DROP-IMPINGING BEHAVIOR ON STRUCTURED SURFACES-A SHORT REVIEW

Abstract

The phenomenon of wall collision of liquid drops is widely seen in spray cooling of surfaces, as well as in spray painting and spray coating. Study of the single-drop impact on the wall is essential to understanding the impingement behavior of sprays against solid surfaces. Primary parameters determining the impingement behavior can be classified into two categories: the drop-side and surface-side parameters. The drop-side parameters include velocity, size (diameter), and liquid properties (density, surface tension, and viscosity) of drops, while the surface-side parameters include surface structure (configuration of microstructure on the surface and permeability), material wettability, and temperature. In this paper, dependence of the drop impingement behavior on those parameters is systematically reviewed, especially focusing on the surface-side parameters. Finally, tentative maps showing the impingement regimes for hydrophobic (nonwettable) and hydrophilic (wettable) surfaces with Weber number, surface roughness (normalized with the drop diameter), and wall temperature (normalized with the saturation temperature) as their axes were constructed and are discussed.