A numerical model for convective-condensation heat transfer of flue gas and its application on fin efficiency calculation

Condensing heat exchangers have been widely employed because they can recover heat and water from the exhaust flue gas efficiently. In this study, the effects of heat transfer condition, water vapor volume fraction and fin geometry parameter on the convective-condensation heat transfer process of the annular finned tube are evaluated through applying a new numerical model for simulation. The outer wall temperature of the base tube promotes the improvement of fin efficiency. But due to the increasing condensation of water vapor, the driving force of the fin temperature rise reduces. Thus, the sensible heat transfer efficiency of the fin drops. Under the working conditions in this study, when the outer wall temperature of the base tube ascends from 320.8 to 330.3 K, the sensible heat transfer efficiency of the fin increases by 9.6%. The effects of water vapor volume fraction on the sensible and latent heat transfer efficiencies of fin show the opposite trends. As the water vapor volume fraction increases from 0.05 to 0.20, the latent heat transfer efficiency of the fin rises from 0 to 0.102, while the sensible heat transfer efficiency reduces from 0.441 to 0.396. Among the fin geometrical parameters, the fin height has the greatest influence on the fin efficiency. When the fin height increases from 7 to 16 mm, the fin sensible and latent transfer efficiencies drop by 33.8 and 76.7%, respectively.