LIQUID-SIDE FOULING OF HEAT-EXCHANGERS - AN INTEGRATED RESEARCH-AND-DEVELOPMENT APPROACH FOR CONVENTIONAL AND NOVEL DESIGNS

Particulate fouling of heal exchangers is a major fouling category wit h 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 pl ate heat exchangers (of two angles of corrugation, 30 and 60 degrees) and particles of mean size similar to 5 mu m. The flow passage geometr y and the fluid velocity have a strong effect on the fouling resistanc e R-f. These results show that fouling (under the test conditions) is adhesion controlled and that the maximum measured resistance RI is alm ost an order of magnitude smaller than the TEMA recommendations. Parti cle adhesion and removal from flat surfaces leads to improved understa nding of particulate fouling mechanisms and facilitates interpretation of the above data. Tangential hydrodynamic forces appear to be respon sible for particle detachment. For a specific particle size, a distrib ution of adhesive strengths is obtained (and not a single value), whic h is strongly influenced by pH and may be time-dependent for very smal l sizes. Various applications of the new results are outlined, includi ng the interpretation of the measured adhesive force distributions in terms of the well-known particle sticking probability. (C) European Co mmunities 1997. Published by Elsevier Science Ltd.