Study On The Heat Transfer Characteristics Of Heat Storage Backfill Body Based On The Coupling Of Phase Change Material And Heat Pipe

With the increasing depth of mining,geothermal heat has become one of the main hazards of deep mine mining.The high temperature environment not only worsens the working conditions,but also poses a threat to the health and safety of miners.Geothermal energy is a clean energy source for heating,and in recent years,the concept of cooling the working face of mine filling-geothermal synergistic mining has been proposed,and the technology in this area has been widely researched.The current results mostly focus on the study of heat extraction in the built-in water pipe heat exchanger filling body,which has limited heat transfer capacity.In this paper,an internally arranged casing type heat pipe heat exchanger filling body working face heat extraction and cooling system is proposed on this basis,and its heat transfer characteristics are numerically simulated and experimentally studied.In this paper,a heat transfer model of the heat pipe coupled phase change reservoir system is established to study the effects of different surrounding rock temperatures,heat transfer fluid temperatures and flow rates,as well as the number and spacing of casing type heat pipe heat exchanger arrangements on the internal temperature field distribution,material phase change processes,and system heat transfer performance of the reservoir.The experimental platform of the heat pipe coupled phase-change backfill system is built to verify the accuracy of the simulation results,and the basic evaluation parameters are proposed to reveal the heat transfer behavior of the backfill body in the heat storage/release state,the phase change characteristics of the phase change material and the time-varying law of heat transfer performance of the heat pipe-casing heat exchanger.The enhanced analysis of the thermal conductivity of the phase change material shows that the enhanced thermal conductivity of the phase change material can significantly improve the extraction of latent heat.At the temperature of the surrounding rock of 328.15 K and the end of heat release,the phase change material with 5%expanded graphite added extracted 43%more latent heat value than the pure phase change material.The thermal environment analysis of the mine shows that the increase of the surrounding rock temperature and the flow rate and the decrease of the inlet temperature of the heat exchange fluid are beneficial to improve the heat storage and heat release capacity of the phase change filling.The increase of the surrounding rock temperature from 308.15 K to 328.15 K increases the total heat storage and heat release by 64.36%and 64.84%,respectively.The heat exchange fluid flow rate increased from 0.25 L/min to 1.25 L/min,the total heat storage and total heat release increased by 46.99%and 30.98%,respectively;the heat exchange fluid inlet temperature decreased from 291.15 K to 279.15 K,the total heat release increased by 69.29%at the end of heat release.The increase of heat transfer fluid flow rate and the decrease of heat transfer fluid inlet temperature can improve the total energy efficiency coefficient,and the maximum energy efficiency coefficient is 86.03%when the flow rate is 1.25 L/min;the total energy efficiency coefficient of the system is increased by 13.98%when the heat transfer fluid inlet water temperature is reduced from 291.15 K to 279.15 K;the total energy efficiency coefficient of the heat pipe coupled phase change filler system is 38.10%higher than that of the pure water pipe system at the surrounding rock temperature of 328.15 K.The analysis of heat pipe-casing heat exchanger arrangement shows that the reduction of heat exchanger to surrounding rock spacing can significantly improve the heat storage and heat release capacity of the phase change filled body.The distance between the heat exchanger and the surrounding rock was reduced from 95 mm to 20 mm,and the total heat storage and total heat release increased by 72.89%and 91.10%,respectively.The increase of the number of heat exchangers can significantly increase the total heat storage in the first phase of the phase change filler;the decrease of the number of heat exchangers is beneficial to improve the total efficiency of the heat pipe coupled phase change filler system.The influence law of heat recovery environment and heat exchanger arrangement on heat storage/release process obtained in this study provides basic information for efficient heat storage and heat recovery in the filling body,and also lays the foundation for deep geothermal development.