Forced convection film condensation on a horizontal tube with and without non-condensing gases

Abstract

Accurate and repeatable heat-transfer data have been obtained for filmwise condensation from pure vapours (steam and R113) and vapour-gas mixtures (steam-air, steam-hydrogen, R113-air and R113-hydrogen) flowing vertically downwards over a single horizontal tube. Surface temperatures were obtained from thermocouples embedded in the tube wall. The heat flux was obtained from coolant measurements which were checked against values obtained by collecting the condensate. The vapour mass flow rate was obtained from the electrical power input to the boiler. The approximate ranges of the variables used were : pressure (4–124 kPa), heat flux (12–455 k W m −2), vapour velocity (0.3–26 m s −1), gas mass fraction (0.02–32%). For pure vapours at low to moderate velocities, the mean vapour-side heat-transfer coefficients were in satisfactory agreement with earlier measurements and with theory. At the higher velocities obtained with steam, the coefficients are somewhat smaller than those predicted by theory incorporating the assumption of uniform wall temperature. For all four vapour-gas mixtures a simple boundary-layer theory-based approximate equation gives results in excellent agreement with the measured mass-transfer resistance. The present results for steam-air mixtures are in good agreement with earlier data.