The complex flow patterns in bubble
columns can be phenomenologically
described by the two-bubble class approach. For the first time, this
approach is applied to bubble columns with dense internals. Internals
of square and triangular pitch tube patterns of two tube sizes (8
× 10–3 and 13 × 10–3 m) with flat and U-tube bottom design and cross-sectional occupation
of ∼25% were inserted in a bubble column of 0.1 m diameter
and 2 m height. Contrary to the well-known gas disengagement technique,
dual-plane ultrafast X-ray computed tomography data have been used
for the bubble class allocation. Experiments were performed at superficial
gas velocities ranging from 0.02 to 0.20 m s–1 to
cover homogeneous and heterogeneous flow conditions. The contributions
of small and large bubble classes on total gas holdup, flow structure
and bubble rise velocities were determined. Furthermore, the regime
transition onset was determined based on the two-bubble class approach.
Eventually, new correlations for regime transition, small and large
bubble rise velocities, and large bubble holdup as well as total gas
holdup are proposed based on sub-channel area, sub-channel hydraulic
diameter, and occlusion area.