Numerical Simulation Study On Heat Storage And Mechanical Behaviors Of Solar Energy Single-Tank Molten-Salt-Based Phase Change Energy Storage System

Solar power is a kind of important renewable energy utilization method,which can effectively solve the energy sustainability.It is very meaningful to develop solar power under the condition which fossil energies are running out and the two-carbon strategy target is proposed.However,the discontinuity of solar energy and low electricity quality make the solar power difficult to be on the power grid.That can be solved by utilizing heat storage technologies.High costs of the existing double-tank heat storage system limits the competitiveness of solar thermal power.The single-tank heat storage system can reduce the costs of solar thermal power to a certain degree.The single-tank molten-salt-based phase-change heat storage system can store more heat by using phase-change materials in the filling bed,which can improve the heat storage capacity of the system effectively.This study launches an impact evaluation of different parameters on the heat storage and mechanical behaviors of a thermal stratification tank using phase change material（PCM）capsules and binary nitrate molten salt.Based on the CFD method,the operations of the single-tank PCM heat storage system are simulated and analyzed.The heat storage and release characteristics of the heat storage tank are studied.Paying attention to the outlet molten salt temperature,effective heat release,effective heat storage,heat storage power,heat release power,liquid phase fraction and normalized temperature,the influences of initial cold molten salt temperature,inlet hot molten salt temperature,inlet molten salt flow rate,PCM diameter,ambient temperature,tank wall structural parameter and tank hight on the heat storage and release characteristics of the heat storage tank are analyzed.On the basis of examining the influences of different parameters on the charging and discharging processes of the heat storage system,the influence law of different parameters on the mechanical behavior of the tank is obtained by using the steel temperature distributions and calculation formulas of mechanical stress.The fixed parameter simulation results show that the heat storage tank can store and release heat stably.The durations of heat storage and heat release are 355 min and 264 min.The maximum heat storage power and heat storage quantity are 5.63 MW and 8.62×10~4 MJ.The maximum heat release power and heat release quantity are 5.49 MW and 7.78×10~4 MJ.The heat release efficiency is 90.3%.The axial maximum mechanical stress（MMS）shows a Gaussian-like distribution after the cyclic inertia is achieved,and the peak MMS is 91.6 MPa.The parametric impact analysis results on the heat storage characteristics demonstrate that for both the heat storage and heat release processes,the effective heat storage quantity and effective heat release quantity can both be increased by augmenting the initial hot molten salt temperature and tank height,or by reducing the initial cold molten salt temperature and PCM capsule diameter.The other parameters have basically no effects on the effective heat storage quantity and effective heat release quantity.The parametric impact analysis results on the mechanical behavior of the tank show that the MMS of the tank can be decreased by increasing the initial cold molten salt temperature,inlet molten salt flow rate,environmental temperature,steel wall thickness,firebrick thickness and ceramic thickness,or by decreasing the initial hot molten salt temperature,PCM capsule diameter and tank height.That will improve the mechanical performance of the PCM heat storage tank.