Numerical Simulation Research On Operation And Mechanical Performances Of Liquid Lead-bismuth Thermocline Tes Tank

Making full use of solar energy is a significant direction for the development of renewable resources.Concentrated solar power（CSP）is a significant way to use solar energy.The energy storage technology overcomes the instability of solar energy to a certain degree.Compared with the double-tank heat storage,single-tank thermocline heat storage tank effectively reduces the floor area and cost,and has great development potential.With the growth of CSP technology,the existing heat transfer medium（such as molten salt）can no longer meet the higher heat collection temperature requirements due to the limitation of temperature range.Liquid lead-bismuth eutectic（LBE）has a wider operating temperature range and excellent thermophysical properties,and is a high-quality potential substitute material for high-temperature heat transfer medium of CSP.In this paper,a numerical model of liquid lead-bismuth eutectic thermocline heat storage tank with filling zone,distributor region and composite wall structure is established,and the CFD approach is used for numerical simulation.The heat storage and release performance,cyclic performance and standby performance of the heat storage tank under fixed parameters are studied.The influence of seven typical parameters on the liquid LBE heat storage tank’s operating and mechanical performances are studied and summarized,including the flow velocity of LBE in the tank,the initial cold LBE temperature,the inlet hot LBE temperature,the filling area’s porosity,the equivalent diameter,specific heat capacity and heat conductivity of the filled particles.The research of the condition of fixed parameters show that in the processes of heat storage and release,the thermocline can move stably in the heat storage tank,revealing that the liquid LBE thermocline heat storage tank has good operation stability.The cyclic characteristics analysis shows that the heat release efficiency,the thermocline thickness and the steel wall’s maximum mechanical stress of the heat storage tank all reach relatively stable states during the sixth cycle.When the tank operates stably,the heat storage time is about 6.8 h,the heat release time is 6.3 h,and the heat release efficiency is 91.98%.After the standby process of the tank begins in the heat release process,the thermocline thickness increases first and becomes 5.8 m at 9.0 h.After that,the thermocline thickness is almost unchanged.When the standby time of the heat storage tank reaches 24 h,the total heat loss of the tank is 2.79×10¹⁰ J.The effect research of typical parameters on the liquid LBE heat storage tank’s operation performance show that the inlet hot LBE temperature,porosity of the filling region,equivalent diameter and heat conductivity of the filling medium are in direct proportion to the thickness of the thermocline thicknesses in the processes of heat storage and heat release,while the flow velocity of LBE in the tank,the initial cold LBE temperature and the specific heat capacity of the filling medium are in inverse proportion to the thermocline thicknesses in the processes of heat storage and heat release.The LBE flow rate in the tank and the inlet hot LBE temperature are directly proportional to the heat storage power and the heat release power,and the initial cold LBE temperature is inversely proportional to the heat storage power and the heat release power.The specific heat capacity of the filling medium only affects the length of time of the heat storage and the heat release power.By reducing the initial cold LBE temperature and increasing the specific heat capacity of the filling medium and the inlet heat LBE temperature,the effective heat storage and effective heat release can be improved.The effect research of typical parameters on the mechanical performance of the liquid LBE heat storage tank are indicate that increasing the flow velocity of LBE in the tank,increasing the initial cold LBE temperature,reducing the inlet hot LBE temperature,reducing the porosity of the filling area,reducing the equivalent diameter of the filling medium,reducing the specific heat capacity of the filling medium and reducing the heat conductivity of the filling medium all can reduce the peak maximum mechanical stress of the steel wall,improving the mechanical performance of the steel wall of the liquid LBE heat storage tank.