Hydrophobic electric heating ice preventing and removing device, system and method

Abstract

The invention provides a hydrophobic electric heating ice preventing and removing device, system and method, the device comprises a flexible heating layer, a composite conductive coating, a temperature sensor and a temperature controller, the flexible heating layer is a flexible film embedded with a heating wire, and the flexible heating layer is suitable for being attached to the surface of a base material; the surface of the flexible heating layer is coated with the composite conductive coating, and the composite conductive coating is prepared by mixing polydimethylsiloxane, a diluent and carbon black; the temperature sensor is connected to the surface of the composite conductive coating, and the temperature controller is electrically connected with the temperature sensor. According to the composite conductive coating, by adjusting the filling amount of the carbon black, cooperative regulation and control of hydrophobicity and conductivity are achieved, ice coating formation can be effectively prevented, ice coating falling can be accelerated, and energy consumption is reduced. The flexible heating layer can adapt to base materials with different curvatures, the application range is wide, and reliable operation can be achieved in the low-temperature and severe icing environment. According to the temperature controller, accurate temperature control can be achieved, heating according to needs is achieved, and the energy utilization efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of anti-icing and de-icing technology, and in particular to a hydrophobic electrothermal anti-icing and de-icing device, system and method. Background Technology

[0002] Wind turbine blades, power transmission and distribution equipment, outdoor electrical appliances, and electrical and electronic products are key facilities for ensuring energy supply, industrial production, and daily life. The safety and stability of these facilities are crucial to the reliable operation of the entire system. Installing anti-icing / de-icing devices on the surfaces of these devices aims to resist the corrosive effects of low-temperature icy and snowy environments and prevent performance degradation, malfunctions, or even damage caused by icing.

[0003] Currently, existing active de-icing methods, such as thermal de-icing and mechanical de-icing, often consume a lot of energy. For large equipment like wind turbine blades, excessive energy consumption can significantly offset the benefits of power generation. At the same time, mechanical de-icing may also damage the blade surface. Although simple hydrophobic coatings can reduce the adhesion of ice and delay icing to some extent, they are only effective under specific conditions such as wet snow and cannot cope with complex scenarios such as supercooled water freezing. Furthermore, they lack active de-icing capabilities and cannot completely solve the icing problem.

[0004] In summary, existing anti-icing technologies have limitations such as high energy consumption, poor adaptability, and limited functionality. In particular, they are unable to meet the requirements of wind turbine blades for efficient, energy-saving, safe, and reliable anti-icing and de-icing. At the same time, they cannot fully adapt to the complex operating conditions of other outdoor equipment. Therefore, there is an urgent need to develop a new type of anti-icing and de-icing device that combines efficient anti-icing, active de-icing, energy-saving, and reliable characteristics to improve the operational safety and economy of various outdoor equipment in harsh environments. Summary of the Invention

[0005] The purpose of this invention is to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a hydrophobic electrothermal anti-icing and de-icing device, system, and method, which can efficiently prevent icing, actively de-ic, improve the safety and operational reliability of equipment in low-temperature icy and snowy environments, and reduce energy consumption.

[0006] The first aspect of this invention provides a hydrophobic electrothermal anti-icing device, comprising: a flexible heating layer, a composite conductive coating, a temperature sensor, and a temperature controller. The flexible heating layer is a flexible film with embedded heating wires, the heating wires being multi-stranded and arranged in a folded pattern. The flexible heating layer is adapted to adhere to the surface of a substrate, and the heating wires are connected to a power source. The composite conductive coating is applied to the surface of the flexible heating layer and is prepared by mixing polydimethylsiloxane, a diluent, and carbon black, wherein the carbon black accounts for 6-12 wt.% of the total weight. The temperature sensor is connected to the surface of the composite conductive coating. The temperature controller is connected between the heating wires and the power source, and the temperature controller is electrically connected to the temperature sensor.

[0007] In some embodiments, the diluent is OS-20 silica gel diluent, the mass ratio of polydimethylsiloxane to diluent is 1:5, and polydimethylsiloxane, diluent and carbon black are stirred by a homogenizer until they are evenly mixed.

[0008] In some embodiments, the carbon black constitutes 6 wt.% of the total mass.

[0009] In some embodiments, the flexible membrane is made of polyimide.

[0010] In some embodiments, the flexible membrane is bonded to the composite conductive coating using epoxy resin adhesive.

[0011] In some embodiments, the surface area of ​​the flexible heating layer is equal to the surface area of ​​the composite conductive coating.

[0012] In some embodiments, the temperature sensor is attached to the center of the surface of the composite conductive coating.

[0013] In some embodiments, the temperature controller has an accuracy of ±0.1°C.

[0014] A second aspect of the present invention provides a hydrophobic electrothermal anti-icing and de-icing system, including the above-mentioned hydrophobic electrothermal anti-icing and de-icing device, and also including an environmental monitoring device, which is electrically connected to a temperature controller to optimize the heating strategy of the flexible heating layer according to real-time climate and external environment.

[0015] A third aspect of the present invention provides a hydrophobic electrothermal anti-icing method, which utilizes the above-mentioned hydrophobic electrothermal anti-icing device and includes the following steps: A composite conductive coating was prepared using polydimethylsiloxane, diluent, and carbon black.

[0016] Cut the flexible film according to the size of the substrate, so that the flexible film covers the surface of the substrate, and embed the heating wire between the two flexible films in a folded-back manner. Then, squeeze and bond to form a flexible heating layer.

[0017] The flexible heating layer is attached to the surface of the substrate.

[0018] The composite conductive coating is uniformly applied to the surface of the flexible heating layer and then cured.

[0019] A temperature sensor is attached to the composite conductive coating, and a temperature controller is connected between the heating wire and the power supply. The temperature controller is also electrically connected to the temperature sensor. The temperature controller adjusts the temperature and on / off state of the flexible heating layer in real time based on the temperature information from the temperature sensor, thereby adjusting the temperature of the composite conductive coating. Attached Figure Description

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings. in: Figure 1 This is a schematic diagram of the structure of the hydrophobic electrothermal anti-icing device according to an embodiment of the present invention; Figure 2 for Figure 1 A schematic diagram of the arrangement of heating wires in the flexible heating layer; Figure 3 The graph shows the relationship between the contact angle of the droplet and the composite conductive coating and the carbon black content. Figure 4 This is a schematic diagram showing the contact angle between a droplet and a composite conductive coating when the carbon black content is 10 wt.%. Figure 5 This is a photograph of the surface of the lightweight hydrophobic coating in Example 1 when it is covered with ice at 3±1℃; Figure 6 This is a photograph of the lightweight hydrophobic coating in Example 1 melting into water droplets at 5±1°C; Figure 7 This is a photograph of the superhydrophobic coating in Example 2 when its surface is covered with ice at 3±1℃; Figure 8 This is a photograph of the superhydrophobic coating in Example 2 melting into water droplets at 5±1℃. Figure 9 This is a photograph of the hydrophilic sample in Comparative Example 1 when the ice melted into water droplets at 5±1℃. Figure 10 This is a photograph of the hydrophilic sample in Comparative Example 1 when a large number of water droplets adhere to it at 7±1℃. Figure label: 1. Temperature sensor; 2. Temperature controller; 3. Power supply; 4. Composite conductive coating; 5. Flexible heating layer; 501. Heating wire; 502. Flexible film; 6. Substrate. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] The hydrophobic electrothermal anti-icing device, system, and method of the present invention are described below with reference to the accompanying drawings.

[0023] like Figure 1 and Figure 2As shown, the first aspect of the present invention provides a hydrophobic electrothermal anti-icing device, comprising: a composite conductive coating 4, a flexible heating layer 5, a temperature sensor 1, and a temperature controller 2. The flexible heating layer 5 is a flexible film 502 with embedded heating wires 501. The heating wires 501 are multi-stranded and arranged in a folded pattern. The flexible heating layer 5 is adapted to adhere to the surface of a substrate 6. The heating wires 501 are connected to a power supply 3. The composite conductive coating 4 is coated on the surface of the flexible heating layer 5. The composite conductive coating 4 is prepared by mixing polydimethylsiloxane (PDMS), a diluent, and carbon black (CB), wherein the carbon black accounts for 6~12 wt.% of the weight. The temperature sensor 1 is connected to the surface of the composite conductive coating 4. The temperature controller 2 is connected between the heating wires 501 and the power supply 3, and the temperature controller 2 is electrically connected to the temperature sensor 1.

[0024] The composite conductive coating 4 of this invention is in direct contact with the environment and serves as an interface with ice. The composite conductive coating 4 uses polydimethylsiloxane as a hydrophobic matrix, carbon black as a thermally conductive functional phase, and a diluent to adjust the viscosity. By adjusting the amount of carbon black (weight percentage), the composite conductive coating 4 achieves synergistic control of hydrophobicity and conductivity, ranging from mild hydrophobicity (contact angle ≈ 109°) to superhydrophobicity (contact angle ≈ 149°, such as...). Figure 4 The surface wettability (as shown) is customized, and the conductivity varies with the carbon black content to match the thermal conductivity of the flexible heating layer 5. The relationship between the contact angle of the droplet and the composite conductive coating 4 and the carbon black content is as follows: Figure 3 As shown.

[0025] Due to the hydrophobic surface properties of the composite conductive coating 4, the actual contact area of ​​the solid-liquid interface is greatly reduced. With the uniform heating effect of the flexible heating layer 5, the energy required for the droplets to separate from the coating surface and evaporate is significantly reduced, which can effectively prevent ice formation and accelerate ice removal. Compared with hydrophilic surfaces, energy consumption is reduced by about 28%, greatly reducing power loss.

[0026] The flexible heating layer 5 of this invention has flexible properties and is used to provide heat to the composite conductive coating 4. The flexible heating layer 5 can be adapted to substrates 6 with different curvatures, such as glass fiber reinforced epoxy boards. It is especially suitable for surface installation of various outdoor electrical appliances, electrical and electronic products with complex shapes and structures such as wind turbine blades and power transmission lines that are at risk of icing. It has a wide range of applications and can operate reliably in low temperature and harsh icing environments, significantly improving the safety and operational stability of various equipment in low temperature and snowy environments.

[0027] The heating wire 501 in this embodiment of the invention has a folded-back structure layout, which can ensure uniform heat distribution on the surface of the composite conductive coating 4, solve the problem of local overheating or uneven heat transfer of traditional heating elements, and significantly improve the anti-icing and de-icing effects and stability.

[0028] The temperature controller 2 of this invention can adjust the temperature and on / off state of the flexible heating layer 5 in real time according to the temperature information of the temperature sensor 1, thereby adjusting the temperature of the composite conductive coating 4, forming a closed-loop feedback system to achieve precise temperature control, reduce energy consumption, ensure the safe and efficient operation of the anti-icing device of this invention, avoid energy waste or de-icing failure caused by temperature fluctuations, achieve on-demand heating, and improve energy utilization efficiency.

[0029] Furthermore, the heating wire 501 is a 5Ω metal wire.

[0030] Furthermore, temperature sensor 1 is an NTC temperature sensor.

[0031] Furthermore, the temperature controller 2 controls the temperature and on / off state of the flexible heating layer 5 through a built-in algorithm, stabilizing the temperature of the composite conductive coating 4 within the target value ±1℃ range, such as 5±1℃, 7±1℃, etc.

[0032] Furthermore, the power supply 3 adopts a 12V DC power supply to provide unified power to the flexible heating layer 5, temperature sensor 1 and temperature controller 2, so as to ensure the stable operation of the anti-icing device in this embodiment of the invention, while reducing the safety risks such as leakage faults caused by high voltage, and improving the safety of the anti-icing device in this embodiment of the invention. It is suitable for complex outdoor power supply scenarios (such as wind power and power transmission and transformation systems).

[0033] Furthermore, the folded-back arrangement of the heating wire 501 can take many forms, which will not be elaborated here. Figure 2 This is one of the forms.

[0034] In some embodiments, the diluent is OS-20 silica gel diluent, the mass ratio of polydimethylsiloxane to diluent is 1:5, and polydimethylsiloxane, diluent and carbon black are stirred by a homogenizer until they are evenly mixed.

[0035] If the amount of thinner is too small, the coating will lack viscosity, resulting in poor adhesion of the coating to the surface of the flexible heating layer 5. If the amount of thinner is too large, it will lead to waste of thinner.

[0036] In some embodiments, the carbon black accounts for 6 wt.% of the total weight. When the carbon black content is 6 wt.%, a light hydrophobic coating is formed, which can achieve the same effect as a superhydrophobic coating without the need to construct the micro-nano hierarchical structure required for superhydrophobic coatings. The material cost is reduced by more than 30%, and the mechanical durability is better. This solves the problem of superhydrophobic coatings being prone to failure due to wear, and balances cost-effectiveness and durability, making it suitable for large-scale industrial applications.

[0037] In some embodiments, the flexible membrane 502 is made of polyimide. It has good insulation properties, preventing the heating wire 501 from conducting electricity to the substrate 6.

[0038] In some embodiments, the flexible membrane 502 is bonded to the composite conductive coating 4 with epoxy resin adhesive, ensuring that there are no air bubbles after bonding.

[0039] In some embodiments, the surface area of ​​the flexible heating layer 5 is equal to the surface area of ​​the composite conductive coating 4. This ensures the heat transfer effect of the flexible heating layer 5 on the composite conductive coating 4.

[0040] In some embodiments, the temperature sensor 1 is attached to the center of the surface of the composite conductive coating 4. This improves the accuracy of temperature monitoring.

[0041] Furthermore, several temperature sensors 1 can be set according to the surface area of ​​the composite conductive coating 4, and the data of all temperature sensors 1 can be summarized in the temperature controller 2 to obtain more accurate temperature data and reduce errors.

[0042] In some embodiments, the temperature controller 2 has an accuracy of ±0.1°C. This improves the accuracy of temperature control over the composite conductive coating 4.

[0043] A second aspect of the present invention provides a hydrophobic electrothermal anti-icing and de-icing system, including the above-mentioned hydrophobic electrothermal anti-icing and de-icing device, and also including an environmental monitoring device, which is electrically connected to a temperature controller 2 to optimize the heating strategy of the flexible heating layer 5 according to real-time climate and external environment.

[0044] By setting up an environmental monitoring device, the hydrophobic electrothermal anti-icing device of this invention can be adapted to different icing environments, such as harsh icing environments like rime ice, thereby improving reliability.

[0045] A third aspect of the present invention provides a hydrophobic electrothermal anti-icing method, which utilizes the above-mentioned hydrophobic electrothermal anti-icing device and includes the following steps: S1. A composite conductive coating was prepared using polydimethylsiloxane, diluent and carbon black.

[0046] S2. Cut the flexible film 502 according to the size of the substrate 6, so that the flexible film 502 covers the surface of the substrate 6, and embed the heating wire 501 between the two flexible films 502 in a folded manner, and squeeze and bond them to form a flexible heating layer 5.

[0047] S3. Attach the flexible heating layer 5 to the surface of the substrate 6, uniformly coat the composite conductive coating 4 onto the surface of the flexible heating layer 5, and cure.

[0048] S4. Attach the temperature sensor 1 to the composite conductive coating 4. Connect the temperature sensor 1 and the heating wire 501 to the temperature controller 2. Connect the temperature controller 2 to the power supply 3. The temperature controller 2 adjusts the temperature and on / off state of the flexible heating layer 5 in real time according to the temperature information of the temperature sensor 1, thereby adjusting the temperature of the composite conductive coating 4.

[0049] The method of this invention can effectively prevent icing formation and accelerate icing removal, while reducing power consumption. It is applicable to various outdoor electrical appliances, electrical and electronic products with complex shapes and structures, such as wind turbine blades and power transmission lines, that are at risk of icing.

[0050] The present invention will be further illustrated by specific embodiments below.

[0051] Example 1 Glass fiber reinforced epoxy board was selected as the coating substrate 6, and its surface needed to be wiped clean with alcohol to remove impurities. The composite conductive coating 4 is composed of polydimethylsiloxane (PDMS, Dow Dowsil 1-2577, cured content 72.8 wt.%), carbon black (CB, Lion ECP600JD) and diluent (Dow-Corning OS-20), wherein polydimethylsiloxane is a hydrophobic matrix, carbon black is a conductive functional phase, and diluent is used to adjust viscosity. Polydimethylsiloxane and diluent are mixed and diluted at a mass ratio of 1:5, and then 6 wt.% carbon black is added. The mixture is stirred for 1 minute using a homogenizer until it is homogeneous, thus forming a coating.

[0052] Select a matching flexible heating layer 5 according to the size of the substrate 6, attach the flexible heating layer 5 to the surface of the substrate 6, and connect the heating wire 501 to the temperature controller 2 and the power supply 3.

[0053] The coating was uniformly deposited on the surface of the flexible heating layer 5 using a near-field spraying method and cured at room temperature for 24 hours to form a slightly hydrophobic composite conductive coating 4. The resulting sample of the slightly hydrophobic coating had a contact angle of approximately 109° between water droplets and the coating surface.

[0054] Testing process: The test protocol, referencing the power industry standard "DLT1247-2013-Test Method for Icing and Flashover of High Voltage DC Insulators," simulates natural icing conditions by spraying supercooled water at low temperatures. The ambient temperature in the climatology chamber was set at -5 to -4°C. Supercooled water droplets were sprayed with an average droplet size of approximately 80 micrometers, and the spray flow rate was controlled at 80–100 L / h·m³. 2 During the icing process, the indoor climate fan is intermittently started and generates circulating air at 1~12m / s, and ice forms on the surface of the composite conductive coating 4.

[0055] When the samples of the lightweight hydrophobic coating were tested, the ice did not melt when the heating temperature was 3±1℃. When the temperature was further increased to 5±1℃, the ice melted into water droplets and slid off the coating surface.

[0056] Example 2 The difference from Example 1 is that the carbon black accounts for 10 wt.% of the sample, and the superhydrophobic coating sample is obtained with a contact angle of about 149° between the water droplet and the coating surface.

[0057] Testing process: The test protocol, referencing the power industry standard "DLT1247-2013-Test Method for Icing and Flashover of High Voltage DC Insulators," simulates natural icing conditions by spraying supercooled water at low temperatures. The ambient temperature in the climatology chamber was set at -5 to -4°C. Supercooled water droplets were sprayed with an average droplet size of approximately 80 micrometers, and the spray flow rate was controlled at 80–100 L / h·m³. 2 During the icing process, the indoor climate fan is intermittently started and generates circulating air at 1~12m / s, and ice forms on the surface of the composite conductive coating 4.

[0058] When the superhydrophobic coating sample was tested, the ice did not melt when the heating temperature was 3±1℃. When the temperature was further increased to 5±1℃, the ice melted into water droplets and slid off the coating surface.

[0059] Comparative Example 1 The difference from Example 1 is that no hydrophobic coating was sprayed on the flexible heating layer 5, making this sample a hydrophilic sample. The contact angle between the water droplet and the surface of the flexible heating layer 5 is less than 90°.

[0060] Testing process: The test protocol, referencing the power industry standard "DLT1247-2013-Test Method for Icing and Flashover of High Voltage DC Insulators," simulates natural icing conditions by spraying supercooled water at low temperatures. The ambient temperature in the climatology chamber was set at -5 to -4°C. Supercooled water droplets were sprayed with an average droplet size of approximately 80 micrometers, and the spray flow rate was controlled at 80–100 L / h·m³. 2 During the icing process, the indoor ventilation fan is started intermittently and generates circulating air at a speed of 1~12m / s, causing ice to form on the surface of the flexible heating layer 5.

[0061] When testing hydrophilic samples, at a heating temperature of 5±1℃, although the ice melted into water droplets, a large number of water droplets adhered to the sample surface. When the temperature was further increased to 7±1℃, a large number of water droplets still adhered to the sample surface.

[0062] By comparing and analyzing the test results of Examples 1 and 2 with those of Comparative Example 1, the following conclusions are drawn: (1) When the coating surfaces in Examples 1 and 2 are heated to 5±1℃, both the light hydrophobic coating surface and the superhydrophobic coating surface can significantly delay the freezing process, and only a small amount of water droplets are attached to the coating surface. However, even when the surface of the uncoated hydrophilic sample in Comparative Example 1 is heated to 7±1℃, a large number of water droplets are still attached to the sample surface. The only way to prevent refreezing is to evaporate the water droplets by heating for a long time, but this will greatly increase the energy consumption.

[0063] (2) Comparing the light hydrophobic coating of Example 1 with the superhydrophobic coating of Example 2, the light hydrophobic coating achieves the same effect with less carbon black. Therefore, the light hydrophobic coating achieves an ideal balance between practical factors such as anti-icing effect, durability, and cost, and has significant potential for scalable industrial applications.

[0064] In this invention, the term "some embodiments," etc., refers to specific features, structures, materials, or characteristics described in connection with that embodiment, which are included in at least one embodiment of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiments. Furthermore, the specific features, structures, materials, or characteristics described may be combined in a suitable manner in any one or more embodiments. Moreover, those skilled in the art can combine and integrate the different embodiments described in this specification and the features of the different embodiments without contradiction.

[0065] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A hydrophobic electrothermal anti-icing device, characterized in that, include: A flexible heating layer, wherein the flexible heating layer is a flexible film with embedded heating wires, the heating wires are multi-stranded and arranged in a folded-back layout, the flexible heating layer is adapted to be attached to the surface of a substrate, and the heating wires are connected to a power source; A composite conductive coating is applied to the surface of the flexible heating layer. The composite conductive coating is prepared by mixing polydimethylsiloxane, a diluent, and carbon black, wherein the carbon black accounts for 6-12 wt.% by weight. A temperature sensor, wherein the temperature sensor is connected to the surface of the composite conductive coating; A temperature controller is connected between the heating wire and the power supply, and the temperature controller is electrically connected to the temperature sensor.

2. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The diluent is OS-20 silica gel diluent, and the mass ratio of polydimethylsiloxane to diluent is 1:

5. Polydimethylsiloxane, diluent and carbon black are mixed evenly by homogenizing.

3. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The carbon black content is 6 wt.%.

4. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The flexible membrane is made of polyimide.

5. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The flexible membrane is bonded to the composite conductive coating with epoxy resin adhesive.

6. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The surface area of ​​the flexible heating layer is equal to the surface area of ​​the composite conductive coating.

7. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The temperature sensor is attached to the center of the surface of the composite conductive coating.

8. The hydrophobic electrothermal anti-icing device according to claim 1, characterized in that, The temperature controller has an accuracy of ±0.1℃.

9. A hydrophobic electrothermal anti-icing system, characterized in that, The device includes the hydrophobic electrothermal anti-icing device according to any one of claims 1-8, and further includes an environmental monitoring device, which is electrically connected to the temperature controller to optimize the heating strategy of the flexible heating layer according to real-time climate and external environment.

10. A hydrophobic electrothermal de-icing method, characterized in that, The hydrophobic electrothermal anti-icing device according to any one of claims 1-8 includes the following steps: A composite conductive coating was prepared using polydimethylsiloxane, diluent, and carbon black. Cut the flexible film according to the size of the substrate, so that the flexible film covers the surface of the substrate, and embed the heating wire between the two layers of the flexible film in a folded-back manner, and then squeeze and bond it to form a flexible heating layer. The flexible heating layer is attached to the surface of the substrate, and the composite conductive coating is uniformly applied to the surface of the flexible heating layer and then cured. A temperature sensor is attached to the composite conductive coating, and a temperature controller is connected between the heating wire and the power supply. The temperature controller is electrically connected to the temperature sensor. The temperature controller adjusts the temperature and on / off state of the flexible heating layer in real time based on the temperature information from the temperature sensor, thereby adjusting the temperature of the composite conductive coating.

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