This study is a step forward from previous researches involving hollow fiber membrane contactors for air humidification. A real application-scale cross-flow hollow fiber membrane module is investigated. The air stream flows transversely across the fiber bundle while being humidified. The novelty is that the shell-and-tube module is converted to a parallel-plates heat mass exchanger in the model set up. The equations governing the heat and moisture transfer from the water to the air, through the membranes, are described. The equations are then normalized with newly defined dimensionless parameters, which summarize the operating conditions and have clear physical meanings. Following this step, the two-variable two-dimensional partial differential equations are numerically solved. Tests are conducted to validate the model. Effects of varying operating conditions on system performance are discussed. It is found that the system is dominated by mass transfer in membranes with a total Lewis number larger than 10. The packing density has a direct influence on performances. In contrast, the geometry of fiber packing arrangement has a negligible effect. This is tremendously different from the traditional metal tube bundles for sensible-only heat transfer. (C) 2012 Elsevier Ltd. All rights reserved.