Pressure gradient and variable wall temperature effects during filmwise condensation from downward flowing vapors onto a horizontal tube

Abstract

A simple model is developed to study the process of combined forced and natural convection film condensation from downward flowing vapors onto a horizontal tube with variable wall temperature, including effects of the pressure gradient and vapor shear stress. In the present work, the result of mean heat transfer shows that, for forced-convection film condensation, as the wall temperature variation amplitude, A, increases, the value of Nu Re −1/2, with inclusion of the pressure gradient effect, goes down appreciably. However, the value of Nu Re −1/2 when ignoring the pressure gradient effect will increase with A at a smaller pace. As for natural-convection film condensation, the mean heat transfer coefficients remain almost uniform for varying A, which are in good agreement with the previous work.