Thermal Diffusivity Measurement of Molten Fluoride Salt Containing ThF₄ (Improvement of the Simple Ceramic Cell)

Abstract

Design conditions of a cylindrical ceramic cell were estimated. One can use it to measure the absolute value of thermal diffusivity of molten salts by applying the stepwise heating method. For a thickness l of the salt specimen, the thickness of the upper and lower parallel ceramic base plates which hold the specimen between them should be greater than 5l and the radius of the base plates should be greater than 15l. This satisfies the theoretical conditions of a semi-infinite solid base plate to sufficient accuracy. Using a ceramic cell which has a large enough value of l, the thermal diffusivity, a, of molten fluoride salt: LiF-BeF₂-ThF₄ (67-18-15 mol%) was measured. The value a = 2.34x10^-7 + 6.10x10^-11(T-788) m²s^-1 was obtained in the temperature range 823 ⩽ T ⩽ 983 K.