Condensation of Ammonia on the Outside of Smooth and Fluted Tubes at Various Tube Positions

摘要

Experiments were conducted to determine the heat transfer performance obtained for ammonia condensing on the outside of six tubes of four distinct types: (1) a smooth tube, (2) two single-fluted tubes, (3) two double-fluted tubes, and (4) an external-finned tube. All tubes tested were 2.54 cm (1.0 in.) in nominal diameter and 1.22 m (4.9 ft) in length. Condensing heat transfer coefficients are reported as composite coefficients (including the resistances of both condensing film and tube wall) for (1) a smooth tube condensing in the horizontal position and at various tilt angles, (2) two single-fluted tubes condensing in the vertical position, and (3) a finned tube condensing in the horizontal position. Overall heat transfer data are given for both double-fluted tubes. Data show that for a given heat flux, a horizontal smooth tube can increase composite coefficients by up to 2.1 times the vertical smooth-tube values. For a single-fluted tube, composite coefficients increased by up to 5.2 times the corresponding vertical smooth-tube values. However, on a horizontal position, the finned tube gave the lowest performance of any other tube tested in this study. Finally, for one double-fluted tube, inside fluting increased the overall heat transfer coefficient by as much as 25% more than that for a tube with identical external flutes and a smooth inside surface. (ERA citation 07:046327)