Experimental determination of the effective thermal conductivity of glass by steady-state method

Abstract

An experimental furnace for the determination of the effective thermal conductivity of molten glass was constructed. As the values of thermal conductivities previously measured by direct experimental methods depend strongly on the thickness of the glass layer it was necessary to make the measurements on thicker layers of glass. The thermal conductivity values have been calculated from temperature distributions measured on the molten glass layer and from the temperature drops on the ceramic bottom of the furnace the thermal conductivity of which was known. From the physical point of view this is a steady-state comparative method with linear heat flow. The values of the effective thermal conductivity of four commercial glasses experimentally determined by this measuring procedure are compared to the radiative thermal conductivities computed from the measured absorption coefficients by means of Rosseland's diffusion approximation. The great differences between effective and radiative thermal conductivities, which have been found especially with weakly absorptive colorless glasses, are critically discussed.