An experimental study of dropwise condensation on horizontal condenser tubes

Abstract

Three types of drop promoting coatings were applied to the outside of 15.9 mm (5/8 in) outside-diameter condenser tubes to determine their effect on heat transfer performance. The coatings included a new fluoroepoxy, a commercial series of fluorocarbon coatings, and sputtered TFE. Coating thickness varied from 0.0 2 to 12.7 microns. Steam at about 21 KPa (3 psia) was condensed on the outside surface of each coated tube, horizontally mounted in the center of a dummy tube bundle. Each test tube was cooled on the inside by water at velocities of 0.80 to 7.60 m/sec (3 to 25 ft/sec). The overall heat transfer coefficient was determined directly from experimental data. The inside and outside, heat transfer coefficients were determined by using the Wilson Plot technique. Of the commercial fluorocarbon coatings, the "Nedox" coating on a copper-nickel tube enhanced the outside heat transfer coefficient by 53% and improved the corrected overall heat transfer coefficient by 27%. Of the sputtered TFE coated tubes, the 0.08-micron thick coating on a copper-nickel tube enhanced the outside heat transfer coefficient by 45% and improved the corrected overall heat transfer coefficient by 21%. Evidence of the effect of the thermal conductivity of the condensing surface substrate, and evidence of an optimum coating thickness were found.