Using a wall-driven flow to reduce the external mass-transfer resistance of a bio-reaction system

The two-dimensional momentum and mass transfer in an immobilized enzyme reactor was numerically investigated. The equations of motion and the mass-transport equation of a substrate, consumed at specified boundaries of the reactor, were solved by using fourth-order discretization schemes. A wall-driven cavity of square cross-section was selected to study the convective transport contributions to the movement of substrate from the bulk solution to an immobilized enzyme surface. The numerical results provided field distributions of the local velocity and substrate concentration as a function of external-mass transfer rates and reaction limitations. The flow field structure of the system under consideration facilitated the interpretation of the effect of hydrodynamic conditions on transport processes and reactor performance was evaluated from the effectiveness factor obtained at different operating conditions. The influence of the operational Peclet number (Pe ≤ 1000) on reactor performance was obtained for different values of the Reynolds number (Re ≤ 700). Results indicated whether mass transport was limited by reaction or by external mass-transfer resistances; the effects of high enzyme activity on operating conditions were also established.