| As an efficient heat transfer element,gravity heat pipes have been applied in the energy field and have shown good comprehensive properties.The main type of China’s geothermal resources is of medium-low temperature.In order to have a better application of gravity heat pipes in medium-low temperature geothermal resources and promote efficient and sustainable utilization of resources,in this paper,are tested.the experimental systems with simulated convective geothermal reservoir and simulated conductive geothermal reservoir were built respectively,aiming to test a series of new type gravity heat pipes filled with mixed working fluid of carbon dioxide and nano-particles and analyze the influence of external working conditions and structural size on the heat transfer performance of the heat pipe.In the experiment of simulated convective geothermal system,the main research factors contain the heat source temperature,hot water volume flow,cold source temperature,cold water volume flow,the length,diameter and outer fins of the heat pipe itself,the following conclusions are obtained: considering the heat transfer power,it is effective to increase the heat source temperature and hot water volume flow,reduce the cold source temperature,increase the cold water volume flow within a certain range and add external fins.When it comes to the overall thermal resistance and equivalent convective heat transfer coefficient of the heat pipes under different working conditions,increasing hot water volume flow,reducing cold source temperature and increasing cold water volume flow can be positive,but the increase of heat source temperature will increase the overall thermal resistance and reduce equivalent convection heat transfer coefficient;comparing six heat pipes of length L=1600 mm,2000 mm,outer diameter D=51 mm,89 mm,110 mm,it can be known that the heat pipe of L/D=1600 mm/ 89 mm is the most beneficial to the heat transfer performance;the two heat pipes with diameter of 51 mm are insufficient of heat transfer power,which is the least recommended in practical applications;the heat pipe with diameter of 110 mm are more suitable for the case of larger heat input.In the simulated conductive geothermal reservoir experiment,the main research factors contain the heat storage volume moisture content,heat source temperature,cold source temperature and cold water volume flow,the following conclusions are drawn: the heat transfer performance of the conductive reservoir is the most critical factor to limit the heat transfer performance of the heat pipes.Increasing the volumetric moisture content of the reservoir has the greatest improvement on the heat transfer power of the heat pipes;increasing the heat source temperature is also conducive to the improvement of the heat transfer power.In most cases,increasing the volume flow and lowering the temperature of the cold water are beneficial to the heat transfer of heat pipes,but when the heat pipes work under the condition of 0%moisture content of the heat storage volume,the increase of the cold water flow rate cannot improve the heat input of the evaporation section,but only enhances the convective heat transfer intensity of the condensation section,so the heat transfer power of the heat pipe is lowered.In the practical project,for the two types of geothermal resource utilization,it is necessary to combine the key influencing factors and production requirements,and select the most suitable heat pipe ensure the coordination of cost and performance. |
