Thermal behaviour of glass batch on batch heating

The heating process of a Ba-Sr glass batch was studied in a 40 L pot furnace, using a multiple thermocouple assembly. The effect of several batch parameters on the heating process was measured, including layer thickness, cullet fraction, water content, and pellets. The results were evaluated using a heat penetration batch model. In the model 2 heating stages, below and above a certain batch transition temp., ns, typically 800 to 900 Deg, are distinguished. Values for the temp.-dependent thermal diffusivity of the batch were derived from exptl. temp. distributions in the batch during heating. Below ns, the thermal diffusivity has an almost const. value of 0.4 * 10-6 m2/s for a std. (powder) batch blanket; for n > ns, the net thermal diffusivity strongly increases with temp., due to the formation of primary melt phases. For ns <n <1100 Deg, the av. value is about 1.4 * 10-6 m2/s. A 100% cullet layer has a 50% higher thermal diffusivity for n <ns; pelletizing the batch has little influence on the virtual thermal diffusivity and (extra) wetting has a retarding effect on batch heating due to extra heat absorption. As for the furnace temp., it appears that increasing the temp. of the glass melt is more effective for improving the batch heating rate than increasing the temp. of the combustion chamber. Practical recommendations are given for batch prepn., charging, and heating in industrial glass tanks. [on SciFinder (R)]