Reconciliation of gas to liquid mass transfer in parallel and transverse flow (cross-flow) hollow fiber membrane contactors (HFMC) for CO2 absorption

Abstract

ABSTRACT Previous studies have found difficulties in reconciling mass transfer between membrane contactors of different geometries, which has been attributed to differences in fluid mixing. In this study, we compare the two most commonly adopted geometries (parallel and transverse flow) and use residence time distribution (RTD) analysis to verify the influence of geometry on fluid mixing in addition to developing a generalized correlation that can collectively describe mass transfer for both geometries. Lumen-side mass transfer was well described by the Lévêque solution in well-developed laminar conditions for both parallel and transverse flow modules. However, considerably lower mass transfer was identified for shell-side flow in the parallel fiber configuration, with RTD analysis providing confirmation that this was due to shell-side bypass which reduced mean fluid residence time in the contactor to below that of the theoretical residence time. The mean residence time calculated from RTD analysis enabled reconciliation of mass transfer data between both geometries, such that mass transfer could be adequately described for both configurations using: . The Reynolds number exponent indicated transitional mass transfer despite operation firmly within the laminar regime, which would indicate an enhancement in mass transfer provided by secondary flow effects within tightly packed fiber bundles. Whilst previously observed, for example in heat transfer analogies, such dependencies are generally more closely associated with parallel flow rather than ‘classical’ cross-flow modules in which fluid flow is explicitly perpendicular to the fiber bundle, and indicates that mass transfer in transverse flow may be better described as parallel flow, which confirms previous assumptions. Importantly, this study demonstrates the capability to reconcile mass transfer between modules of different geometries and permits the opportunity to project process design and scale-up between the two most commonly applied membrane contactor module geometries.