Acoustothermal Atomization of Water Nanofilms

Abstract

We report nonequilibrium molecular simulations of the vibration-induced heating of nanoscale-thick water layers on a metal substrate. In addition to experimentally confirmed acoustothermal evaporation, we observe hitherto unmapped nucleate and film boiling regimes, accompanied by the generation of unprecedented heat fluxes [∼O(10^{9}) W/m^{2}]. We develop a universal scaling parameter to classify the heat-transfer regimes and to predict the thickness of the residual nonevaporating liquid layer. The results find broad application to systems involving drying, coatings, and sprays.

Acoustothermal Nucleation of Surface Nanobubbles

“…Ultrasonic vibration of a wetted surface results in rapid pressure fluctuations inside the liquid and can nucleate bubbles in local regions that drop below the vapor pressure. − These bubbles are unstable and generate powerful shock waves as they collapse, which has applications in industrial and chemical processes, such as nanocomposite synthesis, enhancement of chemical reactions, dental plaque cleaning, and drug delivery . We recently discovered that extremely high frequency vibrations can also nucleate bubbles at the nanoscale by heating, i.e., when the temperature in local regions exceeds the liquid’s boiling point. This heating occurs because surface vibrations dissipate energy into the liquid via viscous dissipation locally near the surface, which gains importance when the liquid film dimensions drop below the Stokes boundary layer height, , where ρ is the liquid density, μ is the dynamic viscosity, and ω is the angular vibrational frequency (see Figure A). ,− High acoustothermal heat fluxes can be generated for small amounts of liquid vibrated at high frequencies (up to ∼10 9 W/m 2 for water nanofilms vibrated at ­(100 GHz)), which can rapidly take the liquid to the vicinity of the liquid–vapor spinodal, causing explosive bubble nucleation or boiling.…”

“…We recently discovered that extremely high frequency vibrations can also nucleate bubbles at the nanoscale by heating, i.e., when the temperature in local regions exceeds the liquid’s boiling point. This heating occurs because surface vibrations dissipate energy into the liquid via viscous dissipation locally near the surface, which gains importance when the liquid film dimensions drop below the Stokes boundary layer height, , where ρ is the liquid density, μ is the dynamic viscosity, and ω is the angular vibrational frequency (see Figure A). ,− High acoustothermal heat fluxes can be generated for small amounts of liquid vibrated at high frequencies (up to ∼10 9 W/m 2 for water nanofilms vibrated at ­(100 GHz)), which can rapidly take the liquid to the vicinity of the liquid–vapor spinodal, causing explosive bubble nucleation or boiling. This phenomenon of vibration-driven boiling can replace laser-irradiation-driven phase change in a range of applications, such as steam cleaning of surfaces, creating micro/nano-surface patterns, selective killing of biological cells, , cell perforation, − distillation, nanowire manipulation, and heterogeneous catalysis .…”

“…1−7 These bubbles are unstable and generate powerful shock waves as they collapse, which has applications in industrial and chemical processes, such as nanocomposite synthesis, 8 enhancement of chemical reactions, 9 dental plaque cleaning, 10 and drug delivery. 11 We recently discovered that extremely high frequency vibrations can also nucleate bubbles at the nanoscale by heating, 12 i.e., when the temperature in local regions exceeds the liquid's boiling point. This heating occurs because surface vibrations dissipate energy into the liquid via viscous dissipation locally near the surface, which gains importance when the liquid film dimensions drop below the Stokes boundary layer height, h / st μ ρω =…”

Evaporation of liquid nanofilms: A minireview

“…The effects of nanofilm thickness, surface temperature, surface material, wettability, and roughness on the heat transfer characteristics, such as evaporation rate, heat transfer rate, and heat flow density, in the evaporation process are considered. 20 …”

Molecular Dynamics Simulation on Behaviors of Water Nanodroplets Impinging on Moving Surfaces

“…They found three phenomena: fully climbing the step, partially climbing the step, and being blocked by the step, which relied on the normalized step height. MD simulations were also adopted to investigate the influences of surfaces vibrating with high frequency on the wetting mechanism, evaporation, and transportation of nanodroplets [23][24][25][26].…”