Forced Convection Condensation on a Horizontal Tube—Experiments With Vertical Downflow of Steam

The paper reports an experimental investigation into the condensation of steam flowing vertically downward over a single horizontal tube. A limited number of experiments with steam-nitrogen mixtures are also reported. For the case of “pure” steam, data have been obtained at near atmospheric pressure for vapor approach velocities in the range 5 to 81 m/s and with superheats in the range 2 to 40 K. The results are compared with theory and earlier experimental data for steam and other fluids. The vapor-side heat transfer coefficients were found to increase with velocity. For vapor velocities in excess of 30 m/s, the rate of increase of the vapor-side coefficient was greater than predicted by laminar condensate flow theory. This behavior has also been observed by earlier workers for refrigerant-113 and ethylene glycol and may indicate onset of turbulence in the condensate film. Superheat had insignificant effect on the heat transfer coefficient for the condensate film. The results for steam-nitrogen mixtures were generally in good agreement with existing equations for the “gas-layer” resistance.