The Bubble Behaviour under Effect of Centrifugal Force

Abstract

The fining process may be enhanced by acting of additive force on bubbles in the glass melt. This study deals with behaviour of single bubbles under effect of centrifugal force in a rotating discontinuous cylinder with glass melt. The model of a single bubble in the combined gravitational and centrifugal field has been set up and calculations of bubble behaviour in the cylinder have been performed for the model TV glass. Two mechanisms of bubble separation were indicated from results of calculations, i.e. the complete dissolution and separation by centrifugal force. The first mechanism is restricted to areas close to cylinder mantel and exhibits relatively long bubble dissolution times. The analysis of model and results revealed the potentially positive role of increasing cylinder radius and partial filling of rotating cylinder with glass melt. The bubble separation is considerably influenced by bubble dissolution or growth during centrifuging, thus the crucial role in this process plays temperature and the bubble initial composition. The until now results show that at lower temperatures the bubbles should contain low content of gases well soluble in glass, to admit higher rotation velocities. Whereas to be enabled the transport of chemically soluble gases from the melt into the bubbles at high temperatures, the bubbles have to be treated at lower rotation velocities (ω =25 – 50 s-1). The small bubbles tend to dissolve close to the cylinder mantle, but from other cylinder regions they have to be separated by centrifuging, and this is a very slow process. Some pretreatments of the glass melt is considered to get rid of bubbles having size under 0.1 mm.