Regenerable protection of surfaces to reduce cavitation erosion

Abstract

The invention relates to a surface arrangement comprising an electrolysis circuit for reducing cavitation erosion, a device comprising the same, the use of the surface arrangement for reducing cavitation erosion and a corresponding method.

Description

[0001] The invention relates to a surface arrangement for reducing cavitation erosion, a device comprising the same, the use of the surface arrangement for reducing cavitation erosion and a corresponding method. Technological background

[0002] Cavitation erosion is the term used to describe erosive material damage to solid surfaces. This damage occurs when pressure drops significantly below the vapor pressure of the liquid. Cavitation bubbles form when the pressure drops below the vapor pressure of the liquid. These bubbles implode in a region of higher pressure. Near solid surfaces, an asymmetric implosion occurs. This asymmetry results in a fluid jet directed toward the solid surface. Such a directed fluid jet can ultimately cause erosive material damage.

[0003] Cavitation erosion is therefore a problem in shipping, pump, pipeline, valve and turbine technology.

[0004] In many areas, attempts are being made to slow cavitation erosion by using special materials, such as specially hardened ones. However, these special materials are more expensive and usually more difficult to machine than conventional materials in the corresponding application areas.

[0005] It is known from the literature that the orientation of the jet of an imploding cavitation bubble depends on the nature of the surface in the vicinity of which it is located. Fig. Figure 1 illustrates a solid surface in direct contact with a liquid. The liquid jet (or jet momentum) of the imploding cavitation bubble is directed toward the surface in this case, causing cavitation erosion at the solid surface. On an ideal free surface, such as a fluid-gas interface, the liquid jet is directed inversely, i.e., away from the surface and toward the liquid bulk. This property of the free surface can be exploited to prevent cavitation erosion.

[0006] Patent CN 107605874 A discloses a cavitation erosion-resistant microstructured surface layer comprising a gas layer between microprotrusions or in microgrooves on a substrate. The microprotrusions or microgrooves have a width D of 10 µm≤D≤150 µm and a height H, or a depth of D≤H≤10D. Application areas described include water management and hydroelectric systems, particularly for propellers or valve cores.

[0007] Patent WO 2020 / 178431 A1 also explicitly addresses the problem of cavitation erosion in ship rudders and pumps, as well as the beneficial effect of jet inversion caused by the enclosed gas. A technical solution is described for preventing cavitation erosion using gas-enclosing microstructured surfaces (GEM). The dimensions of the microcavities are in the low hundreds of picometers.

[0008] A disadvantage of the surfaces described above is that the implosion of a cavitation bubble near the surface (i.e., at a distance of the order of a bubble diameter) can lead to local gas loss from the gas layer trapped in the interstices of the structures. As described in Fig. As shown in Figure 2, in such a case, a portion of the trapped gas flows into the imploding cavitation bubble, causing fluid to simultaneously penetrate the cavity and locally wet the surface. The resulting solid-liquid interface is then subject to cavitation erosion. Summary of the invention

[0009] One or more disadvantages of the prior art are solved or at least mitigated by means of the surface arrangement according to claim 1. The surface arrangement according to the invention for reducing cavitation erosion comprises a DC voltage source connected to an electrode.

[0010] In addition, in a first alternative, the surface arrangement comprises a) a solid surface and an electrically conductive substrate layer arranged directly on the solid surface. A plurality of hydrophobic structural elements are arranged projecting upwards on the surface of the solid surface. The height H of the hydrophobic structural elements is 10 µm to 900 µm, preferably 100 µm to 400 µm. The height H is measured orthogonally to the solid surface. The width B of the hydrophobic structural elements can preferably be 5 µm to 500 µm. In addition, the hydrophobic structural elements delimit a plurality of interstices, with the electrically conductive substrate layer forming the respective floor of the interstices.In other words, adjacent hydrophobic structural elements define the boundary walls of a gap that extends in the plane of the solid surface and is limited in the direction of the solid surface by the electrically conductive substrate layer. The distance between adjacent hydrophobic structural elements, or the diameter of the gap, is D. p can preferably be 10 µm to 2 mm. The gaps are each filled with a closed gas layer.

[0011] In a second alternative b), the surface arrangement comprises an electrically conductive solid surface and a plurality of hydrophobic depressions that extend into the electrically conductive solid surface. The depth T of the hydrophobic depressions is 10 µm to 900 µm, preferably 80 µm to 400 µm, measured orthogonally to the surface of the solid surface. Furthermore, the hydrophobic depressions are filled with a closed gas layer. The distance B k adjacent hydrophobic depressions can preferably be 5 µm to 500 µm, particularly preferably 30 µm to 100 µm. The diameter D k of the hydrophobic depressions can preferably be 10 µm to 2 mm, preferably 50 µm to 1 mm, particularly preferably 100 µm to 500 µm, wherein the diameter D k measured at the widest point of the depression.

[0012] Furthermore, the surface arrangement of the second alternative b) comprises an electrically insulating layer which covers the outer surface of the electrically conductive solid surface and partially covers the inner surface of the hydrophobic depressions.

[0013] The DC voltage source is connected to the electrically conductive substrate layer according to the first alternative a) or to the electrically conductive solid surface according to the second alternative b). Thus, when the surface arrangement is used in a liquid, the DC voltage source, the electrode, and the electrically conductive substrate layer according to the first alternative a), or the DC voltage source, the electrode, and the electrically conductive solid surface according to the second alternative b), form an electrolysis circuit. The electrolysis circuit is interrupted by the closed gas layer between the electrode and the electrically conductive substrate layer according to the first alternative a), or between the electrode and the electrically conductive solid surface according to the second alternative b).

[0014] In a preferred embodiment of the first alternative a), the solid-state surface is completely coated with the electrically conductive substrate layer, and the hydrophobic structural elements are arranged directly on the electrically conductive substrate layer. In this embodiment, the plurality of hydrophobic structural elements can preferably form a network structure that is arranged directly on the electrically conductive substrate layer.

[0015] Alternatively, the structural elements formed as a network structure can also be arranged directly on the solid surface. In this embodiment, the electrically conductive substrate layer is arranged exclusively in the spaces between adjacent hydrophobic structural elements directly on the solid surface.

[0016] The aforementioned mesh structure can consist of interwoven individual fibers, wherein the fibers correspond to the individual hydrophobic structural elements. The fibers preferably have a round cross-section. The interwoven fibers of the mesh structure form meshes that can be essentially triangular, square, pentagonal, or hexagonal. The interwoven fibers of the mesh structure preferably do not lie completely on the electrically conductive substrate layer or the solid surface. Due to the non-planar support on the surface, the woven mesh structure has the advantage that gas exchange can take place between the pores. This gas exchange increases the gas volume for interaction with the cavitation bubbles and thus leads to an improvement in the stability of the gas-retaining layer.

[0017] Preferably, the maximum distance between adjacent hydrophobic structural elements D p(or the diameter of the gap) 10 µm to 2 mm, particularly preferably 200 µm to 800 µm, measured parallel to the surface of the solid surface.

[0018] In a preferred embodiment in which the plurality of hydrophobic structural elements form a network structure and this delimits a plurality of interstices, the maximum extent of an interstice D p preferably 10 µm to 2 mm, preferably 200 µm to 800 µm, particularly preferably 300 µm measured parallel to the surface of the solid surface.

[0019] The width B of an individual hydrophobic structural element is preferably 5 µm to 500 µm, particularly preferably 50 µm to 200 µm, measured parallel to the surface of the solid-state surface. If the plurality of hydrophobic structural elements forms a network structure, for example, the width B of a fiber as an individual hydrophobic structural element can be 5 µm to 500 µm, particularly preferably 200 µm, where the width B corresponds to the diameter of the fiber with a round cross-section. The height H of the network structure in this case corresponds to one to two times the width of the fiber, for example, 200 µm to 400 µm.

[0020] The hydrophobic structural elements preferably consist of an electrically insulating and hydrophobic material or are coated with a layer consisting of an electrically insulating and hydrophobic material. In a preferred embodiment, the hydrophobic structural elements can consist of polytetrafluoroethylene or ethylene-tetrafluoroethylene copolymer. Alternatively, the hydrophobic structural elements can be coated with a layer consisting of polytetrafluoroethylene or ethylene-tetrafluoroethylene copolymer.

[0021] In a preferred embodiment of the second alternative b), the hydrophobic depressions are hemispherical in shape. Furthermore, the hydrophobic depressions can be partially spherical. Partially spherical corresponds to a spherical shape that has a single cross-sectional surface and a larger or smaller volume (preferably a larger volume) than a hemisphere.

[0022] Preferably, the hydrophobic depressions can be interconnected. For example, hemispherically shaped or partially spherically shaped hydrophobic depressions can be interconnected.

[0023] In the embodiments described above, the electrode may preferably be made of graphite.

[0024] In the embodiments described above, the electrically conductive substrate layer may preferably comprise a material selected from an inert metal, an inert metal oxide, carbon, and combinations thereof. Inert metals and inert metal oxides are chemically inert in an electrolysis process (i.e., they do not dissolve). An inert metal is, for example, platinum. An inert metal oxide is, for example, iron oxide. Carbon can be used, for example, in the form of graphite.

[0025] A further aspect of the invention relates to a device which has a surface and at least a part of the surface comprises the surface arrangement according to one of the preceding embodiments.

[0026] The device may, for example, be a hydraulic fluid machine having an inner surface and the inner surface at least partially comprising the surface arrangement according to one of the preceding embodiments.

[0027] Furthermore, the device can be a turbine blade for a hydraulic turbomachine, wherein the turbine blade has a surface which at least partially comprises the surface arrangement according to one of the preceding embodiments.

[0028] In addition, the device may be a hydraulic fitting having an inner surface and the inner surface at least partially comprising the surface arrangement according to one of the preceding embodiments.

[0029] A further aspect of the invention relates to the use of the surface arrangement according to one of the preceding embodiments for reducing cavitation erosion.

[0030] A further aspect of the invention relates to the use of the device comprising the surface arrangement according to one of the preceding embodiments for reducing cavitation erosion.

[0031] Another aspect of the invention relates to a method for reducing cavitation erosion on solid surfaces.

[0032] The method first comprises providing a surface arrangement. The surface arrangement comprises a DC voltage source connected to an electrode; and either a) a solid surface, an electrically conductive substrate layer arranged directly on the solid surface, and a plurality of hydrophobic structural elements arranged projecting on the surface of the solid surface, wherein a height (H) of the hydrophobic structural elements measured orthogonally to the solid surface is 10 mm to 900 µm, particularly preferably 100 µm to 400 µm, the hydrophobic structural elements delimiting a plurality of interstices, the respective bottom of which forms the electrically conductive substrate layer; or b) an electrically conductive solid surface, a plurality of hydrophobic depressions which protrude into the electrically conductive solid surface, wherein a depth (T) of the hydrophobic depressions measured orthogonally to the surface of the solid surface is 10 mm to 900 µm, particularly preferably 100 µm to 400 µm, and an electrically insulating layer which covers the outer surface of the electrically conductive solid surface and partially covers the inner surface of the hydrophobic depressions; wherein the DC voltage source is connected to the electrically conductive substrate layer according to a) or to the electrically conductive solid surface according to b); and wherein according to a) the DC voltage source, the electrode, the electrically conductive substrate layer and a liquid form a closed electrolysis circuit, or according to b) the DC voltage source, the electrode, the electrically conductive solid surface and a liquid form a closed electrolysis circuit.

[0033] The method further comprises generating gas by electrolysis of the liquid at the interface between the liquid and the electrically conductive substrate layer according to a) or at the interface between the liquid and the electrically conductive solid surface according to b) simultaneously with the provision of the previously described surface arrangement.

[0034] The method finally includes terminating the electrolysis by forming a closed gas layer which interrupts the electrolysis circuit between the electrode and the electrically conductive substrate layer according to a) or the electrolysis circuit between the electrode and the electrically conductive solid surface according to b).

[0035] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case. Short description of the characters

[0036] The invention is explained in more detail below using exemplary embodiments and accompanying drawings. The figures show: Fig. 1 Schematic representation of a solid surface 20 in direct contact with a liquid 1 (state of the art). The liquid jet of the imploding cavitation bubble 2 is directed toward the surface and causes cavitation erosion on the solid surface 20. Fig. 2 Schematic representation of a structured solid surface 20 with enclosed gas layer 40 (state of the art) and illustration of the local gas loss due to near-surface implosion of a cavitation bubble 2. Fig. 3 Schematic representation of an embodiment of the surface arrangement 100 according to the invention, wherein the solid surface 20 is completely coated with an electrically conductive substrate layer 12. The electrically conductive substrate layer 12 forms the counterelectrode to the electrode 14 in the electrolysis circuit, which is supplied with electrical energy by the DC voltage source 10 and is interrupted by the closed gas layer 40. The closed gas layer 40 completely fills the space defined by individual adjacent hydrophobic structural elements 30, so that the electrically conductive substrate layer 12 is not in direct contact with the liquid 1. Fig. 4 Schematic top view of a multitude of hydrophobic structural elements 30 in the form of a network structure consisting of interwoven individual fibers 34 with a round cross-section. The network structure forms meshes that define the interstices. The gas layer 40 completely fills the interstices defined by the meshes. The remaining Fig. 3 features are not shown for reasons of clarity. Fig. 5 Schematic representation of a further embodiment of the surface arrangement according to the invention, wherein the solid surface 22 is electrically conductive and has a plurality of hydrophobic depressions 32. The electrically conductive solid surface 22 forms the counter electrode to the electrode 14 in the electrolysis circuit, which is fed with electrical energy by the DC voltage source 10 and is interrupted by the closed gas layer 40. The closed gas layer 40 completely fills the hydrophobic depressions 32 and the electrically insulating layer 50 completely covers the outer surface area of the electrically conductive solid surface 22 and partially covers the inner surface area of the hydrophobic depressions 32, so that the electrically conductive solid surface 22 is not in direct contact with the liquid 1 when the gas layer 40 fills the hydrophobic depressions 32. Fig. 6A Schematic plan view of a plurality of hydrophobic depressions 32 projecting into an electrically conductive solid surface 22. The remaining Fig. 5 features are not shown for reasons of clarity. Fig. 6B Cross section of the Fig. 6A shown solid surface 22 along SS' with hemispherical hydrophobic depressions 32 which are interconnected. Fig. 7 Schematic representation of a further embodiment of the surface arrangement according to the invention, wherein the solid surface 22 is electrically conductive and has a plurality of hydrophobic depressions 32 which are not connected to one another. Fig. 8A Schematic plan view of a plurality of hydrophobic depressions 32 projecting into an electrically conductive solid surface 22. The remaining Fig. 7 features are not shown for reasons of clarity. Fig. 8B Cross section of the Fig. 8A shown solid surface 22 along SS' with partially spherical hydrophobic depressions 32. Fig. 9A to 9C Schematic representations of an electrolysis process according to the invention for restoring the gas layer 40 after a gas loss due to an imploding cavitation bubble 2 near the surface of a surface arrangement according to the invention. Detailed description of the invention

[0037] Fig. Figure 3 shows a first embodiment of the surface arrangement according to the invention. The solid surface 20 is completely coated with an electrically conductive substrate layer 12. A plurality of hydrophobic structural elements 30 are arranged directly on the surface of the electrically conductive substrate layer 12. The height H of the hydrophobic structural elements 30 is 10 µm to 900 µm, preferably 100 µm to 400 µm, measured orthogonally to the surface of the substrate layer 12. The hydrophobic structural elements 30 delimit a plurality of interstices, the respective base of which is formed by the electrically conductive substrate layer 12. The interstices are each filled with a closed gas layer 40.

[0038] This first embodiment of the surface arrangement further comprises a DC voltage source 10 connected to the electrically conductive substrate layer 12 and to an electrode 14. The DC voltage source 10, the electrically conductive substrate layer 12, and the electrode 14, together with the liquid (as electrolyte), form an electrolysis circuit, wherein the electrolysis circuit between the electrically conductive substrate layer 12 and the electrode 14 is interrupted by the closed gas layer 40. In other words, the electrically conductive substrate layer 12 forms the counterelectrode to the electrode 14. The electrode 14 can function either as a cathode or as an anode.

[0039] A further preferred embodiment of the surface arrangement has the features of the first embodiment described above, but differs in that the solid surface 20 is only partially coated with the electrically conductive substrate layer 12, and the plurality of hydrophobic structural elements 30 are arranged directly on the solid surface 20. Preferably, the solid surface 20 is coated with the electrically conductive substrate layer 12 only on those surfaces that correspond to the bottoms of the spaces defined by the hydrophobic structural elements 30.

[0040] Fig. 4 shows an aspect of a particularly preferred embodiment of the surface arrangement 100 in which the solid surface 20 is completely coated with an electrically conductive substrate layer 12. Shown are a plurality of hydrophobic structural elements 30 configured in the form of a mesh structure. The mesh structure is arranged directly on the surface of the electrically conductive substrate layer 12. The mesh structure consists of interwoven individual fibers 34, which preferably have a round cross-section. The diameter of the fibers 34 with a round cross-section is preferably 5 µm to 500 µm, particularly preferably 50 µm to 200 µm. One advantage of the interwoven round fibers of the mesh structure is that the solid-liquid interface 4 is minimized and the gas-liquid interface 3 is maximized, thus achieving improved protection against cavitation erosion.

[0041] The fibers 36 are preferably made of polytetrafluoroethylene. The network structure forms meshes that define the interstices. The maximum dimension of the interstices D p , which are delimited by the meshes, is 10 µm to 2 mm, preferably 200 µm to 800 µm, particularly preferably 300 µm. The gas layer 40 completely fills the space delimited by the meshes.

[0042] This first embodiment of the surface arrangement further comprises a DC voltage source 10 connected to the electrically conductive substrate layer 12 and to an electrode 14. The DC voltage source 10, the electrically conductive substrate layer 12, and the electrode 14 form an electrolysis circuit, wherein the electrolysis circuit between the electrically conductive substrate layer 12 and the electrode 14 is interrupted by the closed gas layer 40.

[0043] In a second alternative embodiment of the surface arrangement 200 according to the invention, the solid surface 22 is electrically conductive and has a plurality of hydrophobic depressions 32. The electrically conductive solid surface 22 can be made of a metal, such as copper or a copper alloy. The depth T of the hydrophobic depressions 32 is 10 µm to 900 µm, preferably 100 µm to 400 µm, measured orthogonal to the (outer) surface of the solid surface. The diameter D k of the hydrophobic depressions 32 may preferably be 10 µm to 2 mm, wherein the diameter D k measured at the widest point of the recess. The distance B k adjacent hydrophobic depressions 32 may preferably be 5 µm to 500 µm, wherein the distance B kfrom edge to edge of the adjacent hydrophobic depressions. The hydrophobic depressions 32 are filled with a closed gas layer 40.

[0044] In addition, the embodiment of the device comprises an electrically insulating layer 50 that completely covers the outer surface of the electrically conductive solid surface 22 and partially covers the inner surface of the hydrophobic depressions 32. The term "outer surface of the electrically conductive solid surface" refers to the portion of the solid surface that does not correspond to the hydrophobic depressions. The term "inner surface of the hydrophobic depressions" therefore corresponds to the portion of the solid surface that forms the hydrophobic depressions. In other words, the walls of the hydrophobic depressions 32 are not completely coated with the electrically insulating layer 50. Preferably, the hydrophobic depressions 32 are not coated with the electrically insulating layer 50 at their deepest point.

[0045] Furthermore, this second embodiment of the surface arrangement according to the invention comprises a DC voltage source 10 connected to the electrically conductive solid surface 22 and to an electrode 14. The DC voltage source 10, the electrically conductive solid surface 22, and the electrode 14 form an electrical circuit, wherein the electrical circuit between the electrically conductive solid surface 22 and the electrode 14 is interrupted by the closed gas layer 40. In other words, the electrically conductive solid surface 22 forms the counterelectrode to the electrode 14. The electrode 14 can function either as a cathode or as an anode.

[0046] Fig. Figure 5 shows a particularly preferred embodiment of the above-described embodiment, wherein the hydrophobic depressions 32 are partially spherical and are interconnected in a gas-permeable manner. A top view of this embodiment is shown in Fig. 6A, where the hydrophobic depressions are arranged at regular intervals and offset from one another. Except for the depressions located at the outer edge of the solid surface 22, each hydrophobic depression 32 is surrounded by six adjacent hydrophobic depressions 32. Fig. Figure 6B shows the cross-section of the solid surface 22 along S-S'. In this preferred embodiment, the partially spherical hydrophobic depressions 32 overlap, thus forming a gas-permeable connection at the interface between adjacent depressions. An advantage of this embodiment is that in the event of a local gas loss, additional gas equalization can occur from neighboring depressions.

[0047] Fig. 7 shows an alternative embodiment of the embodiment in Fig. 5, wherein the hydrophobic depressions 32 are hemispherical in shape and are not connected to each other.

[0048] Fig. Figure 8A shows the alternative embodiment of the embodiment in Fig. 7, wherein the hydrophobic depressions 32 are hemispherically shaped and arranged at regular intervals and offset from one another. With the exception of the depressions located at the outer edge of the solid surface 22, each hydrophobic depression 32 is surrounded by six adjacent hydrophobic depressions 32. Fig. Figure 8B shows the cross-section of the solid surface 22 along SS' and the hemispherical hydrophobic depressions. Advantages of this embodiment include less material removal from the solid surface 22 during its manufacture and a minimized surface area of the solid surface that must be coated by the electrically insulating layer 50.

[0049] All embodiments of the surface arrangement have in common that the gas layer 40 forms a gas-liquid interface 3 when the surface arrangement is used in a liquid, and the gas layer 40 separates the respective electrically conductive element (substrate layer 12 or solid surface 22) from the liquid 1. The electrical circuit is interrupted as long as a closed gas layer 40 exists between the liquid 1 and the electrically conductive substrate layer 12 accessible to the liquid 1, or the electrically conductive solid surface 22 accessible to the liquid 1 (see Fig. 3, Fig. 5 and Fig. 7).

[0050] If the gas layer 40 is not continuous, i.e. the gas layer 40 does not completely cover the electrically conductive substrate layer 12, the liquid 1 is in direct contact with the electrically conductive substrate layer 12 and the circuit is closed (see Fig. 9A). As a result, a current flows, causing the electrolysis of the liquid 1. This means that the current flow causes the reduction or oxidation of the liquid at the interface to the electrically conductive substrate layer 12 and leads to the local formation of gas (see Fig. 9B). If the liquid is, for example, water, oxygen or hydrogen is formed. The resulting gas displaces the intruding liquid and again forms a closed gas layer 40 between the liquid 1 and the electrically conductive substrate layer 12 accessible to the liquid 1 (see Fig. 9C).

[0051] The same applies analogously to the direct contact of the liquid 1 with the electrically conductive solid surface 22 in the hydrophobic depressions 32.

[0052] In a first embodiment, a solid surface is completely coated with an electrically conductive substrate layer made of graphite. A mesh structure made of interwoven polytetrafluoroethylene fibers is applied to the electrically conductive substrate layer. The round polytetrafluoroethylene fibers have a diameter (B) of 200 µm, resulting in a height (H) of the mesh structure of 200 µm to 400 µm. The maximum extent of the gaps (D p ), which is limited by the mesh of the grid structure, is 300 µm. By applying a voltage, the gas layer could be successfully regenerated by electrolysis in experiments as described above.

[0053] In a second embodiment, a solid surface made of copper has spherical depressions. The solid surface is coated on its outer surface with an electrically insulating layer of polytetrafluoroethylene, with the electrically insulating polytetrafluoroethylene layer also coating a portion of the inner surface of the spherical depressions. The depth (T) of the hydrophobic depressions is 80 µm, and the diameter D k is 100 µm and the distance B k neighboring hydrophobic depressions is 30 µm. List of reference symbols 100, 200 surface arrangement 1 liquid 2 Cavitation bubble 3 Gas-liquid interface 4 Solid-liquid interface 10 DC voltage source 12 electrically conductive substrate layer 14 Electrode 20 Solid surface 22 electrically conductive solid surface 30 hydrophobic structural elements 32 hydrophobic recess 34 fibers 40 closed gas layer 50 electrically insulating layer

Claims

[1] A surface arrangement (100, 200) for reducing cavitation erosion, comprising: a DC voltage source (10) connected to an electrode (14); and a) a solid surface (20), an electrically conductive substrate layer (12) arranged directly on the solid surface (20), a plurality of hydrophobic structural elements (30) arranged so as to protrude from the surface of the solid-state surface (20), wherein a height (H) of the hydrophobic structural elements (30) measured orthogonally to the solid-state surface (20) is 10 µm to 900 µm, the hydrophobic structural elements (30) delimit a plurality of intermediate spaces, the respective bottom of which forms the electrically conductive substrate layer (12), and the intermediate spaces are each filled with a closed gas layer (40); or b) an electrically conductive solid surface (22), a plurality of hydrophobic depressions (32) which protrude into the electrically conductive solid surface (22), wherein a depth (T) of the hydrophobic depressions (32) measured orthogonally to the surface of the solid surface (22) is 10 µm to 900 µm and the hydrophobic depressions (32) are filled with a closed gas layer (40), an electrically insulating layer (50) covering the outer surface of the electrically conductive solid surface (22) and partially covering the inner surface of the hydrophobic depressions (32); wherein the DC voltage source (10) is connected to the electrically conductive substrate layer (12) according to a) or to the electrically conductive solid surface (22) according to b); and wherein the DC voltage source (10), the electrode (14) and the electrically conductive substrate layer (12) according to a), or the electrically conductive solid surface (22) according to b) are designed to form an electrolysis circuit when the surface arrangement is used in a liquid (1), and the electrolysis circuit between the electrode (14) and the electrically conductive substrate layer (12) according to a), or between the electrode (14) and the electrically conductive solid surface (22) according to b), is interrupted by the closed gas layer (40). [2] Surface arrangement according to claim 1, wherein the solid surface (20) is completely coated with the electrically conductive substrate layer (12) and the hydrophobic structural elements (30) are arranged directly on the electrically conductive substrate layer (12). [3] Surface arrangement according to one of claims 1 and 2, wherein the plurality of hydrophobic structural elements (30) forms a network structure. [4] Surface arrangement according to claim 3, wherein the network structure defines a plurality of gaps and the maximum extent of a gap (D p ) measured parallel to the surface of the solid surface is 10 µm to 2 mm. [5] Surface arrangement according to one of the preceding claims, wherein the hydrophobic structural elements (30) consist of an electrically insulating and hydrophobic material or are coated with a layer consisting of an electrically insulating and hydrophobic material. [6] Surface arrangement according to claim 1, wherein the hydrophobic depressions (32) are partially spherical or hemispherical in shape. [7] Surface arrangement according to one of claims 1 or 6, wherein the hydrophobic depressions (32) are interconnected. [8] A device having a surface, at least a portion of the surface comprising the surface arrangement according to any one of the preceding claims. [9] Use of the surface arrangement according to one of claims 1 to 7 for reducing cavitation erosion. [10] A method for reducing cavitation erosion on solid surfaces, comprising the steps: - Providing a surface arrangement (100, 200) comprising: a DC voltage source (10) connected to an electrode (14); and a) a solid surface (20), an electrically conductive substrate layer (12) arranged directly on the solid surface (20), a plurality of hydrophobic structural elements (30) arranged so as to protrude from the surface of the solid-state surface (20), wherein a height (H) of the hydrophobic structural elements (30) measured orthogonally to the solid-state surface (20) is 10 µm to 900 µm, the hydrophobic structural elements (30) delimiting a plurality of intermediate spaces, the respective bottom of which forms the electrically conductive substrate layer (12); or b) an electrically conductive solid surface (22), a plurality of hydrophobic depressions (32) which protrude into the electrically conductive solid surface (22), wherein a depth (T) of the hydrophobic depressions (10) measured orthogonally to the surface of the solid surface (22) is 10 µm to 900 µm and an electrically insulating layer (50) which covers the outer surface of the electrically conductive solid surface (22) and partially covers the inner surface of the hydrophobic depressions (32); wherein the DC voltage source (10) is connected to the electrically conductive substrate layer (12) according to a) or to the electrically conductive solid surface (22) according to b); and wherein according to a) the DC voltage source (10), the electrode (14), the electrically conductive substrate layer (12) and a liquid (1) form a closed electrolysis circuit, or according to b) the DC voltage source (10), the electrode (14), the electrically conductive solid surface (22) and a liquid (1) form a closed electrolysis circuit; - Simultaneous generation of gas by electrolysis of the liquid (1) at the interface between the liquid (1) and the electrically conductive substrate layer (12) according to a), or at the interface between the liquid (1) and the electrically conductive solid surface (22) according to b); and - Terminating the electrolysis by forming a closed gas layer (40) which interrupts the electrolysis circuit between the electrode (14) and the electrically conductive substrate layer (12) according to a) or the electrolysis circuit between the electrode (14) and the electrically conductive solid surface (22) according to b).

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