WO2024092617A1

WO2024092617A1 - Heat exchange apparatus and manufacturing method thereof

Info

Publication number: WO2024092617A1
Application number: PCT/CN2022/129555
Authority: WO
Inventors: Hua Cai; Yan Xia; Ning Qi
Original assignee: Nokia Shanghai Bell Co., Ltd.; Nokia Solutions And Networks Oy
Priority date: 2022-11-03
Filing date: 2022-11-03
Publication date: 2024-05-10

Abstract

A heat exchange apparatus(100) and a method for manufacturing the heat exchange apparatus(100). The heat exchange apparatus(100) comprises a first heat conducting member(101) having a first side(1011) and a second side(1012) opposite to the first side(1011), and a second heat conducting member(102) disposed on the second side(1012) of the first heat conducting member(101) to form an internal space(103) therebetween. The internal space(103) comprises at least one flow channel(105) for containing heat transfer agent. A graphene powder layer(106) is coated on at least a part of an internal surface of the at least one flow channel(105).

Description

HEAT EXCHANGE APPARATUS AND MANUFACTURING METHOD THEREOF

TECHNICAL FIELD

Various exemplary embodiments of the present disclosure relate to a heat exchange apparatus and a manufacturing method thereof.

BACKGROUND

5G communication devices generate more heat than 4G products due to usage of a greater density of high-power components in smaller spaces, which needs to be reliably dissipated in order to avoid overheating of the electronic components. Generally, a heatsink made of aluminum or copper may be used to absorb heat generated by the electronic components and dissipate the heat to the environment. In addition, one or more heat pipes may be embedded into the heatsink to enhance thermal transfer from the electronic components to the heatsink. Another option is based on an external liquid cooling technology which uses a pump on a reservoir side to deliver cooling liquid like water to the electronic components through external pipes. The external liquid cooling apparatus has good thermal performance, but it needs regular maintenance because the pump may fail or the pipes may break.

SUMMARY

In general, example embodiments of the present disclosure provide a heat exchange apparatus and a method for manufacturing the heat exchange apparatus. The heat exchange apparatus may seal heat transfer agent internally in one or more flow channels, and a graphene powder layer may be coated on an internal surface of the flow channels to promote thermal transfer ability of the flow channels. In an example embodiment, the flow channel may be designed to circulate the heat transfer agent in a predetermined direction from a heat-intensive zone to a less heat-intensive zone. The heat exchange apparatus has good thermal performance and it does not need regular maintenance because no pump or external pipe is used.

According to a first aspect, example embodiments of a heat exchange apparatus is provided. The heat exchange apparatus may comprise a first heat conducting member having a first side and a second side opposite to the first side, and a second heat conducting member disposed on the second side of the first heat conducting member to form an internal space therebetween. The internal space may comprise at least one flow channel for containing heat transfer agent. A graphene powder layer may be coated on at least a part of an internal surface of the at least one flow channel.

In some example embodiments, the graphene powder layer may have a thickness in a range of 0.05 mm to 0.4 mm, or preferably in a range of 0.08mm to 0.3 mm.

In some example embodiments, the heat transfer agent may comprise cooling liquid which evaporates into vapor when heated in a heat-intensive zone. The vapor may flow within the at least one flow channel to a less heat-intensive zone where the vapor condenses to liquid, so that heat is transferred from the heat-intensive zone to the less heat-intensive zone.

In some example embodiments, the at least one flow channel may include a first part having a first cross section area in the less heat-intensive zone and a second part having a second cross section area in the heat-intensive zone. The first cross section area may be larger than the second cross section area.

In some example embodiments, the at least one flow channel may have a cross section having a U shape with rounded corners, a rectangular shape with rounded corners, a semiellipsoid shape, or an ellipsoid shape.

In some example embodiments, the at least one flow channel may be formed in the second side of the first heat conducting member and/or in a side of the second heat conducting member facing to the first heat conducting member.

In some example embodiments, a plurality of protrusion elements may be formed on the second side of the first heat conducting member and/or a side of the second heat conducting member facing to the first heat conducting member to divide the internal space between the first heat conducting member and the second heat conducting member into the at least one flow channel.

In some example embodiments, the second heat conducting member may be hermetically bonded at portions outside the at least one flow channel to the second side of the first heat conducting member to seal the at least one flow channel.

In some example embodiments, the graphene powder layer may comprise 1 to 10 layered graphene nanometer powder.

In some example embodiments, the heat exchange apparatus may further comprise a heatsink mounted on or integrally formed with the first side of the first heat conducting member.

According to a second aspect, example embodiments of an electronic device are provided. The electronic device may comprise the heat exchange apparatus described above.

In some example embodiments, the electronic device may further comprise a power circuit board disposed on a side of the second heat conducting member opposite to the first heat conducting member, and a thermal pad interposed between the second heat conducting member and the power circuit board.

In some example embodiments, the electronic device may comprise a mobile device, a cellular telephone, a personal data assistant, a motherboard, a computer device, a blade server, a base station, or a core network device.

According to a third aspect, example embodiments of a method for manufacturing a heat exchange apparatus is provided. The method may comprise providing a first heat conducting member having a first side and a second side opposite to the first side, and providing a second heat conducting member to be disposed on the second side of the first heat conducting member. At least one flow channel may be on at least one of the second side of said first heat conducting member or the second heat conducting member, and a graphene powder layer may be coated on an internal surface of the at least one flow channel. The second heat conducting member may be welded to the second side of the first heat conducting member to form therebetween an internal space comprising the at least one flow channel for containing heat transfer agent.

In some example embodiments, the graphene powder layer may be coated on the internal surface of the at least one flow channel by following steps: preparing mixture slurry comprising graphene powder, resin and organic solvent, applying the mixture slurry onto the second side of the first heat conducting member or a side of the second heat conducting member facing to the first heat conducting member by a spraying process, an electrostatic spraying process, a blade coating process, a roller coating process, a brush coating process, or a dip coating process, curing the applied mixture slurry to obtain the graphene powder layer, and removing a part of the graphene powder layer outside the at least one flow channel.

In some example embodiments, the graphene powder layer has a thickness in a range of 0.05 mm to 0.4 mm, or preferably in a range of 0.08 mm to 0.3 mm.

In some example embodiments, the at least one flow channel may be formed to include a first part having a first cross section area in a less heat-intensive zone and a second part having a second cross section area in a heat-intensive zone. The first cross section area may be larger than the second cross section area.

In some example embodiments, the at least one flow channel may be formed to have a cross section having a U shape with rounded corners, a rectangular shape with rounded corners, a semiellipsoid shape, or an ellipsoid shape.

In some example embodiments, the second heat conducting member may be hermetically bonded at portions outside the at least one flow channel to the second side of the first heat conducting member by a brazing welding process, a diffusion welding process, or a glue bonding process to seal the at least one flow channel.

In some example embodiments, the method may further comprise evacuating the at least one flow channel to a predetermined vacuum level through an inlet formed in the first heat conducting member or the second heat conducting member connected to the at least one flow channel, injecting heat transfer agent into the at least one flow channel through the inlet, and sealing the inlet.

It should be appreciated that the summary section is neither used to limit the present disclosure, nor is it intended to identify the prime technical features. For being easily comprehended by the persons skilled in the art, the present disclosure provides the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described, by way of non-limiting examples, with reference to the accompanying drawings, where:

FIG. 1 illustrates an exploded view of a heat exchange apparatus according to an example embodiment of the present disclosure.

FIG. 2A illustrates a top view of a first heat conducting member according to an example embodiment of the present disclosure.

FIG. 2B illustrates a plan view of flow channels coated with a graphene nanometer powder layer according to an example embodiment of the present disclosure.

FIG. 2C illustrate a cross section view of a flow channel according to an example embodiment of the present disclosure.

FIG. 3 illustrates a plan view of a flow channel according to an example embodiment of the present disclosure.

FIG. 4 illustrates a perspective view of a heat exchange apparatus according to an example embodiment of the present disclosure.

FIG. 5 illustrates an exploded view of an electronic device with a heat exchange apparatus according to an example embodiment of the present disclosure.

FIG. 6 illustrates a flow chart of a method for manufacturing a heat exchange apparatus according to an example embodiment of the present disclosure.

FIG. 7 illustrates a flow chart of a method for coating a graphene nanometer powder layer according to an example embodiment of the present disclosure.

FIG. 8 illustrates a plan view of a plurality of flow channels connected to each other according to an embodiment of the present disclosure.

Throughout the drawings, same or similar reference numbers indicate same or similar elements except the requirement of describing an embodiment. A repetitive description on the same elements would be omitted.

DETAILED DESCRIPTION

Herein below, some example embodiments are described in detail with reference to the accompanying drawings. The following description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. It is to be understood that, except in the example embodiments described therein, the structures and materials as generally depicted and shown in the drawings can be arranged and designed in various manners. Accordingly, the example embodiments illustrated with reference to the drawings and the detailed description made below are merely provided as examples, rather than suggesting any limitations to the scope of protection.

In addition, the features, structures or characteristics as described herein may be combined in one or more embodiments in any appropriate manner. More details will be provided below for thorough understanding on the embodiments. Nevertheless, those skilled in the art would realize that various embodiments can be implemented when one or more details are missing, or other methods, components, materials and the like are utilized. In other cases, some or all the known structures, materials or operations may not be demonstrated or described in detail for the sake of clarity. As used herein, the singular form “a” or “one” is to be read as “one or more” unless the context clearly indicates otherwise.

Reference will now be made to the drawings to describe example embodiments of the present disclosure. In some example embodiments, a heat exchange apparatus without any pumps and pipes is provided. The heat exchange apparatus may comprise a first heat conducting member having a first side and a second side opposite to the first side, and a second heat conducting member disposed on the second side of the first heat conducting member to form an internal space between the first heat conducting member and the second heat conducting member. The internal space may comprise at least one flow channel for containing heat transfer agent. A graphene powder layer may be coated on at least a part of an internal surface of the at least one flow channel. In an example embodiment, the heat transfer agent contained in the flow channel may comprise cooling liquid which, when heated in a heat-intensive zone, may evaporate to vapor. The vapor may flow along the flow channel to a less heat-intensive zone where the vapor may condense back to liquid so that heat is transferred from the heat-intensive zone to the less heat-intensive zone. The condensed liquid may flow along the flow channel by the surface tension effect (also known as capillarity) . The graphene powder layer can also facilitate the flowing of the condensed liquid. In an example embodiment, the flow channel may be designed to circulate the heat transfer agent in a predetermined direction from the heat-intensive zone to the less heat-intensive zone so as to further improve the thermal performance of the heat exchange apparatus. The heat exchange apparatus may be used as a cooling apparatus to dissipate heat generated from for example power chips or elements, or as a heating apparatus which provides a heating surface with a uniform temperature distribution.

FIG. 1 illustrates a heat exchange apparatus 100 according to an example embodiment of the present disclosure. As shown in FIG. 1, the heat exchange apparatus 100 may include a first heat conducting member 101 and a second heat conducting member 102. The first heat conducting member 101 and the second heat conducting member 102 may be made of heat conductive materials like metal such as aluminum, copper, iron, stainless steel, silver, gold or an alloy thereof. In the example shown in FIG. 1, the first heat conducting member 101 and the second heat conducting member 102 may be formed as a rectangular plate, but they can also be formed in other shapes depending on application scenarios. The first heat conducting member 101 may have a first side 1011 and a second side 1012 opposite to the first side 1011. It would be appreciated that the term “opposite” used here may refer to another side which may be directly or obliquely opposite to the first side 1011, depending on the cross section shape of the first heat conducting member 101 and the design of the heat exchange apparatus 100. The second heat conducting member 102 may be disposed on the second side 1012 of the first heat conducting member 101 to form an internal space 103 between the first heat conducting member 101 and the second heat conducting member 102. One or more flow channels 105 may be provided in the internal space 103 for containing heat transfer agent (not shown) .

In the heat exchange apparatus 100 shown in FIG. 1, the one or more flow channels 105 is formed in the second side 1012 of the first heat conducting member 101. The second heat conducting member 102 may be bonded (e.g., welded or glue-bonded) to the second side 1012 of the first heat conducting member 101 at portions outside the one or more flow channels 105 so that the one or more flow channels 105 may be hermetically sealed by the second heat conducting member 102, and thus the heat transfer agent may be internally sealed within the heat exchange apparatus 100. In another example embodiment, the one or more flow channels 105 may be formed in a side 1021 of the second heat conducting member 102 facing to the first heat conducting member 101. In yet another example embodiment, the one or more flow channels 105 may be formed in both the second side 1012 of the first heat conducting member 101 and the side 1021 of the second heat conducting member 102. When the second heat conducting member 102 is bonded to the second side 1012 of the first heat conducting member 101, the flow channels formed in the second side 1012 of the first heat conducting member 101 may align to the flow channels formed in the side 1021 of the second heat conducting member 102 to form the one or more complete flow channels 105. In an example embodiment, the second heat conducting member 102 may be bonded to the second side 1012 of the first heat conducting member 101 by a brazing welding process, a diffusion welding process, or a glue bonding process, which will be described in detail below.

As shown in FIG. 1, the heat exchange apparatus 100 may further include at least one inlet 109 for injecting the heat transfer agent into the one or more flow channels 105. The inlet 109 may penetrate through the first heat conducting member 101 or the second heat conducting member 102. In an example, the one or more flow channels 105 may be initially connected to each other, and the heat transfer agent may be injected into each of the flow channels 105 through one inlet 109. After injection of the heat transfer agent, the connections between the flow channels 105 may be broken to separate the flow channels 105 from each other.

In an example embodiment where the heat exchange apparatus 100 is used as a cooling apparatus, a heatsink 104 may be mounted on the first side 1011 of the first heat conducting member 101 for thermal dissipation. In another example embodiment, the heatsink 104 may be integrally formed with the first heat conducting member 101. As shown in FIG. 1, the heatsink 104 may include a plurality of fin sheets, and one or more metal poles may pass through and connect the plurality of fin sheets. In an example, the fin sheets may be solder welded to the one or more metal poles. The one or more metal poles can provide support to the fin sheets and also facilitate heat transfer between the fin sheets. Optionally, a fan (not shown) may be provided to blow air towards the plurality of fin sheets, improving thermal dissipation efficiency of the heatsink 104.

FIG. 2A illustrates a top view of the first heat conducting member 101 according to an embodiment of the present disclosure. As shown in FIG. 2A, four

independent flow channels

105a, 105b, 105c and 105d may be formed in the second side 1012 of the first heat conducting member 101, which may be independently referred to as flow channel 105 or collectively as flow channels 105. The four

independent flow channels

105a, 105b, 105c and 105d each may include a plurality of parallel parts connected to one another at both ends by a U-shaped part so that each flow channel 105 may form a circulating loop. It would be appreciated that the

flow channels

105a, 105b, 105c and 105d may be formed in other/different shapes. The heat transfer agent may be separately sealed in the four

independent flow channels

105a, 105b, 105c and 105d. If heat transfer agent leakage occurs at one of the

flow channels

105a, 105b, 105c and 105d, the remaining three flow channels can still work well. It may reduce damage to the power chips or elements due to overheating. In another example embodiment, the flow channels 105a-105d may form a single continuous circulating loop.

FIG. 2A also shows eight generally rectangular zones 107 overlapping the flow channels 105, which represent heat-intensive zones corresponding to for example power chips or elements on a power circuit board which generate much heat. A zone outside the heat-intensive zones 107 may be referred to as a less heat-intensive zone where less or almost no heat is generated. The heat-intensive zone and the less heat-intensive zone will be described below in more detail.

As discussed above, the flow channels 105 may be formed as grooves or trenches in the second side 1012 of the first heat conducting member 101. In some other example embodiments, the flow channels 105 may be formed by a plurality of protrusion elements on the second side 1012 of the first heat conducting member 101 and/or on the side 1021 of the second heat conducting member 102, which divide the internal space 103 between the first heat conducting member 101 and the second heat conducting member 102 into the flow channels 105. In an example, the plurality of protrusion elements may comprise for example cylinder elements, ridge elements, or vertical plate elements formed on the second side 1012 of the first heat conducting member 101 and/or on the side 1021 of the second heat conducting member 102, and the concave features formed between the protrusion elements may be deemed as the flow channels 105. In the example where the plurality of protrusion elements comprise the cylinder elements, the second heat conducting member 102 may have a protruded/raised periphery to be welded to the second side 1012 of the first heat conducting member 101, and the cylinder elements may be formed with an appropriate density to divide the internal space 103 between the first heat conducting member 101 and the second heat conducting member 102 into one or more flow channels 105.

In another example embodiment, the flow channels 105 may be formed in a plate first, and then the plate may be bonded onto the second side 1012 of the first heat conducting member 101 and/or on the side 1021 of the second heat conducting member 102. Example embodiments of the present disclosure are not limited in any way to shape and formation of the flow channels 105.

FIG. 2B illustrates a plan view of the flow channels 105 according to an example embodiment of the present disclosure. As shown in FIG. 2B, the one or more flow channels 105 may have a graphene powder layer 106 coated on an internal surface of the flow channels 105. In an example embodiment, the graphene powder layer 106 may be first coated on the entire second side 1012 of the first heat conducting member 101 for example by a spraying process, an electrostatic spraying process, a blade coating process, a roller coating process, a bursh coating process, a dip coating process, or a spin coating process, which will be discussed below in more detail, and then parts of the graphene powder layer 106 outside the flow channels 105 may be removed by a surface polishing, finishing or milling process, an etching process, or a mechanical cutting and peeling process, leaving the remaining parts of the graphene powder layer 106 on the internal surface of the flow channels 105.

The graphene powder layer 106 may comprise monolayer or multilayer graphene nanometer powder including for example 1-10 layered graphene nanometer particles with a size less than 1 μm, for example in a range from 1 nm to 1 μm. If the graphene powder layer 106 includes more than 10 layered graphene particles, the graphene particles would behave more like graphite with deteriorated heat conductivity, and the thermal performance of the graphene nanometer powder layer 106 would be degraded. The graphene nanometer powder layer 106 has excellent heat conducting performance, which can promote heat transfer between the heat transfer agent and the first and/or second

heat conducting members

101, 102 and heat transfer along the flow channels 105 e.g. from the heat-intensive zone to the less heat-intensive zone. The graphene nanometers powder layer 106 can also function as a surface modifier layer to improve flowing of the heat transfer agent within the flow channels 105, which also increases the heat transfer speed of the flow channels 105. Therefore, the graphene nanometers powder layer 106 can greatly improve the thermal dissipation efficiency of the heat exchange apparatus 100. In addition, the graphene nanometers powder layer 106 can also facilitate a uniform temperature distribution on the first and second

heat conducting members

101, 102, which is advantageous when the heat exchange apparatus 100 is used in heating applications such as a heating plate.

In an example embodiment, the graphene nanometer powder layer 106 may have a thin thickness in a range of 0.05 mm to 0.4 mm, or preferably 0.08 mm to 0.3 mm. With the thin thickness, the graphene nanometer powder layer 106 can have better adhesion to the first and/or second

heat conducting members

101, 102, and the graphene nanometer powder layer 106 would not peel from the internal surface of the flow channels 105 due to difference in thermal expansion coefficient between the graphene nanometer powder layer 106 and the first and/or second

heat conducting members

101, 102 which are usually made of metal. A thermal cycling test has been conducted in a temperature range from -40℃ to 120 ℃ with a temperature change rate of 10℃ per minute. After 1000 cycles, the graphene nanometer powder layer 106 with a thickness of 0.05 mm to 0.4 mm can still stick to the internal surface of the flow channels 105 made of aluminum or copper. The graphene nanometer powder layer 106 with such a thickness also shows an improved thermal transfer speed up to 30 times of the thermal transfer speed of a traditional solution without the graphene layer.

FIG. 2C illustrate a cross section view of the flow channel 105 according to an embodiment of the present disclosure. As shown in FIG. 2C, the flow channel 105 may have a U-shaped cross section with a width W and a depth D that is much smaller than the width W. The graphene nanometer powder layer 106 is not shown in FIG. 2C. The flow channel 105 may also have other cross section shapes like a rectangular shape with rounded corners, a semiellipsoid shape, or an ellipsoid shape. In an example embodiment, the width W may be in a range from 4 mm to 20 mm, or preferably from 5 mm to 12 mm, and the depth D may be in a range from 2 mm to 10 mm, preferably from 2.5 mm to 6 mm. In an example, the width to depth ratio W/D may be in a range of 2 to 20, preferably 3 to 15, or more preferably 4 to 10. With the large width to depth ratio W/D, the flow channels 105 are formed like a belt that has a large interface with the first and second

heat conducting members

101, 102, which can further promote heat exchange between the heat transfer agent contained in the flow channels 105 and the first and second

heat conducting members

101, 102 in the plate form. The U-shaped cross section of the flow channels 105 may have two rounded corners as shown in FIG. 2C. The rounded corners can reduce or prevent the heat transfer agent in a liquid state accumulating in the corners. With the design shown in FIGs. 2B and 2C, the flow channels 105 can achieve excellent heat exchange/transfer ability with a compact structure and a reduced amount of heat transfer agent.

Although not shown in FIGs. 2A-2C, a porous element, usually known as a wick, may be provided in the flow channels 105. The wick may comprise sintered copper powder or aluminum powder, which is porous like sponge and can adsorb the heat transfer agent in the liquid state and facilitate flowing of the heat transfer agent by the surface tension effect (also known as capillarity) .

FIG. 3 illustrates a plan view of the flow channel 105 according to an embodiment of the present disclosure. Referring to FIG. 3, there may be one or more heat-intensive zones 107 overlapping the flow channel 105. As discussed above, the heat-intensive zone may refer to a region of the first or second

heat conducting member

101, 102 corresponding to a power chip or element on a power circuit board provided in proximity of the heat exchange apparatus 100. The power chip or element generates a large amount of heat which needs to be dissipated or otherwise causes temporary or permanent damage to the power chip or element. The heat transfer agent in the heat-intensive zone 107, which may be initially in a liquid state, would absorb heat and evaporate to vapor, forming a high pressure in a part 1051 of the flow channel 105 in the heat-intensive zone 107. The vapor in the part 1051 of the flow channel 105 would flow and transfer heat towards a part 1052 of the flow channel 105 in a less (or non-) heat-intensive zone where less or no power chip or element is mounted on the power circuit board. While the heat exchange agent in the vapor state flows along the flow channel 105, heat is also dissipated to environment through the first heat conducting member 101 and optionally the heatsink 104 mounted on/integrally formed with the first heat conducting member 101.

In an example embodiment, the part 1051 of the flow channel 105 in the heat-intensive zone 107 may have a first cross section area smaller than a second cross section area of the part 1052 of the flow channel 105 in the less heat-intensive zone. For example, the part 1052 may have a larger width and/or a larger depth than the part 1051. Then when the evaporated vapor flows from the part 1051 to the part 1052, the volume of the vapor increases, and thus the temperature of the vapor decreases, causing condensation of the vapor back to liquid. The condensation of the vapor would increase the pressure difference between the part 1051 and the part 1052 and facilitate flowing of the vapor from the part 1051 to the part 1052, thereby improving heat transfer from the heat-intensive zone 107 to the less heat-intensive zone. Forming the part 1052 with the larger cross section than the part 1051 can also define the circulating direction of the evaporated vapor within the loop of the flow channel 105, as shown by arrows in FIG. 3. It can make the vapor flow in the defined direction along the loop of the flow channel 105 and avoid vapor flow collision and turbulence, thereby improving the heat transfer efficiency of the flow channel 105.

FIG. 3 shows one larger-cross section part 1052 formed downstream of two heat-intensive zones 107. It would be appreciated there may be two larger-cross section parts 1052 formed downstream of the two heat-intensive zones 107, respectively. The larger-cross section part 1052 may be formed at a position close to the heat-intensive zone 107 so as to attract vapor evaporated in the heat-intensive zone 107. In an example, the flow channel 105 may have a cross section area gradually increasing from the first cross section area of the part 1051 at the heat-intensive zone 107 to the second cross section area of the part 1052 at the less heat-intensive zone.

As discussed above, the heat transfer agent contained in the one or more flow channels 105 of heat exchange apparatus 100 may include various cooling liquid that have an appropriate boiling point so that it can evaporate to vapor when it absorbs heat in the heat-intensive zone 107 and condense back to liquid when it discharges heat in the less heat-intensive zone. It is also desirable that the heat transfer agent, in the liquid state or the vapor state, has a high thermal transfer capability to deliver heat generated by the electronic components. Example materials for the heat transfer agent may include but not limited to water, ethylene glycol, propylene glycol, chlorofluorocarbon (CFC) based coolant, hydrochloroflourocarbon (HCFC) based coolant, refrigerants, dielectric coolant, or any combination thereof. The materials may be selected for the heat transfer agent based on for example the usage environment. For example, ethylene glycol may be used at a lower ambient temperature. When ethylene glycol is mixed with water in a certain proportion, the freezing point of the mixture can be effectively reduced to match the requirement of practical use, transportation and storage in extremely cold environments. Freezing of the heat transfer liquid at an extremely low temperature may lead to a force exerted on the graphene nanometer powder layer 106 and the flow channel 105, which may peel off or destroy the graphene nanometer powder layer 106, or even crack the flow channel 105 and cause leakage of the heat transfer agent. Similarly, propylene glycol is also miscible with water, and its mixture with water can effectively reduce the freezing point. Furthermore, propylene glycol is less toxic than ethylene glycol and can be used as a lower toxic substitute for ethylene glycol. Cost may be also a concern for selecting material of the heat transfer agent. For example, the price of ethylene glycol is lower than that of propylene glycol.

FIG. 4 illustrates a perspective view of the heat exchange apparatus 100. As shown in FIG. 4, the first heat conducting member 101 and the second heat conducting member 102 may be hermetically bonded together at portions outside the flow channels 105 so that the flow channels 105 may be hermetically sealed between the first heat conducting member 101 and the second heat conducting member 102. Although not shown, the second heat conducting member 102 of the heat exchange apparatus 100 may be mounted in proximity of for example a power circuit board to dissipate heat generated from one or more power chips or elements mounted on the power circuit board. In another example embodiment, the second heat conducting member 102 may be mounted in proximity of a heating element like a resistance heater and the heat exchange apparatus 100 may be used as a heating apparatus. In an example, the heatsink 104 mounted on the first side 1011 of the first heat conducting member 101 may be omitted, and the first heat conducting member 101 can provide a heating surface 1011 with a uniform temperature distribution.

In the heat exchange apparatus 100 shown in FIGs. 1-4, the heat transfer agent is completely sealed in the internal space 103 between the first heat conducting member 101 and the second heat conducting member 102. The internally sealed working agent, combined with the special flow channel design, can achieve excellent thermal dissipation performance with a compact structure. The overall weight and volume of the heat exchange apparatus 100 are reduced compared to the conventionally heat exchange apparatus that includes a fan, a pump and water pipes. It is much more convenient for product application without the cost for maintenance and repair of the fan, the pump and the water pipes. The heat exchange apparatus 100 does not make any noise because no fans or pumps are used.

FIG. 5 illustrates an exploded view of an electronic device 200 including the heat exchange apparatus 100 according to an example embodiment of the present disclosure. The electronic device 200 may comprise but not limited to for example a mobile device, a cellular telephone, a personal data assistant, a motherboard, a computer device, a base station, a blade server, or a core network device.

As shown in FIG. 5, the electronic device 200 may include the heat exchange apparatus 100 mounted to a chassis or frame 202. The chassis or frame 202 is not limited to the shape or structure shown in FIG. 5, but it can have other shapes or structures depending on the electronic device 200. The heat exchange apparatus 100 has been described above with reference to FIGs. 1-4 and a repetitive description thereof is omitted here. A power circuit board 206 may be mounted on the second heat conducting member 102 of the heat exchange apparatus 100. The power circuit board 206 may have a plurality of power chips or elements 207 mounted thereon, which generate an amount of heat to be dissipated by the heat exchange apparatus 100. In an example embodiment, a thermal pad 204 may be interposed between the heat exchange apparatus 100 and the power circuit board 206 to facilitate thermal conductivity therebetween. In an example embodiment, the thermal pad 204 may be formed of thermal conductive paste or elastic thermal conductive materials so that it can provide better contact and better thermal conductivity between the heat exchange apparatus 100 and the power circuit board 206. In an example embodiment, the thermal pad 204 may be formed of an insulative material to prevent short circuit between the heat exchange apparatus 100 and the power circuit board 206.

FIG. 6 illustrates a flow chart of a method 300 for manufacturing the heat exchange apparatus 100 according to an example embodiment of the present disclosure. Since details of the heat exchange apparatus 100 have been described above with reference to FIGs. 1-4, the method 300 will be described here in a simple manner.

As shown in FIG. 6, the method 300 may comprise a step 302 of providing a first heat conducting member 101 having a first side 1011 and a second side 1012 opposite to the first side 1011, and a step 304 of providing a second heat conducting member 102 to be disposed on the second side 1012 of the first heating conducting member 101. The first heat conducting member 101 and the second heat conducting member 102 may be formed in a desirable shape depending on usage of the heat exchange apparatus 100. In an example embodiment, the first heat conducting member 101 and the second heat conducting member 102 may be formed of thermal conductive material like metal.

The method 300 may further comprise a step 306 of forming at least one flow channel 105 on at least one of the first heating conducting member 101 or the second heat conducting member 102. For example, the at least one flow channel 105 may be formed in the second side 1012 of the first heating conducting member 101 and/or in a side 1021 of the second heating conducting member 102 facing to the first heating conducting member 101. The at least one flow channel 105 may be formed by a machining process or an etching process. The machining process may comprise for example cutting or milling the first and/or second

heating conducting members

101, 102 with a tool to form the flow channels 105. In the etching process, a protection pattern may be formed on the second side 1012 of the first heating conducting members 101 and/or the side 1021 of the second heat conducting member 102, and then etching solution may be applied to etch the exposed portions of the side 1012 of the first heating conducting members 101 and/or the side 1021 of the second heat conducting member 102 to a predetermined depth, thereby forming the flow channels 105. In another example, the flow channels 105 may be formed in an additional plate and then the additional plate may be bonded/attached to the second side 1012 of the first heating conducting members 101 or the side 1021 of the second heat conducting member 102.

The method 300 may further comprise a step 308 of coating a graphene powder layer 106 (e.g., a graphene nanometers powder layer) on the internal surface of the flow channels 105. For convenience of description, here it is assumed that the flow channels 105 are formed in the second side 1012 of the first heat conducting member 101. In an example, the graphene nanometers powder layer 106 may be coated only on the internal surface of the flow channels 105, leaving positions of the second side 1012 outside the flow channels 105 exposed for welding to the second heat conducting member 102. In another example, the graphene nanometers powder layer 106 may be coated on the entire second side 1012 of the first heat conducting member 101 and the entire side 1021 of the second heat conducting member 102 facing to the first heat conducting member 101. The graphene nanometers powder layer 106 may be coated to a thickness in a range of 0.05 mm to 0.4 mm, or preferably in a range of 0.08 mm to 0.3 mm.

FIG. 7 illustrate a process 400 for coating the graphene nanometers powder layer 106 according to an example embodiment of the present disclosure. The process 400 may be performed for example at the step 308 in the method 300 shown in FIG. 6. As shown in FIG. 7, the process 400 may comprise a step 402 of preparing mixture slurry comprising at least graphene nanometer powder, resin and organic solvent. The graphene nanometer powder may comprise commercial available graphene nanometer powder purchased from the market, and it may include monolayer or multilayer (e.g., 1-10 layered) graphene nanometer powder with an average particle size from 1 nm to 1 μm. The resin may comprise thermosetting resin like epoxy resin or photocurable resin like acrylate resin, which, when cured, can provide good adhesion to the internal surface of the flow channels 105. At the step 402, the graphene nanometer powder may be dispersed in the solvent first using for example an ultrasonic disperser, and then the resin may be added to the mixture of the graphene nanometer powder and the solvent and stirred using a mechanical stirrer for certain period so that the graphene nanometer powder is evenly mixed with the resin, obtaining the mixture slurry. In an example embodiment, the graphene nanometer powder may take 30%to 90%of the total weight of the mixture slurry. The amount of the solvent may be appropriately selected so as to set viscosity of the mixture slurry, which may be predetermined based on the process to be used for coating the mixture slurry onto a certain surface. In an example, the mixture slurry may be stirred in the mechanical stirrer until it has the desired viscosity.

At 404, the mixture slurry may be applied onto the entire second side 1012 of the first heat conducting member 101 and/or the entire side 1021 of the second heat conducting member 102. In an example, the mixture slurry may be applied by a spraying process, an electrostatic spraying process, a blade coating process, a roller coating process, a brush coating process, a dip coating process, or a spin coating process. The process for applying the mixture slurry may be selected based on the desirable thickness of the coating layer and it is not limited to the above-mentioned examples.

Then the applied mixture slurry may be cured at 406 to obtain the graphene nanometer powder layer 106 covering the entire second side 1012 of the first heat conducting member 101 and/or the entire side 1021 of the second heat conducting member 102. Depending on the resin used in the mixture slurry, a thermal curing process or a photo curing process may be used at the step 406.

Optionally, parts of the graphene nanometer powder layer 106 outside the flow channels 105 may be removed at 408. The parts of the graphene nanometer powder layer 106 may be removed by for example a surface polishing, finishing or milling process, or a cutting and mechanical peeling process, and the portions of the second side 1012 of the first heat conducting member 101 and/or the side 1021 of the second heat conducting member 102 exposed by removing the parts of the graphene nanometer powder layer 106 outside the flow channels 105 may be used to weld the first heat conducting member 101 and the second heat conducting member 102 together, which will be described below.

Referring back to FIG. 6, the method 300 may further comprise a step 310 of bonding the side 1021 of the second heat conducting member 102 to the second side 1012 of the first heating conducting member 101 to form therebetween an internal space 103 comprising the flow channels 105. In an example embodiment, a porous wick element may be provided in the flow channels 105 before bonding the first and second

heat conducting members

101, 102. The bonding of the first heating conducting member 101 and the second heat conducting member 102 may be performed by a brazing welding process, a diffusion welding process, or a glue bonding process.

In an example, the brazing welding process may comprise applying brazing solder onto portions of the second side 1012 of the first heat conducting member 101 outside the flow channels 105 and attaching the side 1021 of the second heat conducting member 102 onto the second side 1012 of the first heat conducting member 101 to obtain a stacked structure. Then the stacked structure may be heated in an oven to a predetermined temperature for a certain time period. The brazing solder would melt at the predetermined temperature and it would weld the side 1021 of the second heat conducting member 102 to the second side 1012 of the first heat conducting member 101. The brazing solder also forms a sealing member for the flow channels 105 to prevent unintentional leakage of the heat transfer agent contained in the flow channels 105.

Unlike the brazing welding process, the diffusion welding process may not use any solder. In an example, the diffusion welding process may comprise polishing or milling the second side 1012 of the first heat conducting member 101 and the side 1021 of the second heat conducting member 102 to obtain two smooth surfaces, and then attaching the two smooth surfaces to each other to obtain a stacked structure. The stacked structure may be heated in an oven while the first heat conducting member 101 and the second heat conducting member 102 are pressed against each other. Under the pressure and the elevated temperature, diffusion occurs at the interface between the first heat conducting member 101 and the second heat conducting member 102, forming a coalescence at the interface. The flow channels 105 may be hermetically sealed by the coalescence between the first heat conducting member 101 and the second heat conducting member 102.

The first heat conducting member 101 and the second heat conducting member 102 may also be bonded together by the glue bonding process. For example, liquid glue like epoxy resin glue may be applied onto the second side 1012 of the first heat conducting member 101 and the side 1021 of the second heat conducting member 102. In this step, it should be noted that the liquid glue is not applied to the internal surface of the flow channels 105 where the graphene nanometer powder layer 106 is formed. Then the first heat conducting member 101 may be attached to the second heat conducting member 102. When the liquid glue is cured, the first heat conducting member 101 and the second heat conducting member 102 stick to each other.

In an example embodiment, the first heat conducting member 101 may be integrally formed with a heatsink 104. In another example embodiment, the first heat conducting member 101 and the heatsink 104 may be two separate elements, and the method 300 may further comprise a step 312 of mounting the heatsink 104 onto the first side 1011 of the first heat conducting member 101. For example, the heatsink 104 may be mounted onto the first side 1011 of the first heat conducting member 101 by a welding process, a snap-fit process, or by using a chucking fixture.

The method 300 may further comprise a step 314 of evacuating air in the flow channels 105 to a predetermined vacuum level through at least one inlet 109 penetrating through the first heat conducting member 101 or the second heat conducting member 102, and a step 316 of injecting heat transfer agent into the flow channels 105 through the at least inlet 109. FIG. 8 shows an example where the five independent flow channels 105 are connected with each other via

grooves

1053, 1054 and 1055 formed in the first heat conducting member 101. Then the evacuating step 314 and the heat transfer agent injection step 316 may be performed through one inlet 109 as all the flow channels 105 are connected with each other. It would be appreciated that more inlets may be used for example when the flow channels 105 are separated from each other.

A higher vacuum level in the flow channels 105 would be advantageous for evaporation of the heat transfer agent from liquid to vapor and thus for the thermal performance of the heat exchange apparatus 100. However, special equipment such as a high-power turbo pump or molecular pump is needed to achieve a very high vacuum level in the flow channels 105, which would incur high cost. Considering a trade-off between the cost and the thermal performance, in an example, the flow channels 105 may be evacuated at 314 to around 0.8%to 0.9%atmospheric pressure (0.008 to 0.009 atm, or 0.8 to 0.9 kPa, assuming 1 atm is around 100 kPa) . The vacuum level in the flow channels 105 would be slightly effected by the heat transfer agent injection step 316, but the flow channels 105 can still be maintained at a substantial negative pressure with respect to the atmospheric pressure after the step 316, for example at less than 1 kPa.

Then at a step 318, the inlet 109 for injecting the heat transfer agent may be sealed to completely seal the heat transfer agent in the flow channels 105. For example, sealing material may be applied in the inlet 109 to seal it, and a part of the inlet 109 protruding out of the first heat conducting member 101 may be cut away. The

grooves

1053, 1054 and 1055 connecting the flow channels 105 may also be destroyed at the step 318 to separate the flow channels 105. For example, a punch process may be performed to deform portions of the first heat conducting member 101 to block up the

grooves

1053, 1054 and 1055, as shown in FIG. 8.

While the steps are depicted in a particular order in FIGs. 6-7, this should not be understood as requiring that such steps be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Compared with the conventional cooling solutions using a pump, water pipes and optionally a fan, the heat exchange apparatus 100 according to the above example embodiments can achieve better thermal performance with a more compact structure. Experiments show that the heat exchange apparatus 100 can have around 30%reduced volume or 40%reduced weight than the conventional apparatus, while it has a heat transfer speed up to around 30 times of that achievable in the conventional apparatus. The heat exchange apparatus 100 can also save power consumption because it does not need power during operation. A salt fog test and an aging test show that the heat exchange apparatus 100 has high reliability. The salt fog test is performed at a temperature 35℃+1.1℃/-1.7℃ using salt solution containing 5 weight parts of sodium chloride dissolved in 95 weight parts of water. The aging test is performed at a temperature of 120℃ for 1000 hours. The heat exchange apparatus 100 does not show any obvious change in appearance and works well after the salt fog test and the aging test.

The example embodiments of the present disclosure are provided only for description and illustration, rather than being exhaustive or restrictive. Many modifications and variations would be obvious to those skilled in the art. The example embodiments are chosen and described herein to elaborate principles and actual applications, making it clear to those skilled in the art that various modifications adapted to the embodiments of the present disclosure can achieve the anticipated particular technical effect.

Although the example embodiments have been described herein with reference to the drawings, it would be appreciated that the above description is not provided restrictively. Rather, without departing from the scope of disclosure or inventive idea and implementation solution of the present disclosure, those skilled in the art are allowed to make other variations and modifications.

The foregoing embodiments are only to illustrate the principle and efficacy of the present disclosure exemplarily, and are not to limit the present disclosure. A person skilled in the art can make modifications or variations on the foregoing embodiments without taking away from the spirit and scope of the present disclosure. Accordingly, all equivalent modifications or variations completed by those with ordinary skill in the art without taking away from the spirit and technical thinking disclosed by the present disclosure should fall within the scope of claims of the present disclosure.

Claims

A heat exchange apparatus comprising:

a first heat conducting member having a first side and a second side opposite to the first side;

a second heat conducting member disposed on the second side of the first heat conducting member to form an internal space therebetween, the internal space comprising at least one flow channel for containing heat transfer agent; and

a graphene powder layer coated on at least a part of an internal surface of the at least one flow channel.
The heat exchange apparatus of claim 1, wherein the graphene powder layer has a thickness in a range of 0.05 mm to 0.4 mm.
The heat exchange apparatus of claim 1, wherein the heat transfer agent comprises cooling liquid which evaporates into vapor when heated in a heat-intensive zone, the vapor flows within the at least one flow channel to a less heat-intensive zone where the vapor condenses to liquid, so that heat is transferred from the heat-intensive zone to the less heat-intensive zone.
The heat exchange apparatus of claim 3, wherein the at least one flow channel includes a first part having a first cross section area in the less heat-intensive zone and a second part having a second cross section area in the heat-intensive zone, the first cross section area is larger than the second cross section area.
The heat exchange apparatus of claim 1, wherein the at least one flow channel has a cross section having a U shape with rounded corners, a rectangular shape with rounded corners, a semiellipsoid shape, or an ellipsoid shape.
The heat exchange apparatus of claim 1, wherein the at least one flow channel is formed in the second side of the first heat conducting member and/or in a side of the second heat conducting member facing to the first heat conducting member.
The heat exchange apparatus of claim 1, wherein a plurality of protrusion elements are formed on the second side of the first heat conducting member and/or a side of the second heat conducting member facing to the first heat conducting member to divide the internal space between the first heat conducting member and the second heat conducting member into the at least one flow channel.
The heat exchange apparatus of claim 1, wherein the second heat conducting member is hermetically bonded at portions outside the at least one flow channel to the second side of the first heat conducting member to seal the at least one flow channel.
The heat exchange apparatus of claim 1, wherein the graphene powder layer comprises 1 to 10 layered graphene nanometer powder.
The heat exchange apparatus of claim 1, further comprising:

a heatsink mounted on or integrally formed with the first side of the first heat conducting member.
An electronic device comprising the heat exchange apparatus of any one of claims 1～10.
The electronic device of claim 11, wherein the electronic device comprises a mobile device, a cellular telephone, a personal data assistant, a motherboard, a computer device, a blade server, a base station, or a core network device.
The electronic device of claim 11, further comprising:

a power circuit board disposed on a side of the second heat conducting member opposite to the first heat conducting member; and

a thermal pad interposed between the second heat conducting member and the power circuit board.
A method for manufacturing a heat exchange apparatus, comprising:

providing a first heat conducting member having a first side and a second side opposite to the first side;

providing a second heat conducting member to be disposed on the second side of the first heat conducting member;

forming at least one flow channel on at least one of the second side of said first heat conducting member or the second heat conducting member;

coating a graphene powder layer on an internal surface of the at least one flow channel; and

bonding the second heat conducting member to the second side of the first heat conducting member to form therebetween an internal space comprising the at least one flow channel for containing heat transfer agent.
The method of claim 14 wherein coating the graphene powder layer on the internal surface of the at least one flow channel comprises:

preparing mixture slurry comprising graphene powder, resin and organic solvent;

applying the mixture slurry onto the second side of the first heat conducting member or a side of the second heat conducting member facing to the first heat conducting member by a spraying process, an electrostatic spraying process, a blade coating process, a roller coating process, a brush coating process, a dip coating process, or a spin coating process;

curing the applied mixture slurry to obtain the graphene powder layer; and

removing parts of the graphene powder layer outside the at least one flow channel.
The method of claim 14, wherein the graphene powder layer has a thickness in a range of 0.05 mm to 0.4 mm.
The method of claim 14, wherein the at least one flow channel is formed to include a first part having a first cross section area in a less heat-intensive zone and a second part having a second cross section area in a heat-intensive zone, and the first cross section area is larger than the second cross section area.
The method of claim 14, wherein the at least one flow channel is formed to have a cross section having a U shape with rounded corners, a rectangular shape with rounded corners, a semiellipsoid shape, or an ellipsoid shape.
The method of claim 14, wherein the second heat conducting member is hermetically bonded at portions outside the at least one flow channel to the second side of the first heat conducting member by a brazing welding process, a diffusion welding process, or a glue bonding process to seal the at least one flow channel.
The method of claim 14, further comprising:

evacuating the at least one flow channel to a predetermined vacuum level through an inlet formed in the first heat conducting member or the second heat conducting member and connected to the at least one flow channel;

injecting heat transfer agent into the at least one flow channel through the inlet; and

sealing the inlet.