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The assessment of surface layers texture of the fouling gathered on the heat transfer surfaces within regenerative feedwater heat exchangers

Hajduk T.

Journal of KONES

2017

Vol. 24, No. 4

55--60

The fouling presence on the heat transfer surfaces, both on the waterside and the steam side of the steam power plants heat recovery exchangers usually leads to the loss of their heat transfer capacities. This loss appears owing to the high value of heat resistance of fouling. Furthermore, these deposits are most often formed with irregularities in the surface layers. These textures are usually characterized by a varied, often stochastic and difficult to define, geometric structures. The most common measure of their inequalities is the roughness parameter describing the surface geometry. The fouling surface layer texture can, on one hand, cause enhancement of the heat transfer process, but on the other hand, it may contribute to an additional increase in thermal degradation of the heat exchanger. Many experimental studies have shown that the greater the unevenness of the heat transfer surface on the waterside of a given heat transfer device, the smaller increase in the thermal resistance of the impurities over time, thereby increasing the amount of heat transferred. It should be emphasized, however, that the rise in roughness results in an increase in the heat transfer coefficient, while simultaneously intensifying the flow resistance of the working medium. Taking into account the heat transfer surface by steam side, the increase in the roughness promotes the formation of a thicker condensate layer, thus impairing the condensate drainage organization. It can be explained by the fact that deposits settle in a sort of quasi-rib effect, although with undefined ribbed grid, it may lead to the overflow of inter-finned passages. The article shows the previously mentioned phenomena and also presents the descriptive quantities for the fouling surface layer texture, based on the results of the author’s own experimental research.