Modification of molecular interactions at the interface crystal/heat transfer surface to minimize heat exchanger fouling

Recent studies with respect to mitigate heat exchanger fouling spend only minor attention to the possibility of modifying molecular interactions at the interface between heat transfer surface (substrate) and adjacent crystalline deposit (adhesive). New antifouling strategies deal with a defined modification of these interactions to reduce the corresponding adhesive strength favouring the removal process due to the wall shear stress. By means of drop shape analysis the interfacial free energy adhesive/substrate has been determined, On the basis of numerous fouling experiments the interfacial defect model has been identified to serve as a tool to estimate the optimal choice of surface material. For the description of the influence of interfacial energies between two materials on adhesion both van der Waals and hydrophobic interactions making allowance for the presence of polar media have been analyzed. The geometric and harmonic mean approach (van der Waals forces only) is chosen for the description of metallic surfaces. For polymeric materials where repulsive interactions have to be taken into account, the Lewis acid-base approach (also considering hydrophobic interactions) is favoured. (C) 2000 Editions scientifiques et medicales Elsevier SAS.