Preparation Of Electroless Plating On Heat Transfer Surface With Low Surface Free Energy And Study On Their Anti-fouling Property

Fouling is a widespread problem in the design and operation of heat exchanger. Heat transfer surface with lower surface free energy may greatly inhibit fouling.Electroless Ni-P and Ni-W-P coatings were prepared on copper substrates in this paper. X-ray diffraction results showed both the coatings are amorphous. The values of surface free energy for copper sample, Ni-P coating sample, Ni-W-P coating sample were 52.4mN/m, 35.5mN/m,23.4 mN/m respectively. The surface free energy for electroless plating surface dropped obviously.Fouling adhesion test and pool boiling anti-fouling experiments were carried out in calcium sulphate solution. Compared with the copper surface, the scale adhesion speed on the electroless coatings with lower surface free energy were reduced by 46 percent for Ni-P coating and 54 percent for Ni-W-P coating respectively. Asymptotic value of fouling resistance for Ni-P coating surface and Ni-W-P coating surface were reduced sharply. The bubble behavior on heat transfer surface was captured by a high speed camera. Depending on the heat transfer mechanism, two different types of deposits were observed on the heat transfer surface. A needle-like structure was the characteristic of scale formed on a plain copper surface, while a granular structure corresponded to the scale formed on the electroless plating surface.