It is desirable to recover H-2 and enrich CO2 by palladium (Pd) membrane tubes after hydrogen-rich gases are produced. In this study, H-2 separation and CO2 enrichment in a duct using a single membrane tube and two membrane tubes in tandem are investigated numerically. Four different hydrogen-rich gases are tested in the single tube system, while three parameters of Reynolds number (Re), the distance between the two membrane tubes, and pressure difference are considered in the dual tube system. Meanwhile, the interfacial transport phenomena are underlined via examining the local Sherwood number. The results suggest that the H2 recovery and CO2 enrichment decrease dramatically when the Reynolds number increases from 1 to 100, regardless of which gas mixture is fed. This reveals that the Reynolds number plays a prominent role in H-2 permeation and CO2 enrichment, and should be controlled at Re <= 10. The interaction between the two tubes are evidently exhibited at low Reynolds numbers and short distances, so the H-2 recoveries by the two individual tubes are significantly lower than that by the single tube. The flow retardation and H-2 concentration polarization from the leading tube upon the trailing tube deteriorate the H-2 permeation of the latter. However, when the Reynolds number is as high as 100, the interaction and concentration polarization are almost ignorable.