Thin film evaporation in a meniscus is critical to the design of heat pipes and applications related to desalination, lubrication, air conditioning, and medical technologies. Theory suggests that with smaller film thickness, the local evaporation mass flux will increase due to increasing interfacial temperature. The rise of mass flux is followed by a sharp decrease to zero in the non-evaporating region, however, due to interfacial forces that inhibit the escape of vapor molecules. We present the first experimental efforts to locally heat and determine the evaporation heat transfer coefficient *h*~*evap*~ across bulk, thin-film, and non-evaporating regions. We use frequency domain thermoreflectance (FDTR), a non-contact laser-based method with micron-scale lateral resolution. FDTR has been widely used to measure the thermal properties of bulk and thin film solid materials. We propose an experimental procedure and a theoretical model that offer a new paradigm for investigating phase change events using FDTR. A clear minimum is experimentally observed in the measured signal when transitioning from bulk to the non-evaporating region, showing the effect of the thin-film region. We suspect this behavior is a combined result of changes in water thickness and *h*~*evap*~. Calculations from a modified FDTR model and ANSYS simulations are used to separate the two effects and to make a sound prediction of how *h*~*evap*~ varies with film thickness.

 


Local Study of the Evaporation Mass Flux in Thin Liquid Films Using an Integrated Experimental and Computational Approach

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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