The influence of dense vertical tube bundles in a batch bubble column reactor (BCR) of 100 mm diameter and 1100 mm clear liquid height on liquid dispersion and gas-liquid mass transfer was studied. In particular, the effects of different tube patterns (triangular and square pitch), tube diameters (8 and 13 mm) and bottom end designs (flat and U-tube) having a tube diameter-to-pitch ratio of approx. 1.3 were investigated. Dispersion coefficients were determined based on conductive tracer experiments recorded via wire-mesh sensors (wms) with up to 90 measurement points distributed in the column's cross-section in between the tubes. The gas-liquid mass transfer coefficient was determined via fast-responding oxygen needle probes. Tube pitch and pattern were identified as the most crucial design parameters for the extent of liquid dispersion. We found that particularly the U-tube bottom end design induces large liquid circulation patterns, which enhance dispersion. The presence of internals decreases the kja value as a consequence of turbulence damping, which is also confirmed by lower kj values (e.g. 0.6 x 10(-3) m s(-1) for the empty BCR and 0.25 x 10(-3) m s(-1) for the square pitch with 8 mm tubes at 0.05 m s(-1) superficial gas velocity), whereas the pitch is the most decisive design parameter. The U-tube bottom end design was identified as the most beneficial configuration with respect to liquid mixing and gas-liquid mass transfer. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.