In order to improve the boiler efficiency, latent heat recovery from an exhaust flue gas is a very important concept. Condensation heat transfer on horizontal stainless steel tubes was investigated experimentally using an actual flue gas from a natural gas boiler. The experiment was conducted at different air ratios and steam mass concentrations of the flue gas, and in a wide range of tube wall temperature. The condensation pattern was similar to the dropwise condensation near the dew point. As the wall temperature was decreased, the wall region covered with a thin liquid film increased. The heat and mass transfer behavior were well predicted with the simple analogy correlation in the high wall temperature region. But in the low wall temperature region, the total heat transfer rate was higher than that predicted by the simple analogy correlation. At a high steam mass concentration artificially generated with steam injection, the total heat transfer rate was higher than that predicted by the simple analogy correlation. The analogy correlation using the modified Sherwood number taking account of the mass absorption effect was proposed. The modified correlation gave a good prediction of the heat flux at the high steam mass concentration.
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