Experimental and numerical studies on actual flue gas condensation heat transfer in a left-right symmetric internally finned tube

To improve the thermal efficiency of gas fired equipment, latent heat recovery from the flue gas is a very important concept. Based on the analysis of heat transfer enhancement mechanism in an internally finned tube, in this paper, a new type left-right symmetric internally finned tube is proposed. The heat transfer characteristics of the new type left-right symmetric internally finned tube, the centrosymmetric finned tube and the smooth tube is numerically and experimentally investigated. The numerical simulation results indicate that the left-right symmetric internally finned tube has a promising potential for enhancing the convection heat transfer, in particular, its heat transfer coefficient is 4-8 times higher than that of the reference smooth tube and 1.3-1.8 times higher than that of the centrosymmetric finned tube. The experimental results show that the excess air coefficient, the cooling water flow rate, the water inlet temperature, and the Re number have prominent effects on the convection-condensation heat transfer. The left-right symmetric internally finned tube can effectively decrease the radial temperature gradient, reduce the thickness of the non-condensable gas layer and significantly strengthen the water vapor condensation. The convection-condensation heat transfer coefficient of 10 fins left-right symmetric internally finned tube is about 4.1 times higher than that of the forced convection without condensation. A dimensionless number Tv is derived, which takes into account the effects of the water vapor saturation temperature, the average flue gas temperature, the average internal wall temperature and the inlet water temperature. They are represented in an empirical formula for the condensation heat transfer process.