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• The paper describes the mechanisms in the development of biofouling layers (initial surface conditioning, microbial transport and attachment, mass transfer of nutrients to the biofilm surface and through the microbial layer, cell metabolism, and detachment of cells and of larger parts of the biofilm) and summarizes the effects of several factors on the buildup and stability of biofilms (nutrient availability, fluid velocity and turbulence, temperature, surface condition, and nonliving particles). Mass transfer within biofilms is treated in more detail. A biofouling model applied to the development of biofilms in heat exchangers is presented. Finally, references are made to biofouling control methods (biocide and the proper design and operation of heat exchangers) and to future research needs in this area.

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Studies of the deposition of wax from wax/kerosene mixtures onto cooled simulated heat transfer tubes has demonstrated that, following an initial deposition taking a relatively short period of time, the heat transfer resistance fluctuates with time. Theoretical estimates of temperature distribution in the experimental flowing wax/kerosene system suggest that the cloud point temperature of the mixture falls within the laminar boundary layer. Since the cloud point is considered the temperature at which particles of wax appear, the conditions within the boundary layer will influence deposition. Increased flowrate and temperature decrease the number of particles able to deposit while the number is increased by greater wax concentration in the bulk solution.

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