Liquid-side fouling of heat exchangers. An integrated R & D approach for conventional and novel designs

摘要

Particulate fouling of heat exchangers is a major fouling category with very significant technical and economic implications. It is studied here as part of a study aimed at improving design standards for novel and conventional heat exchangers. New fouling data are reported for plate heat exchangers (of two angles of corrugation, 30 and 60°) and particles of mean size 5 μm. The flow passage geometry and the fluid velocity have a strong effect on the fouling resistance Rf. These results show that fouling (under the test conditions) is adhesion controlled and that the maximum measured resistance Rf is almost an order of magnitude smaller than the TEMA recommendations. Particle adhesion and removal from flat surfaces leads to improved understanding of particulate fouling mechanisms and facilitates interpretation of the above data. Tangential hydrodynamic forces appear to be responsible for particle detachment. For a specific particle size, a distribution of adhesive strengths is obtained (and not a single value), which is strongly influenced by pH and may be time-dependent for very small sizes. Various applications of the new results are outlined, including the interpretation of the measured adhesive force distributions in terms of the well-known particle sticking probability.