Condensation of vapor/noncondensable gas mixtures in horizontal tubes is not well understood because condensate stratification and the multidimensional nature add to the complexity of the phenomena. The heat transfer and fluid flow phenomena in a horizontal condenser tube were experimentally studied, along with the heat transfer reduction effect of a noncondensable gas. The temperature gradient across the condenser tube wall was measured locally to investigate the asymmetrical beat transfer characteristics around the condenser tube periphery. The condensation heat transfer coefficients on the tube top were much greater than the values at the bottom and the noncondensable gas significantly reduced the heat transfer rate. (c) 2006 Elsevier Ltd. All rights reserved.