Browsing by Author "Němec, Lubomír"
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- ItemBehaviour of bubble files in glass melting space(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2003) Matyáš, Josef; Němec, LubomírA calculation model of the bubble concentration field inside a melting space is presented, based on the technique of tracing representative bubbles. The bubbles in the model originated from glass batch and from refractory. The appropriate bubble input values were obtained by laboratory experiments. The impact of various initial and boundary conditions, as well as melting conditions, on the bubble distribution inside the melting space was studied: a) the impact if initial amount of entering bubbles and their size distribution, b) the impact of initial redox state of glass, and c) the influence of bubble history. The results demonstrated the significance of the redox state of glass and the average temperature along bubble trajectories for the fining process. The calculated bubble compositions at the output and bubble histories were used to distinguish the bubbles coming from two bubble sources and to reveal the starting positions of defect bubbles. An attempt was made to estimate the bubble impact on the glass flow and on the redox state of glass using the bubble tracing technique. The preliminary calculations indicated that bubbles influence the melt flow.
- ItemEnergy consumption in the glass melting process : Part 1. Theoretical relations(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Němec, LubomírFormulae have been proposed expressing the influence of internal melting factors such as temperature, external pressure, glass composition, size distribution of sand and intensity of glass stirring on the specific energy consumption of glass melting, and the appropriate partial derivatives have been given. The possible ways of exploiting the melting reserve have been discussed. Using the mentioned formulae, the results of laboratory experiments and single glass flow models, the energetic trends resulting from the variation of melting conditions may be revealed.
- ItemEnergy consumption in the glass melting process : Part 2. Results of calculations(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1995) Němec, LubomírA simple model melting space of 1 m³ has been proposed to demonstrate the influence of internal melting factors such as temperature, pressure, glass composition, size distribution in batch and glass flow distribution, on the specific energy consumption of the glass melting process. The laboratory data have been applied to evaluate the constants in proposed relations expressing this influence. The numerical results are graphically presented and show the main tendencies in the energy consumption development; the upper limits of the high-temperature application are obvious as well as the promising role of glass stirring, glass flow distribution and the physical way of refining.
- ItemGlass refining at reduced pressures(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 1992) Němec, Lubomír; Schill, Petr; Chmelař, JosefThe behaviour of bubbles in the glass melt for colour-TV screens has been investigated at reduced pressures using modified high-temperature photography and a mathematical model of single bubbles. The considerable acceleration of the process predicted by the mathematical model and resulting in high values of bubble-growth rates has been confirmed by experiments. Mathematical modelling of the small rectangular continual refining room has shown that the main quantity determining refining efficiency is the already mentioned bubble-growth rate. The value of this quantity needed for effective refining being in the region around 1 · 10^-6 m/s is only slightly dependent on temperature, pressure and glass composition. As is obvious from the presented results, the saturation or oversaturation of glass melt by diffusing gas at given glass composition, pressure and temperature is the general condition of successful refining.
- ItemModelling of the refining space working under reduced pressure(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2000) Kloužek, Jaroslav; Němec, Lubomír; Ullrich, JiříThe refining channel working under reduced pressure and at medium temperatures was modelled experimentally and mathematically. The bubble growth rate was measured in the temperature interval 1200 to 1450 °C and pressures 15 to 50 kPa for the lead glass melt with and without refining agent. The bubble nucleation temperature was determined and the glass foam on the level was observed using high-temperature observation, video recording and image analysis. The temperature-pressure areas were defined in which the bubble nucleation and glass foaming did not interfere with efficient refining. The simplified mathematical model of bubble growth or dissolution under nonisothermal conditions was formulated and applied to the mathematical modelling of glass melt and bubble behaviour in the refining channel. Having applied the critical bubble pathways, the pull rates of the modelled channel have been calculated in the experimentally examined area of admissible temperatures and pressures. Besides temperature, the reduced pressure proved to be an efficient refining factor; the temperature increase by 35 Κ corresponded to the pressure decrease by about 10 kPa under given conditions. The results were discussed with respect to simplified relations between refining efficiency and temperature or pressure. The combination of experimental and mathematical modelling showed to be a sufficient and reliable tool for acquiring the fundamental parameters of the process under real melting conditions.
- ItemPhysico-chemical models of glass melting(Offenbach : Verlag der Deutschen Glastechnischen Gesellschaft, 2004) Němec, Lubomír; Kloužek, Jaroslav[no abstract available]