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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

INFLUENCE OF MICROSTRUCTURE GEOMETRY ON POOL BOILING AT SUPERHYDROPHOBIC SURFACES

Matthew Searle
Brigham Young University, 435 Crabtree Building, Provo, Utah 84602, United States

Daniel Maynes
Brigham Young University, 435 Crabtree Building, Provo, Utah 84602, United States

Julie Crockett
Brigham Young University, 435 Crabtree Building, Provo, Utah 84602, United States

Brian D. Iverson
Brigham Young University, 435 Crabtree Building, Provo, Utah 84602, United States

Abstract

Superhydrophobic (SHPo) surfaces are created by combining surface micro/nanostructure with hydrophobic chemistry. The result is a surface with a sessile solid-liquid contact angle greater than nominally 150°. We seek to describe the influence of SHPo surfaces on thermal transport in pool boiling. While previous researchers have reported on the influence of the relatively high apparent contact angle on pool boiling, the effect of variation in specific microstructure geometry has not yet been studied. To explore this effect, we manufactured microscale rib and circular post patterned surfaces utilizing photolithography to create surfaces with known geometry. Specifically the microstructure pitch, height, and cavity fraction (ratio of projected cavity area to surface area) were varied, with values ranging from 8 μm to 60 μm, 4.2 μm to 15 μm, and 0.5 to 0.97, respectively. We considered saturated pool boiling where the base of the pool was SHPo and the reservoir sides were polycarbonate. The objective of the experiments was to measure heat flux as a function of excess temperature (the temperature difference between the heated base and the saturated liquid) for nine different SHPo surfaces. Our results demonstrated for the first time that the excess temperature at which transition from nucleate boiling to film boiling occurs on rib patterned surfaces decreases substantially as the cavity fraction increases. Pool boiling heat flux on circular post patterned surfaces is negligibly influenced by cavity fraction or pitch once a stable film boiling condition is reached and the Leidenfrost point on rib patterned surfaces increases modestly with increasing feature height.

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