When the spatial gradients in the films are considered, the number of state variables becomes even larger. The radicals in the system have a short chemical time scale, typically in the range of milliseconds. On the other hand, the residence time, representing the average time a species spends in the system, is tens of seconds at each tray. Furthermore, the overall simulation time span for the fouling model is extended to 1 year to capture long-term effects and assess the model performance over the extended period representative of industrial fouling time scales. The large number of state variables and large separation of time scales pose challenges in simulating the fouling model.