Numerical study of the effect of fouling on local heat transfer conditions in a high-temperature fin-and-tube heat exchanger

The paper presents the numerical analysis of a flow around a bundle of externally finned elliptical tubes, used in cross-flow heat exchangers of a flue-gas/water type, arranged serially in two rows. An algorithm that enables determining the variations of flue-gas temperature and local heat transfer coefficient from gas to the tube wall was presented. On the basis of calculations, it was found that the intensity of heat transfer processes differs significantly in different rows. The intensity is higher in the first row and lower in the second one. This fact is confirmed by the values of the local heat transfer coefficients calculated for the case of heat transfer from gas to a wall determined at the same location. The coefficients, calculated for the first row of tubes, are higher compared with those of the second row. The appearance of fouling deposits on the tube's wall inner surface has an impact on the average temperature along the exhaust gas flow path. It also affects the local heat transfer coefficients from the gas-side to the tube walls. The presence of fouling increases the flue-gas temperature, while its influence on the heat transfer coefficient is slight.