A cross-flow hollow fiber membrane bundle for humidification (MBH) is used for seawater desalination. Fluid flow and conjugate heat and mass transfer in the bundle are studied by numerically solving the continuity, momentum, energy and concentration equations for air side, water side and membrane side, simultaneously in a conjugated way. Contrary to previous studies which considered only 2D laminar or turbulent flow, in this research the full three-dimensional turbulent flow in air side is modelled with a three-dimensional low-Reynolds-number k-epsilon turbulence model (3D Low Re k-epsilon). For comparison, besides the proposed 3D turbulence model, other three previously used models, namely, a 2D Low Re k-epsilon turbulence model, a 2D laminar model, and a 3D laminar model, are also used to investigate the effects of air side turbulence on fluid flow and heat and mass transfer properties in the bundle under a wide range of Reynolds numbers from 100 to 900. It is found that the 3D turbulence model best predicts the friction factors and Nusselt and Sherwood numbers for various module packing fractions under higher Reynolds numbers above 650. The results are validated by velocity measurement and performance test with a seawater desalination system. (C) 2017 Elsevier Ltd. All rights reserved.