JP2014115052A - Flat type heat pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat type heat pipe in which a liquid flow path where working fluid flows is assured without decreasing an area of a wick for vaporizing working fluid so as to improve a return flow characteristic.SOLUTION: This flat type heat pipe 1 transfers heat with working fluid evaporating through its heating and condensing while radiating heat. The heat pipe comprises a container 3 formed into a flat shape and having working fluid sealed therein and a wick 2 for generating capillary force for returning the working fluid of liquid phase to a position where it is evaporated. The wick 2 is fixed through sintering to one flat surface 3b at an inner part 3a of the container 3 over an entire longitudinal length of the container 3, the working fluid of gaseous phase may flow between the wick 2 fixed to one flat surface 3b and the other flat surface 3c at the inner part 3a of the container 3, and a groove part 8 for returning the working fluid of liquid phase to an evaporating position where the working fluid of liquid phase evaporates is formed along a longitudinal direction at the surface 2a of the wick 2 opposing against the other flat surface 3c.

Description

  The present invention relates to a heat pipe configured to transport heat by a working fluid enclosed in a container, and more particularly to a heat pipe configured in a flat shape as a whole.

  The basic structure of a heat pipe is a working fluid filled with a fluid that evaporates and condenses in a target temperature range, such as water or alcohol, in a container (container) that has been degassed of non-condensable gas such as air. In addition, a wick for generating a capillary force for refluxing the liquid-phase working fluid is provided inside the container. Therefore, in the heat pipe, the working fluid receives heat from the outside and evaporates, and the vapor flows toward a low pressure portion and then dissipates heat and condenses. As a result, the working fluid transports heat by its latent heat. The condensed working fluid penetrates into the wick. On the other hand, since the capillary force due to the wick is generated at the location where evaporation occurs, the working fluid that has permeated the wick is returned to the location where evaporation occurs due to the capillary force.

  As described above, in the heat pipe, a vapor flow is generated between the evaporation portion where heat is transmitted from the outside and the heat dissipation portion where the working fluid dissipates the outside, and a liquid flow is generated in the opposite direction. As a result, heat is transported. Therefore, in order to improve the heat transport capability or reduce the thermal resistance, it is preferable to generate the vapor flow and the liquid flow smoothly and sufficiently. In addition, heat pipes are used for various purposes, and may be used, for example, for cooling in electronic equipment. In such cases, heat pipes are reduced in size and weight in accordance with downsizing of electronic elements and circuits. It is desirable. Thus, various techniques for securing a flow path for a vapor flow, improving the reflux characteristics of the working fluid, and further reducing the size have been developed.

  Briefly explaining the structure of the heat pipe described in Patent Document 1, the internal space of the intermediate part formed between the evaporation part and the condensation part formed at both ends of the heat pipe container is defined as the heat pipe container. In the longitudinal direction, it is divided into a plurality of hollow portions by partition walls, a plurality of linear bodies are inserted into at least one hollow portion, and no linear bodies are inserted into at least one hollow portion. This heat pipe is said to have no reduction in heat transport efficiency even when processed into a flat shape.

  The structure of the flat heat pipe described in Patent Document 2 will be briefly described. A container formed in a flat shape and filled with a working fluid is bundled with a large number of thin wires, and the thin wires are connected to the central axis thereof. And a wick that generates capillary pressure when the liquid-phase working fluid permeates. And the wick composed of a bundle of thin wires is installed over the entire length in the longitudinal direction of the container so as to be in contact with the upper and lower surfaces or side surfaces of the flat container and not to block the section that becomes the steam flow path. In addition, any portion of the contact portion between the wick and the container is sintered and fixed over the entire length of the wick in the longitudinal direction. This flat heat pipe is said to have excellent heat transport characteristics even when deformation such as bending occurs.

  Moreover, if the structure of the flat type heat pipe described in patent document 3 is demonstrated easily, the wick formed by sintering metal powder will be provided in the container which formed the groove | channel along the axial direction of an internal peripheral surface. A heat pipe is described. This groove is supposed to enhance the capillary force of the flat heat pipe, facilitate the reflux of the working fluid, and improve the heat dissipation efficiency.

JP 2010-25407 A International Publication No. 2010/098303 JP 2011-43320 A

  The heat pipe described in Patent Document 1 is divided into a plurality of hollow portions by partition walls, and the location where the working fluid is vaporized is only the end surface of the wick. There is a possibility that the reflux area may be reduced due to the small area.

  Moreover, the groove | channel formed in the inner peripheral surface of the container described in patent document 2 or patent document 3 is a wick formed by sintering metal powder or a wick that bundles a large number of thin wires. It is easy to enter the groove along the axial direction of the surface, and it is easy to be fixed in a state of being embedded in the narrow groove. For this reason, the groove blocked by the wick hinders the liquid-phase working fluid from flowing back through the evaporation section and the condensation section, resulting in an increase in the overall thermal resistance loss and the maximum heat. There is a possibility that the transportation capacity may be lowered, and there is room for improvement in this respect.

  The present invention has been made paying attention to the above technical problem, and ensures a liquid flow path through which the working fluid flows without reducing the area of the wick where the working fluid evaporates, thereby improving the reflux characteristics. An object of the present invention is to provide a flat heat pipe.

  In order to achieve the above object, the invention of claim 1 is a flat heat pipe that transports heat by a working fluid that is heated to evaporate and dissipates heat to condense. A sealed container and a wick that generates a capillary force for refluxing the working fluid in a liquid phase to a position where it evaporates, and the wick is one flat surface inside the container over the entire length in the longitudinal direction of the container. The working fluid in a gas phase flows between the wick fixed to one flat surface of the wick and the other flat surface inside the container, and the other flat surface. A groove portion for returning the working fluid in a liquid phase to a position where it evaporates is formed along the longitudinal direction on the surface of the wick facing the surface.

  According to a second aspect of the present invention, in the first aspect of the present invention, the groove portion is a flat groove that produces a capillary force that causes the working fluid in the liquid phase to flow back to a position where it evaporates. It is.

  The invention according to claim 3 is the storage portion according to claim 1 or 2, wherein the groove is formed at the position where the liquid-phase working fluid is evaporated, and stores the liquid-phase working fluid. It is a flat type heat pipe characterized by being.

  According to a fourth aspect of the present invention, there is provided the flat heat pipe according to any one of the first to third aspects, wherein another wick is further provided on the inner peripheral surface of the container.

  The invention of claim 5 is the invention according to any one of claims 1 to 4, wherein the wick is a bundle of fine wires formed by bundling a porous structure obtained by sintering a number of powder particles and a number of fine wires. It is a flat type heat pipe characterized by including any one of these.

  According to a sixth aspect of the present invention, in the fourth aspect of the present invention, the other wick includes a fine wire bundle formed by bundling a porous structure obtained by sintering a large number of powder particles and a large number of fine wires. It is a flat type heat pipe characterized by including either a net-like body.

  Further, the invention of claim 7 is the invention according to any one of claims 1 to 6, wherein the wick includes one of a wick having a rectangular cross section and a flat semicircular wick. It is a flat type heat pipe characterized by

  According to this invention, the groove part which recirculate | refluxs the liquid-phase working fluid to the position which evaporates is comprised in the surface of the wick facing the other flat surface inside a container along the longitudinal direction. Since the gas-phase working fluid can flow between the wick and the other flat surface, a capillary force is generated between them to form a reflux path, so that the surface of the wick is a liquid-phase working fluid. It can be avoided in advance. That is, in the wick, an evaporation area for the working fluid to be vaporized can be secured. As a result, the gas-phase working fluid flows sufficiently and sufficiently, and the heat transport characteristics as a flat heat pipe are improved.

  In addition, the liquid-phase working fluid permeates the wick and flows toward a location where evaporation occurs. That is, when the liquid-phase working fluid evaporates, the meniscus formed in the wick decreases, so that a capillary force is generated, and the liquid-phase working fluid is refluxed to the evaporation portion side using the capillary force as a pumping force. So-called reflux characteristics are improved. Furthermore, the liquid-phase working fluid can flow toward a portion where evaporation occurs, using a groove formed in the wick as a flow path. As a result, the overall thermal resistance loss can be reduced, and the maximum heat transport capability can be improved.

  Moreover, according to this invention, the groove part formed in the wick is comprised so that a capillary force may be produced. That is, when the liquid-phase working fluid that has permeated into the groove formed in the wick evaporates, the meniscus in the groove formed in the wick decreases, so that capillary force is generated, and the capillary force is used as a pumping force to generate liquid phase. The working fluid is recirculated to the evaporation portion side, so that the so-called recirculation characteristic is improved.

  Further, according to the present invention, the liquid-phase working fluid is stored in the groove portion of the wick formed at the position where it evaporates. Therefore, the liquid-phase working fluid stored in the groove can absorb the heat at the evaporation position and reduce the temperature at the evaporation position.

  Furthermore, according to this invention, the other wick is further provided in the inner peripheral surface of the container. The liquid-phase working fluid can permeate other wicks and flow toward the point where evaporation occurs. In other words, when the liquid-phase working fluid evaporates, the meniscus formed in the other wicks is lowered, so that a capillary force is generated, and the liquid-phase working fluid is returned to the evaporating part side using the capillary force as a pumping force. It becomes easy to do. As a result, the overall thermal resistance loss can be reduced, and the maximum heat transport capability can be improved.

It is sectional drawing which shows the specific example of the flat type heat pipe which concerns on this invention. It is a schematic diagram which shows an example of the container which concerns on this invention. It is a schematic diagram which shows the example of the wick which concerns on this invention. (A) is sectional drawing which follows the AA line of FIG. 2 in the other specific example of the flat type heat pipe which concerns on this invention. (B) is sectional drawing which follows the BB line and CC line of FIG. 2 in the other specific example of the flat type heat pipe which concerns on this invention. It is a top view which shows the shape of each heat pipe in the characteristic test about the other specific example and comparative example of this invention. It is a figure for demonstrating the method of the characteristic test about the other specific example and comparative example of this invention. It is a graph which shows the measurement result of the thermal performance about the Example of this invention, and a prior art example.

  Next, a specific example of the flat heat pipe 1 according to the present invention will be described. First, the configuration will be described. The heat pipe 1 is a flat type heat pipe 1, which is filled with a working fluid (not shown) that is heated to evaporate and radiates and condenses, and returns to a position where the liquid-phase working fluid is evaporated. A wick 2 that generates a capillary force is disposed in the interior 3 a of the container 3.

  The container 3 of the heat pipe 1 is an airtight hollow container, and is a hollow tube that transports heat between locations separated from each other. In the interior 3a of the container 3, a condensable fluid is sealed as a working fluid in a vacuum deaerated state. One end of the heat pipe 1 is an evaporation unit 4, the other end is a condensing unit 5, and an intermediate part thereof is a heat insulating unit 6. In addition, since it is necessary for the container 3 to transmit heat between the inside 3a and the exterior, it is preferable to be comprised with the raw material with high heat conductivity, for example, it is preferable to use a copper pipe. The container 3 may have a cylindrical cross section.

  The working fluid enclosed in the interior 3a of the heat pipe 1 is a fluid that heats and evaporates, dissipates heat and condenses, thereby transporting heat in the form of latent heat. It is selected as appropriate. For example, water, alcohol, methanol, alternative chlorofluorocarbon, and ammonia are used as the working fluid. The evaporated working fluid is called a gas-phase working fluid or working fluid vapor, and the condensed working fluid is called a liquid-phase working fluid or working fluid.

  As shown in FIG. 1, the wick 2 is a porous structure formed by sintering a large number of powder particles that generate capillary force when the working fluid permeates. The porous structure is configured by sintering copper powder as a granular material, for example. In addition, the wick 2 may be configured by bundling a large number of thin wires that generate capillary force when the working fluid permeates. The thin wire may be any wire that has excellent wettability with the working fluid sealed in the interior 3a of the container 3, such as a metal wire such as copper or carbon fiber.

  Further, the wick 2 has a circular cross section. The wick 2 is fixed to one flat surface 3b of the interior 3a of the container 3. When the cylindrical pipe is flattened, the top of the formed arc-shaped wick 2 is opposed to the inner wall surface 3c of the container 3 (in other words, the other flat surface 3c after being flattened). Avoid contact. This is because, in the wick 2, a surface area where the working fluid is vaporized is secured, and a steam flow path in the interior 3a of the container 3 is secured. Accordingly, the distance between them is, for example, a distance that allows the evaporated working fluid to flow, or a distance that does not generate capillary force between them. As a result, the space formed by the inner wall surface 3c (the other flat surface 3c) of the container 3 and the wick 2 serves as a flow path for the working fluid vapor. The wick may have a rectangular cross section, as shown in FIG. When flattening is performed when the curved rectangular wick 7 is arranged in the interior 3a of the container 3, the shape of the wick 7 changes with the deformation of the container 3, and as a result, the wick 7 has a rectangular cross section. become. The cross-sectional area perpendicular to the longitudinal direction of the wick is preferably about 30 to 40% of the cross-sectional area of the hollow portion of the container.

  Further, as shown in FIG. 1, a plurality of narrow grooves 8 are formed in a rectangular shape along the longitudinal direction of the heat pipe 1 on the surface 2 a of the wick 2 facing the other flat surface 3 c of the container 3. . The narrow groove 8 serves as a flow path through which the liquid-phase working fluid flows, and causes capillary action to recirculate the liquid-phase working fluid toward the evaporation unit 4. The cross-sectional shape of the narrow groove is not particularly limited as long as it causes capillary action and causes the liquid-phase working fluid to flow back to the evaporation portion, as described above. For example, a semicircular shape, a square shape, a fan shape, a sawtooth shape, and a triangular shape. An appropriate shape such as the above may be used. Further, it is only necessary to provide a groove in which the liquid-phase working fluid flows on the surface of the wick facing the inner peripheral surface of the container, and the groove 9 may be provided on the upper surface 7a of the wick 7 as shown in FIG. .

  Here, the space excluding the wick 2 inside the container 3 and the narrow groove 8 formed in the wick 2 is a steam flow path through which the working fluid steam flows. Further, the wick 2 and the narrow groove formed in the wick 2 serve as a liquid flow path through which the working fluid flows.

  Next, the operation of a specific example of the flat heat pipe according to the present invention will be described. When heat is applied to a part of the container 3 (evaporation part 4) and the other part (condensation part 5) is cooled, the working fluid is heated and evaporated, and the vapor is directed to a place where the temperature and pressure are low. It flows and then dissipates heat and condenses.

  The steam channel is a channel along the wick 2 (in other words, between the wick 2 and the other flat surface 3c opposite to the flat surface to which the wick 2 is fixed). Since the peripheral surface 3b is fixed by sintering, a steam flow path is ensured even when deformation such as bending is applied to the heat pipe 1, and as a result, the working fluid vapor flows as necessary and sufficiently flat. Heat transport characteristics as a heat pipe are improved.

  Further, since the working fluid vapor can flow through the vapor flow path, a capillary force is generated between them to form a reflux path, so that the surface 2a of the wick 2 is covered with the liquid phase working fluid. Can be avoided in advance. That is, in the wick 2, it is possible to secure an evaporation area for the working fluid to vaporize. As a result, the working fluid vapor flows sufficiently and sufficiently, and the heat transport characteristics as a flat heat pipe are improved.

  On the other hand, the condensed working fluid permeates into the wick 2 and flows toward a location where evaporation occurs using the gap between the fine wires constituting the wick 2 or the gap of the porous structure as a flow path. That is, when the liquid-phase working fluid evaporates, the meniscus formed between the thin wires of the wick 2 or in the gap between the porous structures is lowered, so that a capillary force is generated, and the capillary force is used as a pumping force. The phase working fluid recirculates to the evaporation section side. And since a larger capillary force is generated when the gap between the thin wires or the gap between the porous structures is small, so-called reflux characteristics are improved.

  Further, the condensed working fluid can flow from the condensing part 5 toward the location 4 where evaporation occurs, using the narrow groove 8 formed in the wick 2 as a flow path. That is, when the liquid-phase working fluid evaporates, the meniscus formed in the narrow groove is lowered, so that a capillary force is generated, and the liquid-phase working fluid is returned to the evaporation portion side using the capillary force as a pumping force. It becomes easy. As a result, the overall thermal resistance loss can be reduced, and the maximum heat transport capability can be improved. In addition, since the liquid-phase working fluid flows into the plurality of grooves 8 in the evaporating section 4, the working fluid accumulated in the grooves can reduce the temperature of the heat source.

  Next, another specific example of the flat heat pipe according to the present invention will be described. Since the configuration of the flat heat pipe 10 is substantially the same as the configuration in the above-described specific example, the description thereof is omitted, and only the configuration related to the groove portion 12 formed in the wick 11 and the other wick 13 is described. explain.

  On the surface 11a of the wick 11 facing the other flat surface 3c of the container 3, as shown in FIG. 4, a groove portion 12 for returning the liquid-phase working fluid to a position to evaporate is provided along the longitudinal direction of the heat pipe 10. It is formed in a rectangular shape. The groove portion 12 is a storage portion that stores the liquid-phase working fluid, and is formed at a position (in other words, an evaporation portion) that evaporates the liquid-phase working fluid. The cross-sectional shape of the groove portion 12 may be any shape as long as it returns to the position where the liquid-phase working fluid is evaporated and stored, as described above. Shape may be sufficient. Moreover, the storage part may be formed by a plurality of narrow grooves.

  Further, another wick 13 is provided so as to cover the inner peripheral surface of the container 3 with a thin layer. The other wick 13 is provided in the evaporation part 4 as shown to Fig.4 (a), and is not provided in the heat insulation part 6 and the condensation part 5 as shown in FIG.4 (b). The other wick 13 is a porous structure formed by sintering a large number of powder particles that generate capillary force when the working fluid permeates. The porous structure is configured by sintering copper powder as a granular material, for example. The other wick may be configured by bundling a large number of thin wires that generate capillary force when the working fluid permeates. The thin wire may be any wire that has excellent wettability with the working fluid sealed in the container 3 such as a metal wire such as copper or carbon fiber. The other wick 13 may be a net-like body as long as it is configured to facilitate the flow of the working fluid. Moreover, the other wick 13 may be comprised so that the inner peripheral surface of a container may be covered with a thin layer over the whole in a longitudinal direction.

  Here, as shown in FIG. 4, the space excluding the wick 11 inside the container 3, the groove 12 formed in the wick 11, and the other wick 13 is a steam flow path through which the working fluid steam flows. The Further, the wick 11 and the groove 12 serve as a liquid flow path through which the working fluid flows.

  Next, the operation of another specific example of the flat heat pipe according to the present invention will be described. When heat is applied to a part of the container 3 (evaporation part 4) and the other part (condensation part 5) is cooled, the working fluid is heated and evaporated, and the vapor is directed to a place where the temperature and pressure are low. It flows and then dissipates heat and condenses.

  The steam channel is a channel along the wick 11 (in other words, between the wick 11 and the other flat surface 3c facing the flat surface 3b to which the wick 11 is fixed). Since the inner peripheral surface 3b of the heat pipe 10 is fixed by sintering, a steam flow path is secured even if the heat pipe 10 is deformed such as bending, and as a result, the working fluid vapor flows sufficiently and sufficiently. Heat transport characteristics as a flat heat pipe are improved.

  Further, since the working fluid vapor can flow through the steam flow path, a capillary force is generated between them to form a reflux path, so that the surface 11a of the wick 11 is covered with the liquid phase working fluid. Can be avoided in advance. That is, in the wick 11, an evaporation area for the working fluid to be vaporized can be secured. As a result, the working fluid vapor flows sufficiently and sufficiently, and the heat transport characteristics as a flat heat pipe are improved.

  On the other hand, the condensed working fluid permeates into the wick 11 and flows toward a portion where evaporation occurs using the gap between the thin wires constituting the wick 11 or the gap of the porous structure as a flow path. That is, when the liquid-phase working fluid evaporates, the meniscus formed between the fine wires of the wicks 11 or in the gaps between the porous structures is lowered, and thus a capillary force is generated, and the capillary force is used as a pumping force to generate liquid. The phase working fluid recirculates to the evaporation unit 4 side. And since a larger capillary force is generated when the gap between the thin wires or the gap between the porous structures is small, so-called reflux characteristics are improved.

  Further, the condensed working fluid penetrates into the other wick 13 provided on the inner peripheral surface of the container 3, and the gap between the thin wires constituting the wick 11, the gap between the nets, or the gap between the porous structures. As a flow path, the liquid can flow toward a portion where evaporation occurs. That is, when the liquid-phase working fluid evaporates, the meniscus formed in the other wick 13 is lowered, so that a capillary force is generated and the liquid-phase working fluid is pumped to the liquid-phase working fluid. It becomes easy to reflux. Therefore, it is possible to further secure an evaporation area for vaporizing the working fluid, and as a result, it is possible to reduce the overall thermal resistance loss and improve the maximum heat transport capability.

  Further, the condensed working fluid flows into the groove 12 formed on the surface 11 a of the wick 11 in the evaporation unit 4 and is stored. For this reason, the working fluid accumulated in the groove 12 absorbs the heat at the evaporation position and evaporates, and the temperature at the evaporation position can be reduced.

  Next, a performance test comparing another specific example and a comparative example in the present invention will be described. In this performance test, a thermal performance test related to “thermal resistance”, that is, “thermal performance” was performed.

  The heat pipe 10 of another specific example is a flat heat pipe and has the same configuration as described above. On the other hand, the heat pipe 14 to be compared has other wicks 11 except that the groove portion 12 is not provided and the other wick 13 is not provided on the inner peripheral surface of the container 3 in the evaporation portion 4. The configuration is the same as that of the specific example. As shown in FIG. 5, both the flat heat pipes 10 and 14 were bent at 90 ° in the central portion in the axial direction and then crushed as described above to obtain flat heat pipes. The size of each part after processing is such that the overall length of the flat heat pipe is 150 mm, the thickness is 2.0 mm, the width of the container 3 is 8.7 mm, and one side of the bent part is sandwiched between them. The length was 60.0 mm and the other length was 60.0 mm. Further, the bending radius (R) of the curved pipe was 18 mm, and water was used as the working fluid. In addition, the wick 11 was arrange | positioned in the center part of the width direction of the flattened container 3. FIG.

Further, as shown in FIG. 6, the heat pipes 10, 14 are brought into contact with the surface (20 mm × 20 mm) of the electric heater 15 with the evaporation part 4 of the heat pipe to be tested, and the upper surface (30 mm ×× 50 mm) was placed in contact with the condenser 5. In addition, the heat pipes 10 and 14 have a heat insulating portion 6 between the electric heater 15 and the heat radiating plate 16. As shown in FIG. 6, the electric heater 15 is energized to heat the evaporator 4, and the heat input amount Q (W), the surface temperature Th (° C.) of the electric heater 15, The temperature Tc (° C.) of the arranged condenser 5 was measured. From these measurement data, the heat resistance R (° C./W) of each heat pipe 10, 14 is
R = (Th−Tc) / Q (1)
Can be expressed as Further, the maximum heat input Qmax (W) in a range where the so-called dry-out of the heat pipes 10 and 14 does not occur was obtained. FIG. 7 shows the test results of other specific examples and comparative heat pipes 10 and 14. This measurement was started after the temperature at each measurement point became constant with respect to the heat input, and a K-type thermoelectric thermometer was used for temperature measurement at each measurement point.

  From the test result of FIG. 7, it can evaluate as follows. In the heat pipe 10 of another specific example, the maximum heat input amount Qmax is 44 W, whereas in the heat pipe 14 to be compared, the maximum heat input amount Qmax is 40 W, so the other specific examples have the maximum heat input amount Qmax. Is expensive. Further, in the heat pipe 10 of another specific example, the thermal resistance R is approximately 0.44 ° C./W, whereas in the heat pipe 14 to be compared, the thermal resistance R is approximately 0.50 ° C./W. In the other specific examples, the thermal resistance R is lower. Therefore, it was confirmed that the flat heat pipe according to the present invention has a maximum heat transport amount higher than that of the comparative example, and the heat resistance has a low value and has an excellent heat transport capability.

  The flat heat pipe according to the present invention is not limited to the above-described specific example. In short, in order to facilitate the flow of the liquid-phase working fluid, the liquid-phase is formed on the surface of the wick facing the inner peripheral surface of the container. It is only necessary to provide a groove portion through which the working fluid flows.

  DESCRIPTION OF SYMBOLS 1 ... Heat pipe, 2 ... Wick, 3 ... Container, 4 ... Evaporating part, 5 ... Condensing part, 6 ... Thermal insulation part, 8 ... Groove part.

Claims (7)

In a flat heat pipe that transports heat by a working fluid that is heated to evaporate and radiates and condenses,
A container formed in a flat shape and filled with the working fluid;
A wick that generates a capillary force for refluxing the working fluid in a liquid phase to a position to evaporate,
The wick is fixed to one flat surface inside the container by sintering over the entire length in the longitudinal direction of the container,
The working fluid in a gas phase flows between the wick fixed to one flat surface and the other flat surface inside the container.
A flat heat pipe, characterized in that a groove portion for recirculating the liquid-phase working fluid to a position to evaporate is formed along the longitudinal direction on the surface of the wick facing the other flat surface.   2. The flat heat pipe according to claim 1, wherein the groove is a narrow groove that generates a capillary force for returning the liquid-phase working fluid to a position to evaporate.   3. The flat heat according to claim 1, wherein the groove portion is a storage portion that is formed at the position where the liquid-phase working fluid is evaporated, and stores the liquid-phase working fluid. pipe.   The flat heat pipe according to any one of claims 1 to 3, wherein another wick is further provided on the inner peripheral surface of the container.   5. The wick includes any one of a porous structure obtained by sintering a large number of powder particles and a thin wire bundle configured by bundling a large number of thin wires. Flat heat pipe as described in 1.   5. The other wick includes any one of a porous structure obtained by sintering a large number of powders and a fine wire bundle formed by bundling a large number of fine wires and a fine mesh. Flat heat pipe as described in 1.   The flat heat pipe according to any one of claims 1 to 6, wherein the wick includes any one of a wick having a rectangular cross section and a flat semicircular wick.

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