Experimental and theoretical study of steam condensation in actual flue gas using a novel heat exchanger for waste heat and water recovery

Recovering latent heat and water from boiler flue gas is a critical pathway toward improving energy efficiency and reducing carbon emissions. However, condensation-based recovery is severely constrained by acidic corrosion and diffusion resistance induced by non-condensable gases. In this study, a corrosion-resistant Ni–Cu–P coated finned-tube heat exchanger was developed for flue-gas condensation, together with an integrated diffusion-based heat and mass transfer model for predicting the condensation HTC. The model accounts for variations in mixture density and molecular weight across the diffusion layer and incorporates the effects of suction and fog formation on heat and mass transfer. Experiments and three-dimensional simulations were conducted to characterize condensation heat transfer, condensate generation, and thermo-environmental performance. Results indicate that strategically distributed perforations on fins promote pressure equalization, liquid-film disruption, and condensate drainage, thereby reducing thermal resistance. The total, latent, and sensible heat transfer coefficients decrease with increasing logarithmic mean temperature difference and coolant inlet temperature but increase with flue-gas velocity. Increasing flue-gas mass flux enhances latent heat recovery while lowering condensation efficiency due to shortened residence time. Condensate flow rate and condensation efficiency exhibit a non-monotonic rise–decline–rebound behavior with decreasing exhaust temperature. Lower exhaust temperatures substantially improve recovered heat flux and CO 2 -equivalent mitigation, with latent heat contribution increasing from 43.7% to 47.0% as temperature decreases from 57 °C to 28 °C. This study provides mechanistic insight into diffusion-controlled flue-gas condensation and offers guidance for high-efficiency, low-carbon boiler waste-heat recovery systems.