Variable Properties in Fouling Estimation in Heat Exchanger Networks with Fouling

Fouling in shell-and-tube heat exchangers reduces heat recovery efficiency in industrial processes, increasing fuel consumption and operational costs. Most studies assume constant physical properties throughout the heat exchanger network (HEN) and over time, despite the impact of temperature-dependent properties on heat transfer and fouling behavior. This work proposes a variable-property framework for HEN simulation with fouling, assuming pseudo-stationary fouling behavior within each time step. Physical properties are updated through a direct substitution approach based on estimated temperatures, with iterative convergence. Temperature-dependent effects on mixing and furnace duty are also incorporated. Results indicate that the proposed approach predicts lower initial fouling rates and outlet temperatures. However, over time, reduced fouling leads to higher predicted outlet temperatures compared to the constant-property approach. Overall, the variable-property model results in a 14.4% increase in estimated operational costs, indicating that constant-property models may underestimate true operating costs. Convergence is achieved in approximately three iterations on average, indicating a favorable tradeoff between improved model fidelity and computational effort.