THE RELATION BETWEEN MASS TRANSFER COEFFICIENT AND FRICTION VELOCITY

 This work aims to study the effect of  the relationship between the mass transfer coefficient and friction/shear velocity by the analysis of experimental results using Rotating Cylinder Electrode (RCE) to evaluate the limiting current density (LCD) under turbulent flow conditions at three different temperatures 40,50,600C. The experimental runs were carried out in NaCl salt solution of increasing concentration, i.e., 0.1, 0.3, and 0.5N to determine the limiting current density and therefore the mass transfer coefficient on two different metals (yellow admiralty brass and carbon steel), one of them is highly corroding (carbon steel) as function of  friction/shear velocity.Experiments showed that increasing the temperature for a given sodium chloride concentration leads to increase limiting current density and hence increased mass transfer coefficient on both metals. A similar trend is obtained for increasing NaCl salt concentration at a given temperature. As limiting current density is mass transfer controlled, slight or limited differences are noted on the two metals due to the fact the surface texture and morphology can not be reproduced equally the same. Temperature and increased NaCl salt concentration affect to different extent the dissolved oxygen concentration and the physical properties of the present system solutions. These variations are reflected on the limiting current and hence on mass transfer coefficient experimental results.Mass transfer coefficient depends mainly on velocity, i.e., Reynolds Number,which are influenced by temperature and solution NaCl concentration.