CN1192202C - Flat-plate loop heat pipe (1) - Google Patents

Abstract

A flat plate loop type heat pipe is prepared as setting at least one loop plate in hollow shell, forming loop by loop plate to be at least one loop, forming said loop to be evaporation zone, steam channel, condensation zone and fluid return channel in series in sequence, filling proper quantity of liquid in shell, making fluid return channel and steam channel be independent channels, setting plate capillary structure on loop plate cover, making flow resistance of steam channel be smaller than that of fluid return channel, radiating heat by condensation zone when evaporation zone is heated to make all fluid in loop stably flow in same direction without conflict and all fluid can flow through loop.

Description

Flat-plate loop heat pipe (1)

technical field

The invention belongs to a flat plate loop heat pipe, in particular to a heat exchange structure with large heat transfer, good temperature uniformity, and little influence on the characteristics of the loop system for the non-condensable gas existing in the plate heat pipe.

Background technique

Existing heat pipes have been widely used in heat dissipation components of electronic components due to their relatively good heat transfer properties. Usually, heat pipe-type heat dissipation components have a heat pipe 1 and a heat conducting block 11 at the end of the electronic component. The heat conducting block 11 is connected to one end of the heat pipe 1, and the other end of the heat pipe 1 can be connected to the heat exchange device through another heat conduction block, or the other end of the heat pipe 1 is directly sandwiched with several cooling fins 12, as shown in Fig. 1 , that is, the heat pipe of the radiating fin 12 formula.

In the manufacture of heat pipes, a relatively high part of the cost is used for the cleaning and degassing steps in the heat pipes, that is, the cleaning and vacuuming operations in the heat pipes. The better the heat effect, the more stable the heat conduction can be ensured. However, there is still a small amount of non-condensing gas in the channel, and the non-condensing gas will accumulate in the channel in the heat pipe. The temperature difference between the heating area and the evaporation area at the heating end is very large, which affects the smoothness of the heat pipe function. Among them, the non-condensable gas is easy to accumulate at the end of the channel in the condensation zone, so that its temperature uniformity and heat transfer function are greatly reduced.

The heat pipe 1 and the heat conduction block 11 provide the generation of vapor flow for the evaporation area of the hot area, so that the vapor flow flows along the channel to the condensation area where the other end is the cold area, and then condenses the vapor flow at the channel of the cold area to form a condensed liquid flow , and then quickly guide the condensed liquid flow from the cold area to the hot area by means of the capillary structure 13 in the channel to supplement the part of the liquid evaporated into gas in the evaporation area to form a circulating flow.

When one end of the heat pipe 1 is heated and the liquid in the heat pipe evaporates, the vapor flows toward the condensation area and condenses into a liquid, and the liquid returns to the evaporation area through the capillary tissue. Since the fluid return circuit of the heat pipe is set in the same channel, the vapor will The flow directions of the liquid flow and the liquid flow conflict with each other in the channel, which reduces the heat transfer, and the remaining non-condensable gas in the channel is stored in the condensation area, forming an area with a large temperature difference, which reduces the temperature uniformity and heat transfer performance. Therefore, it is also greatly reduced. Therefore, traditionally, the manufacturing conditions and maintenance of heat pipes are strictly required, so the cost is greatly increased, and the selling price is increased, which is quite uneconomical. In order to solve the problem of poor heat transfer performance of the existing heat pipe.

Contents of the invention

The technical problem to be solved by the present invention is to provide a flat plate loop heat pipe, in which a multi-layer, multi-channel and multi-circuit structure is formed in the plate heat pipe, and the evaporation area, steam channel, condensation area, and fluid return The channels are connected in series to form a circuit, in which the steam channel may be arranged in a single channel or more than two channels in parallel with each other, and the fluid return channel may also be arranged in a single channel or more than two channels in parallel with each other to form a single-circuit serial and parallel combination structure. That is to form a more efficient heat exchange device. The loop mainly uses the guiding effect of the different flow resistance of the channel, that is, the flow resistance of the steam channel is smaller than that of the fluid return channel, so that the fluid in the loop automatically generates a cyclical and stable one-way and the same direction of flow. As a result, the plate-shaped heat pipe will almost never dry out, so it can produce good heat transfer, and can have a great heat transfer in a limited space. The vapor flow and the condensed liquid flow formed in the channel all flow in the same direction without conflicting with each other; and the circuits on the same plane can form a non-uniform configuration state to meet actual needs.

Another object of the present invention is to provide a kind of above-mentioned flat loop type heat pipe, under the premise of economical consideration, the manufacture of the plate-shaped heat pipe can be carried out at low cost, but the heat transfer of the plate-shaped heat pipe is still maintained. function, and can produce faster guidance, using the phenomenon of asymmetrical heat flow in the circuit and the guidance of the circuit structure, the steam channel, condensation area, fluid return channel, and evaporation area in the heat exchange are sequentially connected in series. The circular channel can prevent the non-condensable gas existing in the shell from accumulating in the condensation area of the channel, and allow the non-condensable gas to circulate continuously along the channel according to the design direction, greatly improving the uniformity of the plate heat pipe. Therefore, even if there is non-condensable gas in the shell of the plate-shaped heat pipe, it has little effect on the functional characteristics of the plate-shaped heat pipe, and can prolong the service life of the plate-shaped heat pipe.

In order to achieve the above object, the structure of the present invention is as follows: comprising a housing and several ring-shaped circuit boards, at least one ring-shaped circuit board is arranged in the hollow housing, so that the ring-shaped circuit board has at least one loop, and the loops are formed sequentially The evaporation zone, steam channel, condensation zone, and fluid return channel are connected in series, and the shell is filled with an appropriate amount of liquid. The fluid return channel and the vapor channel are independent and not shared channels, and are placed on the ring circuit board cover It is equipped with a plate-like capillary structure, and the flow resistance of the vapor channel is smaller than that of the fluid return channel. When the evaporation area is heated, the condensation area dissipates heat, so that all the fluids in the circuit flow stably in the same direction without conflict, and all fluids can flow Passing through all parts of the circuit, the non-condensable gas in the circuit has little effect on the temperature uniformity of the circuit, and flows along the circuit, so that the circuit hot plate becomes a heat exchange device with good temperature uniformity and large heat transfer. Among them, the vapor channel can be arranged in parallel with more than two channels, and the fluid return channel can be arranged in parallel with more than two channels.

In order to better explain the technology, means and effects that the present invention adopts to achieve the intended purpose, the following embodiments of the present invention are described in detail in conjunction with the accompanying drawings. It is believed that the purpose, characteristics and advantages of the present invention can be deeply and specifically explained learn.

Description of drawings

Fig. 1 is the sectional view of prior art scheme;

Fig. 2 is the three-dimensional exploded view of the present invention;

Fig. 3 is a top perspective view of the first annular circuit board turned over in Fig. 2;

Fig. 4 is an unturned top perspective view of the first annular circuit board in Fig. 2;

Fig. 5 is the top view of the second annular circuit board in Fig. 2;

Fig. 6 is a cross-sectional view of the present invention combined in Fig. 2;

Fig. 7 is a flow schematic diagram of the first annular circuit fluid in Fig. 2;

specific embodiment

In Fig. 2, 3, 4, 5, 6 and Fig. 7, one embodiment of the present invention is a kind of loop type heat pipe, has a casing 3, and casing 3 is a hollow closed body, and on casing 3 It is filled with an appropriate amount of liquid. The filling amount of the liquid refers to the capillary tissue in the housing and the capacity of filling liquid for 80-90% of the volume of the passages in each circuit of the first annular circuit board in the circuit.

There is at least one hollow first annular circuit board 5 and at least one second annular circuit 4 which is hollow. A circuit board 4 is formed in the housing 3 with at least one circuit 2, the circuit 2 is to form various passages in the cavity, and the housing 3 is composed of a top shell 31 and a bottom shell 32, and the periphery of the top shell 31 and the bottom shell 32 are formed. The peripheral edges of the bottom case 32 are joined together to form the casing 3 in an airtight manner. Among them, only one of the annular circuit boards can be provided, or two can be arranged in a stacked shape, and the states shown in Figure 3 and Figure 4 can be directly stacked to form another combination.

Wherein the shell 3 can have another type, and the shell is flattened into a flat tube by a circular tube, and the person with both ends closed.

On the first annular circuit board 5 and the second annular circuit board 4, there are protruding or recessed passages. In FIGS. The configuration of the circular circuit board is similar to that of the second annular circuit board.

In Fig. 2, the first annular circuit board 5 and the second annular circuit board 4 are in a square shape, and they are respectively formed into four equal parts in use, that is, they are divided into four areas by crosses, and each area forms a circuit. , is composed of two non-intersecting partition strips 50a, 40a on the parallel sides and two partition strips 50b, 40b on the vertical side and two intersecting edge strips 57, 47 in the diagonal shape. A central gap 58, 48 is formed between the partition bars 50a, 50b or 40a, 40b respectively.

In the space enclosed by a pair of partition strips 40a and 40b and a pair of edge strips 47, or a pair of partition strips 50a and 50b and a pair of edge strips 57, four first partition strips 41, 42 . 1. Edge strips 47, 57 on the parallel side are juxtaposed to form two sub-wide passages, and the spacer strips 47, 57 on the vertical side on the other side are juxtaposed with a bottom spacer strip 46, 56 to form a narrower passage, and make the bottom spacer The strips 46,56 meet the first spacer strips 44,54.

In Fig. 3 and Fig. 4, the parallel side spacers 50a of the first annular circuit board 5, the first and second spacers 51, 52, 53, 54, 55 are respectively connected with the edge strips 57 which are perpendicular to each other. Each is provided with a stepped groove 59f, 59a, 59b, 59c, 59d, 59e, and each groove 59 is located at the outer end of the near-wide passage and the second-widest passage, and forms a state where the wide and second-widest passages intersect transversely, so that Each groove 59 becomes the end of the channel for steam movement, even if the steam of the first annular circuit board 5 passes through the cooling passage of the side part of the wide channel of the first annular circuit board 5, and is in a state of communication between the left and right halves .

In Fig. 5, the parallel side spacers 40 of the second annular circuit board 4, the first and second spacers 41, 42, 43, 44, 45 are respectively provided with a vertically connected edge strip 47. Through the transverse groove 49 , the widest and second widest channels are arranged in parallel; they need to pass through the second plate-shaped capillary tissue 7 , as shown in FIG. 6 .

Each circuit on each circuit board 4, 5 forms a connected shape consisting of a wide channel, a second wide channel and a narrower channel. But the above structure is only a preferred embodiment. Among them, the vapor channel 22 is formed with a wide channel, and the liquid return channel 24 is formed with a narrow channel. The central gap 48 is the evaporation area 21, and the edge of the plate where the second wide channel is located is the condensation area 23. The liquid filled in the shell 3 Its flow direction is shown in FIG. 7 . And the part of the wide channel close to the condensation area already has the function and effect of the condensation area.

Circuit 2 is composed of evaporation zone 21, steam channel 22, condensation zone 23, and fluid return channel 24 in series in sequence. The circuit 2 is filled with an appropriate amount of liquid. within 90% of the volume. Wherein the fluid return channel 24 and the steam channel 22 are not shared channels, that is, the steam channel 22 is an independent channel, and the fluid return channel 24 is also an independent channel, which is different from the steam channel and the fluid channel of the existing traditional heat pipe. Returns a structure where channels share the same channel.

In the region of the circuit 2 of the present invention, two groups of circuits 2 are formed on the upper and lower sides, and the upper and lower pairs of circuits are symmetrically arranged, that is, the middle evaporation zone 21 and the peripheral condensation zone 23 are formed, so that the steam enters The steam passage 22 formed by four wide passages connected in parallel then enters the sub-widest passage of the condensation zone 23, and the condensed liquid returns to the evaporation zone 21 along the fluid return passage 24 formed by the narrower passage, and a cycle is completed. The shape of the circuit can be set according to the requirements. In the figure, the evaporation area is set at the center, or it can be in an eccentric state, or at a corner. The method of the present invention can be applied to form various shapes.

In addition, in Fig. 2, four independent sets of single loops are formed in parallel, which only allow the liquid to converge at the center gap. If necessary, a serial number loop combination can also be formed on the annular circuit board, so as to This enables the present invention to sequentially contact the heat source with different contact points to form another type of heat pipe structure.

And the present invention makes the flow resistance in the fluid return channel 24 greater than that of the steam channel 22, which deliberately causes the imbalance of the heat flow in the channel of the housing to form an asymmetric structure of fluid flow in the channel of the housing 3, so that the evaporation area 21 The formed vapor flows easily and naturally and stably in one direction toward the condensation zone 23, and condenses in the cooling zone 23 to form a condensed liquid flow, so that the condensed liquid flow and non-condensable gas, together with the uncondensed vapor flow, are separated in the circuit. Under the action of different flow resistances and the guidance of the channel structure, they all flow toward the fluid return channel 24 stably in one direction, and flow back to the evaporation region 21 through the fluid return channel 24 .

The evaporation zone 21 referred to in the present invention is exactly the part of the heated position of the circuit 2, which can be connected to the center of at least one end surface (bottom surface) of the housing 3 with a heat source 8, as shown in Figure 6, and the heat source refers to Heat-prone surfaces of electronic components, usually referring to the CPU, but not limited to this component. Therefore, the evaporation area is connected with the heat exchange device to dissipate heat, and the heat exchange device to be dissipated can be a heat transfer block of a heat source, a heat receiving fin group, a water jacket or a condensation area of another group of loops in the present invention, wherein Another group of loops refers to the series connection type of the two loops of the present invention.

In addition, the condensing area 23 of the present invention is exactly the position of the circuit for heat dissipation, and this part is the main radiating area. Of course, the channel itself is also a good heat dissipation structure, which can make the condensing area connect with a heat exchange device 9, as shown in Figure 6 That is, at least the other end surface (top surface) of the condensation zone 23 is connected with the heat exchanging device as a heat dissipation device, and the heat exchanging device is an integrated radiator, heat radiation fin group, cooling water tower or another group of circuits of the present invention. evaporation zone. Therefore, the evaporation area on at least one end surface of the housing can be connected to a heat source for heat exchange, and part to all of the remaining end surfaces of the housing can be connected to a heat exchange device for heat dissipation.

In addition, the steam channel 22 shown in Fig. 2 is a plurality of channels, that is to say, one or two or more steam channels 22 connected in parallel can be provided, so that the total flow resistance of each steam channel is smaller than the fluid return channel, wherein Flow resistance control is to change the total cross-sectional area or total length of the circuit or a combination thereof to form a state of small flow resistance and high flow velocity in the steam channel, while a state of large flow resistance and low flow velocity in the fluid return channel makes the circuit deliberately The heat flow that forms is asymmetrical, impels the determination of flow direction; And, fluid return passage 24 is a plurality of passages in Fig. The resistance condition, and the condensed liquid can only return to the evaporation area through the fluid return channel, that is, the guided flow of the circuit is naturally generated, and the phenomenon of this flow is a stable one-way flow, and it is deliberately restricted, and can only flow toward the designed directional flow, and random flow that violates the design does not occur.

Or let the fluid return channel be filled with liquid to form a liquid seal, which can completely fill the fluid return channel with a capillary tissue to form, and can also reduce the space through which the gas passes to achieve the above-mentioned liquid seal effect. The liquid seal refers to the flow channel The cross-section is reduced or the flow channel is closed by capillary tissue, which is formed by increasing the asymmetry of the flow resistance, so that the fluid circulation is more stable and flows in the design direction, but at this time, the passage of non-condensable gas will be affected by the return channel of the liquid , so that the temperature uniformity of this implementation is poor, and the non-condensable gas can be eliminated through the degassing process of the circuit to improve the temperature uniformity.

Since the circuit 2 has been set up in series, and there is a sequential unidirectional circulation flow, the non-condensable gas existing in the circuit has no space and time to accumulate and stay, and can only flow along the vapor flow or the condensed liquid flow in the circuit Therefore, in the circuit, the present invention can form the gas containing most of the vapor flow and the liquid and non-condensable gas of a small part of the condensed liquid flow in the vapor channel space, and most of the fluid return channel space is condensed The liquid and a small part of the vapor flow of gas and non-condensable gas form a rapid one-way circulation flow. Make all fluids in the heat pipe flow in the same direction without conflict, and all fluids can pass through any channel in the system at any time, so the heat transfer is good, the heat transfer is large, and the temperature difference is small.

In the present invention, a first plate-shaped capillary structure 6 and a second plate-shaped capillary structure 7 are placed outside the stacked first annular circuit board 5 and the second annular circuit plate 4, and the plate-shaped capillary tissue 6, 7. Its length and width are about the same as those of the annular circuit boards 4 and 5, but grooves 61 and 71 are only provided on the plate-shaped capillary tissue relative to the wide channel, and the grooves are shorter than the wide channel, and the grooves In order to allow the area for vapor circulation, the aforementioned transverse groove 49 is connected to the fluid return channel through the capillary tissue 7, and the capillary tissue is used to attract and guide the condensed liquid to the fluid return channel. In FIG. 2 , it is a capillary structure with a large covering type. At least one plate-shaped capillary structure can be provided on one side or both sides of a single ring-shaped circuit board to form a stacked structure. The plate-shaped capillary tissue is also smaller than that of the ring-shaped circuit board, or is arranged between two ring-shaped circuit boards.

Because the capillary is porous, it is easy to become a channel for liquid, so that the capillary is not only set up to the length of the fluid return channel where the condensed liquid flow is located, so that the inner channel becomes smaller and the flow resistance becomes larger, or it extends to the evaporation area alone Either extend to the condensation area alone, or extend to the evaporation area and the condensation area at the same time, or more capillary structures can be provided in the entire circuit, but the flow resistance of the steam channel is smaller than that of the fluid return channel. Among them, the capillary structure is ceramics, sintered powder, foamed metal, woven net, sintered net, grooved plate, fiber bundle or spiral wire. Among them, the fluid return channel should be provided with a space for steam and non-condensable gas to pass through. Moreover, the capillary tissue can be placed in the channel in the form of strips or protrude from the plate-shaped capillary tissue to the channel, and the plate-shaped capillary tissue is not larger than the annular circuit board. For example, a capillary tissue is embedded in the stepped groove of the first annular circuit board, and the communication between the fluid return channel and the steam channel is formed by the capillary tissue.

In Fig. 7, the mark of each action area is arranged on the circle, the condensate evaporation area 21 is in the middle, and the evaporation area of the evaporation flow in the inner half channel of the steam channel 22 is the evaporation area 25 in a broad sense, and in the steam The outer half of the channel 22 is the vapor flow condensation area, which is also combined with the original condensation area 23 to form a generalized condensation area 27, and its two sides are respectively the condensate flow and the non-condensable air flow return area, and the steam channel 22 and the fluid return There are connected passages between the passages 24, but in a broad sense, there is a connecting region 26, which contains the aforementioned connected passages, stepped grooves, condensation regions 23 that run through the horizontal grooves, etc., that is, the connecting region is bounded by the evaporation region. 25 and condensing area 27.

To sum up the structure described above, the present invention uses an independent flow diversion mechanism, and constitutes a structure with unequal flow resistance between the steam channel and the fluid return channel, and cooperates with the generated heat flow imbalance, capillary phenomenon, etc., to form a serial sequence One-way fluid circulation structure, and the steam channel and the fluid return channel can also form a multi-channel parallel structure, as long as the flow resistance in the fluid return channel 24 is greater than that of the steam channel 22, a connected ring can be produced. The circuit, so that the present invention can operate heat transfer without going through the degassing process during the production process. If the internal circuit of the shell is degassed, the thermal conductivity is better and the operating temperature range is wider; thus, It makes the circuit easier to form. Compared with the existing heat pipes in actual use, the speed of heat conduction flow is faster than the existing heat pipes. The heat uniformity is high, the heat transfer is good, and the heat transfer is larger and faster. Therefore, the present invention does not need a degassing process, and the cleaning process is not important, so that the process is simple, the cost is low, the price can be reduced, and it has better economy and better functional characteristics, so the present invention can To provide good usability, the present invention is a completely different mechanism from existing heat pipes.

The above is a detailed description and drawings of preferred embodiments of the present invention, and is not intended to limit the present invention. All scopes of the present invention should be based on the scope of protection claimed by the patent claims. Its embodiments with similar changes and similar structures should all be included in the patent protection scope of the present invention.

Claims (27)

1. A flat plate loop type heat pipe is characterized in that: comprising: A shell, which is a hollow closed body filled with a proper amount of liquid, and At least one ring-shaped circuit board in a hollow shape, which is arranged in the casing, and at least one circuit is arranged on it, and the circuit is sequentially connected by the evaporation area, at least one steam channel, condensation area and at least one fluid return channel. The steam channel and the fluid return channel are independent channels, and the flow resistance in the fluid return channel is greater than that of the steam channel, so that the circuit forms an asymmetric guiding effect, and there is a connection between the steam channel and the fluid return channel The channel, the circuit is to form each channel with Lou Kong; When the liquid is heated from the evaporation area to form a vapor flow to the condensation area to form a condensed liquid flow, let the condensed liquid flow, together with the non-condensable gas in the circuit, together with the non-condensed part of the vapor flow, in the circuit Under the asymmetrical guidance of the channel heat flow, they all flow towards the fluid return channel in a single direction, and return to the evaporation area, and then flow into the evaporation channel, forming a loop circulation flow. 2. The flat plate loop heat pipe according to claim 1, wherein the shell is composed of a pair of top shell and bottom shell. 3. The flat-plate loop heat pipe as claimed in claim 1, characterized in that the evaporation area of at least one end surface of the housing is connected to a heat source for heat exchange, and part to all of the remaining end surfaces of the housing are reheated. Connect with a heat exchange device to dissipate heat. 4. The flat-plate loop heat pipe according to claim 1, characterized in that the shell is in the shape of a flat tube with both ends closed. 5. The flat-plate loop type heat pipe as claimed in claim 1, wherein the filling amount of the liquid refers to filling up the capillary tissue in the housing and the passage in each circuit of the first annular circuit board in the circuit. 80-90% of the volume is filled with liquid capacity. 6. The flat plate loop heat pipe according to claim 1, characterized in that said annular circuit plate is composed of two plates stacked together. 7. The flat plate loop heat pipe according to claim 1, characterized in that the evaporation area of the annular loop plate is eccentrically arranged. 8. The flat-plate loop heat pipe according to claim 1, characterized in that two or more vapor channels of the annular loop plate are arranged in parallel with each other. 9. The flat-plate loop type heat pipe as claimed in claim 1, wherein the flow resistance of the fluid return channel of the annular loop plate is greater than that of the steam channel, which means that the passage cross-sectional area of the fluid return channel is reduced or the flow resistance of the fluid return channel is reduced. Channel length growth or a combination thereof. 10. The flat plate loop heat pipe according to claim 1, characterized in that the fluid return channel of the annular loop plate is sealed with liquid. 11. The flat-plate loop heat pipe according to claim 10, characterized in that said liquid seal means that the section of the flow channel is reduced or the flow channel is closed with capillary tissue. 12. The flat-plate loop heat pipe according to claim 1, characterized in that the fluid return channels of the annular loop plate are arranged in parallel with each other at least two channels. 13. The flat plate loop heat pipe according to claim 1, characterized in that said annular circuit plate is made of capillary action or porous material. 14. The flat plate loop heat pipe according to claim 1, characterized in that the circuits on the annular circuit board are connected in series or in parallel. 15. The flat plate loop heat pipe according to claim 1, characterized in that there is a central gap on the circular circuit board, and the central gap becomes the evaporation area of each circuit. 16. The flat-plate loop type heat pipe as claimed in claim 1, characterized in that said annular circuit board is a first annular circuit board, and the first annular circuit board is composed of several spacers, wherein the spacers It has a stepped groove to form the communication between the fluid return channel and the vapor channel. 17. The flat-plate loop heat pipe according to claim 16, characterized in that a capillary is embedded in the stepped groove of the first annular circuit plate, and the capillary forms the gap between the fluid return channel and the vapor channel. connected. 18. The flat-plate loop heat pipe according to claim 1, characterized in that said annular circuit board is a second annular circuit board, and the second annular circuit board is composed of a plurality of spacers, wherein Separate passages are formed on the spacers, and a through transverse groove is formed on the plate surface between the spacers and the sides. 19. The flat plate loop heat pipe according to claim 1, characterized in that the annular loop plate is composed of a first annular loop plate and a second annular loop plate, and the first annular loop plate is composed of Composed of a plurality of spacers, wherein the spacers have stepped grooves to form the communication between the fluid return channel and the steam channel, the second annular circuit board is composed of a plurality of spacers, wherein the spacers are used to form independent The channel has a through transverse groove on the plate surface between the spacer and the edge. 20. The flat plate loop heat pipe as claimed in claim 1, characterized in that said annular circuit board is a second annular circuit board, and the second annular circuit board is composed of several spacers, wherein the spacers It has an independent channel and is provided with a capillary tissue. The second annular circuit plate is stacked with the capillary tissue, and the capillary tissue is used to form the communication between the fluid return channel and the steam channel. 21. The flat plate loop heat pipe according to claim 1, characterized in that there is also at least one plate-shaped capillary structure disposed between the annular circuit plate and the shell. 22. The flat loop heat pipe according to claim 21, characterized in that the shape of the plate capillary structure can be the same as or different from that of the annular circuit plate. 23. The flat loop heat pipe as claimed in claim 21, characterized in that the plate-like capillary structure is ceramics, sintered powder, foamed metal, braided net, sintered net, grooved plate, fiber bundle or formed by the spiral. 24. The flat-plate loop heat pipe as claimed in claim 21, characterized in that the flow resistance of the fluid return channel formed by the plate-shaped capillary tissue is greater than that of the vapor channel, and at the same time guide the condensed liquid of the annular circuit plate to return to the evaporation area . 25. The flat loop heat pipe according to claim 21, characterized in that said plate capillary structure extends to the evaporation area and/or condensation area of the annular circuit plate. 26. The flat loop heat pipe as claimed in claim 21, characterized in that the plate-shaped capillary tissue extends to the entire circuit of the annular circuit plate, so that the liquid returns to the evaporation area of the annular circuit plate, but the fluid The flow resistance of the return channel still needs to be greater than that of the vapor path. 27. The flat plate loop heat pipe as claimed in claim 1, characterized in that: there is also at least one plate-like capillary structure disposed between a pair of annular circuit plates.

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