Mass-transfer enhancement in large-diameter pipeline under water/gas stationary slug flow

In multiphase flow, gas bubbles are produced that collapse at the liquid/solid interface. In order to examine such effects, mass-transfer studies have been performed in an electrochemical cell and in a large-diameter flow loop under water/gas two-phase stationary slug flow. A limiting current density technique was used for oxidation of Fe(CN)(6)(4-) or reduction of Fe(CN)(6)(3-) in concentrated NaOH solutions. High-frequency and high-magnitude, instantaneous mass-transfer coefficients were found by potentiostatic measurements and may account for the corrosion rate enhancement in water/gas slug flow. A physical model of the stationary slug flow is proposed to explain the mechanism of gas bubble formation and bubble distribution. The effect of the gas bubbles on the mass-transfer enhancement is reported and a mechanism for the mass-transfer coefficient fluctuations is proposed. This study demonstrates that gas bubbles produced in stationary slug flow have a direct enhancement impact on the mass-transfer and corrosion rate of carbon steel pipeline. (C) 2004 The Electrochemical Society.