Top-Down Model of Limescale Formation in Turbulent Pipe Flows

Abstract

We investigate calcium carbonate scale formation at high Reynolds numbers in a large pipe rig facility. The calcium carbonate solution is produced from the injection, at a T-joint inlet, of pH-stabilized sodium carbonate and calcium chloride aqueous solutions. A scanning electron microscopy analysis of the deposited mass along the pipe indicates that after an initial transient regime of ion-by-ion crystal growth, calcium carbonate scale is dominated by particulate deposition. While limescale formation in regions that are closer to the pipe's entrance can be described as the heterogeneous surface nucleation of calcium and carbonate ions driven by turbulent diffusion, we rely upon turbophoresis phenomenology to devise a peculiarly simple kinetic model of deposition at farther downstream regions. Letting $\Phi$ and $R$ be the flow rate and the pipe's radius, respectively, the mass deposition rates per unit time and unit area are predicted to scale as $\Phi^\alpha / R^\beta$ (for certain modeled values of the $\alpha$ and $\beta$ parameters) with suggestive support from our experiments.