An Experimental Method for Controlled Generation and Characterization of Microchannel Slug Flow Boiling

This study uses high-speed imaging to characterize microchannel slug flow boiling using a novel experimental test facility that generates an archetypal flow regime suitable for highfidelity characterization of key hydrodynamic and heat transfer parameters. Vapor and liquid phases of the fluorinated dielectric fluid HFE-7100 are independently injected into a T-junction to create a saturated two-phase slug flow, thereby eliminating the flow instabilities and flowregime transitions that would otherwise result from stochastic generation of vapor bubbles by nucleation from a superheated channel wall. Slug flow boiling is characterized in a heated, 500 μm-diameter borosilicate glass microchannel. A thin layer of optically transparent and electrically conductive indium tin oxide coated on the outside surface of the microchannel provides a uniform heat flux via Joule heating. High-speed flow visualization images are analyzed to quantify the uniformity of the vapor bubbles and liquid slugs generated, as well as the growth of vapor bubbles under heat fluxes ranging from 30 W/m to 5160 W/m. A method is demonstrated for measuring liquid film thickness from the visualizations using a ray-tracing 1 Submitted for review to the International Journal of Heat and Mass Transfer 2 Corresponding author: [email protected] 2 procedure to correct for optical distortions. Characterization of the slug flow boiling regime that is generated demonstrates the unique ability of the facility to precisely control and quantify hydrodynamic and heat transfer characteristics. The experimental approach demonstrated in this study provides a unique platform for the investigation of microchannel slug flow boiling transport under controlled, stable conditions suitable for model validation.