Molecular modeling is a novel approach in the field of fouling research. A method was used to calculate fouling reactions and molecular level interactions between heat transfer surface and flowing fluid. The focus was on the comparison of the reaction mechanisms of Ti( OH)(4) and Si( OH) 4 on a rutile ( 101) surface. The calculated reaction energies indicate strong chemical bonding via condensation reaction of titanium( IV) hydroxyls and weak hydrogen bonding of silanols without a chemical reaction on the surface. The chemical composition and structural properties of fouling layers from a real process were characterized. On the heat transfer surfaces, deposits containing titanium had dense structure and were very difficult to clean while silica was porous and amorphous, causing less severe problems in cleaning. Molecular modeling was found to be an effective tool in predicting reaction mechanisms and interaction forces between the fouling fluid and heat transfer surface at a molecular level.