Accounting for the thermal resistance of cooling water fouling in plate heat exchangers

• Heat transfer enhancement of PHEs has a potential to mitigate fouling.
• The fouling formation in PHE can be described by the “threshold model”.
• The model predicts the effects of wall shear stress and surface temperature.
• The model to predict cooling water fouling development over time was proposed.
• Data obtained for smooth channels can be used directly for plate heat exchangers.

Of the many different approaches available to mitigate fouling, the use of enhanced heat transfer surfaces is a principal method. The flow in channels of plate heat exchangers (PHEs) has high levels of turbulence due to the channels intricate geometry. In principle therefore, this type of heat transfer augmentation should lead to fouling mitigation. The effects of process parameters on fouling in PHE channels are studied in this article. The asymptotic behaviour of water fouling is examined specifically and the net rate of fouling accumulation is described as the difference between the fouling deposition rate and the fouling removal rate. An equation is proposed to account for how the fouling resistance varies with time. The conclusion is that for scaling there exist threshold conditions on wall shear stress, wall temperature and salt content, beyond which fouling deposition starts. The fouling deposition rate expression proposed for tubes incorporating heat transfer enhancement as used by Yang and Crittenden is adapted to be used in a new model for PHEs. Comparison with experimental data published in the literature reveals good agreement with the proposed model. The model can then be used to predict cooling water fouling development over time for all the heat exchangers in a chosen industrial circuit.