Hydrodynamics, mass and heat transfer in bubble columns with vertical internals: an experimental study

The objective of this study is to examine the influence of different vertical tube bundle designs on the bubble dynamics and on the mass and heat transfer rates in a bubble column. The studies in the open literature examining the performance of bubble columns with vertically inserted tube bundles have focused primarily on the coverage of the cross-sectional area of the bubble column by the tube bundle (CSA). The most frequently used coverages are the 5% and the 25% (± 3%) which mimic the heat exchangers utilized in the processes of methanol and Fischer-Tropsch syntheses. Other than that, the designs of tube bundles seem to be arbitrarily chosen and feature a number of different configurations of layouts, tube diameters and tube lengths. From the current state of research, it is thus rather difficult to draw conclusions on the optimal design of a heat exchanger suitable for use in bubble columns. Intuitively, it can be concluded that the most important design features of tube bundles affecting the flow are the distance between the tubes and the unit cell area enclosed by the tubes in their respective arrangements. Accordingly, the study aims on a systematic analysis on the effect of these geometric parameters.
The experiments are conducted in a 10-cm bubble column equipped with a perforated plate gas distributor in the air-water system. Four tube bundle designs have been chosen and arranged in the triangular and square pattern layouts, which represent the two most widely used heat exchanger designs according to TEMA (Tubular Exchange Manufacturer´s Association) and are known to affect the fluid turbulence to different extents. The volumetric mass transfer coefficient, kLa, is measured by the oxygen absorption method using a commercially available oxygen probe and the heat transfer is measured using the extended heat exchanger probe. The gas phase dynamics are obtained with the use of the in-house developed dual-plane ultrafast electron beam X-ray tomography.