Temperature response and thermal performance analysis of a hybrid gravity heat pipe(HGHP) for winter soil warming of grapevine roots:a field experiment

Abstract

ravity heat pipe is a highly efficient heat transfer device that shows great potential for efficient development of shallow geothermal energy.The adiabatic section of the gravity heat pipe does not exchange heat with the external environment during operation, and the use of low-cost PPR materials with low thermal conductivity to replace the expensive metal materials in the adiabatic section can significantly reduce the cost of gravity heat pipe materials.In this study, a new hybrid gravity heat pipe (HGHP) composed of metallic copper and PPR materials is designed, in which the evaporation section and condensation section, which exchange heat with the external environment, are made of metallic copper, and the adiabatic section, which does not exchange heat with the external environment, is made of PPR material, and the analysis of HGHPs and heat transfer characteristics of the similar principle has not yet been reported in the public literature.It was found that the average soil temperature around the condensation section of CGHP and HGHP during the experimental period increased by 4.94℃ and 3.08℃, respectively, compared to the soil temperature of the control group without heat pipe, which was a significant warming effect;Both sets of heat pipes exhibit good isothermal performance,and the CGHP isothermal performance is better than the HGHP;The thermal power of CGHP and HGHP is 55.11 and 42.61 W respectively, which is 22.68% lower than that of CGHP due to the increased thermal resistance of the connecting joints of HGHP.The cost analysis found that the cost of HGHP is 48.39% lower than that of CGHP, and the material cost decreases significantly. This study provides a feasible solution to reduce the cost of shallow geothermal energy development.