MICROELECTROCHEMICAL QUANTIFICATION OF DRAG REDUCING PROPERTIES OF CORROSION INHIBITORS

摘要

The paper reports on new results on drag reducing properties of corrosion inhibitors obtained by electrochemical measurements at microelectrode arrays incorporated flush into a jet impinged surface. With microelectrodes positioned in different distances from the center of the jet, the wall shear stress distribution on the impinged surface could be measured at flow velocities up to 20 m/s with high lateral resolution. It is shown for the first time that instead of the hexacyanoferrate(Ⅱ/Ⅲ) redox system also the mass transport controlled cathodic hydrogen evolution from carbonic acid in CO_2 solutions can be used as tracer system in electrochemical wall shear stress measurements. Thus, drag reduction and corrosion inhibition effects can now be measured in the same experiment. The drag reducing efficiency of corrosion inhibitors correlates well with the corrosion inhibition activity under comparable wall shear stress conditions and the critical micelle concentration of the inhibitor. Electrochemical flow noise measurements revealed after FFT data treatment that inhibitors like quaternary ammonium salts significantly reduce the frequency and damp the amplitude of near-wall turbulence elements.