Energy cascade in a tornado wise flow generated by magnetic stirrer

Abstract

The measurements of the limiting diffusion current and its fluctuations are used to study mass transfer near the stagnation region in a tornado wise flow generated by a magnetic rod stirrer. The paper aims to investigate what kind of information could be provided by the electrochemical method when the probe is submerged in the flow. The power spectral density (PSD) of the current pulsations was measured regard to three angular rotation rates of the stirrer and four different locations on a radius. The analysis of the PSD revealed that the resonance frequencies obeyed to a sub-harmonic interaction mechanism. The existence of the sub-harmonics with their odd harmonics testify the role of some entertained eddies. As for the order of magnitude of the time average value of mass transfer parameters, the diffusion layer thickness right to the electrode and the mass transfer coefficient were calculated respectively to be about 10 μm and 0.10 mm s −1. The turbulence intensity relative to the fluctuations of the limiting current, varies between 11% and 20%, in comparison with the value of 10% commonly retained in planar flows. These values seem account for the three-dimensional complexity of the flow.