Numerical prediction of dropwise condensation performances on hybrid hydrophobic-hydrophilic surfaces

The use of hybrid surfaces, alternating hydrophobic and hydrophilic (or less-hydrophobic) areas, has been recently proposed as a valuable tool for dropwise condensation performances enhancement. The hydrophilic region, in particular, is designed in order to promote the removal of the droplet from the hydrophobic region, reducing their average size and thus increasing the heat transfer performance. Here, dropwise condensation on heterogeneous surfaces composed by a texture of alternating hydrophobic and hydrophilic (or less-hydrophobic) vertical strips is numerically investigated through a Lagrangian-based phenomenological model, originally developed to study droplet evolution in the framework of in-flight icing phenomenon. The effects of droplet nucleation, growth, coalescence and motion are implemented. The model is extended to the case of curved surface. In order to properly assess the hybrid surface, however, a better knowledge of the interaction between the droplet and the film is required. Thus, additional numerical simulations are carried out using an in-house Eulerian full solver of the liquid film layer, in order to understand the migration mechanism of a drop between two different wettability regions. This will give useful information for a proper implementation of the effect of hydrophilic strips in the phenomenological Lagrangian model. A parametric analysis allows to find the optimal geometric configuration of the hybrid pattern, leading to maximum heat transfer performance, for a given set of wettability properties, nucleation density and condensation rate per unit area. Comparison with experimental data from the available literature ensures the capability of the current Lagrangian model to properly catch the physics behind dropwise condensation process on both planar and curved hybrid surfaces. The uncertainty of the estimate of some model input parameter and their influence on the computed solution are be also discussed.