ABSTRACT
This chapter considers flow regimes typical of the most common applications together with methods for the evaluation of the void fraction in two-phase systems and of the conditions for flooding. These two aspects are included owing to the characteristics of the evaluation methods presently used, based on phase-interaction analyses, in connection with the flow regime determination methods. In particular, as the slope angle increases with respect to the horizontal, the wavy flow region increases with respect to the corresponding situation in horizontal geometry. Prevailing forces technique allows a more effective and direct indication of the influence of the various parameters on the acting forces and, therefore, on the different flow regime existence regions. A parameter often used to macroscopically characterize the relative importance of the two phases is the void fraction, defined as the ratio between the cross-sectional area occupied by the vapor phase and the whole cross-sectional area.
