Evaporation from the nanometer-thick liquid region of a meniscus is critical in heat pipes, desalination, lubrication, air conditioning, and medical devices. The highest local evaporation rate is reached close to the three-phase contact line as a result of a competition between a high liquid-vapor interface temperature and an increased disjoining pressure. Historically, the Hertz-Knudsen-Schrage (HKS) relation has been used to predict evaporation rates. While this theory has proven to be suitable for thick films, it has never been validated in thin films where the disjoining pressure is non-negligible. We present the first-ever validation of the HKS relation with disjoining pressure. A non-equilibrium Molecular Dynamics (NEMD) simulation system with Lennard Jones argon is designed to directly extract the evaporation mass flux. The simulation result is then used to demonstrate the validity of the HKS relation for predicting the evaporation mass flux in thin liquid film with accurate properties calculated using NEMD and complementary equilibrium MD simulations. The direct MD evaporation mass flux and that from the HKS relation agree to within 10%. We define an evaporation Kapitza length that estimates where the liquid conduction and evaporation thermal resistances are equal. We propose that surface structures that promote film thicknesses comparable to or smaller than the evaporation Kapitza length, but larger than the adsorbed film thickness, will maximize the evaporation rate.

 


Assessing the Impact of Disjoining Pressure on Thin-Film Evaporation With Atomistic Simulation and Kinetic Theory

Division / Sponsors: 
Heat Transfer Division (HTD), Fluids Engineering Division (FED)

Heat Transfer Summer Conference
Paper Proceedings: https://asmedigitalcollection.asme.org/HT/HT2020/volume/83709

18th International Conference on Nanochannels, Microchannels, and Minichannels
Paper Proceedings: https://asmedigitalcollection.asme.org/ICNMM/ICNMM2020/volume/83693

Fluids Engineering Division Summer Meeting
Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2020/volume/83716

HT-ICNMM2020 - Virtual Conference, SHTC - Virtual Conference, FEDSM2020 - Virtual Conference

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