Phase change of molten salt during the cold filling of a receiver tube

• We describe and prove a numerical model to simulate the cold filling process.
• We show the mechanism of melting-solidification of molten salt during the process.
• We analyze the pressure drop and tube wall temperature under different conditions.
• Increasing initial tube temperature is most benefit for cold filling.

The most critical problems for the molten salt solar power plant are protecting against freezing and preheating of the flow pipes and equipments. A candidate way to solve these problems is cold filling. In this study, the dynamic process of molten salt cold filling into a receiver tube was simulated by combining the volume of fluid method and the enthalpy method. The detailed mechanism of melting-solidification and the evolution of the pressure drop along the tube were demonstrated. The influence of cold filling on the temperature across the tube wall was analysed as well. The results indicate that a lower pressure drop can be obtained by increasing the salt temperature and the initial tube temperature, and that an optimal velocity is required to get minimum pressure drop. The temperature difference between the external and internal surfaces of the tube wall increases with the filling velocity and the filling temperature whereas decreases with the initial tube temperature and the heat flux on the external surface. A large filling velocity and a high filling temperature that results in large temperature difference across the wall of the tube should be avoided. This study gives practical reference to the application of cold filling in molten salt receiver.