Study On Seepage Characteristics And Heat Exchange Efficiency Of Broken Rock Bed Heat Storage System

The use of rocks for heat storage can play a role in"cutting peaks and filling valleys"for renewable energy such as wind and solar energy,but the study of its permeability characteristics and heat exchange efficiency is the key to the construction of large-scale heat storage systems.In this paper,through the self-built experimental device,using different gases as heat transfer fluids,the heat injection and recovery experiments of the broken rock packed bed under different influencing factors are carried out,and the permeability characteristics and the heat injection and recovery efficiency of the broken rock heat storage system are studied.On the basis of the experiment,a numerical model of the rock bed heat storage system under the coupling of heat,fluid and solid multi-fields is established,and the changes in the heat storage capacity of the large-scale rock bed heat storage system under different influencing factors are analyzed.The main results are as follows:(1)Heat injection experiments were carried out using air and CO₂ as heat transfer fluids,and the non-Darcy flow permeability,heat exchange efficiency and heat storage changes of the rock bed before and after the heat injection experiment were tested.The results show that the permeability of the bed packing system gradually decreases with the heat injection;the heat-carrying efficiency of CO₂ is better than that of air.(2)Using CO₂ as the heat transfer fluid,the heat injection and recovery experiments on a packed bed of broken rock under different particle size ratios and injection pressures were carried out,and the heat exchange efficiency and the change law of heat storage in the rock bed during the heat injection-heat recovery process were studied.The results show that the particle size ratio has a small effect on the heat exchange efficiency,but has a greater impact on the permeability.The greater the permeability,the greater the heat storage in the rock bed;the greater the injection pressure,the higher the heat exchange efficiency and the greater the heat storage in the rock bed.(3)The thermal-hydraulic-mechanical coupling numerical model of the rock-packed-bed heat storage system was established,and the gas flow and heat conduction laws in the loose medium and the porous medium were simulated respectively,and the experimental results were compared.The results show that:the massive bulk medium model can vividly show the internal temperature change of the device during the heat injection and recovery process;however,the simulation results of the porous medium model are more consistent with the experimental results.(4)Based on the thermal-hydraulic-mechanical coupling porous media model,the heat injection and production process of the large-scale rock bed heat storage system is simulated,and the influence of different CO₂ injection pressures and different CO₂injection temperatures on the heat storage capacity is analyzed,and the heat storage is given.Specific measures for the economic operation of the system.The results show that increasing the injection pressure can significantly reduce the time for the rock bed to reach thermal equilibrium,and increasing the injection temperature can significantly increase the total heat storage capacity of the rock bed.This paper has 76 pictures,12 tables,and 76 references.