Cross-flow structured hollow fiber membrane bundles where the fibers are arranged either in inline or in staggered arrays are investigated for their bundle side convective mass transfer and pressure drop characteristics. A high speed hot wire anemometry is used to validate the turbulent flow behavior in the bundle at low Reynolds numbers. A mathematical model for the turbulent fluid flow and convective mass transfer across the bundle under uniform mass boundary conditions is set up, which is then validated by an air humidification test. With the validated model, the Sherwood numbers and friction factors across the bundle are obtained for different fiber arrangements, pitch to diameter ratios, and Reynolds numbers. Correlations are then proposed to estimate the friction factors and Sherwood numbers across the bundles with various parameters. It is found that compared to the previous researches and the available correlations, the present results are more appropriate for the cross flow hollow fiber membrane bundles that are usually operated under low Reynolds numbers from 100 to 500, but have turbulent flow behaviors. (C) 2013 Elsevier B.V. All rights reserved.