Rates of mass transfer to patch electrodes in disturbed flows using oxygen reduction under limiting current conditions

The cases of a sudden pipe expansion and a sudden pipe contraction are simulated within a flow loop-based test section designed to approximate disturbed conduit flow. Mass transfer rates to patch electrodes at selected positions within the test section have been measured using a limiting current methodology applied to oxygen reduction at copper in 3.5% wt./vol. NaCl. Using both large-scale polarisation linear sweep voltammetry and a potential step current transient technique with hydrodynamic steps, absolute and relative rates of oxygen mass transfer have been examined as a function of Reynolds number and location within the test section. The highest rates of oxygen transfer were observed both within the high velocity area of the test section and close to known regions of flow disturbance. Under the flow conditions used, patch electrode mass transfer relates to wall shear stress, which allowed areas of high mean and high fluctuating wall shear stress to be identified.