Numerical study of electric-charge diffusion in wall-bounded flows of dielectric liquids*

Flow electrification during transport of dielectric liquids constitutes a major safety hazard.  This is particularly the case in petrochemical and process industries, in which several accidents have occurred in the past due to the dielectric properties of liquid hydrocarbons.  For this reason, it has been the subject of various research efforts over the years.

Typically, flow electrification occurs via diffusion of electric-charge carriers (ions) from the electrical double layer, which is inevitably formed between a liquid-solid interface, to the bulk of the flow. This phenomenon is currently not well understood but it is generally accepted that flow turbulence plays a major role and can dramatically increase the electrification rate.  More specifically, at sufficiently high Reynolds numbers, and for low-conductivity fluids such as liquid hydrocarbons, the thickness of the hydrodynamic boundary layer becomes comparable to that of the electrical double layer. In turn, this leads to increased transport of charges away from the wall region and towards the bulk of the flow.  However, quantitative information on the underpinning mechanisms of this phenomenon is still lacking.

In the first part of this presentation, we outline our numerical method for the simulation of the problem for interest In the second part, we present results from direct numerical simulations of turbulent flow electrification for bulk Reynolds numbers ranging from 4600 to 6700.  Our study focuses on the rate of accumulation of charge in the bulk and on the statistical properties of the charge density distribution.