The present work is an extension of the authors’ previous research, where changes in the dynamic behavior of heat exchangers induced by fouling build-up were studied. In the present work, the authors used the previously elaborated and validated mathematical model of transient heat exchange with the influence of thermal resistance of fouling taken into account. The behavior of specific Heat Exchanger Networks (HENs) coupled with a Crude Distillation Unit together with their control loops is simulated using Simulink/MATLAB and the influence of fouling build-up on specific indices of quality of operation is investigated. According to the presented results, the higher the number of heat exchangers in the PID control loop and the greater the number of heat exchangers interacting in the network, the smaller the influence of fouling on the control quality indices, and in the extreme case, this influence may be negligible. This might be caused by the compensation of the negative effects of fouling build-up when the heat exchangers are interacting in the HEN. Nevertheless, potential adverse effects of fouling on HEN operation can be prevented by periodic adjustments of the optimal values of PID gains.

The article presents mathematical modeling of the impact of fouling on heat transfer in shell-and-tube exchangers using analytical methods and an artificial neural network (ANN). The article shows the limitations of using ANN diagnosis of fouling on the behavior of industrial shell and tube heat exchangers. The analytical heat exchanger model is a reference model used for the comparative assessment of the ANN model. The analytical model is treated by the authors as a model providing accurate numerical calculations, aiming at diagnosis of fouling on the heat exchanger behavior during the operation of an industrial installation. The proposed model of the exchanger is characterized by sufficient accuracy from the point of view of the exchanger diagnosis under fouling, and the calculation error does not exceed 1%. The article compares the numerical results of the heat exchanger duty calculated by the use of the proposed analytical method with the heat exchanger duty obtained by ANN. Comparing the analytical model and the ANN model, the coefficient of determination R² is about 7%, which indicates a significant discrepancy in results between the analytical model and the ANN model. The presented article states that the ANN fouling model operates as an extrapolator. Thus, the application of ANN is limited to the case of small variations in ​​measured inlet process parameters. Meanwhile, the analytical model is more universal because it is less sensitive to the variations in ​​measured process parameters.

Fouling is one of the most troublesome constraints in heat exchanger operation; it reduces heat duty and, as deposits grow, changes the exchanger dynamics, causing PID temperature controllers tuned for clean conditions to lose performance. This study examines whether the minimum temperature difference (ΔT_min) chosen at the design stage can limit this effect. A dynamic model of a shell-and-tube crude oil preheater (220 t/h) was implemented in MATLAB/Simulink R2025b, and closed-loop responses, control-quality indices and stability margins were compared for ΔT_min = 50 K and 10 K for clean and fouled (R_f = 0.00138 m²K/W) exchangers with Ziegler–Nichols PID settings. At ΔT_min = 50 K, fouling increased the set-point ISE by 75%, the settling time from 92 s to 231 s, and the overshoot from 57% to 65%, while reducing the phase margin from 25.7° to 15.8°; retuning was necessary and restored the phase margin to 27.8°. At ΔT_min = 10 K, the corresponding changes were much smaller (ISE increased by 27%, settling time increased from 107 s to 159 s, overshoot increased from 40% to 44%, and phase margin decreased by only 3.4°), so the original settings could be retained. Disturbance-rejection ISE grew 2.2-fold at 50 K versus 1.6-fold at 10 K. A lower ΔT_min is therefore a practical design guideline for reducing fouling-induced controller retuning.

Additive manufacturing enables the fabrication of compact polymer heat exchangers, although their performance is constrained by low wall thermal conductivity and manufacturing-induced surface characteristics. This study experimentally compares two geometrically identical shell-and-tube heat exchangers fabricated by fused filament fabrication from pure PLA and PLA containing 25 vol.% copper particles (PLA + Cu). The combined influence of effective thermal conductivity, surface topography, and hydraulic resistance was investigated under water–water counterflow conditions. The measured thermal conductivity increased from 0.243 ± 0.018 W·m⁻¹·K⁻¹ for PLA to 0.422 ± 0.008 W·m⁻¹·K⁻¹ for PLA + Cu, corresponding to an approximately 74% improvement. The composite also exhibited higher surface roughness (Sa = 17.0 μm versus 13.5 μm) and a developed interfacial area ratio (Sdr = 43.5% versus 19.7%). The PLA + Cu exchanger achieved a maximum heat duty of approximately 289 W and an overall heat-transfer coefficient of 151 W·m⁻²·K⁻¹, compared with approximately 208 W and 93 W·m⁻²·K⁻¹ for PLA. However, the thermal enhancement was accompanied by increased hydraulic losses, with tube-side pressure gradients reaching approximately 5.7 kPa·m⁻¹. Thermal-resistance decomposition identified shell-side convection as the principal limitation of the investigated configuration. Effective convective coefficients estimated using the thermal-resistance model showed approximate consistency with Chilton–Colburn analogy estimates, with mean absolute percentage errors of 7–13%. The findings demonstrate that improved material conductivity does not necessarily translate into proportional overall performance gains and highlight the need to optimize shell-side convection and hydraulic resistance alongside material selection.