Effects of Navier Slip on Film Condensation Heat Transfer over Upward Facing Horizontal Flat Surfaces with Free Edges

TL;DR

This study investigates how Navier slip effects influence film condensation heat transfer on upward facing horizontal surfaces, revealing that increased slip enhances heat transfer by thinning the condensate film and altering velocity profiles.

Contribution

It extends classical Nusselt analysis to include slip effects, providing new insights into condensate film behavior and heat transfer enhancement with slip coefficient variations.

Findings

Condensate film becomes thinner with higher slip coefficient.

Heat transfer rate increases as slip coefficient increases.

Nusselt number follows a power law dependence on slip coefficient.

Abstract

Transport phenomena involving condensate liquids generated from the phase change heat transfer in microchannels and in engineered superhydrophobic surfaces require consideration of slip effects. In this study, the laminar film condensation over upward facing flat slabs and circular disks of finite sizes with free edges in the presence of wall slip effects is investigated. By considering the Navier slip model and extending the classical Nusselt analysis, the mass, momentum, and energy of the liquid film in two-dimensional and axisymmetric coordinates are solved for the film thickness and the heat transfer rate in non-dimensional form. Numerical solution yields the local structure of the condensate film profile and the Nusselt number for different values of the slip coefficient. Investigation of the results reveals that the condensate film on horizontal surfaces becomes thinner and the overall heat transfer rate is enhanced with an increase in the slip coefficient. In particular, a regression analysis of the results indicates a power law dependence of the Nusselt number on the non-dimensional slip coefficient with an exponent close to 0.5. Significant enhancement in phase change heat transfer follow from the modification of the local velocity profiles within the condensate film, especially in resulting from the additional momentum gain near the wall surfaces due to increases in slip effects.