Having more than one phase. Material in a process stream or plant equipment may be in combinations of solid, liquid, and gas or vapour phases, including liquid-liquid. It is not dependent on the number of components present. A single component may have more than one phase present such as liquid and its vapour flowing through a pipeline in the form of bubbles (see Fig. 30 for examples of horizontal and vertical pipe flow). The majority of industrial chemical processes are concerned with multiphase flow systems such as power generation, refrigeration, and distillation, and depend on multiphase evaporation and condensation cycles. Desalination, steel-making, paper manufacturing, and food processing all contain critical steps that depend on the nature of multiphase behaviour.

Fig. 30 Multiphase flow