Preventing biofouling in heat exchangers: an experimental assessment of the effects of water velocity and inorganic particles on deposit detachment

Biofouling is a costly problem in heat exchangers. Biocides can be used to minimize the formation of biofilms, but they are not always effective and, moreover, they are generally deleterious to the environment. The use of proper liquid velocities or of water jets in the exchanger tubes is also a means to prevent the build up of fouling deposits or to clean the surface once they are formed. Often, biofilms incorporate inorganic particles which modify the physical properties of the deposit and, thus, affect the effectiveness of anti-fouling measures. This paper presents experimental data that show the effects of the water velocity and of the presence of clay particles on the accumulation of biofilms and on their mechanical resistance to detachment caused by hydrodynamic forces. The results indicate that the fraction of dry biomass (micro-organisms plus extracellular biopolymers) in biofilms increases with the liquid velocity and that the deposits formed under higher hydrodynamic forces are more resistant to detachment. The resistance to detachment is even greater when the biofilms incorporate small (20 micrometer) clay particles