Super Water-Repellent Surfaces: Potential Application to Drag Reduction of Yachts

2014 ◽  
Vol 7 (1) ◽  
pp. 71-76 ◽  
Author(s):  
Ke Zhang ◽  
Zheng-Chuang Wang ◽  
Ya-Nan Zhang ◽  
Fang-Fang Zhang ◽  
Yi-Fan Hou ◽  
...  
Keyword(s):  
Drag Reduction ◽  
Potential Application ◽  
Water Repellent

Drag Reduction of Polymer Solutions in a Pipe With a Highly Water-Repellent Wall

1999 ◽  
Author(s):  
Keizo Watanabe ◽  
Hiroshi Udagawa
Keyword(s):  
Pressure Drop ◽  
Laminar Flow ◽  
Drag Reduction ◽  
Polymer Solutions ◽  
Tap Water ◽  
Acrylic Resin ◽  
Water Repellent ◽  
Number Range ◽  
Surfactant Solutions ◽  
Laminar And Turbulent Flow

Abstract By applying a highly water-repellent wall pipe in the drag reduction of polymer solutions, a flow system in which drag reduction is obtained in both laminar and turbulent flow ranges has been realized. Experiments were carried out to measure the pressure drop in pipes with a highly water-repellent wall and an acrylic resin wall by means of a pressure transducer. The diameter of the pipe was 6mm. The polymer solutions tested were PE015 aqueous solutions in the concentration range of 30ppm∼1000ppm. The drag reduction ratio for laminar flow was about 11∼15%. To understand this effect, the pressure drop was measured by using surfactant solutions and degassed water, and by pressurizing tap water in the pipeline. It was shown that the laminar drag reduction does not occur in the case of surfactant solutions although degassed water and pressurizing tap water in the pipeline have no effect on the reduction. In the laminar flow range, the friction factor of a power-law fluid with fluid slip was analyzed by applying the modified boundary condition on fluid slip at the pipe wall, and the analytical results agree with the experimental results in the low Reynolds number range.

Drag Reduction in Flow through Square and Rectangular Ducts with Highly Water-Repellent Walls.

1996 ◽  
Vol 62 (601) ◽  
pp. 3330-3334 ◽  
Author(s):  
Keizo WATANABE ◽  
YANUAR ◽  
Katsutoshi OKIDO ◽  
Hiroshi MIZUNUMA
Keyword(s):  
Drag Reduction ◽  
Water Repellent ◽  
Flow Through

Numerical Simulation of Fluid Slip at a Hydrophobic Surface

Volume 4 ◽  
2004 ◽  
Author(s):  
Takao Fujita ◽  
Keizo Watanabe
Keyword(s):  
Boundary Condition ◽  
Laminar Flow ◽  
Circular Cylinder ◽  
Drag Reduction ◽  
Hydrophobic Surface ◽  
Friction Reduction ◽  
Water Repellent ◽  
Two Dimensional ◽  
Hydrophobic Property ◽  
Flow Past

Laminar drag reduction is achieved by using a hydrophobic surface. In this method, fluid slip is applied at the hydrophobic surface. An initial experiment to clarify for a laminar skin friction reduction was conducted using ducts with a highly water-repellent surface. The surface has a fractal-type structure with many fine grooves. Fluid slip at a hydrophobic surface has been analyzed by applying a new wet boundary condition. In this simulation, an internal flow is assumed to be a two-dimensional laminar flow in a rectangular duct and an external flow is assumed to be a two-dimensional laminar flow past a circular cylinder. The VOF technique has been used as the method for tracking gas-liquid interfaces, and the CSF model has been used as the method for modeling surface tension effects. The wet boundary condition for the hydrophobic property on the surface has been determined from the volume ratio in contact with water near the surface. The model with a stable gas-liquid interface and the experimental results of flow past a circular cylinder at Re = 250 without growing the Karman vortex street are made, and these results show that laminar drag reduction occurring due to fluid slip can be explained in this model.

Super water-repellent surfaces with fractal structures and their potential application to biological studies

2006 ◽  
Vol 284-285 ◽  
pp. 490-494 ◽  
Author(s):  
Hu Yan ◽  
Hatsuki Shiga ◽  
Etsuro Ito ◽  
Toshiyuki Nakagaki ◽  
Seiji Takagi ◽  
...  
Keyword(s):  
Potential Application ◽  
Water Repellent ◽  
Fractal Structures ◽  
Biological Studies

scholarly journals Air retaining grids—a novel technology to maintain stable air layers under water for drag reduction

2019 ◽  
Vol 377 (2150) ◽  
pp. 20190126 ◽  
Author(s):  
M. Mail ◽  
M. Moosmann ◽  
P. Häger ◽  
W. Barthlott
Keyword(s):  
Drag Reduction ◽  
Stable Solution ◽  
Water Repellency ◽  
Contact Angles ◽  
Water Repellent ◽  
Lotus Effect ◽  
Ship Hulls ◽  
First Results ◽  
Air Layers ◽  
Micro Pillars

Extreme water repellent ‘superhydrophobic’ surfaces evolved in plants and animals about 450 Ma: a combination of hydrophobic chemistry and hierarchical structuring causes contact angles of greater than 150°. Technical biomimetic applications and technologies for water repellency, self-cleaning (Lotus Effect) and drag reduction (Salvinia Effect) have become increasingly important in the last two decades. Drag reduction (e.g. for ship hulls) requires the presence of a rather thick and persistent air layer under water. All existing technical solutions are based on fragile elastic hairs, micro-pillars or other solitary structures, preferably with undercuts (Salvinia Effect). We propose and provide experimental data for a novel alternative technology to trap persistent air layers by superhydrophobic grids or meshes superimposed to the solid surface: AirGrids. AirGrids provide a simple and stable solution to generate air trapping surfaces for drag reduction under water as demonstrated by first prototypes. Different architectural solutions, including possible recovery techniques for the air layer under hydrodynamic conditions, are discussed. The most promising target backed by first results is the combination of Air Retaining Grids with the existing microbubble technology. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 2)’.

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