3.3. Void fraction and the gas volumetric flow fraction
The gas volumetric flow fraction is defined as the ratio of the gas
volumetric flow rate to the total volumetric flow rate expressed as,
b ¼
Usg
UsgþUsl
. By definition, the gas volumetric flow fraction is also referred
to as the homogeneous void fraction with the assumption of
no slip between the two phases.