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

In this paper, a theoretical model of the electrical double layer development is presented. It takes into account the case of a non-fully developed double layer at the exit of the pipe and a diffuse layer thickness non-negligible compared to the capillary radius. Then the space charge density at the wall ρw is determined by streaming current experiments of a dielectric liquid (n-heptane) containing different concentrations of additive (OLOA 218 A) flowing through a micrometric glass capillary. Results show that ρw increases with the liquid conductivity in a large range of conductivity (from about 53 to 1010 pS/m). Furthermore we point out two fundamental parameters of flow electrification of dielectric liquids: (a) the velocity of the physicochemical 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.