Enhancement of in-tube condensation by doubly augmented tubes

Heat transfer and pressure drop data were taken during condensation of R-113 inside the inner tubes of nine different tube-in-tube condensers. The condensers consisted of three sets with three condensers in each set. In one condenser the inner tube had internal fins on the inside and a smooth surface on the outside. In the second condenser, the inner tube had knurls on the outside surface and a smooth surface on the inside. In the third condenser, the inner tube had the same fins of the first condenser on the inside and the same knurls of the second condenser on the outside. The three sets of condensers differed in the outside diameter of the inner tube and the fin geometric parameters.;On the basis of the results, it was possible to identify the favorable conditions under which it is desirable to use single augmentation, inside or outside, versus double augmentation of the inner tube in condenser design.;A new correlation has been proposed to predict the overall and sectional heat transfer coefficients for condensation inside smooth and internally finned tubes. This correlation predicted well both the overall and the sectional heat transfer coefficients of the present study as well as the data of other investigators.;An analytical model was developed to predict the condensation heat transfer inside longitudinally finned tubes. The model predicted well the experimental data for high surface tension fluids. A parametric study was performed to determine the effects of increasing the number of fins, the width and the height of the fins as well as the finned tube material on the condensation heat transfer coefficient. (Abstract shortened with permission of author.);Over the mass flux range of R-113 tested, the enhancement in the condensation heat transfer coefficient due to internal fins, was as high as 70%. The inside heat transfer coefficient depended on the rate of cooling and the inlet pressure of R-113. The increase in the outside heat transfer coefficient depended on the height of the knurls. Also, the pressure drop during condensation inside internally finned tubes was 200% higher than that for condensation inside smooth tubes.