Onset of Nucleate Boiling on Soft Surfaces: Theoretical Considerations

Surface engineering is often used to alter interfacial phenomena with the aim of reducing superheat required for onset of nucleate boiling (ONB), which can increase efficiency in many industrial applications. Commercially available enhanced boiling surfaces that reduce superheat consist of either porous metal coatings or sub-millimeter metal fins with re-entrant geometries.In the last decade, the majority of the research in this area has focused on boiling enhancement using coatings with nano-to-microscale textures and/or chemical heterogeneities. In this presentation, we will expands beyond these two design variables (texture and chemistry) and provides theoretical arguments highlighting that the superheat required for ONB can be further tuned by modifying the mechanical properties of the boiler surface. Specifically, two bubble formation mechanisms will be evaluated theoretically to determine the effect of surface softening on the superheat required for ONB. First, heterogeneous vapor bubble nucleation on smooth, soft surfaces is mapped in terms of the kinetic limit of the superheat. Second, augmentation of vapor trapping in surface cavities and superheat required to seed bubbles from the ensuing gas pockets induced by softening of the surface is evaluated.