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International Heat Transfer Conference 16

ISSN: 2377-424X (online)
ISSN: 2377-4371 (flashdrive)

WETTING AND EVAPORATION OF OCTAGONAL SALINE DROPLETS ON A MICROPYRAMID PATTERNED SURFACE

Xin Zhong
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore 639798, Singapore

Junheng Ren
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore 639798, Singapore

Karen Siew Ling Chong
Institute of Materials Research and Engineering, A*Star, 2 Fusionopolis Way, Innovis, Level 9, Singapore 138634, Singapore

Kian-Soo Ong
Institute of Materials Research and Engineering, A*Star, 2 Fusionopolis Way, Innovis, Level 9, Singapore 138634, Singapore

Fei Duan
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50, Nanyang Avenue, Singapore 639798, Singapore

DOI: 10.1615/IHTC16.mtr.023441
pages 5827-5832


KEY WORDS: Mass transfer and drying, Two-phase/Multiphase flow, droplet shape control, droplet evaporation, patterned surface

Abstract

Droplet dynamics on surfaces are of vital importance to the designs and manipulations of chip manufacturing, biological and medical science, and thermal management. Droplet shape control has been extensively realized by engineering surfaces with structures, e.g. pillars with different density, geometry and arrangement. In this study, we propose a low-cost approach by simply varying the salt potassium chloride (KCl) concentration in the droplet solution to control the droplet shape on poly(methyl methacrylate) substrates fabricated with micropyramid islands. The droplets with various salt concentrations exhibit octagonal shapes on the micropyramid substrate. The octagonal solid-liquid interface varies toward a rectangle with corners cut by increasing the initial salt concentration. The physical mechanism behind the dependence of the solid-liquid interface on the salt concentration is interpreted by analyzing the free energy difference at the contact line. The saline droplets are found to experience a pinning and then a depinning stage during the lifetimes. During the depinning stage the wetting interface evolves toward a circle and the octagonal shape is lost.

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