Simulation Of The Thermophysical Properties Of Carbonate Molten Salts For Thermal Energy Storage

Energy is already the driving force of a country’s economic development and social progress,and the material basis for human survival and development.However,the global traditional energy resources are facing a serious crisis.Among the many new energy sources,solar energy,as a clean and renewable energy,has attracted more and more attention and has been used in concentrated solar power generation.In order to ensure the relative stability of power generation,it is necessary to take heat storage measures to store solar energy effectively.Molten salt is a heat transfer and storage medium with good use value in the field of solar thermal power generation and industrial energy recovery.The acquisition and prediction of thermophysical properties of molten salt is the basis for the design and analysis of photothermal power generation system using molten salt heat storage.At present,there are few studies on the simulation of thermophysical properties of molten carbonate,and there is a lack of simulation of thermophysical properties of molten carbonate containing lithium carbonate.In this paper,the density,specific heat capacity,viscosity and other thermophysical properties of sodium carbonate,potassium carbonate,lithium carbonate and their mixed molten salts are simulated by molecular dynamics method.The main contents and conclusions are as follows:（1）The thermophysical properties of three kinds of one-component carbonate molten salts were studied by molecular dynamics simulation,and the microstructure of one-component molten salts was calculated and analyzed by radial distribution function.The results show that the density decreases with the increase of temperature,and the simulation results of sodium carbonate and potassium carbonate are in good agreement with the reference values,but the error of lithium carbonate is the largest,which is 19%.For specific heat capacity,the results of the three one-component molten salts are in good agreement with the reference values,and the average error is less than 2%.For viscosity,it decreases gradually with the increase of temperature,and the average error is less than10%compared with the reference value;for thermal conductivity,it tends to decrease with the increase of temperature,and the error of sodium carbonate and potassium carbonate is less than 5%.However,the thermal conductivity simulation prediction error of lithium carbonate is larger,the error is 15.6%.（2）For binary mixed molten salts,the density of all molten salts decreases with the increase of temperature.the density of mixed molten salts is attributed to the cross action of one-component molten salts,which is based on the mixing rule and contains a certain degree of error.The error of the specific heat capacity of the system mixed with Na₂CO₃-K₂CO₃（58mol%:42mol%）is 1.8%.With the increase of the proportion of sodium carbonate,the specific heat capacity of the mixed system increases gradually,and the specific heat capacity of the mixed system increases with the increase of the proportion of lithium carbonate.The specific heat capacity of the mixed system increases gradually with the increase of the proportion of lithium carbonate.For viscosity,the error of Na₂CO₃-K₂CO₃ mixed system is less than 8.5%,and the viscosity of mixed molten salt is obviously lower than that of single component molten salt.The viscosity of Li₂CO₃-Na₂CO₃ with different mixing ratio has no obvious trend,but the viscosity decreases with the increase of temperature,and the viscosity of mixed molten salt is higher than that of single component molten salt.For the thermal conductivity of Li₂CO₃-Na₂CO₃ mixed system at the same temperature,the thermal conductivity of mixed molten salt is higher than that of sodium carbonate and lower than that of lithium carbonate.（3）For ternary mixed molten salt（43.5mol%Li₂CO₃:31.5mol%Na₂CO₃:25mol%K₂CO₃）,compared with the experimental reference value,the error of density is 9%,the error of specific heat capacity is 18.7%,the average error of viscosity is less than 10%,and the average error of thermal conductivity is 0.7%.The trend of thermal conductivity increases gradually with the increase of temperature.