Browsing by Author "Waal, Henk de"

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    Application of ultrasonic measuring techniques in industrial glass melting
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1991) Faber, Anne J.; Simonis, Frank; Breeuwer, René; Waal, Henk de
    The potential applications of ultrasonic measurements in glass melts have been studied, using a measuring system comprising ultrasonic waveguides of polycrystalline translucent Al2O3. These high-temperature buffer rods serve to transport ultrasonic signals into the glass melt and to receive acoustic echoes generated in the melt, respectively. The fundamental acoustic properties of a soda-lime-silica glass composition as a function of temperature have been obtained experimentally: The observed sound velocity varies from 2.86 km/s at 1150 °C to 2.70 km/s at 1300 °C. The observed attenuation of 1 MHz waves has a minimum at 1300 °C of 840 dB/m. For 100 kHz waves the attenuation is a factor 100 lower. It is concluded that 100 kHz ultrasonic signals can be utilized for detection of bubbles with critical radii (≥ 0.2 mm) in a feeder, for measurement of glass flow velocities and for measurements of glass temperature. For measurement of the residual thickness of refractory bricks of a glass tank, application of echo acoustic sensors an the outer surface of the wall probably is more practical.
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    Thermal behaviour of glass batch on batch heating
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Faber, Anne J.; Beerkens, Ruud G. C.; Waal, Henk de
    The heating process of a barium-strontium glass batch has been studied in a 401 pot furnace, using a multiple thermocouple assembly. The effect of several batch batch parameters on the heating process has been measured, including layer thickness, cullet fraction, water content and pellets. The results have been evaluated using a heat penetration batch model. In the model two heating stages, below and above a certain batch transition temperature ϑs, typically 800 to 900 °C, are distinguished. Values for the temperature-dependent thermal diffusivity of the batch have been derived from experimental temperature distributions in the batch during heating. Below the thermal diffusivity has an almost constant value of 0.4 · 10^-6 m2/s for a standard (powder) batch blanket; for ϑ > ϑs the net thermal diffusivity strongly increases with temperature, due to the formation of primary melt phases. For ϑs < ϑ < 1100 °C the average value is about 1.4 · 10^-6 m2/s. A 100 % cullet layer has a 50 % higher thermal diffusivity for ϑ < ϑs; pelletizing the batch is of 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 temperatures it appears that increasing the temperature of the glass melt is more effective for improving the batch heating rate than increasing the temperature of the combustion chamber. Practical recommendations are given for batch preparation, charging and heating in industrial glass tanks.