RECENT EXPERIMENTS FOR LAMINAR AND TURBULENT FILM HEAT-TRANSFER IN VERTICAL TUBES

This study reviews experimental local heat-transfer data for laminar a nd turbulent film heat transfer for downward condensing films, under t he influence of interfacial-waviness and shear-stress effects. Local l aminar-wavy-film heat transfer and transition to turbulence are signif icantly influenced by local wave characteristics, which depend not onl y on the film developing length, but also on the film-formation method . The results demonstrate that the dimensionless film thickness, incor porating shear stress, provides a more appropriate length scale to est imate laminar-wavy-film heat transfer, as well as transition to turbul ence. For turbulent films, a phenomenologically-based local heat-trans fer correlation has been proposed, treating the near-wall and near-int erface regions in series, to derive a 'two-layer resistance model', ba sed on the investigation of turbulence structure across sheared gas-li quid interfaces. (C) 1997 Elsevier Science S.A.