Characterization of Thin Liquid Films on Surfaces with Small Scale Roughness by Optical Interferometry

Two-phase heat transfer techniques such a boiling make use of the high latent heat of fluids to enable dissipation of higher heat fluxes from surfaces compared to conventional single-phase cooling methods. To meet the increasing heat flux dissipation requirements of high-power electronic devices, modifications to the surface properties and roughness are often considered as a means to enhance two-phase heat transfer processes. Although surface roughness of varying length scales has been observed experimentally to enhance boiling heat transfer performance, the physical mechanisms that govern this improvement are not widely accepted. Correlations can be developed to map the behavior of specific surface structure geometries, but a broader investigation of the fundamental forces affecting evaporation at the three-phase contact line, which is critically important to the two-phase heat transfer process, may provide more widely applicable insights. In this thesis, an experimental setup was developed to investigate the effect of small scale surface roughness, with feature sizes below 1 micron, on the liquid film profile of a meniscus formed on a surface. This physical film profile can provide insight into how the surface roughness affects disjoining pressure, an important force that affects the phase change heat transfer process at the contact line. Using an interferometry technique to measure the liquid film profile for a model system of octane on silicon substrate with varying roughness, the change in disjoining pressure in the liquid film was observed. We found that the strength of disjoining pressure in the liquid film increases with increasing surface roughness feature depth.