A physicochemical explanation for flow electrification in low conductivity liquids

The flow electrification phenomenon observed for insulating liquids has been studied for a long time and its dependence on flow parameters and the pipe geometry has been, in a lot of different cases, modeled and is now rather well know. Nevertheless, in terms of the length of the pipe, even if different laws have been obtained empirically, a complete analysis taking into account the electrochemical reaction at the wall pipe-liquid interface has not yet been developed. In this paper, the authors present a modeling of the process in the case of additives or impurities partially dissociated into positive and negative ions. They treat the case of laminar flow and of an interfacial reaction whose conversion is small compared to the amount of positives and negatives dissociated ions in the bulk of the solution. They compute the evolution of the space charge density in terms of the axial and radial coordinates and of the flow velocity. The boundary conditions on the wall are deduced from the kinetics of the wall surface reactions with the additives. Thus the analysis of these chemical reactions allows the computation of the amount of electric charges given to the liquid by a wall unit area as a function of the axial co-ordinate of the area and of the mean flow velocity. Finally comparisons are made and discussed between this modeling and experiments of flow electrification for hydrocarbons liquids