Understanding foams & foaming

Most of the common foams are a two-phase medium of gas and liquid with a particular structure consisting of gas pockets trapped in a network of thin liquid lms and plateau borders. Some well known foams are bubble baths, dishwater detergents and the foam head on beers. Many oils foam when trapped gas is suddenly released under conditions of an abrupt drop in pressure. In some re ners in which the throughow of gas at high temperature and pressure is required to crack hydrocarbons, the gas-liquid mixtures will foam strongly. The foam traps gas with gas fractions of 80% or higher. Clearly in such situations, in which it is desired that solid catalysts contact liquids, the production of foam is not wanted. In other applications, foams are useful; for example foams which have a high yield stress and can be used in a uid for carrying particles in applications ranging from the transport of cuttings in drilling and the placement of sands in cracks in oil producing reservoirs to increase the conductivity of reservoirs for secondary oil recovery. Obviously, bubble bath and shampoo companies should like to produce appropriate foams for dish and hair washing. Technologies which are impacted by foams and foaming are widespread. Foams are not well understood and they are very hard to control. A foam cannot be created without the vigorous introduction of gas from a bubbly mixture. Bubble baths and dishwater soap won't foam unless gas is stirred in by a water jet or another mixing mechanism. Foaming oils won't foam unless the drop in pressure is su ciently abrupt. To avoid a head of foam on beer it is necessary to pour the beer very slowly. To understand foaming it is necessary to try to be precise about the critical values of bubble release required to make and maintain a foam. All static foams are unstable, but some are more unstable than others. The stability of foams is another subject in which our understanding is far from complete. Foams collapse by draining and lm rupture. To keep a foam