Study On Molten Salt Thermophysical Properties For Heat Transfer And Storage

Molten salt is an ideal medium for heat transfer and storage in nuclear reactor andconcentrated solar power system because of its low viscosity, low vapor pressure at hightemperature, large specific capacity, high thermal conductivity and wide temperature range.Thermophysical properties such as liquidus temperature, density, viscosity, thermalconductivity, heat capacity are basic parameters for thermal hydraulics concerning theefficiency of heat transfer, and safety analysis involving the safty of the whole system.According to requirements of heat transfer system design and Molten Salt Reactor physicsanalysis, this paper focuses on the investigation on the thermophysical properties of moltensalts by experimental determination and CALPHAD（CALculation of Phase Diagram）method.Facsage6.4and Pandat were used to optimize the LiF-NaF-KF ternary phase diagrams,and the relevant databases were obtained. The phase diagrams of LiF-BeF2-ThF4-UF4werecalculated by using the well optimized parameters of each phase from literature.After a detailed investigation of the measurement method of thermophysical propertiesfor molten salts, the Archimedes, cooling curves, bubble maximum pressure, rotating anddifferential scanning calorimetry methods were adopted to determine the density, liquidustemperature, surface tension, viscosity and heat capacity of molten salts respectively.In order to get accurate levels of thermophysical properties of molten salts, theintegrated testing device for density, liquidus temperature and surface tension measurement,rotating viscometer, Laser flash themal analyzer and DSC were developed or improvedrespectively. The experimental results of density, liquidus temperature and surface tensionmeasurements were well enough for the needs of heat transfer design. The feasibility of lowviscosity measurement by rotating method was verified, and good experimental results wereobtained in conditions of room temperature. A special crucible was designed and thecorresponding method of sample preparation was established for the thermal diffusivitymeasurement of liquid salts. The experimental specifications of heat capacity measurementfor liquid salts by DSC were explored and preliminary results were gained.The thermophysical properties of NaNO3-KNO3(60-40wt%), NaNO3-NaNO2-KNO3（7-40-53wt%）, Li2CO3-Na2CO3-K2CO（332.1-33.4-34.5wt%）, KCl-MgCl2(66-34mol%),LiF-NaF-KF（46.5-11.5-42mol%）, KF-ZrF4(58-42mol%) were obtained by experimentmeasurement, and the corresponding thermophysical properties database can providereference for the applications of these salts in heat transfer and storage.