A theoretical study of freezing fouling: limiting behaviour based on a heat and mass transfer analysis

An analysis is presented of freezing fouling for liquids in laminar flow through ducts. Solidification occurs on a cooled wall while the bulk liquid remains unsaturated. The approach assumes that intrinsically rapid heterogeneous nucleation occurs at the solid/liquid interface, so that solidification is controlled by heat and mass transfer rates rather than by the intrinsic rate of crystallisation. A simple one-dimensional model for a single crystallising solute predicts that a range of fouling behaviours can occur, ranging from linear fouling to asymptotic (Kern–Seaton) behaviour, depending on the operating conditions, without any need to invoke removal effects. Maximum fouling rates can be estimated and the occurrence of quasi-asymptotic fouling can be identified, so permitting an apt choice of parameters for the design and operation of systems subject to such fouling effects. The model is illustrated by a case study on ‘coring’ in food fat distribution pipelines.