Liquid leakage protection device

Abstract

A liquid leakage protection device, which relates to the technical field of cold-plate-type liquid cooling. The liquid leakage protection device comprises a cold plate, wherein the cold plate comprises a heated plate and a cover plate, the heated plate and the cover plate being connected to form a liquid cooling cavity for containing a liquid-cooling working medium. The liquid leakage protection device further comprises an enclosure structure arranged at the periphery of the liquid cooling cavity, wherein the enclosure structure arranged at the periphery of the liquid cooling cavity can prevent the liquid-cooling working medium leaking from the liquid cooling cavity from flowing onto an operating component, which comes into contact with the heated plate, thereby preventing damage to the operating component and preventing data security from being affected; moreover, the enclosure structure and the cold plate form a liquid storage tank to store the liquid-cooling working medium leaking from the liquid cooling cavity, and thus it can be ensured that after the liquid-cooling working medium leaks, there is sufficient time to save data and then safely shut down an apparatus. In the liquid leakage protection device, the enclosure and collection of a liquid leak are performed on the cold plate where liquid leakage frequently occurs, and thus it is ensured that a server apparatus can be safely shut down, and hardware and data security of the server are also protected.

Description

Liquid leakage protection device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on January 19, 2024, with application number 202410084899.3 and invention name “A Liquid Leakage Protection Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of cold plate liquid cooling, and in particular to a liquid leakage protection device. Background Art

[0003] At present, cold plate liquid cooling technology is a mainstream heat dissipation technology for servers.

[0004] In the existing system, the cold plate is the core component of the cold plate liquid cooling device. The cold plate is used to contact working parts such as the motherboard. The liquid cooling medium flows through the cold plate through connecting pipes or setting flow channels. The advantage of using this heat dissipation method is that it converts the traditional convection heat exchange between air and the motherboard (fan heat exchange) into convection heat exchange and heat conduction between liquid cooling medium-cold plate-motherboard, which greatly increases the convection heat transfer coefficient and has obvious advantages in motherboard heat dissipation.

[0005] However, in the process of implementing the present invention, the inventors found that there are at least the following problems in the prior art:

[0006] Manufacturing defects in the cold plate cause the cold plate to be located at a high risk of leakage in the entire cold plate liquid cooling device. Liquid coolant leaking from the cold plate will pose a serious threat to the server's hardware and data security. The current way to deal with leakage is to urgently power off the entire server equipment once a leak is detected. However, the emergency power-off operation of the server equipment will still cause damage to the server hardware and affect the security of the data.

[0007] Therefore, it is necessary for those skilled in the art to provide a leakage protection device that can ensure the safe shutdown of server equipment in a timely manner.

[0008] Summary of the Invention

[0009] The purpose of this application is to provide a liquid leakage protection device that can collect liquid cooling medium leaked from the cold plate, thereby ensuring the safe shutdown of the equipment.

[0010] To achieve the above-mentioned objectives, the present application provides a liquid leakage protection device, including a cold plate, the cold plate including a heated plate and a cover plate, the heated plate and the cover plate are connected to form a liquid cooling chamber for accommodating liquid cooling medium, the liquid leakage protection device also includes a retaining structure, the retaining structure is arranged on the periphery of the liquid cooling chamber to prevent the liquid cooling medium leaked from the liquid cooling chamber from flowing to the working parts in contact with the heated plate, the retaining structure and the cold plate form a liquid storage tank, so that the liquid cooling medium leaked from the liquid cooling chamber can be stored in the liquid storage tank.

[0011] In some embodiments, the enclosure structure and the cold plate further form a guide channel connected to the liquid storage tank, and the liquid cooling medium leaked from the liquid cooling cavity is guided through the guide channel and then flows into the liquid storage tank.

[0012] In some embodiments, the enclosure structure includes:

[0013] A ring is provided around the cover plate to form a liquid storage tank;

[0014] The blocking portion is connected to the bottom of the enclosure to form a guide channel and block the path for the liquid-cooling medium in the liquid-cooling cavity to leak to the working component.

[0015] In some embodiments, the blocking portion comprises:

[0016] An outer edge is provided on the heated plate and extends out of the cover plate;

[0017] A shielding plate is arranged on the outer periphery of the enclosure, and the shielding plate abuts against the outer edge;

[0018] The sealing retaining ring is abutted between the outer edge and the shielding plate to seal the gap between the outer edge and the shielding plate.

[0019] In some embodiments, a mounting groove is provided on the outer edge, the sealing retaining ring is installed in the mounting groove, and the depth of the mounting groove is less than the thickness of the sealing retaining ring.

[0020] In some embodiments, the baffles are distributed around the ring, and the size of the baffles on both sides of the ring along the first direction is larger than the size of the baffles on both sides of the ring along the second direction, so that the baffles can cover the working parts to prevent the liquid cooling medium leaking from the pipes connected to the cold plate from dripping into the liquid storage tank and causing the liquid cooling medium to splash onto the working parts.

[0021] In some embodiments, an outer cover is further included, which is arranged on the ring to prevent the liquid cooling medium in the liquid storage tank from leaking out.

[0022] In some embodiments, a liquid pumping mechanism is further included, which is connected to the liquid storage tank to extract the liquid cooling medium in the liquid storage tank. The liquid pumping mechanism includes:

[0023] a liquid extraction tube, one end of which extends into the liquid storage tank;

[0024] A liquid extraction component connected to a liquid extraction pipe to extract the liquid cooling medium in the liquid storage tank through the liquid extraction pipe;

[0025] A liquid leakage detection component is provided in the liquid storage tank to detect the amount of liquid cooling medium in the liquid storage tank;

[0026] The control component is electrically connected to the leakage detection component and the liquid extraction component to control the liquid extraction component to open and extract the liquid cooling medium in the liquid storage tank when the amount of the liquid cooling medium in the liquid storage tank exceeds the warning amount.

[0027] In some embodiments, the cover plate is provided with a liquid collecting trough and a guide slope located on the periphery of the liquid collecting trough. The liquid cooling medium on the cover plate is guided by the guide slope and collected in the liquid collecting trough, and the liquid extraction pipe extends into the liquid collecting trough.

[0028] In some embodiments, the liquid leakage detection member is a sheet-like structure, and the liquid leakage detection member covers the surface of the cover plate away from the heated plate.

[0029] Compared with the above background technology, the leakage protection device provided in the embodiment of the present application includes a cold plate, which includes a heated plate and a cover plate. The heated plate and the cover plate are connected to form a liquid cooling chamber for accommodating liquid cooling medium. Furthermore, the leakage protection device also includes a barrier structure provided on the periphery of the liquid cooling chamber. It can be seen that, on the one hand, the barrier structure provided on the periphery of the liquid cooling chamber blocks the liquid cooling medium leaked from the liquid cooling chamber from flowing to the working parts in contact with the heated plate, thereby preventing damage to the working parts and affecting data security. On the other hand, the barrier structure and the cold plate form a liquid storage tank to store the liquid cooling medium leaked from the liquid cooling chamber. This ensures that there is enough time to save data after the liquid cooling medium leaks, and then the equipment can be safely shut down. Compared with the traditional setting method, the leakage protection device provided in the embodiment of the present application, for the cold plate position where leakage is high, carries out leakage enclosure and collection processing, so as to ensure that the server equipment can be safely shut down, protecting the hardware and data security of the server. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0031] FIG1 is a schematic structural diagram of a liquid leakage protection device according to an embodiment of the present application;

[0032] FIG2 is a top view of the liquid leakage protection device shown in FIG1 ;

[0033] FIG3 is a cross-sectional view of the liquid leakage protection device shown in FIG1 ;

[0034] FIG4 is a front view of FIG3;

[0035] FIG5 is a schematic structural diagram of the assembly of the liquid leakage protection device and the outer cover shown in FIG1 ;

[0036] FIG6 is a schematic diagram of the application of the liquid leakage protection device in an embodiment of the present application;

[0037] FIG. 7 is a top view of FIG. 6 .

[0038] Among them: 1-leakage protection device; 11-cold plate, 12-enclosing structure, 13-liquid storage tank, 14-guiding channel, 15-outer cover, 16-liquid extraction mechanism; 111-heating plate, 112-cover plate, 113-liquid cooling chamber; 121-enclosing ring, 122-sealing part; 1221-outer edge, 1222-shielding plate, 1223-sealing ring; 12211-installation slot. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] In order to enable those skilled in the art to better understand the present application, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0041] It should be noted that the directional terms such as "upper end, lower end, left side, right side" described below are all defined based on the drawings in the specification.

[0042] 1 to 4 , the leakage protection device 1 provided in the embodiment of the present application includes a cold plate 11 , the cold plate 11 includes a heated plate 111 and a cover plate 112 , and the heated plate 111 and the cover plate 112 are connected to form a liquid cooling chamber 113 for accommodating a liquid cooling medium.

[0043] It should be noted that the cold plate 11 in this embodiment is formed by welding the heated plate 111 and the cover plate 112. Due to limitations of the welding process, a weld (also known as a leakage gap) will be formed after the heated plate 111 and the cover plate 112 are connected, causing the liquid cooling medium in the liquid cooling chamber 113 to leak out from the leakage gap.

[0044] To this end, the leakage protection device 1 also includes a retaining structure 12, which is arranged on the periphery of the liquid cooling chamber 113 to prevent the liquid cooling medium leaking from the liquid cooling chamber 113 from flowing to the working parts in contact with the heated plate 111. In addition, the retaining structure 12 and the cold plate 11 form a liquid storage tank 13, so that the liquid cooling medium leaking from the liquid cooling chamber 113 can be stored in the liquid storage tank 13.

[0045] It can be seen that, on the one hand, the enclosure structure 12 arranged at the periphery of the liquid-cooling chamber 113 blocks the liquid-cooling medium leaked from the liquid-cooling chamber 113 from flowing to the working parts in contact with the heated plate 111, thereby preventing damage to the working parts and affecting data security. On the other hand, a liquid storage tank 13 is formed by the enclosure structure 12 and the cold plate 11 to store the liquid-cooling medium leaked from the liquid-cooling chamber 113. This ensures that there is enough time to save data after the liquid-cooling medium leaks, and then the equipment can be safely shut down.

[0046] Compared with traditional methods, the leakage protection device 1 provided in the embodiment of the present application carries out leakage containment and collection processing for the cold plate 11 position where leakage is frequent, thereby ensuring that the server equipment can be shut down safely and protecting the hardware and data security of the server.

[0047] In some embodiments, the liquid storage tank 13 may be located on the periphery of the cold plate 11 and adjacent to the cold plate 11 . In this way, the liquid coolant in the liquid cooling cavity 113 can be directly stored in the liquid storage tank 13 after leaking from the cold plate 11 .

[0048] In some embodiments, the liquid storage tank 13 is located above the cover plate 112. Furthermore, the enclosure structure 12 and the cold plate 11 also form a guide channel 14 connected to the liquid storage tank 13. In this way, the liquid cooling medium leaked from the liquid cooling chamber 113 is guided through the guide channel 14 and then flows into the liquid storage tank 13.

[0049] The following is a detailed description using the example of the liquid storage tank 13 being located above the cover plate 112 .

[0050] The enclosure structure 12 includes a ring 121 and a sealing portion 122. The ring 121 surrounds the cover plate 112, and the ring 121 and the cover plate 112 together form the liquid storage tank 13. The ring 121 is a rectangular ring structure that wraps around the outer periphery of the cover plate 112, which is equivalent to establishing a fence structure outside the cover plate 112, facilitating the storage of leaked liquid cooling medium on the cover plate 112. The sealing portion 122 is connected to the bottom of the ring 121 to form a guide channel 14 together with the cold plate 11, and block the path of liquid cooling medium in the liquid cooling chamber 113 from leaking to the working components.

[0051] In other words, the cover plate 112 serves as the bottom surface of the liquid storage tank 13 , and the surrounding ring 121 serves as the side surface of the liquid storage tank 13 , thereby forming a liquid storage structure with an open top.

[0052] It can be seen that the sealing portion 122 and the partial ring 121 are both arranged around the outer periphery of the cover plate 112, thereby forming a guide channel 14 with the cold plate 11. The guide channel 14 can be a gap between the enclosure structure 12 and the cold plate 11. One end of the guide channel 14 extends to the liquid leakage gap of the cold plate 11, and the other end extends to the liquid storage tank 13. The two ends of the guide channel 14 are respectively connected to the liquid leakage gap of the cold plate 11 and the liquid storage tank 13. In this way, the liquid cooling medium leaked from the liquid cooling chamber 113 is guided through the guide channel 14 and flows into the liquid storage tank 13.

[0053] Of course, according to actual needs, all or most of the structure of the guide channel 14 is a structure arranged along the longitudinal or vertical direction, or a small part of the guide channel 14 can be arranged along the transverse or horizontal direction, wherein the longitudinal guide channel 14 is the gap between the enclosure structure 12 and the cover plate 112, and the transverse guide channel 14 is the gap between the step surface of the heated plate 111 and the cover plate 112. The step surface of the heated plate 111 is to further prevent the liquid-cooling medium in the liquid-cooling chamber 113 from leaking outward.

[0054] In some embodiments, the sealing portion 122 includes an outer edge 1221, a shielding plate 1222, and a sealing ring 1223. The outer edge 1221 is disposed on the heated plate 111 and extends beyond the cover plate 112. The shielding plate 1222 is disposed on the outer periphery of the enclosure 121 and abuts against the outer edge 1221. The sealing ring 1223 abuts between the outer edge 1221 and the shielding plate 1222 to seal the gap between the outer edge 1221 and the shielding plate 1222.

[0055] It can be seen that the sealing portion 122 formed by the sealing ring 1223, the outer edge 1221 and the baffle 1222 is a sealing structure. The liquid-cooling medium leaked from the liquid-cooling chamber 113 cannot flow through the sealing structure, thereby achieving the purpose of blocking the path of the liquid-cooling medium in the liquid-cooling chamber 113 from leaking to the working parts.

[0056] That is to say, after the liquid-cooling medium in the liquid-cooling chamber 113 leaks, it flows along the upper surface of the heated plate 111. Due to the presence of the sealing portion 122 formed by the sealing retaining ring 1223, the outer edge 1221 and the shielding plate 1222, it can be ensured that the liquid-cooling medium cannot leak to the working parts below the heated plate 111, thereby ensuring the stability of the working parts.

[0057] To facilitate the installation of the sealing ring 1223, a mounting groove 12211 is provided on the outer edge 1221. The sealing ring 1223 is installed in the mounting groove 12211, and the depth of the mounting groove 12211 is less than the thickness of the sealing ring 1223. In this way, when the sealing ring 1223 is installed, the sealing ring 1223 is compressed by its own elasticity, thereby ensuring that the gap between the outer edge 1221 and the shielding plate 1222 is sealed.

[0058] It should be noted that the above-mentioned baffles 1222 are distributed around the circle 121, and the size of the baffles 1222 on both sides of the circle 121 along the first direction is much larger than the size of the baffles 1222 on both sides of the circle 121 along the second direction. In this way, the baffles 1222 around the circle 121 can cover the heated plate 111 and the working parts below, playing a shielding role, and preventing the liquid cooling medium leaking from the pipe connected to the cold plate 11 from dripping into the liquid storage tank 13 and causing the liquid cooling medium to splash onto the working parts.

[0059] It should be noted that the so-called first direction refers to the length direction of the structure shown in FIG. 2 , and the so-called second direction refers to the width direction of the structure shown in FIG. 2 .

[0060] Please refer to Figure 5. In order to prevent the liquid cooling medium in the liquid storage tank 13 from leaking out, the leakage protection device 1 also includes an outer cover 15. The outer cover 15 can be connected to the baffle 1222 through a detachable connecting component (screws, bolts, etc.), and the outer cover 15 is arranged on the ring 121. The outer cover 15 can cover the upper port of the ring 121 to prevent the liquid cooling medium in the liquid storage tank 13 from leaking out from the upper port of the ring 121.

[0061] Of course, the outer cover 15 is provided with slots for allowing the pipe assembly connected to the cold plate 11 to pass through, so as to facilitate the connection of the pipe assembly to the cold plate 11 .

[0062] In some embodiments, the blocking portion 122 or the enclosure structure 12 is integrally formed, such as by integral injection molding or metal. The advantage of using metal as an integral molding is that it not only provides shielding but also dissipates heat from the server's working components. The integral blocking portion 122 also blocks the path of liquid coolant from the liquid cooling chamber 113 leaking to the working components.

[0063] Please refer to FIG. 6 and FIG. 7 together. In order to further meet the protection requirements, the leakage protection device 1 further includes a liquid pumping mechanism 16 . The liquid pumping mechanism 16 is connected to the liquid storage tank 13 to pump out the liquid cooling medium in the liquid storage tank 13 .

[0064] It is understandable that, compared to the prior art method of shutting down the device immediately after a leak occurs, in this embodiment, when the liquid-cooling medium in the liquid-cooling chamber 113 leaks, the leaked liquid-cooling medium is stored in the liquid storage tank 13, thereby extending the time from the liquid-cooling medium leaking to shutting down the device, thereby delaying the shutdown of the device. On this basis, in order to further extend the time, the liquid-cooling medium in the liquid storage tank 13 can be extracted through the liquid extraction mechanism 16 to achieve the purpose of extending the protection time. In this way, the device can be shut down after clicking the save data button on the device page, which is beneficial to ensure data security.

[0065] In this embodiment, the liquid pumping mechanism 16 includes a liquid pumping tube, a liquid pumping component, a liquid leakage detection component and a control component.

[0066] Specifically, the liquid extraction pipe is arranged perpendicular to the cold plate 11, and one end of the liquid extraction pipe extends into the liquid storage tank 13. The liquid extraction component is connected to the liquid extraction pipe, and the liquid extraction component extracts the liquid cooling medium in the liquid storage tank 13 through the liquid extraction pipe. The liquid extraction component can be a liquid extraction pump, and the leakage detection component is arranged in the liquid storage tank 13. The leakage detection component is used to detect the amount of liquid cooling medium in the liquid storage tank 13 and feed back the detected data to the control component. The control component is electrically connected to the leakage detection component and the liquid extraction component. The control component is used to control the liquid extraction component to open and extract the liquid cooling medium in the liquid storage tank 13 when the amount of liquid cooling medium in the liquid storage tank 13 exceeds the warning amount.

[0067] That is, by adopting the above-mentioned liquid pumping mechanism 16, the liquid cooling medium in the liquid storage tank 13 can be pumped out when the amount of the liquid cooling medium in the liquid storage tank 13 reaches a certain value, thereby facilitating the protection of the server equipment.

[0068] To facilitate extraction of the liquid coolant from the liquid storage tank 13, the cover plate 112 is provided with a liquid collecting tank and a guide slope located on the outer periphery of the liquid collecting tank. The liquid coolant on the cover plate 112 is guided by the guide slope and collected in the liquid collecting tank. Simultaneously, a liquid extraction pipe extends into the liquid collecting tank. In this way, the liquid extraction assembly extracts the liquid coolant collected in the liquid collecting tank through the liquid extraction pipe.

[0069] For example, the liquid collecting tank can be located at the center of the cover plate 112 or at the edge of the cover plate 112. The present application does not impose any specific restrictions on the location of the liquid collecting tank, provided that it can ensure that the liquid can be easily extracted after collection.

[0070] In some embodiments, the liquid leakage detection element can be a liquid leakage detection sensor, which can be a sheet-like structure. The sheet-like structure of the liquid leakage detection element is entirely covered on the surface of the cover plate 112 away from the heated plate 111. In this way, when liquid cooling medium appears at any position on the upper surface of the cover plate 112, the liquid leakage detection element can detect it in real time and feed the detected data back to the control component.

[0071] Of course, according to actual assembly requirements, the sheet-like liquid leakage detection component may also be provided with a plurality of avoidance structures (such as avoidance grooves) to facilitate avoidance of the structure provided on the cover plate 112 .

[0072] It should be noted that, in this specification, relational terms such as first and second are merely used to distinguish one entity from other entities, but do not necessarily require or imply any actual relationship or order between these entities.

[0073] The above is a detailed introduction to the liquid leakage protection device provided by the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the scheme and core ideas of the present application. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present application, several improvements and modifications can be made to the present application, and these improvements and modifications also fall within the scope of protection of the claims of the present application.

Claims

1. A liquid leakage protection device, comprising a cold plate, the cold plate including a heat receiving plate and a cover plate, a liquid cooling cavity for accommodating a liquid cooling working medium being formed after the heat receiving plate and the cover plate are connected, characterized in that, The liquid leakage protection device further includes a surrounding structure disposed around the liquid cooling cavity to block the liquid cooling working medium leaked from the liquid cooling cavity from flowing onto the working components in contact with the heat receiving plate. The surrounding structure and the cold plate form a liquid storage tank, so that the liquid cooling working medium leaked from the liquid cooling cavity can be stored in the liquid storage tank.

2. The liquid leakage protection device according to claim 1, wherein The surrounding structure and the cold plate also form a diversion channel communicating with the liquid storage tank, and the liquid cooling working medium leaked from the liquid cooling cavity flows into the liquid storage tank after being diverted through the diversion channel.

3. The liquid leakage protection device according to claim 2, wherein The surrounding structure includes: A surrounding ring that surrounds the cover plate to form the liquid storage tank; A blocking portion connected to the bottom of the surrounding ring to form the diversion channel and block the path of the liquid cooling working medium in the liquid cooling cavity from leaking to the working components.

4. The liquid leakage protection device according to claim 3, characterized in that, The blocking portion includes: An outer edge disposed on the heat receiving plate and protruding from the cover plate; A shielding plate disposed on the outer periphery of the surrounding ring, and the shielding plate is in abutment with the outer edge; A sealing ring that abuts between the outer edge and the shielding plate to seal the gap between the outer edge and the shielding plate.

5. The liquid leakage protection device according to claim 4, characterized in that, An installation groove is provided on the outer edge, and the sealing ring is installed in the installation groove, and the depth of the installation groove is less than the thickness of the sealing ring.

6. The liquid leakage protection device according to claim 4, wherein, The shielding plates are distributed around the surrounding ring, and the sizes of the shielding plates on both sides of the surrounding ring along the first direction are larger than the sizes of the shielding plates on both sides of the surrounding ring along the second direction, so that the shielding plates can cover the working components to prevent the liquid cooling working medium leaked from the pipeline connected to the cold plate from dripping into the liquid storage tank and splashing onto the working components.

7. The liquid leakage protection device according to claim 3, wherein, It further includes an outer cover that covers the surrounding ring to prevent the liquid cooling working medium in the liquid storage tank from leaking out.

8. The liquid leakage protection device according to any one of claims 1-7, characterized in that, It further includes a liquid pumping mechanism connected to the liquid storage tank to pump out the liquid cooling working medium in the liquid storage tank. The liquid pumping mechanism includes: A liquid pumping pipe, one end of which extends into the liquid storage tank; A liquid pumping assembly connected to the liquid pumping pipe to pump out the liquid cooling working medium in the liquid storage tank through the liquid pumping pipe; A liquid leakage detection member disposed in the liquid storage tank to detect the amount of the liquid cooling working medium in the liquid storage tank; A control assembly electrically connected to the liquid leakage detection member and the liquid pumping assembly to control the liquid pumping assembly to start and pump out the liquid cooling working medium in the liquid storage tank when the amount of the liquid cooling working medium in the liquid storage tank exceeds the warning amount.

9. The liquid leakage protection device according to claim 8, characterized in that, A liquid collecting groove and a diversion slope located on the outer periphery of the liquid collecting groove are provided on the cover plate. The liquid cooling working medium on the cover plate is diverted through the diversion slope and collected in the liquid collecting groove, and the liquid pumping pipe extends into the liquid collecting groove.

10. The liquid leakage protection device according to claim 8, characterized in that, The liquid leakage detection member is in a sheet structure and covers the surface of the cover plate away from the heat receiving plate.

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