The physical structure of all the recommended void fraction correlations
listed in Tables 3 and 4, for the entire range and for each
specified range of the void fraction is shown in Table 5. It can be seen
that the correlations of Dix [35], Goda et al. [29], Rouhani and Axelsson
[24], Sun et al. [26] and Woldesemayat and Ghajar [30] treat the
distribution parameter as a variable in terms of phase flow rates and
mixture quality. The Gomez et al. [22] is the only correlation that expresses
the drift velocity as a variable in terms of void fraction.
The good performance of these correlations for vertical up and
down orientations is logically justified in the next section by illustrating
the resemblance in the physical structure of these correlations
and the requirement of an ideal void fraction correlation for
vertical upward and downward flow.