EXPERIMENTAL-DETERMINATION OF THE EFFECTIVE THERMAL-CONDUCTIVITY OF GLASS BY STEADY-STATE METHOD

An experimental furnace for the determination of the effective thermal conductivity of molten glass was constructed. As the values of therma l conductivities previously measured by direct experimental methods de pend strongly on the thickness of the glass layer it was necessary to make the measurements on thicker layers of glass. The thermal conducti vity values have been calculated from temperature distributions measur ed on the molten glass layer and from the temperature drops on the cer amic bottom of the furnace the thermal conductivity of which was known . From the physical point of view this is a steady-state comparative m ethod with linear heat flow. The values of the effective thermal condu ctivity of four commercial glasses experimentally determined by this m easuring procedure are compared to the radiative thermal conductivitie s computed from the measured absorption coefficients by means of Rosse land's diffusion approximation. The great differences between effectiv e and radiative thermal conductivities, which have been found especial ly with weakly absorptive colorless glasses, are critically discussed.