Effect of suspended particles on the rate of mass transfer to a rotating-disk electrode

The addition of 0 to 40 vol % spherical glass particles of 4 to 75 microns diameter to the electrolyte was found to significantly increase limiting currents for the reduction of Fe(CN)5 (-3) on rotating disk electrodes. The increase is largest, more than three fold, at high rotation speeds (2870 rpm), large electrodes (1.41 cm radius), high particle content (40 vol %) and intermediate particle diameter (approx. 10 microns). Calculations of viscous power dissipation have shown that increasing limiting current by the addition of particles at constant rotation rate requires a much lower increasing in stirring power than that required for obtaining the same limiting current by use of higher rotation rate in the absence of particles. A tentative theoretical model, involving mass transfer enhancement by means of a fresh fluid layer entrained by rotating particles, provides reasonable agreement with observed behavior.