<p>The properties of liquid films in microchannels formed by flow boiling determine the heat transfer coefficient and other thermal management capabilities.&nbsp; The annular flow regime describes the flow of a thin liquid film along a microchannel perimeter, maintained by a continuous vapor core in the center.&nbsp; Prior studies have characterized liquid films in this flow regime at adiabatic and diabatic conditions, proposing models for the onset of annular flow based on visual observation.&nbsp; However, the transient nature of liquid film formation and evaporation events at microscale make the identification of the annular regime more intricate than these observations alone suggest. This study analyzes the thermofluidic properties of annular liquid films in microchannels, compared to the elongated bubble and wavy annular regimes. Our results illustrate that the annular liquid film may be associated with intermittent dryout events dictated by the sufficiency of the liquid film supply, instead of just a continuously moving flow. Expanding upon previous studies that utilize visualization, the onset of annular flow is determined by the thermal characteristics associated with the moving film throughout five stages of this flow: film formation, film development, steady flow of evaporating film, film thinning, and dryout.&nbsp; To further define the annular flow regime, we present hydrodynamic properties of annular film and vapor core, such as velocity, thickness, and interfacial shear stress as a function of cross-sectional vapor quality. A threshold for interfacial shear stress in continuous annular films as a function of vapor quality and mass flux is also introduced.</p>

Annular Liquid Film Development and Thermohydraulic Behavior in Microchannels

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2021/volume/85505

ASME 2021 International Electronic Packaging Technical Conference and Exhibition (InterPACK2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.