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Second Thermal and Fluids Engineering  Conference

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

SUB-BOILING NUCLEATION IN SUPERHYDROPHOBIC MICROCHANNELS

Adam Cowley
Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602, USA

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

This work experimentally studies the effects of heating on laminar flow in a superhydrophobic microchannel. The microchannel walls consist of a rib/cavity structured superhydrophobic surface and a glass surface separated by nominally 180 μm thick spacers. The superhydrophobic side is in contact with an aluminum block that is heated via electric heaters and a camera is used to visualize the flow through the glass side. Thermocouples are embedded in the aluminum to obtain the temperature profile along the length of the channel. The friction factor-Reynolds product (fRe) is obtained via pressure drop and volumetric flow rate measurements. Temperatures are kept below the boiling temperature of the working fluid, water. Five surface types/configurations are investigated: smooth hydrophilic, smooth hydrophobic, superhydrophobic with ribs perpendicular to the flow, superhydrophobic with ribs parallel to the flow, and superhydrophobic with ribs parallel to the flow with several breaker ridges perpendicular to the flow. When water that is saturated with air is used, the cavities on the superhydrophobic surfaces act as pre-existing nucleation sites and allow air to be desorbed out of the water onto the surface. Large bubbles eventually form and adversely affect fRe and lead to higher temperatures along the channel. The surface type/configuration has a large impact on the rate of bubble nucleation and removal.

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