NDLI: Role of interface shape on the laminar flow through an array of superhydrophobic pillars

Content Provider	Springer Nature Link
Author	Kim, Jeong Hyun Rothstein, Jonathan P.
Copyright Year	2017
Abstract	In this study, measurements of the pressure drop and the velocity vector fields through a regular array of superhydrophobic pillars were systematically taken to investigate the role of air–water interface shape on laminar drag reduction. A polydimethylsiloxane microfluidic channel was created with a regular array of apple-core-shaped and circular pillars bridging across the entire channel. Due to the shape and hydrophobicity of the apple-core-shaped pillars, air was trapped on the side of the pillars after filling the microchannel with water. The measurements were taken at a capillary number of Ca = 6.6 × 10−5. The shape of the air–water interface trapped within the superhydrophobic apple-core-shaped pillars was systematically modified from concave to convex by changing the static pressure within the microchannel. The pressure drop through the microchannel containing the superhydrophobic apple-core-shaped pillars was found to be sensitive to the shape of the air–water interface. For static pressures which resulted in the apple-core-shaped superhydrophobic pillars having a circular cross section, D/D 0 = 1, a drag reduction of 7% was measured as a result of slip along the air–water interface. At large static pressures, the interface was driven into the apple-core-shaped pillars, resulting in decrease in the effective size of the pillars and an increase in the effective spacing between pillars. When combined with a slip velocity measured to be 10% of the average velocity between the pillars, the result was a pressure drop reduction of 18% compared to the circular pillars at a non-dimensional interface diameter of D/D 0 = 0.8. At low static pressures, the pressure drop increased significantly as the expanded air–water interface constricted flow through the array of pillars even as large interfacial slip velocity was maintained. At D/D 0 = 1.1, for example, the pressure drop increased by 17% compared to the circular pillar. This drag increase was the result of an increased form drag due to a decrease in porosity and permeability of the pillar array and a decrease in the skin friction drag due to the presence of the air–water interface. For D/D 0 = 1.1, the slip velocity was measured to be 45% of the average streamwise velocity between the pillars. When compared to no-slip pillars of similar shape, the drag reduction was found to increase from 6 to 9% with increasing convex curvature of the air–water interface.
Starting Page	1
Ending Page	12
Page Count	12
File Format	PDF
ISSN	16134982
Journal	Microfluidics and Nanofluidics
Volume Number	21
Issue Number	4
e-ISSN	16134990
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2017-04-08
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Superhydrophobic surface Pressure drop Particle image velocimetry Engineering Fluid Dynamics Biomedical Engineering Analytical Chemistry Nanotechnology and Microengineering
Content Type	Text
Resource Type	Article
Subject	Nanoscience and Nanotechnology Materials Chemistry Condensed Matter Physics Electronic, Optical and Magnetic Materials

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