Spatial void fraction measurement in an upward gas–liquid flow on the slug regime

• The local void fraction is not uniform along the radial and axial directions.
• The slug unit void fraction has a nearly flat profile at the pipe core.
• The liquid slug void fraction peaks near the wall due to the gas entrainment.
• There is a minimum void fraction downstream the Taylor bubble rear.

Spatial void fraction measurements of a vertical upward air–water flow on the slug regime are made. The experimental technique uses simultaneously a contact needle and two single wire sensors. The data processing combines the information of both types of sensors. The liquid slug local void fractions along the radial and axial directions are estimated employing time and ensemble averages. The spatial void fraction along the axial direction disclosed two patterns, one associated to the pipe core and the other near the wall. The data is further processed to render the average void fraction along the radial and axial directions and the slug unit void fraction profile. Uncertainty analysis and data consistency tests are applied the check data reliability.