Theoretical analysis of filmwise condensation in inclined tubes with nondivergent and irrotational flow components

The present theoretical study investigates laminar film condensation of a saturated vapor in inclined circular tubes. Nusselt thin film assumptions are implemented to derive the governing differential equations for mass, momentum, and energy. The impact of both rotation and divergence of the nonconservative Nusselt velocity vector field on film growth and mass conservation are investigated and a new film thickness equation was introduced. A transformation for effective peripheral angle during stratification is derived based on the assumed linear liquid-vapor interface of Chato at the lower region of the tube. The optimal inclination angle for heat transfer is 28.2 degrees from the horizontal for a tube of infinite length. For a finite tube the inclination angle decreases with length from 90 degrees to 28.2 degrees but for tubes of length L-e*L*> 2, optimal inclination angle is in the range of 28.2 degrees and 46.6 degrees. An expression for entrance length, L-e* was introduced as a function of inclination angle. The results for heat transfer ratio have been compared with experimental data and an empirical correlation from literature and a good agreement is obtained and shown between them. (C) 2020 Elsevier Ltd. All rights reserved.