ABSTRACT
This chapter provides some of the most frequently applied foaming techniques. The techniques for creating bubbles can be improved by generating a flow of the foaming solution, creating a so called "co-flow" of the gas and the liquid. The average size of the bubbles is between some a hundred micrometer and up to a few millimeter, and the foam formation rate is rather low and of the order of one liter per minute. Bubbling a gas into a stationary liquid is an important industrial process, encountered in bubble column reactors or in flotation tanks. At free liquid surfaces, gas entrainment often arises at high fluid velocities and at sudden changes of the flow velocity. For low viscosity liquids, the initial foaming rate can be rather high; however, the subsequent bubble break up can take much longer.
