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. (C) 2001 Elsevier Science B.V. All rights reserved.