Effect of Vapor Velocity on Laminar and Turbulent-Film Condensation

Abstract

The liquid condensate layer (film) on vertical plates or tubes under the influence of the gravity force flows downward in essentially laminar flow over the upper part of the surface but may change to turbulent flow over the lower part if the condensation rate is sufficiently high. Colburn (1) reviewed the results of Kirkbride and developed a correlation equation based on a very elementary description of the condensate layer which was considered to be composed of a laminar sublayer and a turbulent outer region. The laminar layer was considered to have the sole resistance to heat transfer. This type of analysis was extended by Carpenter and Colburn (2, 3) to include the effect of vapor shear stress. Seban (4) performed an analysis of the turbulent condensate film assuming the existence of the “universal velocity distribution” of Prandtl-Nikuradse. The calculated results extend over a wide range of Prandtl numbers and agree well with the empirical results of Colburn (1) in the range N_Pr = 2 to 5. This paper presents analyses showing the effect on rates of condensation of vapor shear stress at the liquid-vapor interface. Both laminar and turbulent films are considered and are combined to give analytical results for the case of laminar flow on the upper portion of a plate and turbulent flow on the lower portion. The analysis of the turbulent film is essentially an extension of the one presented by Seban (4). The system considered is a vertical flat plate, Fig. 1, with pure saturated vapor condensing on the plate whose temperature is uniform. Flow acceleration and momentum changes are neglected in the analysis. The physical properties are assumed to be constant.