Cooling-Water Fouling in Heat Exchangers

Abstract The formation of deposits on heat transfer surfaces is an important problem during convective and nucleate boiling heat transfer to water. Possible deposition mechanisms are crystallization from dissolved salts, particulate fouling from suspended material, and microbial and macrobial growth. To account for unreliable design procedures and operational problems, heat exchangers are typically overdesigned by 70 to 80%, of which 30 to 50% is attributed to fouling. Further refinement of heat-exchanger design procedures will be possible only in conjunction with more sophisticated methods to include the effects of fouling. While the installation of excess heat transfer surface may extend the operation time of heat exchangers, it provides no remedy against the deposition of dirt. Heat-exchanger fouling can be reduced by proper heat-exchanger design, by appropriate selection of heat-exchanger type, and by mechanical and/or chemical mitigation methods. All methods require an understanding of the mechanisms of dirt deposition and of the influence of operating parameters on the deposition rate. It is still not possible to predict a fouling resistance versus time relationship for a given water composition. However, it is possible to estimate the effects of flow velocity, foulant concentration and surface temperature on the deposition rate and to use this knowledge to optimize the design of heat exchangers. In this paper, results of numerous experimental and theoretical investigations during the past 20 years are presented. The state of the art in fouling mitigation is reviewed, and special attention is drawn to areas where future academic and industrial research is required.