Sub-Channel Flow Behavior in Vertical Tube Bundles in Bubble Columns

Bubble columns are simple multiphase reactor and contactor devices, which are widely applied due to their superior heat and mass transfer characteristics. Furthermore, they are relatively simple in construction due to the absence of moving parts. Bubble columns are used for various chemical processes such as methanol and Fischer-Tropsch synthesis. Since most of the processes running in bubble columns are of exothermic nature, a variety of heat exchangers, e.g. internal heat exchanging tube bundles, are installed in order to ensure proper reaction conditions. Such tube bundles cover a significant ratio (up to 60 %) of the entire column cross-section. Accordingly, the column performance is dominated by the hydrodynamics proceeding at smaller characteristic length scale in the sub-channels. However, the evolving sub-channel flow has not been studied yet.
Therefore, this study focusses on the analysis of the multiphase flow in the sub-channels of an internal heat exchanging tube bundle with longitudinal flow of various configurations (square and triangular pattern) and tube diameter sizes (8 mm and 13 mm). The investigations were carried out in a 100 mm (inner diameter) bubble column for an air / deionized water system using a perforated plate type sparger. To ensure comparability, the covered rector’s cross-sectional area was kept similar for all configurations.
The hydrodynamic parameters were studied separately for sub-channels at various radial positions in the bundles as well as for the entire column. Approaches to link experimental data from both scales for a multiscale evaluation are suggested. Furthermore, the results are compared with an advanced horizontal stage-model considering breakup and coalescence mechanisms to calculate the bubble size distribution, breakup and coalescence rates and the overall gas holdup.