A PHYSICOCHEMICAL EXPLANATION FOR FLOW ELECTRIFICATION IN LOW-CONDUCTIVITY LIQUIDS IN CONTACT WITH A CORRODING WALL

Electrification during flow of insulating liquids in pipes has been st udied for a long time. Its dependence on flow parameters and pipe geom etry has been modeled for many different cases and is quite well known . Even though different laws of flow electrification have been obtaine d empirically in terms of the pipe length, a complete analysis taking into account the electrochemical reactions at the pipe wall-liquid int erface is lacking. In this paper, we present a model of the process in the case of a corroding wall and a liquid containing additives or imp urities partially dissociated into positive and negative ions. We trea t the case of laminar flow and an interfacial reaction whose conversio n is small compared to the concentrations of positive and negative ion s in the bulk solution. We compute the evolution of the space charge d ensity in terms of the axial and radial coordinates, and the flow velo city. The boundary conditions on the wall are deduced from the kinetic s of the wall surface reactions with the additives. Thus, analysis of these chemical reactions allows us to compute the net flux of electric al charge from the wall to the liquid. This flux is a function of the axial distance along the pipe and the mean flow velocity. Finally, com parison is made between our model and experiments on flow electrificat ion for hydrocarbons liquids.