Laminar drag reduction in microchannels using ultrahydrophobic surfaces
- 1 December 2004
- journal article
- research article
- Published by AIP Publishing in Physics of Fluids
- Vol. 16 (12), 4635-4643
- https://doi.org/10.1063/1.1812011
Abstract
A series of experiments is presented which demonstrate significant drag reduction for the laminar flow of water through microchannels using hydrophobic surfaces with well-defined micron-sized surface roughness. These ultrahydrophobic surfaces are fabricated from silicon wafers using photolithography and are designed to incorporate precise patterns of microposts and microridges which are made hydrophobic through a chemical reaction with an organosilane. An experimental flow cell is used to measure the pressure drop as a function of the flow rate for a series of microchannel geometries and ultrahydrophobic surface designs. Pressure drop reductions up to 40% and apparent slip lengths larger than are obtained using ultrahydrophobic surfaces. No drag reduction is observed for smooth hydrophobic surfaces. A confocal surface metrology system was used to measure the deflection of an air–water interface that is formed between microposts and supported by surface tension. This shear-free interface reduces the flow resistance by allowing the fluid to contact only a very small effective area of the silicon surface. The impact of the surface topology on the drag reduction is explored in detail and the results are found to be in good qualitative agreement with the predictions of analytical theory.
Keywords
This publication has 24 references indexed in Scilit:
- Ultrahydrophobic Surfaces. Effects of Topography Length Scales on WettabilityLangmuir, 2000
- Ultrahydrophobic Polymer Surfaces Prepared by Simultaneous Ablation of Polypropylene and Sputtering of Poly(tetrafluoroethylene) Using Radio Frequency PlasmaMacromolecules, 1999
- Pearl dropsEurophysics Letters, 1999
- Trialkylsilane Monolayers Covalently Attached to Silicon Surfaces: Wettability Studies Indicating that Molecular Topography Contributes to Contact Angle HysteresisLangmuir, 1999
- Ultrahydrophobic and Ultralyophobic Surfaces: Some Comments and ExamplesLangmuir, 1999
- Drag reduction of Newtonian fluid in a circular pipe with a highly water-repellent wallJournal of Fluid Mechanics, 1999
- Slip in Entangled Polymer Melts. 1. General FeaturesMacromolecules, 1998
- Slip in Entangled Polymer SolutionsMacromolecules, 1998
- Purity of the sacred lotus, or escape from contamination in biological surfacesPlanta, 1997
- Slippage of Water over Nonwettable SurfacesJournal of Applied Physics, 1956