Numerical Calculation Of Flow In Pipe With Phase Change

Large scale concentrated solar power plants using molten salts as heat transfer fluid have lower electrical cost and great commercial prospect.However,high freezing temperature is one of the biggest drawbacks of molten salts.Therefore,the flow loop of molten salt and other elements in the system should be warmed by heat trace which increases the parasitic electrical consumption.In addition,the heat traces can’t be fixed on certain absorb panels of the receiver,they need several hours to be preheated by conduction.These limit the operation strategy and the availability of the solar power plant and affect the efficiency.Cold filling is a potential solution to the above problems.In this paper,the solidification phenomenon of molten salt during the filling process is numerically investigated with volume of fluid model.As the molten salt is filled into a cold pipe,the molten salt adjacent to the cold wall is rapidly cooled,and the solidification phenomena appears.After that,the enthalpy method is chose to describe the phase change of the molten salt between liquid and solid.The simulation is verified by the Molten Salt Electric Experiment(MSEE)receiver data.The flow and heat transfer characteristics of molten salt in the micro-circular straight pipe are demonstrated in detail.The variation of solidification layer is mainly dependent upon the cold pipe wall and high temperature fluid.When the molten salt is filled into the whole pipe,the solidification phenomenon dominates the phase change process first.After the whole pipe is filled with molten salt,the pipe wall temperature is increased,and the solidification layer begins to melt due to the high temperature fluid heating.In addition,the maximum flow distance model is proposed in order to describe the blockage characteristics and is in good agreement with the experimental data.The effects of different factors on the filling process of molten salt are also studied.At the same time,the discharge process of molten salt storage tank connected with the pipe is simulated numerically,being validated by theory in the literature.The results show that the discharging performance of the storage tank is mainly dependent on the tank height and Reynolds number.The heat transfer efficiency of the molten salt storage tank increases with the height of the storage tank,but decreases as the Reynolds number increases.The study in this paper will provide guidance for the practical application of molten salt cold filling,and are also of certain reference for the numerical simulation of phase change problems and the applications of molten salt in other fields.