ABSTRACT
Experimental studies of foam stability can be broadly divided into two categories: steady state and unsteady state. In steady-state experiments, gas is bubbled through a surfactant solution at a constant flow rate. Foam is formed at the surface of the liquid and moves up at a rate that depends on the gas flow rate. Foam is continuously skimmed off at a certain distance from the liquid pool, which is replenished by adding a surfactant solution at a constant rate. This results in the formation of a steady-state moving foam column in which the properties at any position do not change with time. The goal is to study properties such as liquid holdup and bubble size along the length of the foam. Steady-state foams will not be discussed further in this article. The interested reader is encouraged to read several extensive reviews and articles available in the literature [2129]. We shall restrict our discussion to the unsteady-state decay of standing foams.
