Study On The Enhancement Of Thermal Properties Of Sodium Chloride Molten Salt And Its Adsorption Properties With Iron Surface

As one of the potential heat storage agents in Concentrating solar power（CSP）systems,it has great importance of studying the enhancement of the thermal properties and the adsorption properties in the corrosive process of chloride molten salts.It is representative for the research of sodium chloride molten salt,which is the most common chloride molten salt.In this paper,the enhancement of thermal properties of Na Cl molten salt and the adsorption properties of corrosive media on theγ-Fe（1 1 1）surface are investigated by molecular dynamics and first principles methods,respectively.The main work includes:（1）Different models of nano Cu O/Na Cl molten salt composite phase change materials（CPCMs）were developed,and the reliability and accuracy of the models were verified.Their thermal properties were investigated by using molecular dynamics simulations,including shear viscosity,specific heat capacity,melting enthalpy,thermal conductivity,etc.It was found that as the mass fraction of copper oxide nanoparticles increased from 0 to 1.6%and 8.3%,the thermal conductivity increased by 5.45%and 9.51%on average and decreases with increasing temperature;the specific heat capacity in the liquid state was increased with a maximum value of 2.07%.While,the shear viscosity in the liquid state increased by 4.43%and 8.12%on average and the melting enthalpy decreased by 16.89%and 18.77%,respectively.（2）The microstructural properties of the different CPCMs were analyzed and it can be found that when the mass fractions of nano Cu O particles added to the sodium chloride molten salt were 0,1.6%and 8.3%,the temperature ranges for the phase change processes of different systems were 1200 K-1300 K,1100 K-1200 K and 1100K-1200 K,respectively.The addition of copper oxide nanoparticles lowered the melting point of the sodium chloride molten salt.（3）In addition,as one of heat storage performances,the microscopic enhancement mechanism of the specific heat capacity of the sodium chloride molten salt phase change material with nano Cu O particles can be described as:the addition of nano Cu O particles enhances the interaction between atoms in the system,and aggravates the collision between atoms,which manifests in the energy composition that the average potential energy in the system is significantly increased,while the average kinetic energy is almost unchanged.The increasement in the average potential energy includes the increasement of coulomb interaction energy,bond stretching energy and bond bending energy.（4）The adsorption models of different corrosive media on the surface ofγ-Fe（11 1）were established,and the reliability and accuracy of the models were verified.The adsorption properties of different corrosion media on theγ-Fe（1 1 1）surface were investigated by the method of first principles.It was found that the most stable adsorption sites of Cl and H on the surface ofγ-Fe（1 1 1）were Fcc sites,and the most stable adsorption sites of O and OH are Hcp sites,and the most stable adsorption site of H₂O is Top sites.Moreover,the adsorption energy of the most stable adsorption sites of different corrosive media on the surface ofγ-Fe（1 1 1 1）is ranked as O>OH>Cl>H>H₂O.