CFD modelling of CaCO₃ crystallization fouling on heat transfer surfaces

Supersaturation of inversely soluble salts, like calcium carbonate, causes crystallization fouling on heated surfaces of heat exchangers. In this paper, crystallization fouling of calcium carbonate is studied by CFD modelling. Crystallization fouling is modelled in 2D and 3D flat plate geometries, which correspond to an experimental set-up of an idealised heat exchanger. The model is validated with experimental data under various operating conditions and is used to identify the regions where different parameters have the greatest effect on fouling. The CFD model presented in this paper is a novel combination of a fouling model, which includes the surface integration term and the shear stress dependent residence time, and the hydrodynamics and heat transfer modelled by CFD. The crystallization fouling CFD model predicts the experimental mass deposition rate and the linear fouling resistance within the experimental uncertainty in most of the studied conditions. The crystallization fouling CFD model is very sensitive to the heat exchanger surface temperature, but also relatively sensitive to the shear stress. The validated crystallization fouling model may be utilised to study fouling of industrial heat exchangers when the fouling is controlled by the surface integration. If mass transfer controls the crystallization fouling, the mass transport of ions should be included to the model.