We constructed a three-dimensional model to study the effect of operating conditions, and physical and geometrical parameters in a hollow fiber membrane module under Direct Contact Membrane Distillation (DCMD) operation. The normalized permeate flux was calculated for different module arrangements, various hollow fiber physical properties (e.g. length and thickness), and operating conditions. The results indicated that the permeate flux decreases when we increase the fiber length, thickness, and tortuosity. In contrast, increasing the feed velocity and temperature, and the porosity of fibers result in increased permeate flux. We found that the normalized permeate flux significantly drops once the interspacing parameter of fibers-the ratio of external radius of fibers to the center-to-center distance between neighboring fibers-approached 0.47. The temperature difference across the membrane decreases with reducing the membrane thickness; however, the effective driving force, pressure gradient over the membrane thickness, for water transport through the membrane increases.