An analytical investigation is presented for film condensation on a downward-facing horizontal doubly rippled surface. Small undulations having constant radius of curvature are combined with larger cylindrical grooves designed to aid condensate runoff. A direct expression for the condensate film thickness at the top of an undulation crest, as well as on a small-diameter horizontal cylinder, is derived. An upper-bound expression for the condensation rate on the rippled surface is then obtained which predicts that the condensation rate will be five times the rate attainable on a flat horizontal surface of the same projected area. This analytical expression is compared with experimental data.

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