Modelling of the refining space working under reduced pressure

The 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 K 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.