Thermal-blanket Effect Observed on Molten Glass in Drop Shaft Experiments

Abstract

Temperature change of a BaO- B20 3 glass melt was measured in micro gravity (µg) environment in drop shaft ex­periments using two different sample-heating methods; a direct heating method and an indirect heating method. In­ situ observation of the flow pattern in the melt has also been made simultaneously. For the direct heating method, a high rate of thermal convection in the melt was observed at 1 G before a drop. It was observed that the convection rate decreased and the sample temperature increased in µg during the drop. For the indirect heating method, neither the thermal convection nor the sample temperature increase was observed. A mechanism of the temperature rise or the thermal-blanket effect for direct heating was proposed; the heat removal rate from the sample by the inner and atmospheric thermal convection decreased in µg. A simple model for heat transfer based on the sample and furnace configurations used in the present experiments was proposed. The model predicted that the temperature of the sample increased by a greater amount and with a steeper slope with the decreasing atmospheric convection rate in µg, which is in qualitative agreement with the results observed in the drop experiments.