Ceramics-Silikáty 55 (3) 232-239 (2011)

BUBBLE REMOVAL FROM GLASS MELTS WITH SLOW VERTICAL CIRCULATIONS

M. Jebavá, L. Němec

A simple model of bubble behaviour in a melting space with a vertical circulation of the molten glass was derived. Subsequently, two cases were considered. The first case with a constant, radially independent value of the angular velocity of the glass-melt rotation approximately demonstrated the heating through the wall of the pot furnace for glass melting, and the second case, where the angular velocity decreased from the centre of the space towards the wall, represented the heating of the pot furnace from above. The chosen values of the angular velocities corresponded to temperature gradients commonly occurring in melting spaces. The starting positions of critical (last removed) bubbles were sought along with their trajectories and fining times. The much higher calculated fining times of critical bubbles in the rotating melt as compared with the fining times of the bubbles just rising through the quiescent glass melt were explained by the deceleration of the bubble rising with respect to the fixed coordinates through the downward part of the glass vertical circulation. This fact leads to a long retention of the bubble in the melt and consequently to high energy consumption and low melting performance. The semiempirical equations were presented, providing the fining time of the critical bubble as a function of the bubble-growth rate and melt-rotation velocity.

Keywords: Bubbles, Glass-melt circulation, Pot furnace, Mathematical modelling, Fining efficiency