Bionic automatic air-supplementing cavitation-erosion-resistant surface

Abstract

The invention discloses a bionic automatic air supply cavitation erosion resistant surface. The surface comprises a substrate, an electrode plate and a hydrophobic material layer which is arranged on the electrode plate and used for resisting cavitation erosion. The electrode plate is connected with a direct-current power supply, and when the electrode plate is in contact with liquid water, electrolytic reaction is generated to generate gas; as the hydrophobic material has hydrophilic property underwater, gas generated by the electrode can be maintained in pores of the hydrophobic material and does not escape. When surrounding cavitation bubbles collapse, gas in the holes can change the jet flow direction, the surface is prevented from being impacted by high-speed jet flow, and therefore important parts are protected. And when the gas in the pores is insufficient, the electrolytic reaction is generated to supplement the gas, and the electrolytic reaction is automatically finished after gas supplementation is completed. According to the intelligent cavitation-erosion-resistant structure surface, cavitation erosion of materials can be avoided, gas can be automatically supplemented through electrolytic reaction, meanwhile, energy waste caused by the electrolytic reaction in a calm state is avoided, and the intelligent cavitation-erosion-resistant structure surface is an intelligent cavitation-erosion-resistant structure surface.

Description

Technical Field

[0001] The present invention is designed for industrial fields such as shipbuilding, water conservancy, and chemical industry, and specifically relates to a method of utilizing automatic air replenishment to generate an air layer to alleviate cavitation and protect the structural surface of important components. Background Art

[0002] Cavitation is widely present in fluid devices such as underwater propellers, turbines, dam gates, and hydraulic pumps. Cavitation refers to the phenomenon that in a flowing liquid, when the pressure in a local area suddenly drops below the corresponding temperature saturation pressure, the liquid vaporizes to form bubbles. When the cavitation bubbles enter a higher pressure area with the liquid flow, they lose their existence conditions and suddenly collapse. The collapse of the cavitation bubble will produce a high-pressure and high-speed jet toward the solid wall. Repeated jet impact will cause fatigue damage to the wall material and even surface erosion, which is the cavitation phenomenon. Cavitation damage of key components will seriously affect mechanical efficiency and service life. Cavitation damage can be alleviated to a certain extent by enhancing the strength of targeted materials, but it still succumbs to cavitation after a long period of cavitation testing. In recent years, studies have found that cavitation produces a reverse jet away from the wall at the boundary of the gas layer wall. The reverse jet reverses the direction of the cavitation collapse jet impact, which can effectively alleviate the cavitation damage of the wall material. However, the gas layer on the wall is difficult to exist stably and is easily separated from the wall by the strong disturbance of the shock wave generated by the fluid flow or cavitation collapse. The present invention designs a bionic automatic air-replenishing anti-cavitation surface, which can enable cavitation to generate reverse jets and intelligently replenish gas when gas is insufficient on the surface, thereby solving the problem of poor durability of traditional gas layer surfaces. Summary of the invention

[0003] In order to alleviate and inhibit the damage of cavitation to the surface of materials, the present invention provides a bionic automatic air-replenishing anti-cavitation surface, which can effectively reduce the damage of cavitation and improve the efficiency and service life of the device.

[0004] In order to achieve the above-mentioned effective anti-cavitation protection process, the technical solution adopted by the present invention is:

[0005] The structure surface is placed in an area prone to cavitation, and comprises a substrate, an electrode sheet, and a hydrophobic material layer arranged on the electrode sheet for resisting cavitation.

[0006] The substrate is embedded or adhered on parts of underwater rotating machinery or parts of water conservancy and chemical industry that are susceptible to cavitation.

[0007] The electrode sheet is connected to a DC power supply. When the electrode sheet contacts liquid water, an electrolytic reaction will occur to generate gas. The other electrode of the DC power supply is connected to an inert electrode to form a current path.

[0008] The hydrophobic material layer has air affinity under water, and the gas generated by the electrode will be maintained in the pores of the hydrophobic material without escaping.

[0009] When the cavitation bubbles around the structural surface collapse, the gas in the pores will change the direction of the jet, protecting the surface from the impact of the high-speed jet and thus protecting important components.

[0010] In addition, the electrolysis reaction only occurs when strongly disturbed liquid enters the pores. Under calm conditions, the pores on the surface can maintain gas for a long time without electrolysis reaction, avoiding the energy waste caused by continuous electrolysis reaction.

[0011] The hydrophobic material layer is uniformly arrayed with through-hole structures arranged in a regular hexagonal honeycomb pattern, and the diameter d of the through-holes needs to ensure that gas does not escape, satisfying: d ≤ 1.0 mm.

[0012] Only a gas layer surface with a certain thickness can change the jet direction of cavitation bubbles. The gas equivalent thickness D* of the hydrophobic material layer is defined as: where d is the diameter of the through-holes in the hydrophobic material layer, a is the through-hole spacing, and N is the thickness of the hydrophobic material layer. To change the jet direction of cavitation bubbles, the equivalent thickness D* of the hydrophobic material layer needs to satisfy: D* ≥ 0.05R, where R is the equivalent radius of the cavitation bubbles.

[0013] The electrode sheet is uniformly arrayed with conical structures arranged in a regular hexagonal honeycomb pattern. To ensure that the hydrophobic material can stably maintain gas, the height h of the cone should satisfy: h < N; the cones on the electrode sheet correspond one by one to the through-holes in the hydrophobic material layer and are used in cooperation.

[0014] Current research on cavitation erosion believes that the frequent impact of the jets generated when cavitation bubbles collapse near the solid surface is the main cause of material damage. The present invention utilizes the gas affinity of the hydrophobic material underwater to maintain the gas electrolytically generated by the electrode sheet at the pores of the hydrophobic layer to change the collapse direction of cavitation bubbles, which can effectively inhibit the material damage caused by cavitation. In addition, the electrolysis reaction only occurs when the surrounding cavitation bubbles collapse or other strong disturbances cause the gas to escape and thus the liquid enters the pores. Under calm conditions, the pores on the surface can maintain gas for a long time without electrolysis reaction.

[0015] The beneficial effects of the technical solution of the present invention are:

[0016] The present invention provides a brand-new and efficient anti-cavitation erosion technology. By inlaying electrolytic sheets and hydrophobic surface layers at the positions prone to cavitation erosion of mechanical components, the gas layer formed on the hydrophobic surface is used to change the jet direction of cavitation bubbles, thereby alleviating the damage of materials.

[0017] The present invention can electrolytically supplement gas, solving the problem of surface failure caused by gas dissolving in the liquid or escaping. At the same time, it avoids the energy waste caused by continuous electrolysis reaction under calm conditions, and is an intelligent anti-cavitation erosion structural surface layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the device of the present invention and a schematic diagram of its anti-cavitation principle;

[0019] Figure 2 is a schematic diagram of a substrate of the device of the present invention;

[0020] Figure 3 This is a schematic diagram of the structure of a regular hexagonal honeycomb cone array of electrode sheets of the device of the present invention;

[0021] Figure 4 Schematic diagram of the structure of the regular hexagonal honeycomb through-hole array of the hydrophobic material layer of the device of the present invention;

[0022] Figure 5 This is a high-speed camera image of the collapse of cavitation bubbles near a smooth surface (the numbers in the image represent time, in milliseconds);

[0023] Figure 6 High-speed video of the collapse of cavitation bubbles near the cavitation-resistant surface layer (numbers in the figure represent time, unit: milliseconds). DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] like Figure 1-4 As shown, the surface layer of the structure of the present invention includes a substrate, an electrode sheet and a hydrophobic material layer arranged on the electrode sheet for anti-cavitation. The surface layer is arranged on the part or surface impacted by the liquid. The electrode sheet is connected to a DC power supply. When the electrode sheet contacts liquid water, an electrolytic reaction will occur to generate gas. The other electrode of the DC power supply is connected to an inert electrode to form a current path. The hydrophobic material layer has gas affinity under water, and the gas generated by the electrode will be maintained in the pores of the hydrophobic material without escaping.

[0026] During the manufacturing process, the through hole diameter d of the hydrophobic material layer is ensured to be less than or equal to 1 mm, the height h of the cone on the electrode sheet is less than the thickness N of the hydrophobic material layer, and the through hole diameter d, hole spacing a and hydrophobic material layer thickness N should also meet the following requirements: Where R is the equivalent radius of the cavitation bubble.

[0027] During installation or processing, ensure that the anti-cavitation surface layer is placed in the area where cavitation is prone to occur. And try to avoid installing it in the cavitation initiation area.

[0028] Example:

[0029] Since the cavitation process of underwater moving parts is not easy to observe, in this example, the cavitation process is observed by electric spark induction. The references are as follows:

[0030] [1]Wei Z, Zhang C, Shen C, et al. Manipulation of the collapse direction of the cavitation bubbles near the boundary with attached gas plastron[J]. Physics of Fluids, 2023, 35(8).

[0031] [2]Huang G, Zhang M, Ma X, et al. Dynamic behavior of a single bubble between the free surface and rigid wall [J]. Ultrasonics sonochemistry, 2020, 67: 105147.

[0032] In this example, the equivalent radius R of the cavitation bubble induced by the electric spark is 5 mm; the through hole diameter d of the device hydrophobic material layer is 1 mm, the hole spacing a is 1.6 mm, and the thickness N is 3 mm; the cone height h of the array on the device electrode sheet is 2 mm.

[0033] like Figure 5 and Figure 6 As shown in the figure, the anti-cavitation structure surface layer and the smooth surface for comparison were placed near the cavitation bubble, and high-speed camera observation revealed that:

[0034] The cavitation bubble collapses near the control smooth surface and the jet cavitates towards the surface.

[0035] The cavitation bubble jet near the anti-cavitation surface layer moves away from the surface layer to avoid cavitation.

[0036] It can be seen from this example that the present invention changes the jet direction when the cavitation bubble collapses, making it away from the surface of the structure, thereby effectively alleviating the cavitation erosion of the material and efficiently protecting the surface of the structure.

[0037] The above contents are only preferred examples of the present invention and are not intended to limit the present invention in any form. Any technician familiar with the profession can use the above disclosed technical content as the basis, and any simple modification, equivalent change and modification made to the above embodiments by the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A bionic automatic air-replenishing anti-cavitation surface, characterized in that: The invention is composed of a substrate (1), an electrode sheet (2) and a hydrophobic material layer (3); the surface can cause cavitation to generate a reverse jet, thereby avoiding the jet impact damage of the cavitation on the surface; and when there is insufficient gas on the surface, the gas can be replenished by self-regulation, thereby solving the problem of poor durability of the traditional gas layer surface; The substrate (1) should be made of insulating material and embedded or adhered to the part susceptible to cavitation. The material of the substrate (1) includes but is not limited to ceramic, glass, rubber, resin, etc. The cone height h of the array on the electrode sheet (2) is less than the thickness N of the hydrophobic material layer (3), and the material of the electrode sheet (2) includes but is not limited to copper, platinum, titanium, nickel, graphite, etc.; The through hole diameter d of the hydrophobic material layer (3) array is less than or equal to 1 mm, and the through hole diameter d, the hole spacing a and the hydrophobic material layer thickness N should also satisfy: Wherein R is the equivalent radius of the cavitation bubble, and the hydrophobic material layer (3) includes, but is not limited to, polytetrafluoroethylene (PTFE), polydimethylsiloxane (PDMS), fluorine-containing materials, micro-nanostructure materials, etc.; The cones on the electrode sheet (2) correspond one to one with the through holes of the hydrophobic material layer (3) and are used in conjunction with each other.

2. The bionic automatic air-replenishing anti-cavitation surface according to claim 1, characterized in that: The parts susceptible to cavitation are parts of hydraulic equipment or parts of water conservancy and hydropower equipment.

3. The bionic automatic gas-replenishing anti-cavitation surface described in claim 1 can maintain the gas generated by electrolysis of the electrode sheet (2) in the through holes of the hydrophobic material layer (3), and stop the electrolysis reaction after being filled with gas.

4. The bionic automatic air-replenishing anti-cavitation surface described in claim 1 can change the direction of the surrounding cavitation collapse jet and protect the surface from damage.

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