Browsing by Author "Kuhn, Wolf Stefan"

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    Approximate analytical Solutions for the heat transfer in glass melting furnaces
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1999) Kuhn, Wolf Stefan
    Temperatures and convections in glass melts are governed by coupled partial differential equations. These equations can, in general, only be solved by numerical methods. A considerable simplification of the partial differential equation for heat transport is possible under certain conditions. These conditions are frequently met in glass tanks. They allow the formulation of an ordinary differential equation for the heat transport with Solutions in the form of simple equations. These equations are analytical expressions of the vertical temperature profile in the glass melt. The Peclet number for the vertical flow component in the melt under the free surface appears to be the essential parameter in these expressions. It characterizes the combined heat transport by conduction and convection. However, flow velocity and thermal diffusivity vary strongly over the depth of the glass bath, thus rendering the Peclet number Position dependent. On this theoretical basis, it follows a detailed numerical and analytical study of the dependence of the vertical temperature profile on wall heat loss, primary recirculation and pull.
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    Numerical precision of minimum residence time calculations for glass tanks : Recalculation of Round Robin Test 1 of Technical Committee 21 "Modelling of Glass Melts" of the International Commission on Glass (ICG)
    (Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Moukarzel, Camille; Kuhn, Wolf Stefan; Clodic, Denis
    Prediction of glass quality is a main objective of glass furnace modeling. Minimum residence time (MRT) counts among the crucial parameters for representing glass quality. Numerical simulation is an efficient tool for estimating this parameter. For a Round Robin a simple case had been chosen with a parallepiped-shaped glass tank to test the performance of numerical codes and their application in glass melting simulation. It was shown that the numerical discretization fixed by the participants is sufficient to represent the temperature and velocity fields. However, significant differences in the calculation of the MRT (6.2 to 7.8 h) between the different participants of the Round Robin were noticed. In this work it is shown that the grid resolution and the number of tracer particles have to be increased at certain locations to capture correctly the shortest path-time trajectory. The final value of 5.5 h for the MRT does not significantly change with further refinement of the grid and of trajectory calculation. The two principal methods known for the calculation of massless virtual particle trajectories are numerical tracing and flow-field stream lines. One established method to check the reliability of stream line calculations is the successive refinement of the numerical resolution. However, for large glass tanks, this method can be quite tedious or even unfeasible. Simplified methods are proposed to check the reliability of MRT calculation.