Fluid flow and heat transfer in novel cross flow hollow fiber membrane contactors are studied. The fiber banks are randomly potted in contactor shells and their distribution topology varies from case to case. The packing densities and the inlet flow Reynolds numbers are from 0.35 to 0.5 and 20 to 180, respectively. It is found that the pressure drops and heat transfer coefficients of the contactors are correlated to the topological characteristics of the void spaces among the fibers. Especially, the topological features of the large cavities among the fibers show dominant effect. Two typical large cavities are identified, namely isolated cavities and cut-through cavities. Two non-dimensional parameters sigma and gamma, which are based on the Delaunay subdivision of the cross sectional images of a contactor, are used to characterize the topological features of the void spaces among the fibers. The sigma and gamma characterize the uniformity of the void spaces and the channel size of the cut-through cavities, respectively. The pressure drops/Nusselt numbers of a contactor exhibit power law relations to the topological parameter gamma. The constants in correlations are found to be dependent on the packing densities. The results can be used to predict the pressure drops and Nusselt number of those massively produced hollow fiber membrane contactors with randomly distributed fibers. Solid inserts that are used to reduce the size of cut-through cavities are suggested. (C) 2019 Elsevier Ltd. All rights reserved.