In the present analysis for vertical upward orientation it was observed
that the void fraction is always less than the gas volumetric
flow fraction, i.e. a < b. For vertical downward two phase flow a
careful analysis of the variation of this parameter with the void fraction
showed that for void fraction values typically less than 0.2, the
gas volumetric flow fraction (b) is less than the void fraction (a),
while the converse is true for a > 0.2. This observation regarding
the variation of the void fraction with respect to the gas volumetric
flow fraction is supported by the analysis of Yamazaki and Yamaguchi
[17].