Browsing by Author "Matěj, Jiří"
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- ItemCurrent density and temperature distribution along a horizontal electrode in an all-electric glass melting furnace(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Bernard, Vladimír; Matěj, Jiří; Novák, LadislavTemperature in the immediate vicinity of the heating electrode has been measured in a real all-electric glass furnace, equipped with horizontal electrodes and melting lead crystal glass, as well as in its low-temperature physical model. It has been found by direct measurement in the real furnace that the maximum temperature difference between the electrode body and the molten glass in horizontal distance of 20 cm away from the electrode was only 9 K. In contrast to the actual current density, which reaches the highest values at the very tip and then decreases rapidly, the temperature maximum was not found at the tip of the electrode, but occurred approximately at two thirds of its length. The increase in the temperature of the melt in the vicinity of the electrode compared with the temperature at the electrode surface has been tried to measure in the low-temperature physical model. This temperature increase has been found immeasurably low and within a very small distance from the electrode, but its existence has clearly been demonstrated in a model experiment at about 4.5 times higher current loading of the electrode than in the basic adjustment of the model parameters. The actual current density at the electrode tip was about twice higher than the mean current density at the electrode both in the real furnace and in the model.
- ItemOptimum loading of molybdenum electrodes in corrosive glass melts(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1993) Matěj, Jiří; Bernard, VladimírAt given current density, the voltage between electrodes and the generated power increase with the equipment size providing the geometrical similarity is maintained. The current density affects the corrosion rate of molybdenum electrodes to a different degree depending on the type of molten glass. In minimizing the corrosion of electrodes, the total loss of electrodes which is proportional to their area and to the linear corrosion rate should be considered, the corrosion rate depending on the temperature near the electrode surface. It was found experimentally that under the conditions of a maximum suppression of corrosion phenomena in 24 % lead glass by a current of reduced frequency, the corrosion rate will not significantly depend on the current density. On the basis of a parabolic approximation for the found temperature dependence of the corrosion rate of molybdenum electrodes in 24 % lead glass and on the basis of model measurements investigating the dependence of surface temperature of electrodes on their area in a specific arrangement of the given furnace and for constant power input, a semi-empirical equation was derived, describing the relation between the total electrode loss rate Q and the total electrode area A (1/ϱ) Q̇ = α/A+ ß+ γA . The course of this relationship which passes through a minimum has been calculated for the given furnace. The calculated area corresponding to a minimum electrode loss rate is in good agreement with the area of electrodes placed in the operating furnace on long-term experience. The calculated value of the electrode loss rate in this minimum does not differ from the operational evidence more than the deviations of individual series of laboratory experiments.