Study On The Effect Of Particle Agglomeration On The Thermal Conductivity Of Molten Salt Nanofluids

To cope with the energy crisis and environmental degradation,countries around the world have strengthened the development and utilization of new energy technologies.Solar energy has received widespread attention due to its large storage capacity and clean and safe characteristics.Photovoltaic power generation technology is one of the important technologies for utilizing solar energy,and equipping it with a thermal storage system can improve the energy utilization rate of the system.Molten salts are favored because of their high operating temperature and low vapor pressure,and have become a widely used heat transfer and storage medium in solar thermal power plants.Although molten salts have many advantages,they have the disadvantage of low thermal conductivity,which can lead to problems such as large size of the thermal storage system and high amount of thermal storage material,which in turn causes the cost of the solar thermal power system to increase.It has been found that adding nanoparticles to molten salts to form nanofluids can significantly improve their thermal conductivity,but the underlying thermal conductivity mechanism has not been clarified.Nanoparticle agglomeration is currently the more accepted explanation,and the mechanism of its effect on the thermal conductivity of molten salts needs to be explored in depth.In this paper,the effects of particle agglomeration on the thermal conductivity of solar salt-based nanofluids are investigated at the microscopic and mesoscopic scales using molecular dynamics and lattice Boltzmann methods,respectively.The mechanism of the agglomeration to enhance the thermal conductivity of nanofluid is also investigated in depth,in order to provide a theoretical reference for the thermal performance regulation of molten salt-based nanofluids.In this paper,molecular dynamics was used to investigate the thermal conductivity under dispersion and different agglomerated structures.The results show that the addition of SiO2 particles does enhance the thermal conductivity of the solar salt base solution,and at 10 wt.%particle content,the thermal conductivity is enhanced by 8.9%in the case of particle dispersion,and the thermal conductivity is higher after agglomeration than that of particle dispersion,and the enhancement effect decreases as the fractal dimension increases.This phenomenon was entered into an in-depth mechanism analysis,and the effect of Brownian motion theory and interfacial layer mechanism on the change of thermal conductivity enhancement after particle agglomeration was denied based on the MSD curves of different structural models and the analysis of atomic number density curves of base liquids.The thermal resistance of the solid-liquid interface was calculated using non-equilibrium molecular dynamics,and the VDOS curves of different structures were analyzed,and it was found that the interfacial thermal resistance decreased after particle agglomeration,and the change of interfacial thermal resistance was proportional to the fractal dimension.The composition of thermal conductivity was decomposed,and it was found that the contribution of the particle term in the thermal conductivity increased after agglomeration and was inversely proportional to the fractal dimension;the thermal conductivity was decomposed by heat flow fluctuation,and the contribution of the potential energy term in the thermal conductivity increased and was negatively correlated with the fractal dimension.The effects of particle content share,system temperature,particle type,number of agglomerate particles,number of agglomerate backbone particles,and degree of aggregation were investigated using molecular dynamics and lattice Boltzmann methods at fractal dimension 1.8.The simulation results show that the thermal conductivity enhancement effect of adding alumina particles is better than that of silica particles,and the thermal conductivity increases and then decreases with the increase of the number of agglomerate particles,increases with the increase of the particle percentage,is proportional to the number of agglomerate main chain particles,is proportional to the degree of aggregation,and shows a negative temperature dependence.