Abstract:

Objective In order to address the critical challenges of fouling, corrosion, and performance degradation in heat exchangers used for waste heat recovery from stenter exhaust in the textile printing and dyeing industry, this study aims to develop a comprehensive and practical design solution. The primary objectives are to identify an optimal material with balanced thermal conductivity, corrosion resistance, and cost, to optimize the core structural parameters of a plate heat exchanger for enhanced comprehensive performance, to establish an accurate fouling prediction model tailored to the oily-fibrous exhaust conditions, and to validate the overall system performance through long-term laboratory and field engineering tests.

Method Five candidate materials (carbon steel, 304 stainless steel, 316 stainless steel, 316L stainless steel, and TA1 titanium alloy) were evaluated. Thermal conductivity was measured using the steady-state plate method from 20℃ to 300℃, and corrosion resistance was assessed by potentiodynamic polarization tests in a simulated acidic exhaust environment (H₂SO₄ (pH=4), 80℃). A multi-objective optimization framework was developed by coupling computational fluid dynamics (CFD) simulations with the NSGA-II algorithm to optimize the channel spacing and fin spacing ratio. The objectives were to maximize heat transfer rate, while minimizing pressure drop and material volume. The technique for order preference by similarity to ideal solution (TOPSIS) was subsequently employed to select the optimal solution from the Pareto front. A novel asymptotic fouling prediction model was established by introducing a wall shear stress modification to the Kern-Seaton theory, coupling the deposition and shear-driven removal rates. This model was validated through a 3 000 h fouling experiment. Finally, the optimized heat exchanger system was installed and tested on an industrial stenter line for three months to evaluate its real-world thermal performance, stability, and economic benefits.

Results The material tests showed that while carbon steel had the highest thermal conductivity (50.2 W/(m·K)) at room temperature, its conductivity decreased at elevated temperatures, and its corrosion rate (0.144 mm/a) was unacceptably high. Titanium alloy exhibited the best corrosion resistance (0.000 6 mm/a) and stable thermal conductivity but at a prohibitive cost (5-8 times that of 304 stainless steel). 304 stainless steel demonstrated an optimal balance, with a thermal conductivity of 16.3 W/(m·K) at 100 ℃, a value that increased with temperature, and a corrosion rate below 0.01 mm/a. The CFD and NSGA-II multi-objective optimization revealed the inherent trade-offs among heat transfer rate (Q), pressure drop (ΔP), and material volume (V_m), with the conflicting nature of these objectives evident from the resulting Pareto front. Based on the material selection of 304 stainless steel, the TOPSIS analysis identified the optimal structural parameters as a channel spacing (d) of 2.0 mm and a fin spacing ratio (α) of 0.5. Under this material-specific context, this configuration yielded a TOPSIS closeness coefficient of 0.824, significantly outperforming other candidates. Compared to the initial design, this optimized structure achieved an 18.7% increase in heat transfer rate, a 22.3% reduction in pressure drop, and a 15% decrease in material volume. The proposed wall shear stress-modified asymptotic fouling model accurately captured the typical fouling growth trend. The predicted fouling resistance values showed excellent agreement with the 3 000 h experimental data, with a mean relative error of only 3.94%. Sensitivity analysis confirmed that the model could quantitatively describe the influences of the removal rate constant and wall shear stress on fouling dynamics. In the field engineering trial, the system operated stably over three months without significant fouling or corrosion. The exhaust gas was cooled by an average of 56 ℃ (from 182 ℃ to 126 ℃), while fresh air was preheated by 158 ℃. The system achieved a heat recovery efficiency of 25.2% and an exergy efficiency of 18.7%. The annual economic and environmental benefits are substantial, with projected savings of 73 800 m³ (Standard m³) of natural gas and a reduction of 199 tons of CO₂ emissions per year (based on 6 000 operating hours).

Conclusion This research successfully delivers a validated, integrated solution for waste heat recovery from stenter exhaust. 304 stainless steel is confirmed as the most cost-effective and durable material choice. The identified structural parameters (d=2.0 mm, α=0.5) represent an optimal engineering compromise, significantly enhancing thermal-hydraulic performance while reducing material costs. The novel fouling model provides a reliable tool for predicting maintenance needs and optimizing cleaning schedules. The successful industrial application demonstrates that the designed system offers high efficiency, robust long-term stability, and significant energy-saving and emission-reduction potential, providing a practical and scientifically-grounded technology pathway for sustainable development in the textile industry.

Key words: plate-fin heat exchanger, stenter, waste heat recovery, 304 stainless steel, structural optimization, fouling model