| Rock is considered as an ideal solid heat storage material because of its many advantages,such as large specific heat capacity,low cost and suitability for large-scale applications.Still,the complete rock is of dense structure and is not conducive to heat exchange with the heat-carrying medium.The rock-packed bed filled with complete rock and crushed stone particles can ensure a large energy storage density and have better permeability,effectively improving the heat storage performance.In this thesis,the heat injection and heat extraction experiments of the rock bed were carried out by an experimental setup built independently,and the permeability characteristics and heat exchange efficiency of the rock-packed bed heat storage system with different rock layouts are studied.Based on the experiments,a numerical model of the ThermalHydraulic-Mechanical coupling model of the rock bed heat storage system was established.The heat storage capacity and heat storage rate of the large-sized rock bed heat storage system under different influencing factors are analyzed.The main results obtained in this thesis are as follows:(1)The porosity and permeability characteristics of rock-packed beds with different layouts of complete rock and crushed stone particles were tested.The results show that the overall porosity of the rock-packed bed is determined by the rock slab’s interstitial space.The larger the interstitial space,the larger the packed bed’s porosity,and the permeability of the rock-packed bed is correspondingly larger.(2)The experiments of rock-packed bed heat injection and extraction under different rock layouts and fluid injection pressure were carried out to study the variation of heat storage capacity and heat storage efficiency of the rock-packed bed heat storage system during the heat injection and extraction process.The results show that the larger the interstitial space of rock-packed bed,the faster the rate of heat injection and extraction and the higher the heat storage capacity of the system in the same injection time,while when the interstitial space is similar,the increase of the number of filled layers accelerates the heat injection and extraction process of the heat storage system,and the heat storage capacity of the system is higher in the same injection time.With the same filling conditions,increasing the fluid injection pressure increases the heat input of the heat storage system and promotes the heat exchange between the fluid and the rock,thus improving both the heat storage capacity and the heat storage efficiency of the heat storage system.(3)Based on the experimental results,it can be obtained that the interstitial space,the number of filled layers and the volume of the rock slab are the main geometric parameters affecting the heat storage performance of the rock bed.Increasing the rock slab’s interstitial space increases the packed bed’s permeability,and the heat exchange between the fluid and the rock increases in the same heat injection time,which accelerates the heat injection and extraction process in the rock-packed bed.When the interstitial space is similar,the more layers are filled,the larger the heat exchange area between the rock slab and the gap,and the more heat is input to the rock slab,and the more layers filled means the rock slab volume is small,the heat conduction distance in the rock slab is small,and the rock slab temperature changes fast,which can effectively increase the heat of the rock-packed bed in the same heat injection time.Therefore,designing the rock bed heat storage system needs to consider these three parameters comprehensively and coordinately.(4)The numerical model of rock-packed bed heat storage system under the coupling of thermal-hydraulic-mechanical is established to simulate the experimental process of rock bed heat injection and extraction,and the correctness of the model is verified by comparing it with the experimental results.Based on the model,the rock bed heat storage system’s heat injection and extraction process with actual engineering dimensions is simulated.The results show that the increase in the number of voids in the bed accelerates the system’s heat storage and release rate but also reduces the heat storage density of the system and decreases the maximum heat storage capacity.Increasing the fluid injection temperature not only increases the heat input to the heat storage system but also increases the temperature gradient in the heat storage system,which can effectively improve the heat storage and release rate. |
