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Second Thermal and Fluids Engineering  Conference

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

A THEORETICAL MODEL FOR THE DESIGN OF BIPHILIC SURFACES

Smreeti Dahariya
Department of Mechanical and Nuclear Engineering, Kansas State University, Kansas 66506, USA

Amy Rachel Betz
Department of Mechanical and Nuclear Engineering, Kansas State University, Kansas 66506, USA

Abstract

The juxtaposition of hydrophilic and hydrophobic regions are called "biphilic" surfaces. They have received a significant amount attention for enhanced boiling surfaces. In previous experiments, results showed that biphilic surfaces are more efficient in achieving high heat transfer coefficient on surfaces with variable wettability due to increased control on the bubble nucleation, growth, and detachment. In this work, a theoretical model has been developed for various combinations of hydrophilic − hydrophobic surfaces with variable wettability on the hydrophilic regions (10°, 20° and 30°) while keeping the wetting angle constant (120°) on hydrophobic regions. The model is based on considering the force balance (buoyant force greater than surface tension of the liquid) of a bubble departing from the hydrophobic surface, since the hydrophobic region promotes to bubble nucleation sites. The heterogeneity of the surface affects the pattern of bubble growth which aids the pinning effect and bubble necking phenomenon. The hydrophilic regions play a significant role in pinning the bubble at the hydrophilic-hydrophobic interface. The pinning effect at the lower wetting angle leads to a bigger departure diameter than the higher wetting angle of hydrophilic regions which rises to form a train of bubble-like structure called a bubble jet, therefore preventing the formation of a vapor layer on the boiling surface.

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