A comparative study between the effect of swirl flow and axial flow on the rate of diffusion controlled corrosion in a double tube heat exchanger

The rate of diffusion-controlled corrosion of an annulus under swirl flow was studied by measuring the limiting current of the cathodic reduction of potassium ferricyanide depolarizer in the presence and absence of polyox WSR-301 drag-reducing polymer. It was found that the rate of diffusion-controlled corrosion of the inner cylinder of the annulus increases with increasing swirl flow solution velocity and decreases with increasing the active height of the cylinder. The data in the absence of polymer (blank solution) under swirl flow were fitted by a dimensionless equation. The importance of this equation in predicting the rate of diffusion-controlled corrosion and the corrosion allowance during the design of the swirl flow equipment was highlighted. For a given set of conditions, the rate of accelerated swirl flow corrosion was much higher than that of axial flow. Drag reducing polymer was found to inhibit the rate of diffusion-controlled corrosion by a maximum of 23%, if other benefits of the polymer are considered such as the decrease in the shear stress and the associated decrease in the erosion-corrosion tendency besides the decrease in pressure drop and pumping power requirement it may be concluded that the use of drag-reducing polymers in industry is worthwhile.