US20110067416A1

US20110067416A1 - Thermal exchanging device

Info

Publication number: US20110067416A1
Application number: US12/888,924
Authority: US
Inventors: Shao-Hsiung Chang
Original assignee: Delta Electronics Inc
Current assignee: Delta Electronics Inc
Priority date: 2009-09-24
Filing date: 2010-09-23
Publication date: 2011-03-24

Abstract

A thermal exchanging device is provided to exchange heat with a hot heat source and a cold heat source. The thermal exchanging device includes a vacuum chamber, a working material capable of being excited magnetically, and a working fluid capable of undergoing a transition between two phase flows of liquid and vapor. The working fluid is provided in the chamber to communicate with the working material. When the working material is magnetically excited, the working fluid is configured to exchange heat with the cold heat source. Otherwise, the working fluid is configured to absorb heat from the hot heat source.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority from U.S. provisional application No. 61/245,441, filed on Sep. 24, 2009, the entirety of which is incorporated by reference herein.

BACKGROUND

1. Field of the Invention
The present invention is in the technical field of a thermal exchanging device, more particularly to a magnetically driven thermal exchanging device utilizing a magneto-caloric material (MCM) to generate a two-phase flow of liquid and vapor by means of magnetization and demagnetization mechanism.
2. Description of the Related Art
A conventional thermal exchanging device that utilizes the magneto-calorific properties of certain materials, such as Gadolinium or certain alloys, has the particularity of heating up when a magnetic field is applied (magnetization process) and of cooling to a temperature lower than the initial temperature following the diminishing effect of the magnetic field (demagnetization process). For instance, when the magneto-calorific material (MCM) is magnetized, the magnetic moment of the MCM becomes aligned causing a rearrangement of the atoms to thereby generate heat from the MCM. On the other hand, when the MCM is demagnetized, the magnetic moment of the MCM becomes randomized causing a disorder of the atoms to thereby absorb heat from outside of the MCM.
As shown in FIG. 1 a, a conventional thermal exchanging device 1 includes a bed 11 containing a pool of fluid immersed with a porous magneto-calorific material (MCM), a magnet 12, and cold and hot side chambers 13, 14. During the magnetization process, the magnet 12 applies the magnetic field onto the bed 11, thereby the temperature of the MCM increases so as to induce a thermal flux. As the magnetic field constantly applies to the MCM, the fluid is pushed through MCM so as to arrive at the hot side chamber 14, shown in FIG. 1 b. On the other hand, during the demagnetization process or when a zero magnetic field is applied to the MCM, the temperature of the MCM cools down, shown in FIG. 1 c. Thereafter, as shown in FIG. 1 d, the fluid is pushed back to the cold side chamber 13. Evidently, this phenomenon utilizes the fluid force convection to force the fluid through the boundary of the MCM.
It is to be noted that the operating efficiency of the thermal exchanging device is primarily determined by the amount of heat transfer between the MCM and the fluid. Thus, in order to optimize the operating efficiency of the thermal exchanging device, two contributing factors are considered significant: MCM's surface area and fluid flow rate. As such, the optimization can be achieved either by dispensing a large amount of fluid through the surface of the MCM, or by increasing the surface area of the MCM. However, as the surface area of the MCM increases, the surface area of gaps or the pores of the MCM decreases, thereby limiting the amount of fluid to pass therethrough. As a result, a higher driving force is required to force the fluid through the MCM, which in turn requires a stronger pump to achieve this task. Consequently, the coefficient of performance (COP) of the thermal exchanging device is reduced.

SUMMARY

The present invention overcomes the aforementioned disadvantages by offering a magnetically driven thermal exchanging device that is simple in design while having an efficient and reliable performance.
A thermal exchanging device is provided to exchange heat with a heat source. The heat source has hot and cold sources. The thermal exchanging device includes a vacuum chamber, a working material capable of being excited magnetically, and a working fluid capable of undergoing a transition between two phase flows of liquid and vapor. The working fluid is provided in the chamber to communicate with the working material. When the working material is magnetically excited, the working fluid is configured to exchange heat with the cold heat source. Otherwise, the working fluid is configured to absorb heat from the hot heat source.

BRIEF DESCRIPTION OF DRAWINGS

The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIG. 1 a, FIG. 1 b, FIG. 1 c, and FIG. 1 d are side schematic views of a conventional thermal exchanging device;

FIG. 2 a is a side schematic view of the first preferred embodiment of a thermal exchanging device according to the present invention, illustrating how heat is transferred inside a chamber thereof and exchanged with an external heat source when the working material is magnetically excited;

FIG. 2 b is an side schematic view of the first preferred embodiment of the thermal exchanging device, illustrating how heat is transferred inside the chamber thereof and absorbed from the external heat source when the working material is not magnetically excited;

FIG. 3 is a side schematic view of the thermal exchanging device having a thermal controlling switch according to the first preferred embodiment of the present invention;

FIG. 4 is a side schematic view of the second preferred embodiment of the thermal exchanging device, illustrating an activation unit having one valve so as to be operable to selectively close one of the two portions of the chamber, according to the present invention;

FIG. 5 is a side schematic view of the second preferred embodiment of the thermal exchanging device, illustrating the two valves of the activation unit closing the top and bottom portions of the chamber, according to the present invention; and

FIG. 6 is a side schematic view of the third preferred embodiment of the thermal exchanging device according to the present invention.

DETAILED DESCRIPTION

Referring to FIG. 2 a, FIG. 2 b, and FIG. 3, the first preferred embodiment of a thermal exchanging device of the present invention can operate with an external heat source for performing a heat exchange therebetween. As shown in FIG. 3, the thermal exchanging device 2 includes a magnetic-generating source 26, a vacuum chamber 21, a magnetically excited working material 22, a working fluid 25, a heating unit 24, a wick structure 23, and a thermal controlling unit 27. The external heat source Q has hot and cold sources Q₁, Q₂, in which the hot heat source Q₁, for example, has a temperature that is higher than the Curie temperature of the working material 22 and the cold heat source Q₂, for example, has a temperature that is lower than the Curie temperature of the working material 22. The working material 22 is excited by the magnetic-generating source 26 to thereby create a thermal flux in the chamber 21. The working fluid 25 is provided in the chamber 21 so as to communicate with the working material 22 for exchanging heat therebetween. In addition, the working fluid 25 is capable of undergoing a transition between single and/or two phase flows of liquid and vapor.
The magnetic-generating source 26 is selected from one of a permanent magnet, a Halbach magnet, and an electrical conductive coil magnetic set. In this preferred embodiment, the electrical conductive coil magnetic set is a superconductor coil, and the working material 22 is a porous magneto-caloric material made of gadolinium and the grain size of the porous magneto-caloric material which is between 50 to 150 micrometers. The porous magneto-caloric material is provided with more than one Curie temperature. When the working material 22 is near its Curie temperature, the magnetic state of the working material 22 will change between ferromagnetism and paramagnetism so as to cause a change of the magnetic entropy of the working material 22. Further, the porous magneto-caloric material is selected from one of a powder shape and a wire mesh shape. In this preferred embodiment, the magneto-caloric material is a bulk material with thin slits provided therethrough and/or has a plurality of stacked plates with gaps spaced therebetween. The working fluid 25 is characterized by having more than one boiling point temperature. In this preferred embodiment, the working fluid is water.
The working material 22 can be magnetically excited by the magnetic-generating source 26. When the working material 22 is magnetically excited, the working fluid 25 operates to exchange heat with the cold heat source Q₂. Similarly, when the working material 22 is not magnetically excited, the working fluid 25 operates to absorb heat from the hot heat source Q₁. The heating unit 24 is disposed on an outer surface of the chamber 21 and operable to exchange heat with the external heat source Q. The working material 22 is surrounded by the wick structure 23 in the chamber 21 so as to facilitate flowing of the working fluid 25 and the working material 22 in the chamber 21 by means of, for example, capillary action. The wick structure 23 also has a portion 231 in thermal contact with the heating unit 24. Additionally, as shown in FIG. 3, the thermal controlling unit 27 has a switch 271 that is switchable between a first position P₁and a second position P₂for controlling the flow direction of heat exchange between the heating unit 24 and the external heat source Q. The thermal controlling unit 27 further includes a first port 272 that is in contact with the heating unit 24, a second port 273 that is in contact with the hot heat source Q₁, and a third port 274 that is in contact with the cold heat source Q₂. One of the first position P₁and second position P₂is defined by selectively connecting the first port 272 to one of the second and third ports 273, 274. For instance, during a heat generation stage where the working material 22 is magnetically excited by the magnetic-generating source 26, the switch 271 bridges the first port 272 and the second port 273 so as to allow the working fluid 25 to expel heat to the cold heat source Q₂. Similarly, during a heat absorption stage where the magnetic field is weakened or removed, the switch 271 bridges the first port 272 and the second port 273 so as to allow the working fluid 25 to absorb heat from the hot heat source Q₁. Thus, by using the thermal controlling unit 27 to control the thermal cycle (heat generation and heat absorption) of the thermal exchanging device 2, both heating and cooling process can be realized and operated continuously.
Since the working fluid 25 is encapsulated in the vacuum chamber 21, a portion of the working fluid 25 vaporizes to a higher vapor stream so as to fill up a portion of the empty space of the chamber 21. The vaporization process will stop when the vapor pressure reaches to the working fluid's 25 saturation point. At this moment, the vapor and liquid phases are in equilibrium with each other until the temperature of the working fluid 25 changes again. Contrarily, when the temperature of the working material 22 decreases to result in cooling the working fluid 25, the working fluid 25 condenses to a lower vapor pressure stream.
Referring to FIG. 2 a, which illustrates the thermal exchanging device 2 undergoing the heat generation stage, where the working fluid 25 is expelling heat to the cold heat source Q₂of the external heat source Q. It is noted that the magnetic-generating source 26 and the thermal controlling unit 27 are not shown in FIG. 2 a in this view. When the magnetic field is applied to the working material 22, the thermal flux generated by the working material 22 will increase the temperature of and absorb by the working fluid 25 to result a higher vapor pressure stream of the working fluid 25. The higher vapor pressure then moves to and comes in contact with the right hand side of the chamber 21. The vapor then expels to the cold heat source Q₂of the external heat source Q through the heat exchanging unit 24 and condenses into the liquid phase again. Thereafter, the liquid phase of the working fluid 25 is drawn to the wick structure 23 through the capillary action so that the working fluid 25 is absorbed by the working material 22 again. This cycle continues to process until the temperatures of both the working material 22 and the cold heat source Q₂of the external heat source Q reach to equilibrium.
Referring to FIG. 2 b, which illustrates the thermal exchanging device 2 undergoing the heat absorption stage, where the working fluid 25 is absorbing heat from the hot heat source Q₁of the external heat source Q. It is noted that the magnetic-generating source 26 and the thermal controlling unit 27 are not shown in FIG. 2 a in this view. When the magnetic field is weakened or removed, the temperature of the working material 22 decreases such that the surrounding vapor of the working fluid 25 condenses. As such, the vapor pressure of the working fluid 25 that is proximate to the working material 22 is now lower than the vapor pressure at the right hand side of the chamber 21. Then, the vapor pressure at the right hand side of the chamber 21 will circulate back to the working material 22 and continue to further condense. As a result, the liquid at the right hand side of the chamber 21 will continue to absorb heat from the cold heat source Q₂through the heat exchanging unit 24. This process continues to cycle until the heat absorbed by the working material 22 can sufficiently compensate the change in the magnetic entropy of the working material 22.
Reference is now made to FIG. 4, there is shown the second preferred embodiment of the present invention. The second embodiment of the present invention discloses a thermal exchanging device 3 which differs from the thermal exchanging device 2 of the first embodiment in that this embodiment uses an activation unit instead of the thermal controlling unit for controlling the heat exchange flow direction. This embodiment also includes a support member 39 disposed in a vacuum chamber 31 for separating the chamber 31 into two portions 311, 312. The activation unit 38 has a valve 381 provided on the support member 39 and operable to selectively close one of the two portions 311, 312 of the chamber 31. Moreover, in this embodiment, the thermal exchanging device 3 has two heating units 341, 342 that are opposite to each other and respectively in contact with the hot and cold sources Q′₁, Q′₂of an external heat source. In this embodiment, the working material 32 is magnetically excited by the magnetic-generating source 36, and the two portions 311 and 312 are top and bottom portions of the chamber 31 respectively. The working material 32 is surrounded by the wick structure 33 in the chamber 31. The top and bottom portions 311, 312 are respectively adjacent to and in contact with the heating units 341, 342 respectively. During the heat generation stage, the valve 381 closes the bottom portion 312 of the chamber 31 so that heat can flow into the top portion 311 of the chamber 31, as indicated by the right hand arrow shown in FIG. 4, to thereby exchange heat with the heating unit 341. Similarly, during the heat absorption stage, the valve 381 flips from the bottom portion 312 to close the top portion 311 of the chamber 31 so that heat can be absorbed from the hot heat source Q′₁through the heating unit 341, indicated by the left hand arrow shown in FIG. 4. In an alternative to this embodiment, as shown in FIG. 5, the thermal exchanging device 4 can also comprise a support member 49 disposed in a vacuum chamber 41 for separating the chamber 41 into two portions 411 and 412. Two heating units 441, 442 are opposite to each other and respectively in contact with the hot and cold sources Q′₁, Q′₂. The thermal exchanging device 4 further comprises an activation unit 38 having two valves 481 and 482, and each of the valves 481 and 482 closes a respective one of the top and bottom portions 411 and 412. Likewise, in this embodiment, the working material 42 is surrounded by the wick structure 43 in the chamber 41, and the working material 42 is magnetically excited by the magnetic-generating source 46, wherein the valve 481 is open and the valve 482 is closed during the heat generation stage. During the heat absorption, the valve 482 is open and the valve 481 is closed.
Referring to FIG. 6, there is shown the third preferred embodiment of the present invention. The third embodiment of the present invention discloses a thermal exchanging device 5 which differs from the thermal exchanging device 4 of the second embodiment in that the valves 581, 582 are provided on opposite sides of the working material 52 such that each of which is disposed adjacent to a respective one of the heating units 541, 542. In this embodiment, the working material 52 is surrounded by the wick structure 53 in the chamber 51, and the valve 581 is open so as to allow the vapor of the working fluid 55 to flow through an vacuum chamber 51 to thereby generate heat towards the cold heat source Q″₂through the heating unit 541. Similarly, the valve 582 is open so as to allow the working fluid 55 to absorb heat from the hot heat source Q″₁, indicated by the right hand arrows shown in FIG. 6.
The present invention operates in a fundamentally the same manner as the refrigeration. It should be noted that, in other embodiments of the present invention, the thermal exchanging device can be used in conjunction in other applications, such as in cooling or heating devices for operating as a power-conversion device. In addition, it is to be noted that the chamber 21, 31, 41, or 51 is kept airtight in a vacuum manner so that the internal pressure of the chamber 21, 31, 41, or 51 is lower than the atmosphere (atm) pressure, which results in decreasing the boiling point of the working fluid 25, 35, 45, or 55 inside the chamber accordingly. As a consequence of this phenomenon, the working fluid 25, 35, 45, or 55 can be more convenient to undergo the two-phase transition.
As described from the foregoing, the advanced design of the thermal exchanging device according to the present invention provides a high efficiency, high speed and low cost solution with operational advantages explained below:
1. The convection coefficient (h) for heat transfer using a two-phase flow of liquid and vapor is about 5˜50 times higher than that of a pure liquid. Also, the heat absorption for vaporizing one gram of water is 574 Calorie (2400 Joule), whereas the heat absorption for raising one centigrade degree of one gram of water is one Calorie (4.184 Joule). By comparison, the heat absorption for evaporating the two-phase flow fluid is 500 times higher than raising one-centigrade degree of the water. Therefore, the two-phase flow can absorb or expel a greater amount of heat than that of the traditional forced-liquid flow used on the thermal exchanging device. As a result, the two-phase flow phenomena can increase the speed at which the working fluid and the working material exchange heat.
2. The wick structure, based on the principle of capillary action, can transport the working fluid and the working material seamlessly through the chamber. In effect, by virtue of the capillary action, less energy is required to draw the working fluid across the chamber, compared to the conventional forced-liquid flow of the working fluid. Consequently, the operating efficiency of the thermal exchanging device is much higher than that that of the conventional thermal exchanging device.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.

Claims

1. A thermal exchanging device, comprising:

a vacuum chamber;

a working material capable of being excited magnetically; and

a working fluid capable of undergoing a transition between two phase flows of liquid and vapor, the working fluid being provided in the chamber to communicate with the working material;

wherein when the working material is magnetically excited, the working fluid is configured to exchange heat with a relative cold heat source; and

wherein otherwise, the working fluid is configured to exchange heat with a relative hot heat source.

2. The thermal exchanging device as claimed in claim 1, further comprising a magnetic-generating source to excite the working material.

3. The thermal exchanging device as claimed in claim 1, further comprising a wick structure surrounding the working material in the chamber to facilitate flowing of the working fluid and the working material in the chamber.

4. The thermal exchanging device as claimed in claim 3, further comprising a heating unit disposed on outer surface of the chamber and operable to exchange heat between the wick structure and the heat sources.

5. The thermal exchanging device as claimed in claim 4, further comprising a thermal controlling unit having a switch switchable between a first position and a second position for controlling the flow direction of heat exchange between the heating unit and the heat sources, the first position being defined by a heat generation stage where heat is exchanged between the heating unit and the cold heat source, the second position being defined by a heat absorption stage where heat is exchanged between the heating unit and the hot heat source.

6. The thermal exchanging device as claimed in claim 5, wherein the thermal controlling unit further comprises a first port in contact with the heating unit, a second port in contact with the hot heat source, and a third port in contact with the cold heat source, one of the first and second positions is defined by selectively bridging the first port to one of the second and third ports.

7. The thermal exchanging device as claimed in claim 6, wherein the switch is adapted to bridge the first and second ports upon demagnetization of the working material.

8. The thermal exchanging device as claimed in claim 6, wherein the switch is adapted to bridge the first and third ports upon magnetization of the working material.

9. The thermal exchanging device as claimed in claim 3, further comprising:

two heating units opposite to each other and respectively in thermally contact with the hot and cold heat sources;

a support member provided in the chamber to separate the chamber into two portions, and

an activation unit having one valve provided on the support member and operable to selectively close one of the two portions of the chamber.

10. The thermal exchanging device as claimed in claim 9, further comprising two valves close to the two portions of the chamber respectively.

11. The thermal exchanging device as claimed in claim 3, further comprising:

two heating units oppositing to each other and respectively in contacting with the hot and cold heat sources; and

an activation unit having two valves respectively provided on opposite sides of the working material.

12. The thermal exchanging device as claimed in claim 1, wherein the working material is a porous magneto-caloric material with more than one Curie temperature, and the porous magneto-caloric material is a powder shape or a wire mesh shape.

13. The thermal exchanging device as claimed in claim 1, wherein the working material includes a plurality of stacked plates with gaps spaced therebetween.

14. The thermal exchanging device as claimed in claim 1, wherein the working material is a bulk material with holes disposed therethrough.

15. The thermal exchanging device as claimed in claim 1, wherein the working material is a bulk material with thin slits provided therethrough.

16. The thermal exchanging device as claimed in claim 1, wherein the working fluid is water.

17. The thermal exchanging device as claimed in claim 1, wherein the working fluid has more than one boiling point temperature.