(484b) Computational Study of Oscillating 3-Phase Contact Line on Flat Surfaces

Micro-scale transport phenomena have gained prominence in various fields like the semiconductor industry where the increasingly complex design of micro-chips demands a method for cooling each chip individually, and space research, where extremely small devices are needed for an efficient cooling system. Understanding phase-change heat and mass transfer in the contact line region also helps in the optimization of industrial processes like boiling, condensation, wetting, spreading, coating, etc. Three-phase contact line is the region where solid, liquid, and vapor phases are in close proximity to each other. Due to the presence of a low heat transfer resistance and a high heat flux, the contact line controls the transport processes in the thin liquid film. Our aim is to study phase-change phenomena at this 3-phase contact line by obtaining the interfacial characteristics at the meniscus of a thin evaporating film. A COMSOL model was previously developed that simulates the fluid dynamics and heat transfer in a thin liquid meniscus on a solid substrate. After reaching a steady-state, the solid wall temperature was oscillated with different frequencies and an amplitude from 0.5-2K. The effects of oscillation on the liquid film thickness and heat transfer across the meniscus were studied. It was observed that the liquid film also oscillates on oscillating the wall temperature for lower frequencies of oscillation. However, for higher frequencies, oscillations in the film were damped out. The heat flux profiles at the solid-liquid boundary show that there exists an optimal oscillation frequency at which the evaporative heat flux is maximum. This optimal frequency requires that condensation occur for a fraction of the oscillation period. The condensation reduces the effects of intermolecular forces that retard evaporation. We discuss the effect that fluid and solid properties have on the behavior of the evaporating liquid, the oscillation of the film, and which properties most affect the optimal oscillation frequency. Knowing what the optimal frequency is will help in better designing of a heat transfer process, giving the maximum heat transfer efficiency.