Numerical Study On Thermal Storage Performance Of A Shell And Tube Bundle Latent Heat Thermal Storage

With the rapid development of economy and the improvement of human living standard,the consumption of traditional fossil energy is gradually increasing.The extensive use of fossil energy has led to environmental pollution and climate deterioration,thus the effective use of energy and the development of new energy sources become extremely important.The development of heat storage(TES)system is an important performance to improve the utilization rate of energy.Heat storage is that energy is stored firstly,and then need to use,which eliminate the mismatch between energy supply and energy demand.The thermal storage performance of a shell and tube bundle latent heat thermal storage is numerically analyzed.Firstly,a three-dimensional numerical model of a shell and tube bundle,latent heat thermal storage with 27 pipes is established by coupled heat transfer method.In this thermal storage,the pipes outer space is filled with phase change material(PCM),n-octadecane.The heat transfer fluid(HTF),air,flows through the inner pipes and exchanges heat with PCM.Then,the model is divided into 82 regions,which meshed by using composite grid.Finally,the phase change heat transfer of PCM and the convective heat transfer of HTF are closed coupled via the boundary conditions.The numerical results show:(1)Before the phase change process is completed,the latent heat energy of heat storage pipe bundle and heat storage unit gradually increases with the inlet velocity and inlet temperature of HTF,and then it keeps a constant value when the phase change process is completed.(2)During the whole heat storage process,the transient energy efficiency ratio of heat storage pipe bundle and heat storage unit has two peaks.The first peak all appears in the initial stage of heat storage process.The second peak of heat storage unit appears in the completed stage of heat storage process,and the second peak of heat storage pipe bundle appears in the uncompleted stage of heat storage process.As the heat transfer fluid inlet flow rate and the inlet temperature increase,the two peaks of the transient energy efficiency ratio appear in the forward time.With the increase of the inlet flow rate,the transient energy efficiency ratio decreases and the effect of the inlet flow rate is more and more weakened.However,the transient energy efficiency ratio increases with the increase of the inlet temperature.(3)With the increase of inlet velocity,the average energy efficiency ratio of heat storage unit and heat storage pipe bundle gradually decrease,but the heat storage rate increases.With the increase of inlet temperature,the average energy efficiency ratio and the heat storage rate of heat storage unit and heat storage pipe bundle gradually increase.(4)Compared the time needed to complete phase change process in heat storage pipe bundle and the time needed to complete phase change process in heat storage unit,the heat storage pipe bundle is heat storage unit 8.3%,9.0%,9.7%,10.0%,10.2% and 10.4% of the time,respectively.Thus,when studying heat storage unit in heat storage pipe bundle,the heat transfer effect between pipe bundle is not neglected.(5)In the same pipe diameter of HTF,the average energy efficiency ratio and the heat storage rate of heat storage unit gradually decrease with the outer diameter of PCM increasing,but the mechanical energy and the time by the phase change process consumed gradually increase.In the same volume of PCM,the average energy efficiency ratio and the heat storage rate of heat storage unit gradually increase with the inner pipe diameter of HTF increasing,but the mechanical energy and the time by the phase change process consumed gradually decrease.