Condensation heat transfer on horizontal tubes with ribs of constant curvature

New heat transfer data are obtained for film condensation of pure, saturated, practically nonflowing vapor of refrigerants 11 and 12 on single horizontal tubes with transverse annular fins of constant curvature. The fin and the trough are circumscribed by semicircles of the same radius. The properties of the liquid, the film Reynolds number and the surface curvature radii were varied within wide ranges. There was a three-fold and more intensification of the surface-mean heat transfer coefficient as compared to a horizontal smooth tube of the same diameter at the same difference between the saturated steam and the wall temperatures.