KR100539664B1 - Apparatus of reducing fluid friction and Method thereof - Google Patents

Abstract

An apparatus and method for reducing fluid friction forces are disclosed. The disclosed fluid friction reducing device comprises a nanostructured surface consisting of a nanotube array in which a plurality of nanotube columns of 1 nanometer to 200 nanometers diameter (D) are arranged on a substrate at intervals of 0.1 micrometers to 20 micrometers (L). It is provided. In addition, the tube array reduces frictional force with the fluid to 50% or less, thereby realizing a low energy, high speed, state-of-the-art, eco-friendly vehicle.

Description

Apparatus of reducing fluid friction and method

1 is a water-repellent structure disclosed in the article, "Nanostructured surfaces for dramatic reduction of flow resistance in droplet-based microfluids (IEEE, 2002)". Is a simplified cross-sectional view.

2 is a perspective view briefly showing a nanotube array structure according to an embodiment of the present invention;

Figure 3 is a simplified cross-sectional view showing a nanotube array structure according to an embodiment of the present invention.

The present invention relates to an apparatus and method for reducing fluid friction, and more particularly, to an apparatus and method for reducing fluid friction using carbon nanotube arrays.

Ships sailing seas require strong power engines and ancillary machinery to navigate at high speeds, especially due to frictional resistances, sowing resistances, eddy current resistances, air resistances, etc., and particularly high energy consumption. In particular, friction resistance acts as a major cause of slowing down the ship's speed. Even if the outer surface of the ship is formed as a smooth surface, the frictional resistance is 80-85% of the total resistance in the low speed vessel and 50% of the total resistance in the high speed vessel. Is coming. In the case of rough surfaces, the frictional force acts much larger, and when friction factors such as corrosion and moss on the ship's surface are combined, the frictional force becomes even larger. Friction resistance is the single biggest factor affecting ships and a lot of factors affecting the speed of other means of transportation, and research to reduce it has been actively conducted until recently.

1 is a paper published in IEEE 2002 by Joonwon Kim and Chang-Jin "CJ" Kim, "Nanostructured surfaces to significantly reduce fluid resistance in microfluidics based on droplets. for dramatic reduction of flow resistance in droplet-based microfluids).

Referring to FIG. 1, in the nanostructure for reducing fluid resistance, an uneven structure 13 is formed on a transparent substrate 15 having an uneven structure, and a hydrophobic material 12 is coated on an upper surface of the uneven structure. The substrate 15 is made of transparent Borofloat glass or silicon. The substrate 15 is etched using a dry reactive ion etching (DRIE) technique to form the uneven structure shown. In the figure, pitch P is 10 micrometers, the width | variety A of unevenness | corrugation is 3 micrometers, the space | interval B between unevenness | corrugation is 7 micrometers, and the height h of uneven | corrugated is about 15 micrometers.

It is reported that the frictional force with the droplets on the surface of the nanostructure shown in the paper is reduced by about 1/100 than that of the flat surface of the same material, and when formed into a small tube, the frictional force is reduced by 1/20.

However, the experiment has a limitation in that the frictional force reduction effect can be obtained only in the case of microfluids that can ignore the gravity effect on the droplets, that is, the pressure effect acting between the droplets and the object surface. In order to apply to more macroscopic material systems where the effect of gravity is important, it is necessary to consider the pressure, and a finer and higher density uneven structure is required.

The nanostructure having such an uneven structure has a technical limitation in forming a complicated manufacturing process and forming an uneven width A. In particular, the uneven structure has a weak strength and can be damaged even with small frictional force.

Therefore, the technical problem to be achieved by the present invention is to improve the problems of the prior art described above, to extend the range of low-friction force technology to several tens of atmospheric pressure, improve the durability and frictional force reduction effect and significantly reduce the friction between fluid and solid It is to provide a friction reducing device that can be made.

The present invention to achieve the above technical problem,

A plurality of nanotube columns having a diameter of 1 nanometer to 200 nanometers (D) on a substrate comprising nanostructured surfaces consisting of nanotube arrays arranged at intervals of 0.1 micrometers to 20 micrometers (L). Provides a friction reducing device.

The nanotubes may be carbon nanotubes.

The maximum hydraulic pressure P that can maintain the frictional force reducing effect when the fluid having the surface tension σ contacts the nanotube array at the contact angle θ satisfies Equation 1.

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The nanotube array has a hydraulic threshold of about 10 atm.

The nanostructured surface preferably reduces friction by 50% or less compared to flat surfaces.

The nanotubes may be coated with Teflon on the surface.

It is preferable that an oxide film is further formed on the substrate.

The present invention also to achieve the above technical problem,

Arranging a plurality of nanotube columns of 1 nanometer to 200 nanometer diameter (D) on the substrate at intervals of 0.1 micrometers to 20 micrometers (L) to form a nanotube array; And

And contacting a fluid having a predetermined surface tension (σ) on the nanotube array.

The nanotubes are carbon nanotubes.

The carbon nanotubes are preferably formed by plasma chemical vapor deposition.

In the first step, an oxide film may be further formed on the substrate.

When a fluid having a surface tension σ contacts the nanotube array at a contact angle θ, the hydraulic pressure P satisfies Equation 1.

The nanotube array preferably has a hydraulic pressure threshold of about 10 atm, and the nanostructure surface preferably reduces frictional force by 50% or less than a flat surface.

Teflon may be further coated on the surface of the nanotubes.

The present invention adopts a nanotube array structure in which nanotube columns of a predetermined size are arranged at predetermined intervals, thereby dramatically reducing the friction force between the fluid and the solid.

Hereinafter, a friction force reducing device and a method thereof according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a perspective view briefly showing a frictional force reducing device according to an embodiment of the present invention.

Referring to FIG. 2, in the friction reducing apparatus according to the embodiment of the present invention, a column of a plurality of carbon nanotubes 33a and 33b having a diameter D having a diameter of 1 nm to 200 nm on the substrate 31 is 0.1 micrometer. And carbon nanotube arrays arranged at intervals of 20 to 20 micrometers. Herein, vertically aligned carbon nanotube columns may be manufactured using a plasma enhanced chemical vapor deposition (PECVD) process.

Here, it can be replaced by nanotubes formed of other materials instead of carbon nanotubes. However, since carbon nanotubes are very flexible and strong mechanically, they are not easily broken or broken by external force, so they have a very high durability against external scratches. An oxide film may be formed on the substrate 31 to enhance adhesion of the carbon nanotube columns 33a and 33b to the substrate 31.

As the vessel progresses at a constant speed, water near the hull surface travels along the vessel and forms a fluid layer that causes frictional resistance that reduces the vessel's speed. This fluid layer is called the boundary layer, and the momentum supplied from the hull to the fluid in the boundary layer is a measure of the frictional resistance. Loss of energy continues because the hull moves forward, leaving behind frictional force tracks moving in the same direction, accelerating water to form a boundary layer. Slip boundary conditions between fluids and solids are the microscopic cause of this drag. Reducing the contact surface of water and solids reduces the area under which slip slip boundary conditions are applied, thereby reducing friction between the solids and the fluids.

3 is a schematic view showing a carbon nanotube array in contact with water in the friction reducing apparatus according to an embodiment of the present invention.

Referring to FIG. 3, a fluid is supported by surface tension on a plurality of carbon nanotube columns 33a and 33b constituting the carbon nanotube array 33 and an air layer between the carbon nanotube columns 33a and 33b. It is trapped. The contact angle θ is maintained between the carbon nanotube columns 33a and 33b and the fluid. Higher hydraulic pressures (P) can push the air layer out and allow water to penetrate. The maximum hydraulic pressure depends on the diameter (D) of the nanopillars and the spacing (L) between the pillars. It also depends on the surface tension σ and the contact angle θ of the fluid.

When arranging nanotubes of diameter (D) nanometers with reduced area of solids in contact with the fluid at intervals of average L nanometers, it is important to know how much fluid surface tension can hold the air layer up to hydraulic pressure (P). From (σ) and the contact angle (θ) of the specific liquid and the carbon nanotubes can be calculated as shown in Equation 1 below.

Table 1 is a prediction of the relative pressure resistance (FR _rel ) for the smooth surface and the pressure threshold according to the diameter (D) and spacing (L) of the carbon nanotube column when the fluid of FIGS. Estimates are shown in Table 1 because the relative frictional resistance (FR _rel ) for smooth surfaces is expected to decrease in proportion to (D / L) ² .

P _limit D (nm) (kg / m ² ) 2 5 10 20 30 50 100 200 One L (nm) 6782 10724 15166 21448 26268 33912 47958 67823 FR _rel 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 10 L (nm) 2145 3391 4796 6782 8307 10724 15166 21448 FR _rel 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.00% 0.01% 100 L (nm) 678 1072 1517 2145 2627 3391 4796 6782 FR _rel 0.00% 0.00% 0.00% 0.01% 0.01% 0.02% 0.04% 0.09% 1,000 L (nm) 214 339 480 678 831 1072 1517 2145 FR _rel 0.01% 0.02% 0.04% 0.09% 0.13% 0.22% 0.43% 0.87% 10,000 L (nm) 68 107 152 214 263 339 480 678 FR _rel 0.09% 0.22% 0.43% 0.87% 1.30% 2.17% 4.35% 8.70% 100,000 L (nm) 21 34 48 68 83 107 152 214 FR _rel 0.87% 2.17% 4.35% 8.70% 13.04% 21.74% 43.48% 86.96%

The predicted values in Table 1 are the results of assuming that the contact angle (θ) in Equation 1 is 180 degrees and the surface tension (σ) of water is 0.072 N / m at room temperature (25 ℃). Experimentally, the contact angle (θ) between carbon nanotubes and water is not known exactly. However, it is assumed that the carbon nanotubes are hydrophobic from the fact that the carbon nanotubes are not dispersed in water and almost disappear. Therefore, the contact angle θ is assumed to be 90 degrees or more.

When the carbon nanotubes and water have extremely weak hydrophobicity at the contact angle of 90.6 degrees, the pressure threshold is reduced to about 1/100, and the pressure threshold is reduced to about 1/10 with only slight hydrophobicity at the contact angle of 95.7 degrees. As the contact angle decreases, only the pressure threshold decreases but the frictional force reduction effect remains the same. Therefore, even if the contact angle has a weak hydrophobicity close to 90 degrees can still obtain a very large friction force reduction effect. In addition, by applying a hydrophobic material, for example, Teflon coating at the end of the nanotube to increase the contact angle can increase the pressure threshold. That is, it is possible to maintain the air layer even under a higher pressure and to broaden the application range of the frictional force reducing effect.

For example, when carbon nanotubes having a diameter D of 50 nm are used to obtain a frictional force reducing effect at a pressure of 100 kg / m ² or less, the distance L between nanotubes may be about 3 μm. At this time, the solid-fluid friction force is expected to decrease in proportion to (D / L) ^{2 + δ} , from which the upper and lower limits of the friction reduction range can be predicted. The exact value of δ should be determined by experiment. However, it can be expected that the value δ will have a value between -1 and 0. For this example, solid-fluid friction is expected to decrease significantly from a maximum of 1/5000 to a minimum of 1/70 compared to a smooth surface.

A frictional force reduction method according to an embodiment of the present invention for reducing contact frictional force with a fluid comprises a plurality of nanotube columns of 1 nanometer to 200 nanometer diameter (D) on a substrate at 0.1 micrometer to 20 micrometer spacing ( L) to form a nanotube array, and then contacting the fluid on the upper surface. At this time, the hydraulic pressure (P) of the fluid has a value as shown in Equation 1 when contacting a fluid having a surface tension of σ on the nanotube array. When the technical limit of the interval L between nanotube columns is about 100 nm, the threshold of the hydraulic pressure P is about 10 atm.

In particular, the nanotubes are preferably formed of carbon nanotubes, and carbon nanotubes may use both single-walled or multi-walled carbon nanotubes, and both metallic or semiconducting carbon nanotubes. It is available. In order to increase the hydrophobicity of the nanotubes, hydrophobic materials such as teflon coatings may be further coated on the nanotube surfaces.

The friction reducing apparatus and method of the present invention can propose a nanotube array having a predetermined diameter and spacing to implement a nanostructured surface having reduced frictional force between a fluid and the nanotube array to 50% or less. Such a low friction surface can significantly improve the speed by greatly reducing the energy consumed in the vehicle when used in a vehicle such as a ship. At the same time, such a surface can have various super water-repellent and anti-pollution properties, so that contaminants on the surface can be easily removed. Vessels may also have an environmentally friendly effect, replacing the use of toxic pate, which is used to prevent surface friction increase due to marine life.

While many details are set forth in the foregoing description, they should be construed as illustrative of preferred embodiments, rather than to limit the scope of the invention. Therefore, the scope of the present invention should not be defined by the described embodiments, but should be determined by the technical spirit described in the claims.

As described above, an advantage of the frictional force reducing device and method according to the present invention is to provide a super water-repellent or anti-pollution device having a nanotube array that can reduce the frictional force between the solid and the fluid to 50% or less, and can be used in ships, etc. It is applied to the surface of the same vehicle to significantly reduce the frictional resistance can realize a high-speed, low-energy eco-friendly vehicle.

Claims (16)

A plurality of nanotube columns having a diameter of 1 nanometer to 200 nanometers (D) on a substrate comprising nanostructured surfaces consisting of nanotube arrays arranged at intervals of 0.1 micrometers to 20 micrometers (L). Friction reduction device. The method of claim 1, The nanotube is a friction force reducing device, characterized in that the carbon nanotubes. delete The method of claim 1, And a maximum hydraulic pressure (P) capable of maintaining a frictional force reducing effect when a fluid having a surface tension (σ) contacts the nanotube array at a contact angle (θ).

The method of claim 4, wherein The nanotube array has a hydraulic pressure threshold of about 10 atm. The method of claim 1, And the nanostructured surface reduces friction with the fluid by 50% or less compared to the flat surface. The method of claim 1, The nanotube is a friction force reducing device, characterized in that the surface is coated with Teflon. The method of claim 1, And an oxide film is further formed on the substrate. Arranging a plurality of nanotube columns of 1 nanometer to 200 nanometer diameter (D) on the substrate at intervals of 0.1 micrometers to 20 micrometers (L) to form a nanotube array; And Contacting a fluid having a predetermined surface tension (σ) on the nanotube array. The method of claim 9, Friction reduction method characterized in that the nanotubes are carbon nanotubes. The method of claim 9, The carbon nanotubes are formed by a plasma chemical vapor deposition method. The method of claim 9, wherein in the first step: Friction force reduction method characterized in that the oxide film is further formed on the substrate. The method of claim 9, The maximum hydraulic pressure (P) that can maintain the frictional force reduction effect when the fluid having a surface tension (σ) in contact with the nanotube array at the contact angle (θ) satisfies the following equation.

The method of claim 13, The nanotube array has a hydraulic pressure threshold of about 10 atm. The method of claim 1, And the nanostructured surface reduces friction with the fluid by 50% or less compared to the flat surface. The method of claim 9, Friction reduction method characterized in that the coating of the Teflon further on the surface of the nanotube.

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