Steady-state mass transfer in radial flow-through thin layer cells—I. Reversible metal systems

The convective diffusion model, prevailing in radial thin layer flow cells (thickness 2h ? 10^?2 cm) with central solution inlet at ultra-low flow rates J ? 10^?2 cm³ s^?1, has been investigated by numerical finite-difference techniques for the transport-controlled conversion of metal ions at a coulometric asymmetrical or symmetrical metal detector, mounted on one or on both sides of the thin layer, respectively. At symmetrical detectors, the concentration profiles and the conversion efficiency have been evaluated by assuming negligible radial diffusion and are in good agreement with previous eigenvalue solutions. At unsymmetrical detectors, the mass transfer study has been carried out in consideration of radial diffusion. The diffusional contribution to the radial flux becomes increasingly apparent in the concentration profiles and the conversion efficiency, as the internal detector boundary r₀ is shifted downstream at constant h and J, or as J and h are lowered proportionally at constant r₀. This effect can be diminished by choosing appropriate correlations between r₀, h and J, which are established together with the limiting conditions for coulometric detector operation.