Flow electrification of dielectric liquids in insulating channels: Limits to the application of the classical wall current expression

Recently, a series of experiments concerning flow electrification have been made in our laboratory. These experiments, where a dielectric liquid is forced to flow through relatively short insulating channels, show that experimental results cannot be reproduced using the classical the wall current equation. We present here some results which allow us to obtain the two parameters governing the wall current: the space charge density near the wall for a fully developed double layer, rho(w infinity), and the coefficient K, related to the intensity of the physico-chemical reactions taking place at the solid-liquid interface. We show that the latter should not be considered to be independent of the flow rate. Two possible explanations for this behavior are presented. (c) 2007 Elsevier B.V. All rights reserved.