TECHNICAL FIELD

The disclosure relates generally to heat pipes, and more particularly, the disclosure relates to a heat pipe and methods of manufacturing the heat pipe.

BACKGROUND

A heat pipe is a special device that can transfer heat over long distances due to a combination of processes of (a) evaporation of a liquid phase of an internal working media from a porous structure (wick), (b) transport of a gas phase of the internal media through a vapor channel, (c) condensation of a gas phase of the internal media on the wick and (d) transport of a liquid phase of the internal media through the wick from condensation areas to evaporation areas in one closed loop inside a hermetical envelope (case).

In known approaches, different application areas of the heat pipe consider that a cooler block and a heater block do not have strong mechanical interconnection between each other. In such case, for example, the cooler block can move in a space relative to the heater block. In an existing heat pipe, one end of the heat pipe is fixed, and another end is moved by ±1.5 millimetre (mm) in a vertical direction. In order to avoid damaging or decoupling of the heat pipe from the cooler block and the heater block, the heat pipe should be flexible, i.e. a force reaction to the heat pipe from either of the heater block or the cooler block should be low, such as less than 2.5 newton units (N). The existing heat pipe is a flat heat pipe that has the force reaction during such movement about 25 N to 50 N, which is very far from low values required for flexibility, such as 2.5 N.

Several known solutions solve the problem by attaching a bellow shape section to the heat pipe. However, the known solutions have a problem for the fabrication of the heat pipe in mass production mode. Additionally, a mesh on the bending area of the heat pipe is not attached to a substrate (wall) which leads to low capillary forces. Known solutions also use a wick that is located near an outer wall and not in the centre of the heat pipe that leads to high elongation, high stress, and ultimately destruction of the heat pipe. Known solutions also propose additional springs in the heat pipe but do not solve the destruction problem completely and also occupy internal space, which leads to low thermal performance. The known solutions also propose sophisticated designs that have many components that must be assembled during a fabrication process. Hence, they are not suitable for mass production. Further, the known solutions propose locating the wick close to a flexible wall in the heat pipe that causes wick layers to be far from the neutral plane (zero-stress area near axis of the heat pipe) and become elongated during bending, which leads to increasing of force reaction and probable destruction of the wick.

Therefore, there arises a need to address the aforementioned technical problem in existing systems or technologies to create a heat pipe that is suitable for mass production and has a reduced force reaction so that to be flexible.

SUMMARY

It is an object of the disclosure to provide a heat pipe and methods of manufacturing the heat pipe that is suitable for mass production and has a decreased force reaction, from either a heating block or a cooling block, so that to be flexible.

This object is achieved by the features of the independent claims. Further, implementation forms are apparent from the dependent claims, the description, and the figures.

The disclosure provides a heat pipe and methods of manufacturing the heat pipe with small force reaction for mass production.

According to a first aspect, there is provided a heat pipe. The heat pipe includes an envelope with a working fluid, an inner layer of wick and a flexible bellows. The envelope has a condenser end, an evaporator end, and an adiabatic section in between the condenser end and the evaporator end. The inner layer of wick is arranged on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. The adiabatic section includes a perforation of walls of the envelope forming a passage for a vapor and a compressed area where walls of the envelope are offset towards a central axis of the envelope. The flexible bellows covers the compressed area and defines a channel for the vapor with ends of the flexible bellows sealed to walls of the envelope outside of the perforation. The heat pipe according to the present disclosure achieves a decreased force reaction, as compared with traditional heat pipes, so that to be flexible. For example, in an implementation a force reaction less than 2.5-newton units (N) has been achieved. Further, the heat pipe is simple in design which is suitable for mass production. At the same time, the thermal performance of the heat pipe is equal to traditional non-flexible heat pipes from mass production which demonstrates that there is no drawback on thermal performance with the simple design and the flexibility.

In a first possible implementation form, the perforation of the walls of the envelope includes longitudinal through holes made from two opposite sides of the envelope.

In a second possible implementation form, the compressed area includes a planar channel for transporting the condensed working fluid with two tapered parts from each end of the planar channel.

In a third possible implementation form, the planar channel is arranged essentially in a plane of the central axis of the envelope.

In a fourth possible implementation form, the flexible bellows has an oval shape in a cross section.

In a fifth possible implementation form, the compressed area is provided with a fixing means imposed on the walls of the envelope offset towards the central axis of the envelope.

In a sixth possible implementation form, the fixing means is one of a wire winding, a foil wrapping and a contact resistance welding.

In a seventh possible implementation form, the perforation of the walls of the envelope includes one or more additional through holes forming the passage of the vapor.

In an eighth possible implementation form, the perforation of the walls of the envelope extends to a major part of a circumference of the envelope. In a ninth possible implementation form, the walls of the envelope and/or the layer of wick in the compressed area are provided with one or more transversal groves and/or through holes.

In a tenth possible implementation form, on an inner surface of the flexible bellows arranged is an outer layer of wick in communication with the inner layer of wick.

In an eleventh possible implementation form, on an outer surface of the envelope in the compressed area arranged is a second outer layer of wick in communication with the inner layer of wick.

In a twelfth possible implementation form, the condenser end to the evaporator end are flattened.

In a thirteenth possible implementation form, an outer surface of the flexible bellows is provided with a layer of low thermal conductivity material.

In a fourteenth possible implementation form, the wick includes one or more of sintered particles, mesh, fibers and grooves.

According to a second aspect, there is provided a method of manufacturing a heat pipe. The method includes providing an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof. The method includes arranging a layer of wick on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. The method includes perforating walls of the envelope in the adiabatic section to form a passage for a vapor. The method includes offsetting the walls of the envelope towards a central axis of the envelope to define a compressed area in the adiabatic section. The method includes covering the compressed area by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. The method includes filling the envelope with the working fluid. The method includes sealing the condenser end and the evaporator end of the envelope.

According to a third aspect, there is provided a method of manufacturing a heat pipe. The method includes providing an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof. The method includes perforating walls of the envelope in the adiabatic section to form a passage for a vapor. The method includes arranging a layer of wick on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. The method includes offsetting the walls of the envelope towards a central axis of the envelope to define a compressed area in the adiabatic section. The method includes covering the compressed area by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. The method includes filling the envelope with the working fluid. The method includes sealing the condenser end and the evaporator end of the envelope.

According to a fourth aspect, there is provided a method of manufacturing a heat pipe. The method includes providing an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof. The method includes perforating walls of the envelope in the adiabatic section to form a passage for a vapor. The method includes offsetting the walls of the envelope towards a central axis of the envelope to define a compressed area in the adiabatic section. The method includes arranging a layer of wick on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. The method includes covering the compressed area by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. The method includes filling the envelope with the working fluid. The method includes sealing the condenser end and the evaporator end of the envelope.

A technical problem in the prior art is resolved, where the technical problem is that in order to avoid damaging or decoupling of the heat pipe from a cooler block and a heater block, the heat pipe should be flexible, i.e. a force reaction to the heat pipe from either of the heater block or the cooler block should be decreased, for example, below 2.5 N.

Therefore, in contradistinction to the prior art, according to the heat pipe and methods of manufacturing the heat pipe, the heat pipe is flexible due to a decreased force reaction as compared with traditional heat pipes. The heat pipe is simple in design which is suitable for mass production. At the same time, the thermal performance of the heat pipe is equal to traditional non-flexible heat pipes from mass production which demonstrates that there is no drawback on thermal performance with the simple design and the flexibility.

These and other aspects of the disclosure will be apparent from and the implementation(s) described below.

BRIEF DESCRIPTION OF DRAWINGS

Implementations of the disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1A illustrates a heat pipe with a flexible bellows in accordance with an implementation of the disclosure;

FIG. IB illustrates an exemplary view of the heat pipe of FIG. 1A with the flexible bellows before a fabrication process in accordance with an implementation of the disclosure;

FIG. 1C illustrates a perspective view of the heat pipe of FIG. 1A accordance with an implementation of the disclosure;

FIG. ID illustrates a longitudinal cross-section view of the heat pipe of FIG. 1A in accordance with an implementation of the disclosure;

FIG. IE illustrates a cross-section view of the heat pipe of FIG. 1A in accordance with an implementation of the disclosure;

FIG. 2 illustrates a heat pipe with one or more wires to form a connection between one or more compressed walls in accordance with an implementation of the disclosure;

FIG. 3 illustrates a heat pipe with additional through holes for vapor flow in accordance with an implementation of the disclosure;

FIG. 4 illustrates a heat pipe with additional holes for vapor flow in accordance with an implementation of the disclosure;

FIG. 5 illustrates a heat pipe with a cut upper wall in accordance with an implementation of the disclosure;

FIG. 6 illustrates a heat pipe with additional vapor holes in a wall of the heat pipe in accordance with an implementation of the disclosure;

FIG. 7 illustrates a heat pipe in accordance with an implementation of the disclosure;

FIG. 8 illustrates a scheme of mechanical testing for a heat pipe in accordance with an implementation of the disclosure;

FIG. 9 is a graph that illustrates a mechanical reaction of cyclic loading of a heat pipe over time in accordance with an implementation of the disclosure;

FIGS. 10A-10B are flow diagrams that illustrate a first method of manufacturing the heat pipe in accordance with an implementation of the disclosure;

FIGS. 11 A-l IB are flow diagrams that illustrate a second method of manufacturing a heat pipe in accordance with an implementation of the disclosure; and

FIGS. 12A-12B are flow diagrams that illustrate a third method of manufacturing a heat pipe in accordance with an implementation of the disclosure.

DETAILED DESCRIPTION OF THE DRAWINGS

Implementations of the disclosure provide a flexible heat pipe with a small force reaction for mass production.

To make solutions of the disclosure more comprehensible for a person skilled in the art, the following implementations of the disclosure are described with reference to the accompanying drawings.

Terms such as "a first", "a second", "a third", and "a fourth" (if any) in the summary, claims, and foregoing accompanying drawings of the disclosure are used to distinguish between similar objects and are not necessarily used to describe a specific sequence or order. It should be understood that the terms so used are interchangeable under appropriate circumstances, so that the implementations of the disclosure described herein are, for example, capable of being implemented in sequences other than the sequences illustrated or described herein. Furthermore, the terms "include" and "have" and any variations thereof, are intended to cover a non-exclusive inclusion. For example, a process, a method, a system, a product, or a device that includes a series of steps or units, is not necessarily limited to expressly listed steps or units but may include other steps or units that are not expressly listed or that are inherent to such process, method, product, or device.

FIG. 1A illustrates a heat pipe 100 with a flexible bellows 104 in accordance with an implementation of the disclosure. The heat pipe 100 includes an envelope 102 with a working fluid, an inner layer of a wick 108, and a flexible bellows 104. The envelope 102 has a condenser end, an evaporator end, and an adiabatic section in between the condenser end and the evaporator end. The inner layer of the wick 108 is arranged on an inner surface of the envelope 102 for transporting a condensed working fluid from the condenser end to the evaporator end. The adiabatic section includes a perforation of the walls of the envelope 102 forming a passage for a vapor and a compressed area 106 where walls of the envelope 102 are offset towards a central axis of the envelope 102. The flexible bellows 104 covers the compressed area 106 and defines a channel 112 for the vapor with ends of the flexible bellows 104 sealed to walls of the envelope 102 outside of the perforation. The perforation of the walls of the envelope 102 optionally includes longitudinal through holes 110 made from two opposite sides of the envelope 102. The envelope 102 may be a copper tube. The wick 108 may be a sintered wick or a sintered porous structure including a sintered powder, a mesh wick, or one or more grooves. Optionally, the wick 108 includes one or more of sintered particles, mesh, fibers and grooves. The wick 108 is optionally located on the inner surface of the envelope 102 and two opposite sides of a middle area of the envelope 102 that includes the longitudinal through holes 110..Remaining area of the middle area is pressed together in such a way that a portion of the walls and one or more layers of the wick 108 form a flat plate near an axle of the heat pipe 100. Optionally, a felt, one or more grooves, a non-sintered mesh, or felts are used for the sintered porous structure.

The envelope 102 has a structure that is used for liquid/fluid circulation. An area of the heat pipe 100, with the longitudinal through holes 110, is encapsulated to the flexible bellows 104. In the area of the heat pipe 100, open sides of the flexible bellow 104 undergoes a soldering procedure together with the envelope 102 on the area without the longitudinal through holes 110. The soldering procedure may be performed in such a way that the channel 112 is formed between the internal surface of the flexible bellows 104 and the area of the envelope 102, with the longitudinal through holes 110.

With reference to FIG. 1A, FIG. IB illustrates an exemplary view 101 of the heat pipe 100 with the flexible bellows 104 during a fabrication process in accordance with an implementation of the disclosure. The heat pipe 100 includes the envelope 102, the flexible bellows 104, a compressed area, an inner layer of the wick 108, and the longitudinal through holes 110. For the fabrication, a round heat pipe with the envelope 102 as a copper wall and the wick 108 as a sintered wick layer is used. Optionally, an inner surface of the flexible bellows 104 arranged is an outer layer of the wick 108 in communication with the inner layer of the wick 108. Optionally, an outer surface of the envelope 102 in the compressed area 106 arranged is a second outer layer of the wick 108 in communication with the inner layer of the wick 108. Optionally, an outer surface of the flexible bellows 104 is provided with a layer of low thermal conductivity material. Optionally, a material of the flexible bellows 104 is different than a material of the walls. Two holes on the two sides of a middle area of the envelope 102 are formed, and the remaining compressed area 106 or the walls are pressed together in the middle area in such a way that a portion of the walls and one or more layers of the wick 108 become a flat plate near an axle of the heat pipe 100. Remaining walls of the envelope 102 are not compressed completely such that the open holes have a function of the longitudinal through holes 110 for circulation of the vapor between ends of the heat pipe 100 and a volume of the flexible bellows 104. The flexible bellows 104 may be moved to the middle area of the heat pipe 100 in order to cover the area of the heat pipe 100 with the longitudinal through holes 110 and the compressed area 106. The compressed area 106 may include a planar channel for transporting the condensed working fluid with two tapered parts from each end of the planar channel. The planar channel may be arranged in a plane of a central axis of the envelope 102. The plane may be a neutral plane. The wick 108 of the heat pipe 100 is located in the middle of a cross section of the heat pipe 100 near the neutral plane that has minimum stress during bending. Hence deformation of the wick 108 and remaining parts of the wall is very small, and stress and a force reaction are also significantly decreased so that to provide flexibility of the heat pipe 100. Ends of the flexible bellows 104 are soldered to the envelope 102. After that, the condenser end to the evaporator end are flattened. The walls of the envelope 102 and/or the layer of the wick 108 in the compressed area 106 can further be provided with one or more transversal groves and/or through holes to further decrease the force reaction and increase the flexibility of the heat pipe 100.

The heat pipe 100 may be fabricated by (i) producing the round heat pipe with the wick 108 that is the sintered wick, (ii) performing one or more technological operations such as (a) cutting the longitudinal through holes 110 on the sides of the heat pipe 100 according to a length of a flexible area, (b) pressing the two walls with the wick 108 together to the axle of the heat pipe 100, (c) inserting the heat pipe 100 into the flexible bellows 104, (d) soldering the flexible bellows 104 to the heat pipe 100 and (e) charging the heat pipe 100 by water. The one or more technological operations are fit for the production in a mass production mode. The heat pipe 100 has a negligible increase of cost compared to the round heat pipe. Since the flexible bellows 104 has to connect with the wick 108, any size of waves may be selected and the bending of the flexible bellows 104 is achieved with minimum force.

Optionally, the flexible bellows 104 has an oval shape in the cross-section. The flexible bellows 104 may be in other shapes, such as a flat shape, a flat shape. Optionally, a case of the heat pipe 100 that is outside the flexible bellows 104 may be flat or round or any other shape.

With reference to FIG.1A and FIG. IB, FIG. 1C illustrates a perspective view 103 of the heat pipe 100 in accordance with an implementation of the disclosure. The perspective view 103 is achieved after the fabrication process. The perspective view 103 includes the envelope 102 and the flexible bellows 104.

With reference to the FIG.1A and FIG. IB, FIG. ID illustrates a longitudinal crosssection view 105 of the heat pipe 100 in accordance with an implementation of the disclosure. The longitudinal cross-section view 105 includes the envelope 102, the flexible bellows 104, the compressed area 106, the wick 108, the longitudinal through holes 110, and the channel 112. With reference to the FIG.1A and FIG. IB, FIG. IE illustrates a cross-section view 107 of the heat pipe 100 in accordance with an implementation of the disclosure. The crosssection view 107 of the heat pipe 100 includes the envelope 102, the flexible bellows 104, the compressed area 106, the wick 108, and the longitudinal through holes 110. Optionally, a diameter of the envelope 102 is changed.

FIG. 2 illustrates a heat pipe 200 with one or more wires 210 to form a connection between one or more compressed walls in accordance with an implementation of the disclosure. The heat pipe 200 includes an envelope 202, a compressed area 204, a wick 206, a through hole 208, and the one or more wires 210. The compressed area 204 or the one or more compressed walls are fixed using the one or more wires 210 of the heat pipe 200 to control force reaction during bending. The compressed area 204 is provided with a fixing means imposed on the walls of the envelope 202 which is offset towards the central axis of the envelope 202. The fixing means is one of a wire winding, a foil wrapping, and a contact resistance welding.

FIG. 3 illustrates a heat pipe 300 with additional through holes 304A-N for vapor flow in accordance with an implementation of the disclosure. The heat pipe 300 includes an envelope 302 and the additional through holes 304A-N. The perforation of the walls of the envelope 302 includes the additional through holes 304A-N forming the passage of the vapor.

FIG. 4 illustrates a heat pipe 400 with additional holes 402 for vapor flow in accordance with an implementation of the disclosure. The heat pipe 400 includes one or more additional vapor holes 402. For achieving a low force reaction, such as less than 2.5 N, a compressed area of an envelope of the heat pipe 400 is configured to be as long as possible. In the heat pipe 400, the additional vapour holes 402 for vapor may be configured as small as possible but a vapor pressure drop is higher for a stable operation of the heat pipe 400. In order to achieve a stable operation of the heat pipe 400, the one or more additional vapor holes 402 may be created within the compressed area as illustrated in FIG. 3 and FIG. 4. Optionally, a number and a shape of such additional vapor holes 402 may be different.

FIG. 5 illustrates a heat pipe 500 with a cut upper wall in accordance with an implementation of the disclosure. The heat pipe 500 includes a compressed area 502 and a wick 504. To decrease the force reaction of the heat pipe 500, one of remaining walls of the compressed area 502 are removed and a thermal problem of the heat pipe 500 may be resolved through optimization of a thickness and a shape of the wick 504. Thereby, the perforation of the walls of the envelope of the heat pipe 500 extends to a major part of a circumference of the envelope.

FIG. 6 illustrates a heat pipe 600 with walls of the envelope and/or the layer of wick in the compressed area provided with transversal groves or through holes 602 to further decrease a force reaction of the heat pipe 600 and increase its flexibility in accordance with an implementation of the disclosure. The heat pipe 600 includes the one or more transversal groves or through holes 602.

FIG. 7 illustrates a heat pipe 700 in accordance with an implementation of the disclosure. The heat pipe 700 is in contact with a heater 702, a cooler 704, and comprises one or more temperature sensors 706A-D. The heat pipe 700 may be fabricated with sample walls. The heater 702 and the cooler 704 may be 40 millimetres (mm) wide. A temperature sensor 706A may be placed at a surface of an envelope of the heat pipe 700 where a centre point of the heater 702 is located, with 20 mm of width on either side of the envelope. A temperature sensor 706D may be placed at a surface of the envelope where a centre point of the cooler 704 is located, with 20 mm of width on either side of the envelope. The heat pipe 700 may be used for a thermal testing, where a wick of the heat pipe 700 is a sintered copper powder. For the thermal testing, the heat pipe 700 is configured using the round heat pipe taken from a mass production factory and side holes are cut in the round heat pipe. The walls are pressed to each other and flexible bellows of the heat pipe 700 are soldered. Optionally, the walls are pressed to each other and the flexible bellows using a bonding method

The thermal testing of the heat pipe 700 is performed after the mechanical test and the following results are recorded:

Temperature difference between two ends of the heat pipe 700 is in the range of 1.5 °C to 2.5 °C while in a frame of heating power of 40 to 50 watts. Similar results may be achieved in the mass production of the heat pipe 700 with equal overall sizes of the heat pipe 700. Hence, the thermal performance of the heat pipe 700 is improved. The thermal testing provides that the heat pipe 700 has low force reaction and simple in design, which is suitable for mass production. The thermal performance of the heat pipe 700 that is flexible is equal to the round heat pipe that is non-flexible.

FIG. 8 illustrates a scheme 800 of a mechanical testing for a heat pipe in accordance with an implementation of the disclosure. The scheme 800 includes a grip of a tensile machine 802 that is connected to a first hinge 806A and a second hinge 806B that hold an envelope of the heat pipe. The scheme 800 includes a tight connection 808 that tightly fixes a first end of the envelope of the heat pipe for tooling at a point 804A. A second end of the heat pipe is hinged by the first hinge 806A and the second hinge 806B at a point 804B. Using the scheme 800, a mechanical characteristic test of the heat pipe is performed by measuring a mechanical reaction during 20 cycles of loading, which may be carried out using a tensile machine and tooling.

With reference to FIG. 8, FIG. 9 illustrates a graph 900 that demonstrates the mechanical reaction of cyclic loading of the heat pipe over time in accordance with an implementation of the disclosure. As illustrated in the graph 900, a grip is moved cyclically by ±1.5 mm 20 times, which is a displacement of a point during a mechanical characteristic test. A velocity of the movement of the grip may be less than 0.2 mm per second. During the cyclic loading, the reaction force of the heat pipe is recorded. During 20 cycles of loading, the force reaction of the heat pipe may be below 2.5 N, while the force reaction of the round heat pipe without the flexible bellows is above 20 N.

FIGS. 10A-10B are flow diagrams that illustrate a first method of manufacturing a heat pipe in accordance with an implementation of the disclosure. At a step 1002, an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof is provided. At a step 1004, a layer of wick is arranged on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. At a step 1006, walls of the envelope in the adiabatic section are perforated to form a passage for a vapor. At a step 1008, the walls of the envelope are offset towards a central axis of the envelope to define a compressed area in the adiabatic section. At a step 1010, the compressed area is covered by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. At a step 1012, the envelope is filled with the working fluid. At a step 1014, the condenser end and the evaporator end of the envelope are sealed.

FIGS. 11A-1 IB are flow diagrams that illustrate a second method of manufacturing a heat pipe in accordance with an implementation of the disclosure. At a step 1102, an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof is provided. At a step 1104, walls of the envelope in the adiabatic section are perforated to form a passage for a vapor. At a step 1106, a layer of wick is arranged on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. At a step 1108, the walls of the envelope are offset towards a central axis of the envelope to define a compressed area in the adiabatic section. At a step 1110, the compressed area is covered by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. At a step 1112, the envelope is filled with the working fluid. At a step 1114, the condenser end and the evaporator end of the envelope are sealed.

FIGS. 12A-12B are flow diagrams that illustrate a third method of manufacturing a heat pipe in accordance with an implementation of the disclosure. At a step 1202, an envelope having a condenser end, an evaporator end, and an adiabatic section in between thereof is provided. At a step 1204, walls of the envelope in the adiabatic section are perforated to form a passage for a vapor. At a step 1206, the walls of the envelope are offset towards a central axis of the envelope to define a compressed area in the adiabatic section. At a step 1208, a layer of wick is arranged on an inner surface of the envelope for transporting condensed working fluid from the condenser end to the evaporator end. At a step 1210, the compressed area is covered by flexible bellows to define a channel for the vapor with ends of the flexible bellows being sealed to walls of the envelope outside of the perforation. At a step 1212, the envelope is filled with the working fluid. At a step 1214, the condenser end and the evaporator end of the envelope are sealed.

The heat pipe of the present disclosure provides a simple design which is suitable for mass production. At the same time, thermal performance of the heat pipe is equal to nonflexible heat pipes traditionally used for mass production, which demonstrates that there is no drawback on thermal performance with the simple design.

Although the disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the disclosure as defined by the appended claims.