Charging of a low-conductivity liquid flowing through a cylindrical pipe with allowance for the finite rate of a surface electrochemical reaction

Abstract

A study is made of the charging of a low-conductivity liquid flowing through a cylindrical metal pipe with allowance for the finite rate of an electrochemical reaction that takes place on the walls of the pipe and is responsible for the charging. The solution of the problem uses the system of equations and boundary conditions derived by Gogosov, Tolmachev, and Nikiforovich [1]. The source of the space charge in the liquid is assumed to be a surface electrochemical reaction of ions of a contaminating impurity dissolved in the liquid [2–4]. The resulting current is found as a function of the flow velocity, the geometrical dimensions of the pipe, and the rate of the surface electrochemical reaction. It is shown that in the initial section of the pipe a kinetic regime is always realized in which the rate of the charging process is limited by the rate of the chemical reaction. Far from the initial section there is a diffusion regime, in which the rate of the charging process is determined by the rate of supply of ions to the surface of the pipe. With increasing velocity of the liquid the current tends to a limiting value, which depends only on the rate of the surface reaction, i.e., the current is saturated. The results given in the paper of experiments on the charging of hexane flowing through small-diameter pipes confirms the theory. The current was observed to be saturated in the experiments. A method is proposed for the experimental determination of the rate of a surface electrochemical reaction and the concentration of an ionic impurity.