Space charge density at the wall in the case of heptane flowing through aninsulating pipe

In this paper, a theoretical model of the electrical double layer developme nt is presented. It takes into account the case of a non-fully developed do uble layer at the exit of the pipe and a diffuse layer thickness non-neglig ible compared to the capillary radius. Then the space charge density at the wall p(w) is determined by streaming current experiments of a dielectric l iquid (n-heptane) containing different concentrations of additive (OLOA 218 A) flowing through a micrometric glass capillary. Results show that p(w) i ncreases with the liquid conductivity in a large range of conductivity (fro m about 53 to 1010 pS/m). Furthermore we point out two fundamental paramete rs of flow electrification of dielectric liquids: (a) the velocity of the p hysicochemical reactions at the wall which induces the development time of the space charge density at the wall, (b) the relaxation time on which the development of the diffuse layer inside the liquid depends. (C) 2001 Elsevi er Science B.V. All rights reserved.