Chemical Engineering Research & Design, Vol.78, No.5, 773-778, 2000
The flow of foam films in vertical tubes
Free soap films are useful models for foam, and principles established from their studies an important fur a sound understanding of the behaviour of complex industrial foams. In this paper, the flow of single and multiple foam films was studied in tubes of diameters in the range 15.7-38.7 mm. The films were stabilized with Sodium Dodecyl Sulphate (SDS) at concentrations varying from 0.5 to 20 cmc, whilst the viscosity of the solutions was varied over the range 0.99 - 11.6 mPa s by adding glycerol. The pressure drop of a train of isolated films was a linear function of the film velocity and the number of films. A lower pressure drop was, however, recorded when the films were made to bridge into one another to form a foam proper. Larger diameter tubes exhibited less pressure drop, and the pressure drop in a perspex tube could be as much as twice that in a glass tube of the same diameter, indicating that the wetting properties of the tube are an important parameter in determining pressure drop. The lubricating liquid layer on the tube wall is a key factor in determining pressure drop. A complex relationship exists between the thickness of this liquid layer, liquid viscosity, and pressure drop.