Abstract
Fouling is a persistent issue in industrial heat-transfer equipment, increasing energy demand and reducing efficiency. This is also true in the dairy industry where falling-film evaporators are central to powder production. Most dynamic models, however, neglect gradual fouling, limiting predictive accuracy during extended operation. As a result, model-based control can become unreliable when fouling becomes significant. The dynamic models by Bojnourd et al. [1] are widely used but assume clean-surface operation. While this captures short-term thermal behavior, it cannot represent the progressive decline in heat-transfer performance caused by fouling. Díaz-Ovalle et al. [2] introduced a fouling-layer model that explicitly describes the growth of a fouling deposit over time. Building on this concept, the present work incorporates a simple dynamic fouling model for falling-film evaporators and validates it using industrial data from a four-effect evaporator using thermal vapor recompression. Two fouling-modelling strategies are evaluated: a mechanistic fouling layer model and an empirical model describing the observed loss in heat-transfer efficiency. The fouling layer model substantially reduces prediction error, demonstrating that it captures the dominant fouling behavior. Although the empirical model fits all observed discrepancies, it lacks predictive capability and therefore cannot be applied for model-based prediction or control.