Augmentation of Horizontal In-Tube Condensation by Means of Twisted-Tape Inserts and Internally Finned Tubes

Abstract

Low pressure steam was condensed inside horizontal tubes of different internal geometries to investigate passive heat transfer augmentation techniques. A smooth tube, the smooth tube having two twisted-tape inserts, and four internally finned tubes were tested. The twisted-tape inserts were found to increase average heat transfer coefficients by as much as 30 percent above smooth tube values on a nominal area basis. The best performing internally finned tube increased average heat transfer coefficients by 150 percent above the nominal smooth tube values. Techniques were developed to correlate the improved heat transfer performance of the two twisted-tape inserts and the four internally finned tubes. The equations developed provide a reasonably accurate description of both the sectional and the average heat transfer coefficients. The finned tube correlation was also reasonably successful in predicting the data from the one other investigation of this augmentation technique for which detailed data were available.