Two-bubble class approach based on measured bubble size distribution for bubble columns with and without internals

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 m s-1 to 0.20 m s-1 to cover homogeneous and heterogeneous flow conditions. The contributions of small and large bubble classes on total 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 velocity, large bubble holdup as well as total holdup are proposed based on sub-channel area, sub-channel hydraulic diameter and occlusion area.