A numerical study on convective condensation of flue gas in tubular heat exchangers

The accurate calculation of heat transfer process in the condensing heat exchanger plays a crucial role in the waste heat recovery. In this study, the convective-condensation heat transfer process in a condensing heat exchanger with five small heat exchangers is analyzed through utilizing a new numerical simulation model. The method that loads the latent heat of condensation as the heat generation rate is adopted. Under the two working conditions in this study, the deviations of outlet temperature between numerical and experimental results are 1.3 and 2.2 K, respectively, while the deviations of total condensate water flow are 8.5 % and 5.5 %, respectively. Under the drier working condition, the average temperature reduction (5.8 K) per row of tubes in the first small heat exchanger where no condensation occurs is higher than that (2.6 K) in the third small heat exchanger where the water vapor starts to condense. It indicates that the release of latent heat of condensation slows down the cooling rate of the flue gas. In the small heat exchanger where the water vapor starts to condense, the amount of condensate water on the wall of each row of tubes increases first and then decreases slowly along the flow direction of the flue gas.