Modelling mass transfer entrance lengths in turbulent pipe-flow with applications to small cathodes for measuring local mass transfer rates

Abstract

Pipe-wall mass transfer, in the developing concentration boundary layer region, under fully developed hydrodynamic conditions is simulated with a low-Reynolds number,k−e, eddy viscosity turbulence model. The predictions are in good agreement with the electrochemical measurements of Berger and Hau, in the rangeRe=104 to 105, forSc=2244, and of Son and Hanratty, in the rangeRe=1×104–5×104, forSc=2400, in both the developing boundary layer region and the fully developed region. The application of small cathodes embedded in a larger active cathode to measure local mass transfer rates is also simulated. The size of the electrode and the thickness of the electrical insulation around the small electrode give rise to errors that increase as the insulation thickness increases and the electrode size decreases.