Experimental study on electrification phenomena in dielectric liquid flows over metal walls

The present paper deals with an experimental study of electrification phenomena occurring between a metal wall and a dielectric liquid flowing over it. Measurements were carried out using a hydraulic mineral oil and a fluorocarbon as test liquids and wire meshes made of stainless steel, copper, brass and aluminum. The findings are as follows; the mineral oil was charged negative against stainless steel, copper and brass but positive against aluminum, while the fluorocarbon was charged positive against anyone of these four metals. Electric charges detected as currents out of the wire meshes increased with the liquid velocity passing through the meshes and differed depending on the metal type even if the velocity was the same. Moreover, it was confirmed that contact of metal with a flowing liquid not only generates but also relaxes electric charges; the amount of charges either generated or relaxed per unit volume of the liquid flowing over metal decreases as the flow becomes faster.