The Determination of Thermal Diffusivities of Thermal Energy Storage Materials: Part II—Molten Salts Beyond the Melting Point

Abstract

A quasisteady method for measuring the thermal diffusivity of molten salts at temperatures above their melting point is described. Essentially, the difference between the temperature at the surface and at the center of a cylindrical container is measured for a constant rate of surface temperature rise. The liquid, whose thermal diffusivity is to be measured, is contained in a narrow annular groove concentric with the surface. The advantages of this method are: (a) no heat flux measurements are needed; (b) no liquid temperature need be measured; (c) theoretically assumed boundary conditions can be experimentally realized; (d) absence of convection can be experimentally verified. Results of measurements are reported for liquid lithium fluoride and sodium nitrate. The results for sodium nitrate agree with previously published results. The thermal conductivity of lithium fluoride can be empirically expressed in terms of the melting point, the molecular weight and the density, as k=0.9Tm1/2ρm2/3M−7/6