Applications of surface modification techniques in enhancement of phase change heat transfer

When saturated vapor passes over a colder substrate, liquid drops nucleate and grow by coalescence with surrounding drops. Typically speaking, nucleation and growth rates of water droplets are faster on a hydrophilic surface than on a hydrophobic surface. However, heat transfer efficiency degrades once surface becomes filmwise condensation. In this paper, vapor condensing on a gradient surface to prevent filmwise condensation is studied. New gradient surfaces are fabricated. It is demonstrated that 10% increase of condensation heat flux can be achieved on a silicon wafer with C = 1 mm gradient surface. The main mechanism for heat transfer enhancement is found to be that drops condensing on C = 1 mm gradient surface begin to move at a much smaller size compared with those on silicon wafer without modification.