H₂SO₄-H₂O binary condensation on H-type finned heat transfer surfaces in flue gas

SO₃ in coal-fired flue gas converts to H₂SO₄ vapor, which co-condenses with H₂O on heat transfer surfaces and poses corrosion risks. Under the quasi-phase-equilibrium and quasi-steady-state assumptions, an H₂SO₄-H₂O binary condensation model and computational method for heat transfer surfaces were developed. Numerical simulations were performed to investigate the condensation characteristics on H-type finned tubes and the effects of flue gas parameters. The results show that sulfuric acid condensation is highly non-uniform. The local condensation flux decreases in the following order: the windward fin edge surface, the windward bare tube surface, the outer fin edge surface, and the windward U-shaped region of the main fin surface. In contrast, almost no condensation occurs on the leeward bare tube surface, the leeward fin edge surface, or the tube-shielded region of the main fin surface. This distribution is determined by geometry-induced flow structures and non-uniform wall temperature. The spatial non-uniformity of condensation flux is governed mainly by flue-gas velocity. The regions with medium and high condensation flux expand with higher velocity. Other parameters mainly affect the area-averaged condensation flux. Increasing velocity or H₂SO₄ concentration approximately linearly increases the condensation rates of both H₂SO₄ and H₂O, whereas increasing H₂O concentration and decreasing temperature mainly enhance H₂O condensation. Liquid-film sulfuric acid concentration increases with local temperature and decreases with gas-phase H₂O concentration. Based on the thermodynamic vapor–liquid equilibrium condition under flue gas conditions, a rapid calculation method for liquid-film sulfuric acid concentration was established using local temperature and gas-phase H₂O concentration as inputs, avoiding complex iterations.