MODELING MASS-TRANSFER ENTRANCE LENGTHS IN TURBULENT PIPE-FLOW WITH APPLICATIONS TO SMALL CATHODES FOR MEASURING LOCAL MASS-TRANSFER RATES

Pipe-wall mass transfer, in the developing concentration boundary laye r region, under fully developed hydrodynamic conditions is simulated w ith a low-Reynolds number, k-epsilon, eddy viscosity turbulence model. The predictions are in good agreement with the electrochemical measur ements of Berger and Hau, in the range Re = 10(4) to 10(5), for Sc = 2 244, and of Son and Hanratty, in the range Re = 1 x 10(4)-5 x 10(4), f or Sc = 2400, in both the developing boundary layer region and the ful ly developed region. The application of small cathodes embedded in a l arger active cathode to measure local mass transfer rates is also simu lated. The size of the electrode and the thickness of the electrical i nsulation around the small electrode give rise to errors that increase as the insulation thickness increases and the electrode size decrease s.