Numerical study of heat transfer characteristic on the melting process of quaternary mixed nitrate

The research aims to study the phase change heat transfer process of the mixed molten salt in a cylinder tank with the bottom heating by the numerical and experimental method. A VOF and enthalpy-porosity coupled model was used to discern the phase change interface of mixed molten salt in a bottom heating cylinder tank. The results show that the phase change heat transfer process of molten salt is directly affected by natural convection intensity, while the position of the phase change interface determines the development of natural convection. During the melting process, the obvious temperature gradient and the solid-liquid interface fluctuation can be observed, and the melting time can be reduced with the increases in heating power. On this basis, the effects of thermophysical properties of PCM and heating mode on the phase transition process are further studied. The results show that the melting time of mixed salt can be increased by 4.8% and 4.2%, respectively, when the specific heat capacity and latent heat of salts increases by 20%, while it's thermal storage density can be accordingly increased by 16.24% and 3.76% at the same condition. Comparing with other heating mode, the bottom and side heating mode with the smaller heating area (H-star <= 0.5) has a faster heat storage rate, which can be applied to the design of the single heat storage tank.