Computational fluid dynamics simulations are conducted for binary mixture fluid flows in a hollow fiber membrane. The membrane is modeled as a functional surface, where the mass fluxes of each species will be determined based on the local partial pressures, the permeability, and the selectivity of the membrane. Baseline Reynolds Stress (BSL Reynolds Stress) turbulence model and the Brinkman-Forchheimer equations are employed to study spatial structure of the flow inside the lumen and the porous layer for Reynolds number up to 400. The process of separating CO2 from CH4 is improved by the presence of orifices in the membrane system by about 60%. The degree of improvement is greater at higher flow rate. The influence of the momentum mixing induced by orifices strongly depends on the permeability and the thickness of the support layer. It is demonstrated here that altering flow inside the lumen by placing flow restricting devices can be used in the hollow fiber membrane system design in the application of gas-gas separation. (C) 2015 Elsevier Ltd. All rights reserved.