scholarly journals Experimental Analysis of The Effect of Hydrophobic Coating on Pressure Drop in Small Pipes

2020 ◽  
Vol 77 (1) ◽  
pp. 24-35
Author(s):  
Michael J Knights ◽  
Roy Donald ◽  
Diego Galletta ◽  
Pun Kul ◽  
Faik A Hamad
Keyword(s):  
Drag Reduction ◽  
Flow Condition ◽  
Surface Condition ◽  
Friction Drag ◽  
Frictional Drag ◽  
Pipe Surface ◽  
Hydrophobic Coating ◽  
Coated Surface ◽  
Inner Diameter ◽  
Laminar State

In this paper, experimental results are reported to quantify the effect of hydrophobic coating LT-8 on frictional drag of water flow in pipes of 450 mm length. Five pipes of 1, 2, 3, 4, and 5 mm inner diameter were tested. The results from 1, 2 and 3 mm diameter pipes demonstrated an average frictional drag reduction of 9%, 11.5% and 3%, respectively, while the results from 4mm and 5mm pipes showed an increase in frictional drag of 12% and 10%, respectively. The 2mm and 4mm pipes were also tested with a half application of hydrophobic coating. The half coated 2mm pipe showed decrease in drag while 4mm pipe showed increase in drag. The results indicate a relationship between drag reduction/ increase within the percentage of coated surface. The main conclusions are, the flow changed from laminar state to the liquid-air wetting surface condition (Cassie-Baxter wetting state) at the pipe surface and then destabilized by the turbulent boundary layer and entered the liquid wetting surface (Wenzel wetting state) will be appeared. This transition lead to a reduction in friction drag for laminar flow condition and increase in drag for turbulent flow condition.

Microstructured Surfaces for Drag Reduction Purposes: Experiments and Simulations on Rectangular 2D Riblets

2005 ◽  
Vol 899 ◽  
Author(s):  
Håkan Rapp ◽  
Igor Zoric ◽  
Bengt Kasemo
Keyword(s):  
Drag Reduction ◽  
Plane Channel ◽  
Viscous Sublayer ◽  
Friction Drag ◽  
Frictional Drag ◽  
Navier Stokes Equation ◽  
Number Range ◽  
Structured Surfaces ◽  
Structured Surface ◽  
Wall Unit

AbstractIt is well established that properly structured surface exhibits a lower friction drag, when exposed to a turbulent boundary layer, than a smooth surface under the same flow conditions. The observed drag decrease is usually attributed to an increased thickness of the viscous sublayer. In this work we examine the friction drag reducing mechanism. Two parallel approaches towards achieving this goal are presented. Photolithography was used to manufacture rectangular riblets in the 10∝m range on a standard 4” silicon wafer. A special compact plane channel system was designed and used for measurements of the frictional drag on structured surfaces in the turbulent flow covering a wide Reynolds number range. Navier-Stokes equation, for the examined drag reducing geometry, was solved in the laminar regime with appropriate boundary conditions. The resulting velocity field was used to extract the protrusion heights difference for streamwise and spanwise flows over the structured surface. The latter was then related to the experimentally measured drag reduction slope. We show that in case of a rectangular riblet, with a size of the order of one wall unit, the observed drag reduction can be accounted for within the above model.

Friction drag reduction based on a proportional-derivative control scheme

2021 ◽  
Vol 33 (7) ◽  
pp. 075115
Author(s):  
Chi Wai Wong ◽  
Xiaoqi Cheng ◽  
Dewei Fan ◽  
Wenfeng Li ◽  
Yu Zhou
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Control Scheme ◽  
Friction Drag Reduction ◽  
Derivative Control

Effects of the air layer of an idealized superhydrophobic surface on the slip length and skin-friction drag

2016 ◽  
Vol 790 ◽  
Author(s):  
Taeyong Jung ◽  
Haecheon Choi ◽  
John Kim
Keyword(s):  
Drag Reduction ◽  
Skin Friction ◽  
Superhydrophobic Surface ◽  
Slip Length ◽  
Joint Probability ◽  
Turbulent Channel Flow ◽  
Water Interface ◽  
Friction Drag ◽  
Recirculating Flow ◽  
Air Water Interface

The anisotropy of the slip length and its effect on the skin-friction drag are numerically investigated for a turbulent channel flow with an idealized superhydrophobic surface having an air layer, where the idealized air–water interface is flat and does not contain the surface-tension effect. Inside the air layer, both the shear-driven flow and recirculating flow with zero net mass flow rate are considered. With increasing air-layer thickness, the slip length, slip velocity and percentage of drag reduction increase. It is shown that the slip length is independent of the water flow and depends only on the air-layer geometry. The amount of drag reduction obtained is in between those by the empirical formulae from the streamwise slip only and isotropic slip, indicating that the present air–water interface generates an anisotropic slip, and the streamwise slip length ($b_{x}$) is larger than the spanwise one ($b_{z}$). From the joint probability density function of the slip velocities and velocity gradients at the interface, we confirm the anisotropy of the slip lengths and obtain their relative magnitude ($b_{x}/b_{z}=4$) for the present idealized superhydrophobic surface. It is also shown that the Navier slip model is valid only in the mean sense, and it is generally not applicable to fluctuating quantities.

scholarly journals 710 Experimental Study on Friction Drag Reduction Effect of Flexible Tube(1)

2006 ◽  
Vol 2006 (0) ◽  
pp. _710-a_
Author(s):  
Zhigang GAO ◽  
Masatomo OHWAKI ◽  
Motoyuki ITOH ◽  
Shinji TAMANO ◽  
Kazuhiko YOKOTA
Keyword(s):  
Experimental Study ◽  
Drag Reduction ◽  
Friction Drag ◽  
Flexible Tube ◽  
Reduction Effect ◽  
Friction Drag Reduction

Air Layer on Superhydrophobic Surface for Frictional Drag Reduction

2020 ◽  
Vol 64 (02) ◽  
pp. 118-126
Author(s):  
Bradley C. Peifer ◽  
Christopher Callahan-Dudley ◽  
Simo A. Makiharju
Keyword(s):  
Drag Reduction ◽  
Superhydrophobic Surface ◽  
Energy Savings ◽  
Surface Hydrophobicity ◽  
Net Energy ◽  
Frictional Drag ◽  
Gas Flux ◽  
Still Images ◽  
Painted Surface ◽  
Air Layer Drag Reduction

We examined the feasibility of combining a superhydrophobic surface (SHS) and air layer drag reduction (ALDR) to achieve the frictional drag reduction (DR) shown achievable with traditional ALDR, but at a reduced gas flux to increase the achievable net energy savings. The effect of a commercial SHS coating on the gas flux required to maintain a stable air layer (AL) for DR was investigated and compared with that of a painted non-SHS at Reynolds numbers up to 5.1 X 106. Quantitative electrical impedance measurements and more qualitative image analysis were used to characterize surface coverage and to determine whether a stable AL was formed and maintained over the length of the model. Analysis of video and still images for both the SHS and painted surface gives clear indications that the SHS is able to maintain AL consistency at significantly lower gas flux than required on the non-SHS painted surface. Hydrophobicity of the surfaces was characterized through droplet contact angle measurements, and roughness of all the flow surfaces was measured. The results from these preliminary experiments seem to indicate that for conditions explored (up to Rex = 5.1 X 106), there is a significant decrease in the amount of gas required to establish a uniform AL (and hence presumably achieve ALDR) on the SHS when compared with a hydraulically smooth painted non-SHS.

Frictional Drag Reduction: Review and Numerical Simulation of Microbubble Drag Reduction in a Channel Flow

2018 ◽  
Vol Vol 160 (A2) ◽  
Author(s):  
S Sindagi ◽  
R Vijayakumar ◽  
B K Saxena
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
Channel Flow ◽  
Void Fraction ◽  
Rectangular Channel ◽  
Air Injection ◽  
Spanwise Direction ◽  
Flat Plates ◽  
Frictional Drag ◽  
Injection Point

The reduction of ship’s resistance is one of the most effective way to reduce emissions, operating costs and to improve EEDI. It is reported that, for slow moving vessels, the frictional drag accounts for as much as 80% of the total drag, thus there is a strong demand for the reduction in the frictional drag. The use of air as a lubricant, known as Micro Bubble Drag Reduction, to reduce that frictional drag is an active research topic. The main focus of authors is to present the current scenario of research carried out worldwide along with numerical simulation of air injection in a rectangular channel. Latest developments in this field suggests that, there is a potential reduction of 80% & 30% reduction in frictional drag in case of flat plates and ships respectively. Review suggests that, MBDR depends on Gas or Air Diffusion which depends on, Bubble size distributions and coalescence and surface tension of liquid, which in turn depends on salinity of water, void fraction, location of injection points, depth of water in which bubbles are injected. Authors are of opinion that, Microbubbles affect the performance of Propeller, which in turn decides net savings in power considering power required to inject Microbubbles. Moreover, 3D numerical investigations into frictional drag reduction by microbubbles were carried out in Star CCM+ on a channel for different flow velocities, different void fraction and for different cross sections of flow at the injection point. This study is the first of its kind in which, variation of coefficient of friction both in longitudinal as well as spanwise direction were studied along with actual localised variation of void fraction at these points. From the study, it is concluded that, since it is a channel flow and as the flow is restricted in confined region, effect of air injection is limited to smaller area in spanwise direction as bubbles were not escaping in spanwise direction.

Turbulent Friction Drag Reduction on Clark-Y Airfoil by Passive Uniform Blowing

AIAA Journal ◽  
2020 ◽  
Vol 58 (9) ◽  
pp. 4178-4180
Author(s):  
Shiho Hirokawa ◽  
Masahiro Ohashi ◽  
Kaoruko Eto ◽  
Koji Fukagata ◽  
Naoko Tokugawa
Keyword(s):  
Drag Reduction ◽  
Friction Drag ◽  
Turbulent Friction ◽  
Friction Drag Reduction
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