Study on condensation heat transfer process of wet flue gas containing non-condensable gases in a horizontal tube

To effectively recover the waste heat from the wet flue gas of gas-fired boilers, a comprehensive understanding of its heat transfer and hydrodynamic properties is essential. This study investigates the condensation heat exchange behaviors of wet flue gas within a horizontal tube using numerical simulation. A computational flow dynamic model is established and validated against experimental data. The influence of key parameters, including the Reynolds number, humidity ratio, wall subcooling, gas superheat, and length-diameter ratio on the in-tube heat transfer and flow is analyzed. The results indicate that an increasing the humidity ratio significantly enhances condensation heat transfer. When the humidity ratio increases from 0.05 to 0.2 kg∙kg _a ⁻¹ , the heat transfer factor increases by an average of 5.94%. While increase in Reynolds number and gas superheat promote condensation heat transfer, they also lead to higher flow losses, with the effect of gas superheat being relatively minor. In contrast, an increase in wall subcooling elevates thermal resistance, thereby inhibiting heat transfer. Tube geometry has a pronounced effect on the condensation heat transfer processes. When the length-diameter ratio increases from 30 to 48, the heat transfer factor and friction factor increase by an average of 64.09% and 467%, respectively.