Numerical Simulation of Gas Separation by Hollow Fiber Membrane

Abstract Numerical analyses are performed for reverse osmosis gas separation modules consisting of hollow fiber membranes. Computational fluid dynamic simulations are conducted to study steady state flow and mass transport in three-dimensional separation modules. The fluid is a binary mixture of carbon dioxide (CO2) and methane (CH4). The mixture flows in a direction parallel to the membrane axis. The separation module consists of an inline and a staggered arrangement of hollow fibers with two different spacing. Equations governing the laminar flow of binary mixture, Navier-Stokes equation, and mass transport equations, are solved for Reynolds number of 1000, 1500, and 2000. The hollow fiber membrane is treated as a permeable, functional surface, where the mass flux of the species is computed as a function of local concentration, local partial pressures, the permeability, and the selectivity of the membrane. Flow and concentration field inside the module are characterized and the suction rate and concentration along surfaces of membranes are determined. Membrane flux performance is determined for the inline and the staggered configuration at all flow rates considered. Sherwood number of hollow fiber membranes is calculated for each configuration and spacing at all flow rates. It is shown here that area averaged Sherwood number asymptotes to a constant value away from the inlet. Sherwood number increases in both configurations as flow rate is increased and it decreases in both configurations as the spacing decreases. Merit number that compares the performance of different modules is introduced. The results show that modules consisting arrays of hollow fiber membranes in the staggered arrangement perform better than those with the inline arrangement at all values of spacing and flow rates considered in this study. This study aids in designing and optimizing gas separation modules consisting of hollow fiber membranes.