RUI: Thermal Transport across Liquid-gas Interfaces

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Evaporation and condensation of micro/nanodroplets are of great importance to various engineering and environmental applications such as spray cooling, spray combustion, and cloud formation. It is essential to accurately predict the evaporation/condensation rates for these small droplets for achieving a more efficient use of micro/nanodroplets in these applications. Although evaporation and condensation processes have been studied for over a century, the existing relationships that model evaporation and condensation processes often predict results that are inconsistent with, or even contradictive to experimental data. The main objective of this project is to use numerical and theoretical methods to fundamentally understand heat and mass transfer across liquid-gas interfaces, and evaluate the thermal resistance at liquid-gas interfaces to help elucidate these inconsistencies. The education activities will attract underrepresented high school students in the central valley (California) to the engineering program, train the students to conduct research in micro/nanoscale heat transfer, and guide minority students to Ph. D. programs in STEM.Two heat transfer mechanisms, namely, evaporation and heat conduction, often occur simultaneously at evaporating liquid surfaces, such as the water evaporation in air. To elucidate the roles of each of the two mechanisms in heat transfer across liquid-gas interfaces, this project uses molecular dynamics (MD) simulations coupled with the kinetic theory of gases to quantitatively analyze heat and mass transfer at evaporating/condensing liquid surfaces under a variety of driving force conditions. Furthermore, MD simulations can determine the temperature, density, and the mass accommodation coefficient of fluid near the liquid-gas interface with high fidelity, which allows the validation of the various relationships that model the heat and mass transfer at liquid-gas interfaces. Based on MD simulation results and kinetic theory analysis, this project will derive appropriate boundary conditions for continuum-level modeling of evaporation/condensation processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.