DEVICES FOR HEAT TRANSFER

Abstract

Devices and methods of heat transfer are provided. In an example, a thermo-reversible hydrogel is provided in a first portion of a casing of a device. A wicking surface is provided in an inner surface of the casing between the first portion and the second portion.

Description

BACKGROUND

Heat transfer devices are used to transfer heat between a heat source and a heat sink. Heat transfer devices include two regions, a first region coupled to the heat source and a second region coupled to the heat sink. In the first region, heat is received from the heat source and is then transferred to the second region, for example, by conduction, convection, radiation, phase transition, and the like. Subsequently, heat is transferred from the second region to the heat sink.

BRIEF DESCRIPTION OF DRAWINGS

The following detailed description references the figures, wherein:

FIG. 1 illustrates an example device for heat transfer, according to an example implementation of the present subject matter;

FIG. 2 is an example method of heat transfer, according to an example implementation of the present subject matter;

FIG. 3(a) illustrates an example heat pipe, according to an example implementation of the present subject matter;

FIG. 3(b) illustrates an example heat pipe, according to another example implementation of the present subject matter,

FIG. 4 illustrates an example vapor chamber, according to an example implementation of the present subject matter;

FIG. 5 illustrates an example device for heat transfer, according to an example implementation of the present subject matter; and

FIG. 6 illustrates an example method of preparing a device for heat transfer, according to an example implementation of the present subject matter.

DETAILED DESCRIPTION

Heat transfer devices include devices such as heat pipes and vapor chambers. Heat transfer devices can be used in various systems, such as in spacecraft, electronic devices, solar heat transfer systems, and the like. Generally, heat transfer devices that work on principles of phase transition include a sealed casing enclosing a working fluid of high heat capacity. The working fluid is selected based on compatibility with the casing. For example, when the casing is made of copper, the working fluid can be water.

In such a heat transfer device, during operation, working fluid evaporates, for example, in an evaporation area dose to a heat source. The vapors are transferred to a second region where the vapors condense, for example, in a condensation area close to a heat sink. To return the condensed working fluid to the evaporation area for subsequent heat transfer, a fluid transfer mechanism, such as capillary action of a wicking surface, may be used.

The present subject matter relates to devices for heat transfer with increased heat dissipation performance, and methods of preparing heat transfer devices. An example device for heat transfer includes a casing. The casing includes a first portion to receive heat from a heat source. A thermo-reversible hydrogel is provided in contact with an inner surface of the first portion and is soaked in a working fluid. A wicking surface is also provided along the inner surface of the casing. The casing further includes a second portion, which is disposed substantially opposite to the first portion. The first portion and second portion are fluidly coupled by the wicking surface and a vapor region.

The device of the present subject matter can be prepared by sintering a wicking material, such as copper powder, on an inner surface of the casing followed by coating the thermo-reversible hydrogel in the first portion of the casing and drying the hydrogel.

In operation, in a first example, when a first temperature of the first portion is higher than a second temperature of the second portion, vapors of the working fluid are formed at the first portion. This case arises when, for example, the heat source that is in contact with the first portion is switched on. The vapors of the working fluid are transferred to the second portion through the vapor region. At the second portion, the vapors are condensed and the condensed working fluid is transferred to the first portion by the wicking surface. At the first portion, the condensed working fluid is absorbed by the hydrogel, thereby increasing the rate of return of the condensed working fluid and increasing heat dissipation.

On the other hand, in a second example, when the second temperature is higher than the first temperature, vapors of the working fluid are formed at the second portion. This case arises when, for example, the heat source is switched off and the first portion cools down faster than the second portion. In this case, the vapors of the working fluid are transferred from the second portion to the first portion, for condensation, through the vapor region, while the condensed working fluid is transferred from the first portion to the second portion by the wicking structure. Further, at the first portion, the vapors are absorbed by the hydrogel, thereby increasing a rate of return of vapors and increasing heat dissipation.

The thermo-reversible hydrogel in the device increases rate of dissipation of heat from the working fluid by absorption of the condensed working fluid in the first example and absorption of the vapors in the second example. Therefore, the device of the present subject matter can be used for rapid cooling.

The present subject matter provides devices for heat transfer which provide rapid cooling without substantial increase in weight. Therefore, the devices can be used to cool devices, such as Liquid Crystal Display (LCD) panels, Light Emitting Diodes (LEDs), Central Processing Units (CPUs) and the like. Further, the increased heat dissipation performance and rapid cooling helps in increasing power efficiency and reducing risks of explosion due to overheating.

The following description refers to the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the following description to refer to the same or similar parts. While several examples are described in the description, modifications, adaptations, and other implementations are possible. Accordingly, the following detailed description does not limit the disclosed examples. Instead, the proper scope of the disclosed examples may be defined by the appended claims.

Example implementations of the present subject matter are described with regard to personal computers (PCs) and laptop computers. Although not described, it will be understood that the implementations of the present subject matter can be used with other types of devices as well, such as televisions, tablets, smartphone devices, solar panels, aircraft and the like.

FIG. 1 illustrates an example device 100 for heat transfer, according to an example implementation of the present subject matter. The device 100 may be used, for example, in electronic circuitry, spacecraft, and the like. Based on the application, the device 100 may be fabricated as a micro-device or a nano-device.

In an example, the device 100 may be one of a heat pipe and a vapor chamber. A heat pipe is a substantially hollow, cylindrical heat transfer device provided between a heat source and a heat sink to transfer heat between the heat source and a heat sink. A vapor chamber may be understood as a flattened heat pipe with substantially planar heat transfer surfaces and a hollow region therebetween. Function of heat pipes and vapor chambers is based on principles of conduction and phase transition.

The device 100 includes a casing 102. In an example, the casing 102 is fabricated from a material which has high thermal conductivity. For example, the casing may be fabricated from a metal, such as copper, aluminum, alloy, and the like. In an example, when the device 100 is a heat pipe, the casing 102 can be fabricated as an elongated hollow cylinder with both ends of the cylinder sealed. In another example, when the device 100 is a vapor chamber, the casing 102 can be fabricated as a hollow, longitudinally flattened structure.

The casing 102 includes a first portion 104. In an example, when the device 100 is a heat pipe, the first portion 104 is present substantially towards a first end of the heat pipe as will be explained later with reference to FIGS. 3(a) and 3(b). In an example, when the device 100 is a vapor chamber, the first portion 104 is present substantially towards a first flattened surface of the vapor chamber as will be explained later with reference to FIG. 4. The first portion 104 is to receive heat from a heat source 106. The first portion 104 may, therefore, be coupled to the heat source 106.

The heat source 106 is a device from which heat is to be removed, for example, for cooling the device. For this, heat from the heat source 106 is received by the device 100. For example, in an electronic device, such as a computing device, the heat source 106 may be a Central Processing Unit (CPU) which may get heated during start-up and running of the computing device and hence may have to be cooled by using the device 100. The casing 102 of the device 100 receives heat from the heat source 106 at the first portion 104.

The casing 102 also includes a working fluid (not shown). The working fluid is selected based on thermal conductivity and compatibility with the material of the casing 102. For example, when the casing 102 is a copper casing, the working fluid can be water, ethanol, and the like.

A thermo-reversible hydrogel 108 is provided in the first portion 104 and is soaked in the working fluid. The thermo-reversible hydrogel 108 may be coated in the first portion 104. In an example, a thickness of the thermo-reversible hydrogel 108 in the first portion 104 is in a range of 100-800 μm. Thermo-reversible hydrogels are hydrogels which form a gel when cooled and form a viscous fluid state when exposed to heat. Thermo-reversible hydrogels, therefore, do not undergo permanent change. Further, transition from gel to viscous fluid and vice versa can be performed repeatedly based on heat received by the hydrogel. The thermo-reversible hydrogel 108 may be made of polymers selected from ethylene maleic anhydride copolymer, carboxymethyl cellulose, polyvinyl alcohol copolymers, starch grafted copolymer of polyacrylonitrile or polyacrylamide super absorbents, and combinations thereof.

In operation, when no heat is received, the thermo-reversible hydrogel 108 retains its gel form. In the gel form, molecules of the thermo-reversible hydrogel 108 form a three-dimensional cross-linked network where the network traps the working fluid. When the thermo-reversible hydrogel 108 receives heat from the heat source 106 through casing 102, the gel forms a viscous fluid, thereby releasing the working fluid for phase transition and heat transfer.

The working fluid evaporates due to the heat and forms vapors which are transferred, for example, by diffusion to a second portion 110 of the casing 102 of the device 100. The second portion 110 is present substantially opposite to the first portion 104. In an example, when the device 100 is the heat pipe, the second portion 110 is the second end of the cylinder as will be explained later with reference to FIGS. 3(a) and 3(b). In an example, when the device 100 is the vapor chamber, the second portion 110 is the second flattened surface of the vapor chamber as will be explained later with reference to FIG. 4.

In the present description, a temperature of the first portion 104 is referred to as a first temperature and a temperature of the second portion 110 is referred to as a second temperature.

At the second portion 110, as the second temperature of the second portion 110 is lower than the first temperature of the first portion 104, the vapors condense. The condensed vapors are transferred to the first portion 104 by a wicking surface 112 by capillary forces. The wicking surface 112 is provided along an inner surface of the casing 102 between the first portion 104 and the second portion 110. In an example, the wicking surface 112 may extend into the first portion 104 and the second portion 110. The wicking surface 112 may be one of a sintered metal powder, a screen, and a grooved wicking surface. In an example, the wicking surface 112 is fabricated from the material of the casing 102. For example, when the casing 102 is copper, the wicking surface 112 may be formed from sintered copper powder.

FIG. 2 depicts an example method of heat transfer in device 100, according to an example implementation of the present subject matter. At block 202, heat is received at the first portion 104 of the casing 102. On receiving heat, the thermo-reversible hydrogel 108 releases the working fluid. The heat causes the working fluid to form vapors. The vapors diffuse towards the second portion 110. At the second portion 110, at block 204, the vapors of the working fluid are cooled. The vapors, therefore, condense at the second portion 110. The wicking surface 112 transfers the condensed working fluid from the second portion 110 to the first portion 104 for absorption by the thermo-reversible hydrogel 108. The method of heat transfer is further explained with respect to FIGS. 3(a) and 4.

In an example, the second temperature may be higher than the first portion, for example, when the first portion 104 loses heat faster than the second portion 110. In this example, vaporization of the working fluid is caused at the second portion 110. The vapors then diffuse from the second portion 110 to the first portion 104 where the vapors are condensed and absorbed by the thermo-reversible hydrogel 108. This example is further explained with respect to FIG. 3(b).

FIG. 3(a) depicts operation of an example heat pipe 300 when heat is received from a heat source, according to an example implementation of the present subject matter. Hereinafter, ends of the heat pipe 300 are referred to as bases. The heat pipe 300 includes the casing 102 which is substantially cylindrical and includes a first base 302 and a second base 304. The first portion 104 of the casing 102 of the heat pipe 300 is present substantially towards the first base 302 and the second portion 110 of the casing 102 of the heat pipe 300 is present substantially towards the second base 304. In an example, the first base 302 may be rounded to increase surface area available for coating the thermo-reversible hydrogel 108.

A working fluid 306 is provided in the first portion 104. The thermo-reversible hydrogel 108 is soaked in the working fluid 306. In an example, when the thermo-reversible hydrogel 108 is saturated with the working fluid 306, any excess working fluid 306 may be retained unbound in the first portion 104. The first portion 104 may receive heat from a heat source (not shown).

When heat is supplied to the first portion 104 as depicted by arrows 308, any excess working fluid 306 vaporizes and additionally, the thermo-reversible hydrogel 108 releases the soaked working fluid 306 for vaporization. The vapors 310 are transferred to the second portion 110, for example, by diffusion. As the second temperature is less than the first temperature, the vapors 310 are condensed. In an example, the second portion 110 may be open to surrounding environment at ambient conditions, and, therefore, may be at a lower temperature than the first portion 104. During condensation, the vapors 310 reject heat at the second portion 110 as shown by arrows 312. The condensed working fluid 314 is then transferred by capillary action by the wicking surface 112.

The operation as depicted in FIG. 3(a) may occur during start-up and running of the computing device. For example, during start-up, a processing unit of a computing device may generate heat and act as the heat source. Therefore, the heat pipe 300 may be disposed such that the first portion 104 is in close proximity to the processing unit. For example, the heat pipe 300 may be coupled to an enclosure housing the processing unit. The second portion 110 may be disposed such that the second portion 110 is in dose proximity to other components on the computing device. In an example, the second portion 110 may be open to ambient conditions. In another example, the second portion 110 may be disposed in proximity to a fan to increase heat rejection at the second portion 110.

However, when the computing device is switched off, the processing unit may cool down to a temperature lower than that in the second portion, i.e., the second temperature may be higher than the first temperature. In another example, the second portion may be at a higher temperature, for example, due to the ambient temperature bring higher than the temperature in the first portion. This example is as depicted in FIG. 3(b).

FIG. 3(b) depicts operation of the example heat pipe 300 when the second temperature is higher than the first temperature, according to an example implementation of the present subject matter. As shown in FIG. 3(b), the heat pipe 300 receives heat at the second portion 110 as shown by arrows 308. The received heat causes vaporization of working fluid at the second portion 110. The vapors 310 of the working fluid are transferred from the second portion 110 to the first portion 104 where the vapors 310 are condensed and absorbed by the hydrogel. The condensed working fluid 314 is then transferred from the first portion 104 to the second portion 110 by the wicking surface 112. This facilitates further cycles of heat transfer as more of the previously vaporized working fluid returns to the hydrogel.

In another example, the device for heat transfer may be a vapor chamber. FIG. 4 depicts operation of an example vapor chamber 400, according to an example implementation of the present subject matter. The vapor chamber 400 includes the casing 102 which includes a first flattened surface 402 and a second flattened surface 404 which are substantially opposite to each other. The first portion 104 is present substantially proximate to the first flattened surface 402 and the second portion 110 is present substantially proximate to the second flattened surface 404.

In one example, the first flattened surface 402 includes well structures 406 for holding the thermo-reversible hydrogel 108. However, the thermo-reversible hydrogel 108 may be provided on the first flattened surface 402 without the well structures 406. In another example, the thermo-reversible hydrogel 108 may be coated over the wicking surface 112 in the first portion 104.

In operation, when heat is supplied at the first portion 104 as shown by arrows 406, the thermo-reversible hydrogel 108 releases absorbed working fluid which vaporizes. The heat may be supplied to the first portion 104, for example, by a heat source (not shown). The vapors as depicted by arrows 408 diffuse within the vapor chamber 400. Since the second temperature of the second portion is lower than the first temperature of the first portion, the vapors 408 condense. In an example, the second portion 110 may be coupled to a condenser to condense the vapors 408. The condensed vapors 410 are then transferred to the thermo-reversible hydrogel 108 by the wicking surface 112 provided between the first portion 104 and the second portion 110. It will be understood that the vapor chamber 400 will also facilitate in removing heat from the second portion 110 and return of the vaporized working fluid back to the hydrogel when the first portion cools to a temperature lower than the second portion, as discussed above with reference to the heat pipe 300.

FIG. 5 illustrates another example device 500 for heat transfer, according to an example implementation of the present subject matter. The device 500 may comprise a casing (not shown). The device 500 includes a first portion 502 and a second portion 504. In an example, the casing may comprise the first portion 502 and the second portion 504. The first portion 502 includes a thermo-reversible hydrogel 506 soaked in a working fluid 508. The thermo-reversible hydrogel 506 may be, for example, coated on a surface of the first portion 502. In an example, multiple layers of the thermo-reversible hydrogel 506 may be provided in the first portion 502. Each layer may be a same hydrogel or a different hydrogel. In an example, the thermo-reversible hydrogel 506 can be provided as patterns or grooves to increase surface area of absorption and, thereby, heat dissipation.

A vapor region 510 is provided in between and fluidly couples the first portion 502 and the second portion 504. The vapor region 510 is enclosed by a wicking surface 512. The wicking surface 512 also fluidly couples the first portion 502 and the second portion 504. The vapor region 510 and the wicking surface 512 are for heat transfer between the first portion 502 and the second portion 504.

In operation, for example, during start-up of an electronic device, heat is received at the first portion 502, for example, due to contact with a heat source, such as a processor. When heat is received at the first portion 502, a first temperature of the first portion 502 becomes higher than a second temperature of the second portion 504. In this example, the vapor region 510 is to transfer vapors of the working fluid 508 from the first portion 502 to the second portion 504 for condensation and the wicking surface 512 is to transfer condensed working fluid from the second portion 504 to the first portion 502. At the first portion 502, the thermo-reversible hydrogel 506 is to absorb the condensed working fluid.

Further, for example, when the electronic device is switched off or when an ambient temperature is high, the second temperature of the second portion 504 may be higher than a first temperature of the first portion 502. Therefore, at the second portion 504, working fluid vaporizes. In this example, the vapor region 510 is to transfer vapors of the working fluid 508 from the second portion 504 to the first portion 502 for condensation and the wicking surface 512 is to transfer condensed working fluid from the first portion 502 to the second portion 504. The thermo-reversible hydrogel 506 is to absorb the vapors at the first portion 502.

As explained, the thermo-reversible hydrogel 506 increases rate of dissipation of heat from the working fluid 508 by absorption of the condensed working fluid and absorption of the vapors. Therefore, the heat transfer device of the present subject matter can be used for rapid cooling without substantially increasing weight of the heat transfer devices.

FIG. 6 depicts a method 600 of preparing a heat transfer device, according to an example implementation of the present subject matter. The order in which the method 600 is described is not intended to be construed as a limitation, and any number of the described method blocks may be combined in any order to implement the method 600, or alternative methods. Although the method 600 may be implemented in a variety of systems, the method 600 is explained in relation to the aforementioned devices for heat transfer, for ease of explanation.

At block 602, a wick material powder is sintered along an inner surface of a casing of a device for heat transfer. As will be understood, sintering is a process of forming a solid, porous mass of the wick material without melting the wick material powder to liquefaction. In an example, prior to sintering of the wick material powder, a first portion of the casing may be sealed, for example, by welding. For sintering, the wick material powder is filled into the casing. In an example, the sintering is performed at about 700-1300° C. for about 30-60 minutes. Sintering of the wick material powder helps in forming a wicking surface along an inner surface of the casing. In an example, the device for heat transfer may be device 100, 300, 400 and the casing may be casing 102, respectively. In another example, the device may be device 500 which may include a casing (not shown).

After sintering, at block 604, a thermo-reversible hydrogel is coated at a first portion of the casing. In an example, the thermo-reversible hydrogel is coated on top of the wicking surface. In another example, the wicking surface may be scrapped or removed by other techniques and the thermo-reversible hydrogel may be coated directly on the casing. In an example, the first portion may be first portion 104 of the device 100, 300, 400. In another example, first portion may be first portion 504 of device 500.

The thermo-reversible hydrogel is coated by spraying a solution comprising the thermo-reversible hydrogel on the inner surface of the casing at the first portion. In an example, the solution includes the thermo-reversible hydrogel in a range of about 0.1-3.0% weight by volume of the solution. The solution may be made with a working fluid as a solvent. The thermo-reversible hydrogel may be sprayed at a pressure in a range of about 0.0005-0.002 Torr. In an example, multiple layers of the thermo-reversible hydrogel may be coated at the first portion.

After coating the thermo-reversible hydrogel, at block 606, the thermo-reversible hydrogel is dried. In an example, the thermo-reversible hydrogel is dried at a temperature of about 105-120° C. for about 15-40 minutes.

The drying of the thermo-reversible hydrogel is followed by injecting a working fluid into the first portion of the casing under vacuum. This helps increase the amount of working fluid absorbed by the hydrogel. The amount of working fluid injected may be varied so that the hydrogel is soaked in the working fluid and some excess working fluid remains in contact with the hydrogel.

Therefore, the methods and devices of the present subject matter provide an increase in rate of heat dissipation without increasing weight of the device. The increased rate of heat dissipation is due to absorption of condensed working fluid and absorption of vapor by the thermo-reversible hydrogel. Increased heat dissipation reduces chances of damage of the heat source, for example, due to overheating.

The preceding description has been presented to illustrate and describe examples of the principles described. This description is not intended to be exhaustive. Many modifications and variations are possible in light of the above teaching.

Claims

1. A device for heat transfer comprising:

a casing, wherein the casing comprises: a first portion to receive heat from a heat source; a thermo-reversible hydrogel provided in the first portion; and a wicking surface provided along an inner surface of the casing and connecting the first portion to a second portion of the casing.

2. The device of claim 1, wherein the device is one of a heat pipe and a vapor chamber.

3. The device of claim 1, wherein the thermo-reversible hydrogel is selected from ethylene maleic anhydride copolymer, carboxymethyl cellulose, polyvinyl alcohol copolymers, starch grafted copolymer of polyacrylonitrile or polyacrylamide super absorbents, and combinations thereof.

4. The device of claim 1, wherein the wicking surface is one of a sintered metal powder, a screen, and a grooved wicking surface.

5. The device of claim 1, wherein a thickness of the thermo-reversible hydrogel is in a range of 100-800 μm.

6. The device of claim 1, wherein the first portion comprises a working fluid and wherein the thermo-reversible hydrogel is soaked in the working fluid.

7. The device of claim 6, wherein the casing and the wicking surface are fabricated from copper and wherein the working fluid is water.

8. A method of preparing a device for heat transfer, the method comprising:

sintering a wick material powder along an inner surface of a casing of the heat transfer device;

coating a thermo-reversible hydrogel on an inner surface of a first portion of the casing of the heat transfer device; and

drying the thermo-reversible hydrogel.

9. The method of claim 8, wherein coating the thermo-reversible hydrogel comprises spraying a solution comprising the thermo-reversible hydrogel on the inner surface at a pressure in a range of about 0.0005-0.002 Torr, wherein the solution comprises the thermo-reversible hydrogel in a range of about 0.1-3.0% weight by volume of the solution.

10. The method of claim 8, wherein sintering is performed at about 700-1300° C. for about 30-60 minutes.

11. The method of claim 8, wherein drying of the thermo-reversible hydrogel is performed at a temperature of about 105-120° C. for about 15-40 minutes.

12. The method of claim 8, wherein the method further comprises injecting a working fluid into the first portion of the casing under vacuum.

13. A device comprising:

a first portion comprising a thermo-reversible hydrogel soaked in a working fluid;

a second portion substantially opposite to the first portion;

a vapor region between the first portion and the second portion; and

a wicking surface enclosing the vapor region, wherein the vapor region and the wicking surface fluidly couple the first portion and the second portion for heat transfer between the first portion and the second portion.

14. The device as claimed in claim 13, wherein, when a first temperature of the first portion is higher than a second temperature of the second portion:

the vapor region is to transfer vapors of the working fluid from the first portion to the second portion for condensation;

the wicking surface is to transfer condensed working fluid from the second portion to the first portion; and

the thermo-reversible hydrogel is to absorb the condensed working fluid.

15. The device as claimed in claim 13, wherein, when a second temperature of the second portion is higher than a first temperature of the first portion:

the vapor region is to transfer vapors of the working fluid from the second portion to the first portion for condensation;

the wicking surface is to transfer condensed working fluid from the first portion to the second portion; and

the thermos-reversible hydrogel is to absorb the vapors.