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- ItemElectrical modelling and scale-up rules for glass melters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Α scale-up rule is developed to estimate the resistance for each circuit of a projected glass melter. Given all the internal sizes and contours including shapes of the electrodes as well as the power and power ratios and the resistivity of the molten glass for the proposed melter, this rule permits calculating the voltage and current for each of its circuits. Single-phase circuit-interactions, distributions of equipotential surfaces and lines of current and some safety considerations are discussed and illustrated for a multiplicity of electrodes and single-phase power supplies by using two-dimensional, isothermal, salt water models of electric melters. Phase relations that occur between currents in non-linear fluid conductors when additional transformers are used as currentbalancing means are also explored. This material is useful for understanding and designing electric melters.
- ItemElectrical characteristics of horizontal glass melting furnaces and delivery Systems(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Leakage currents and their low resistance paths through refractories from the interior of glass melting furnaces to the binding steel are discussed. By defmition, a ground current flows from an electrode, through the intervening glass to ground through grounding conductors. All melters have leakage currents and may have ground currents. Current and voltage characteristics and phasor diagrams have been analyzed for some circuits that can be used in horizontal melters. The furnaces may be heated solely with electricity or in conjuncdon with fossil fuels. Phasor diagrams may be helpful in the design stage of a melter, may be useful for trouble-shoodng and to display electrical distributions for all parts in a precise form. Hence, totally unexpected voltage differences become easily understandable. Phasor diagrams can disclose wiring errors and/or undesirable voltage distributions and may suggest ways to improve electrical characteristics. For symmetrically built and cross-fired furnaces they show side-to-side symmetry and indicate that the central plane of these units can be Virtual or phantom grounds. They may also indicate the conditions minimizing voltage differences between adjacent electrodes. Voltage phasor diagrams are even more useful for longitudinally fired furnaces. For these units they also explain why ground currents occur and how to minimize them. Data from a salt water model with two cross-fired circuits connected to the same phase disclosed linear relations between the electric currents and voltages over a large range. In this ränge each line current was a hnear function of the two line voltages and vice versa and these variables could be treated as scalars. In addition, either line current could be forced to zero by appropriate voltage(s) in the other circuit. Somewhat similar results were obtained when two different phases were used but now neither current could be forced to zero by adjusting the voltage in the other circuit. Again in the linear range each hne current was a linear function of the line voltages and vice versa but the variables now had to be treated as phasors and not as scalar quantities. Salt water modelling with a longitudinally fired melt end yielded representative data showing how the applied voltages may be located on a ground current's voltage phasor in both the capped and uncapped condition.
- ItemPhysical modelling of flow behavior in a stirred glass system(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1997) Spremulli, Paul F.As stirring efficiency made the use of isothermal models plausible, dimensional analysis was used to extend model laws to include stirrers, gobbing cams and to indicate the conditions required to get data representative of actual or proposed units. Based on fullsize modelling, the production department installed stirred glass set-ups and made excellent products. Correlation between modelling and production was excellent and included mechanical variables and temperatures. Furthermore, a new delivery system, including a new gobbing cam designed for a very fluid photosensitive glass, was based on modelling and behaved exactly as predicted. Upsets in the stirred glass, delivery Systems resulted in slow cyclic weight variations of about 1 %. As the weights of the items being made were specified to within ±1.0%, it was clear that control had to be improved. The weight changes were not caused by compositional changes in the glass but to some Instrumentation problems and to some unique, unknown problem(s) associated with stirring. Thus, a better understanding of how temperature and the stirrers controlled flow was needed. Assuming that flow is inversely proportional to viscosity showed that the change in weight should be about 0.9%/°C. This number is about 1 0% too low compared with the empirical value of 1 %/°C quoted by Operators. Next data from a full-size, stirred model were summarized in an equation which relates flow to the viscosity of the fluid and to the rotational speed and vertical position of the stirrer. Partial differentiations and evaluations of this equation at a nominal operating condition showed that the weight should first, vary by 1.02%o/°C, second, decrease by 0.90% per rpm increase and third, increase by 0.80% when the stirrer was raised (0.006") or 1 % when it was at the 5/8" position.
- ItemPhasors for fluid conductors and vertical electric glass melters(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1996) Spremulli, Paul F.Phasors are useful in electrical engineering but they are even more useful when used to display and/or explain phenomena associated with fluid conductors. Phasor diagrams include not only the applied voltages but all the voltages found in the fluid. This has been illustrated by constructing and discussing phasor diagrams for a variety of circuits used in vertical glass melters. It has been shown that these diagrams can disclose wiring errors and/or undesirable voltage distributions. In many cases they can lead to designing improved circuits and/or alternate circuits which may have equivalent voltage distributions. Phasor diagrams have also been used as an aid in designing new circuitry with symmetrical electrical distributions. Simultaneous consideradon of current and voltage phasors yields correct phase angles and equations to calculate power.