. Using latent thermal functionally fluid (LFTF) as the working fluid for heat transfer, operating parameters of heat pipe and microencapsulated phase change material mass concentration on GHP thermal performance was investigated. The results show that the thermal resistance decreases and the thermal efficiency increases when the liquid filling ratio varies between 20% and 60%. When the liquid filling ratio is 60%, the thermal efficiency reaches its maximum and increases by 7.50% compared to deionized water (DW). When the tilt angle varies from 50° to 90°, the heat transfer coefficient of GHP increases and the thermal resistance decreases. When the heating power is increased from 60 W to 100 W, the start-up time shortens and the thermal efficiency increases significantly. When the heating power is 100 W, the thermal efficiency increases by 4.41% compared to DW. The optimum mass concentration of LFTF is 10%, and the thermal efficiency is improved by 11.67% compared to DW. The degree of heat transfer hindrance by LFTF at higher mass concentration is much larger than the enhancement effect by the fluid itself.