Modelling foaming in industrial glasses

Modelling foaming in industrial glasses

Franck Pigeonneau* 1, Florence Rouyer 2

1 MINES Paris | PSL Research University, CEMEF, CNRS UMR 7635, Sophia Antipolis cedex, France
2 Laboratoire Navier CNRS UMR 8205, Gustave Eiffel university, 14/20 Boulevard Newton 77420 Champs sur Marne, France

The melting of raw materials in industrial glass furnace leads to bubble generation. Bubble density and size distribution are initially correlated to the granulometry of raw materials [1]. The carbonate decomposition leads to CO2 release which is a source of large quantity of bubbles due to the low solubility of CO2 [2]. The chemical reaction on silica seeds with precursor liquid leads also to a bubble generation. These phenomena are the origin of the presence of foam above raw materials generally called primary foam. To remove the bubble, glass makers add fining agents. The out-gassing occurring generally at high temperature, T around [1300-1500]°C can lead to a foam creation. A layer of few centimeters of foam can spread over a large part of the glass bath.

From the point of view of the heat transfer, the presence of a foam layer is harmful to the energetic efficiency. According to Fedorov and Viskanta [3], few centimeters of foam reduces dramatically the transmittance. By corollary, the temperature in combustion space increases which is detrimental to the refractory materials.

The creation of a steady-state thickness of foam is a balance of source of bubbles rising from the liquid bath and death of the bubble at the top of the foam. According to Pilon and Viskanta [4], three situations can exist for which the control parameter is the superficial gas velocity jg resulting from a fluid mechanics analysis. Below a threshold jm, the foam is unstable. When jg is equal to jm, a foam appears. Above this threshold, a foam is created.

In this lecture, the origin of gas source resulting to fining process will be first presented to determine the main characteristic of the superficial gas velocity. After a review of the onset of foaming, the mechanisms leading to the death of foam will be presented based on film stability as already studied in [5]. A simple model to describe the creation of foam will be also presented.


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