On the study of electrochemical turbulent noise in a stirred vessel

Electrochemical measurements of turbulent fluctuations of limiting diffusion current have been performed in a stirred reactor, where an axisymmetric mean flow is produced using a small cylindrical impeller. We used an electrochemical probe with three electrodes: two small circular electrodes geometrically included in another circular, large electrode. The first small electrode was in the centre of the large electrode, the second small electrode was new the leading edge. An electrochemical reaction is carried out on the surface of the electrodes, under conditions that the reaction rate is fast enough and the concentration of the reacting species is zero at the probe surface. Three signals are simultaneously measured, when the probe is placed very close to the agitator extremity. Spectral and wavelets analysis emphasize the presence of spikes for the three signals. There is significant evidence to indicate that a strong local energy concentration appears, at some particular frequencies. Further signal analysis is performed by calculating third-order and fourth-order structure functions (e.g. the skewness and flatness factors respectively). For each electrode, a different qualitative behaviour could be noted. This is an unexpected result for a "perfectly agitated" stirred reactor.