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 < Prliq < 4.5), ethanol (12.4 < Prliq < 18.4) and isopropanol (23 < Prliq < 55) as the test fluids. A counter current flow situation is established with the liquid film (0.68 < Refilm < 2000) and the vapour (1000 < Revap < 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 laminar-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 Prliq numbers. This has been correlated with very good agreement.