Conjugated shear stress and Prandtl number effects on reflux condensation heat transfer inside a vertical tube

Local reflux condensation heat transfer coefficients have been measured inside a vertical tube with water (2.6 < Pr-liq < 4.5), ethanol (12.4 < Pr-liq < 18.4) and isopropanol (23 < Pr-liq < 55) as the test fluids. A counter current flow situation is established with the liquid film (0.68 < Re-film < 2000) and the vapour (1000 < Re-vap < 16,500) flowing downward and upward, respectively. The heat transfer has found to be impeded by the shear stress only in cases of a very thin film, i.e. in the smooth laminar range, and it can well be correlated by a simple analytical model. In the larninar-wavy range including developing turbulence the heat transfer coefficients are found to increase with the shear stress, an effect which proved to be enhanced with rising Pr-liq numbers. This has been correlated with very good agreement. (c) 2005 Elsevier Ltd. All rights reserved.