Laminar film condensation from a downward-flowing steam-air mixture onto a horizontal circular tube

Abstract

This investigation develops a numerical model of laminar film condensation from a downward-flowing steam-air mixture onto a horizontal circular tube. The significant non-similarity of the coupled two-phase flow laminar film condensation is such that the boundary layer governing conservations of momentum, species and energy in the mixture and liquid phases are solved by finite-volume methods. Numerical analysis of both the local condensate film thickness and heat transfer characteristics elucidated the simultaneous effects of inlet-to-wall temperature difference and inlet air concentration, the Reynolds number of the mixture, and the dimensionless parameter, F, by adopting a unified condensate parameter. The local Nusselt number and liquid film thickness increase as both the non-condensable air mass fraction and the tube temperature decreases. The numerical results on local heat transfer and film thickness for low/no non-condensable gas (air) agree closely with the theoretical results of Yang [Sheng-An Yang, Superheated laminar film condensation on a nonisothermal horizontal tube, J. Thermophys. Heat Transfer 11(4) (1997) 526–532], Fuji [T. Fujii, H. Uehare, C. Kurata, Laminar filmwise condensation of flowing vapor on a horizontal tube, Int. J. Heat Mass Transfer 15 (1972) 235–246] and Homescu and Panday [D. Homescu, P.K. Panday, Forced convection condensation on a horizontal tube: Influence of turbulence in the vapor and liquid phases, J. Heat Transfer Trans. ASME 121(4) (1999) 874–885]. Meanwhile, the comparison of average heat transfer coefficient with the experimental data from Rose and Lee [W.C. Lee, J.W. Rose, Forced convection film condensation on a horizontal tube with and without non-condensing gases, Int. J. Heat Mass Transfer 27(4) (1984) 519–528] demonstrates reasonably good agreement with the parameter F ( = gdh fg μ L / ⌊ k L U 0 2 ( T 0 - T W ) ⌋ , the ratio of gravity to mixture velocity) and G (= ( T 0 - T W ) ( k L / h fg μ L ) ( ρ L μ L / ρ m μ m ) , the suction effect).