
126 Foam Fractionation: Principles and Process Design
under gravity due to its high effective viscosity. Because dry foam exhibits
Herschel–Buckley rheology (see the constitutive equation, Equation 3.20, in
Section 3.11), it cannot ow unless its yield stress is exceeded. Liquid drain-
age is minimal. In this case, the method of foam collection does not affect the
underlying performance of the process, but judicious selection of method can
improve the energy efciency and convenience. As discussed at the begin-
ning of this chapter, the driving force for foam ow originates in the gas
compressor; because the gas compressing system normally has ...