US20100307724A1

US20100307724A1 - Heat exchanger

Info

Publication number: US20100307724A1
Application number: US12/867,930
Authority: US
Inventors: Yoshio Ichii; Tadashi Iwamatsu; Hiroyuki Hirakawa; Hirofumi Kanda
Original assignee: Individual
Current assignee: Sharp Corp
Priority date: 2008-02-21
Filing date: 2009-02-19
Publication date: 2010-12-09
Also published as: JP2009200252A; CN101953241B; CN101953241A; JP4314307B1; WO2009104684A1

Abstract

A heat exchanger (1) includes: a heat sink (3) which is in contact with a heating element (2); and an electron emitting element (4) which is provided so as to be separated from the heat sink (3) by a space and which provides electrons to the heat sink (3) via air in the space. The electron emitting element (4) includes: an electrode substrate (7); a thin-film electrode (9); a power supply (10) which applies a voltage between the electrode substrate (7) and the thin-film electrode (8); and an electron acceleration layer (8) which accelerates the electrons inside itself in response to the voltage applied by the power supply (10) so that the electrons are emitted from the thin-film electrode (9). The electron acceleration layer (8) is made at least partially of an insulating material. As a result, the heat exchanger (1) has a heat exchange capability which can be maintained and improved independently of a structure in which electric field concentration tends to occur.

Description

TECHNICAL FIELD

The present invention relates to a heat exchanger.

BACKGROUND ART

Conventionally, a rotary-blade airflow generator (hereinafter referred to as “fan”) has normally been used as a means of cooling a heating element. However, the use of a fan for such cooling causes a problem of large noise made by the fan in operation. To solve this problem, cooling with use of an ionic wind caused by a corona discharge has been devised to replace the cooling with the use of a fan (see, for example, Patent Literatures 1 and 2). The use of an ionic wind eliminates wind noise peculiar to operation of a fan, and thus reduces noise. Further, the following is known (see Non Patent Literature 1): A heat source (heating element) is cooled more effectively when air blown by a fan is used in combination with an ionic wind than when air blown by a fan is solely used. Non Patent Literature 2 describes a condition necessary for a corona discharge to be stably generated.
The following describes the cooling effect achieved with the use of an ionic wind, in comparison with the cooling effect achieved with a sole use of air blown by a fan. The description deals with (i) a case of cooling a heat source by causing only air blown by a fan to come into contact with the heat source, and (ii) a case of cooling a heat source by causing a combination of air blown by a fan and an ionic wind to come into contact with the heat source.
In the case of cooling a heat source by causing only the air blown by the fan to come into contact with the heat source, it is difficult to remove gas molecules present near the heat source. This is because the airflow generated by the fan has a laminar flow on its surface and, according to fluid dynamics, the gas molecules present along a surface of the heat source thus have a flow rate of 0. Consequently, according to fluid dynamics, in the case of cooling the heat source by causing only the air blown by the fan to come into contact with the heat source, the gas molecules present near the heat source remain unremoved.
On the other hand, in the case of cooling a heat source by causing the combination of the air blown by the fan and the ionic wind to come into contact with the heat source, ions, each of which has an electric charge, travel along lines of electric force to arrive at the vicinity of the surface of the heat source. These ions then stir gas molecules which are present near the surface of the heat source and which have relatively large molecular momentums. This conceivably allows the heat source to be cooled with high efficiency. An ionic-wind cooling device has been disclosed which uses the above phenomenon and which thus generates an ionic wind with use of wire electric discharge occurring between cooling fins of a heat sink (see, for example, Patent Literature 3).

CITATION LIST

Patent Literature 1

Japanese Patent Application Publication, Tokukai, No. 60-20027 A (Publication Date: Feb. 1, 1985)

Patent Literature 2

Japanese Patent Application Publication, Tokukai, No. 2006-100758 A (Publication Date: Apr. 13, 2006)

Patent Literature 3

Japanese Patent Application Publication, Tokukaihei, No. 9-252068 A (Publication Date: Sep. 22, 1997)

Non Patent Literature 1

David B. Go, Suresh V. Garimella, and Timothy S. Fisher, J. Appl. Phys., 102, 053302 (2007)

Non Patent Literature 2

Electrophotography-Bases And Applications, The Society of Electrophotography of Japan, CORONA PUBLISHING CO., LTD. (1988), p. 213

SUMMARY OF INVENTION

However, the wire electric discharge (corona discharge) performed by the ionic-wind cooling device disclosed in Patent Literature 3 poses a problem described below.
As described in Patent Literature 2, stable generation of a corona discharge is said to require a discharge voltage of 6 to 8 kV and an interelectrode distance of approximately 10 mm. Thus, a cooling device using a corona discharge involves a risk of a high voltage. In addition, the large interelectrode distance problematically results in a large-size cooling device.
Downsizing a cooling device requires reducing the interelectrode distance. However, a reduction in (or narrowing of) the interelectrode distance makes a streamer-type corona discharge likely to occur. This results in a local temperature rise. This temperature rise then leads to breaking of a wire electrode and/or damage to a heat source. This indicates that a cooling device having a small interelectrode distance lacks utility.
Downsizing a cooling device without changing the interelectrode distance requires reducing the number of discharge sections (each including a combination of a wire electrode and a discharge electrode so as to perform discharge). This problematically prevents maintenance and improvement of a cooling capability of the cooling device.
Also, the ionic-wind cooling device disclosed in Patent Literature 3 has a structure, such as the cooling fins of the heat sink, in which electric field concentration tends to occur. According to this arrangement, an ionic wind is generated by performing the wire electric discharge between the cooling fins, between which electric field concentration tends to occur. This arrangement, however, impedes continuous and stable supply of an ionic wind.
The problems described above are caused not only in a cooling device which uses an ionic wind to cool a heat source as a target of heat exchange, but also in a heating device which uses an ionic wind to raise a temperature of or heat a target of heat exchange. In other words, the above problem can be caused in any heat exchanger which uses an ionic wind to exchange heat between a target of heat exchange and a contact member which is in contact with the target of heat exchange.
The present invention has been accomplished in view of the above problem. It is an object of the present invention to provide a heat exchanger having a heat exchange capability which can be maintained and improved independently of a structure in which electric field concentration tends to occur.
The inventors of the present invention have found the following and thus arrived at the present invention: In place of a conventional wire electric discharge element, an electron emitting element which can emit electrons in an internal electric field (i.e., an electron emitting element which requires no external electric field) is provided so as to face (i.e., so as to be separated from) a contact member which is in contact with a target of heat exchange. This allows (i) an electric charge to be stably provided into an atmosphere and thus (ii) an ionic wind to be generated even if there is provided close to the electron emitting element a structure, such as fins of a heat sink, in which electric field concentration tends to occur.
In order to solve the above problem, a heat exchanger includes: a contact member which is electrically conductive and which is for contacting with a target of heat exchange; and an electron emitting element which is provided so as to be separated from the contact member by a space and which provides electrons to the contact member via air in the space, the electron emitting element including: an electrode substrate; a thin-film electrode; first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and an electron acceleration layer which accelerates electrons inside itself by the voltage applied from the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode, the electron acceleration layer being formed at least partially from an insulating material.
The heat exchanger of the present invention includes the electron emitting element provided so as to be separated from the electrically conductive contact member which is in contact with the target of heat exchange. Further, the electron emitting element includes: the electrode substrate; the thin-film electrode; the first voltage applying means for applying the voltage between the electrode substrate and the thin-film electrode; and the electron acceleration layer which accelerates the electron inside itself in response to the voltage from the first voltage applying means so that the electron is emitted from the thin-film electrode. In addition, the electron acceleration layer is formed at least partially with an insulating material. This arrangement allows for provision of the electron emitting element which can emit electrons in an internal electric field. In other words, the electron emitting element provides electrons to the contact member via the air present in the space between the electron emitting element and the contact member. These electrons collide with air molecules present in the space. This collision ionizes the air molecules. Further, these ionized air molecules move along an electric field, and thus generate an ionic wind. The ions then arrive at the contact member. This stirs air molecules which are present along the surface of the heat source.
As described above, according to the above arrangement, the electron emitting element which can emit electrons in an internal electric field is provided, instead of a conventional wire electric discharge element, so as to be separated from the contact member. As a result of this, even with a structure in which electric field concentration tends to occur in the vicinity of the contact member, the electron emitting element can stably provide electrons into the atmosphere, and thus generate an ionic wind. In addition, it is possible to stably provide an ionic wind even if the contact member has a complex shape. In other words, the heat exchanger of the present invention generates an ionic wind not with use of a conventional wire electric discharge element which causes a corona discharge, but with use of the electron emitting element which can emit electrons in an internal electric field. Thus, it is not necessary to reduce the number of discharge sections for device downsizing, unlike in conventional ionic-wind cooling devices. Furthermore, it is not necessary to reduce the distance between electrodes for wire electric discharge. Thus, the above arrangement prevents problems associated with conventional ionic-wind cooling devices which cause a corona discharge, the problems including a problem concerned with a distance between electrodes for wire electric discharge. In a case where, for example, the contact member is a heat sink, the above arrangement, in view of device downsizing, allows a device having a certain size to include more fins than a conventional ionic wind generator. This consequently improves a heat exchange capability.
As described above, the above arrangement allows for provision of the heat exchanger having a heat exchange capability which can be maintained and improved independently of a structure in which electric field concentration tends to occur.
Additional objects, features, and strengths of the present invention will be made clear by the description below. Further, the advantages of the present invention will be evident from the following explanation in reference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view illustrating a preferable example of a heat exchanger (cooling device) in accordance with an embodiment of the present invention.

FIG. 2 is an enlarged view illustrating main portions of a heat sink and an electron emitting element included in the heat exchanger illustrated in FIG. 1.

FIG. 3 is an enlarged cross-sectional view illustrating a main portion of an electron acceleration layer included in the heat exchanger illustrated in FIG. 1.

FIG. 4 is an energy band diagram for a particle layer (electron acceleration layer) of the electron emitting element included in the heat exchanger illustrated in FIG. 1.

FIG. 5 is a cross-sectional view illustrating an arrangement of a heat exchanger used in Example 1

FIG. 6 is a graph illustrating a result of verifying a cooling effect with use of the heat exchanger of Example 1.

FIG. 7 is a cross-sectional view illustrating an arrangement of an electron emitting element included in a heat exchanger (cooling device) in accordance with another embodiment of the present invention.

FIG. 8 is a plan view illustrating an arrangement of a rotary-blade airflow generator included in a heat exchanger (cooling device) in accordance with still another embodiment of the present invention.

FIG. 9 is a perspective view illustrating an arrangement of an electron emitting element included in a heat exchanger (cooling device) in accordance with yet another embodiment of the present invention.

REFERENCE SIGNS LIST

- 1 heat exchanger (heat exchanger, cooling device)
- 2 heating element (target of heat exchange)
- 3 heat sink (contact member)
- 4, 16 electron emitting element
- 5 power supply (second voltage applying means)
- 6 ground
- 7 electrode substrate
- 8 electron acceleration layer
- 9 thin-film electrode
- 10 power supply (first voltage applying means)
- 11 insulator particle (second dielectric material)
- 12 metal particle (conductive particle formed with an electric conductive material and surrounded by a first dielectric material)
- 13 air pipe
- 14 fan
- 15 temperature measuring terminal
- 17 substrate thin-film electrode
- 18 flexible substrate
- 19 rotary-blade airflow generator
- 20 blade
- 20 a surface
- 21 electron emitting element
- 22 mesh substrate
- 22 a surface
- 30 ion

DESCRIPTION OF EMBODIMENTS

A heat exchanger of the present invention is a device which uses an ionic wind to exchange heat between (i) a target of heat exchange and (ii) a contact member which is in contact with the target of heat exchange. The heat exchange includes: temperature raising or heating, i.e., transferring heat from a contact member having a higher temperature to a target of heat exchange, the target having a lower temperature; and cooling, i.e., transferring heat from a target of heat exchange, the target having a higher temperature, to a contact member having a lower temperature. Embodiments below each describe, as an example of the heat exchanger of the present invention, a cooling device for cooling a heating element. The heat exchanger described in each of the embodiments below can naturally be used as a heating device for raising a temperature of or heating a target of heat exchange.

Embodiment 1

One embodiment of the present invention is described below with reference to FIGS. 1 through 9. Note that an arrangement described below is merely a specific example of the present invention. Thus, the present invention is not limited to this arrangement. FIG. 1 is a cross-sectional view illustrating a preferable example of a heat exchanger (cooling device) 1 according to the present embodiment.
The heat exchanger 1 is a device for releasing, to the outside, heat generated by a heating element (target of heat exchange) 2. The heat exchanger 1 includes: a heat sink (contact member) 3; an electron emitting element 4; and a power supply (second voltage applying means) 5. The heat sink 3, which is made of a conductive material, is in contact with the heating element 2. The heat sink 3 has a surface 3 a opposite from the heating element 2 which surface is in contact with air. The heat sink 3 includes a plurality of convexities 3 b formed at least partially along the surface. The electron emitting element 4 is provided so as to face the surface 3 a of the heat sink 3. The electron emitting element 4 is separated from the surface 3 a of the heat sink 3 by a space, and thus provides electrons to the heat sink 3 via the air in the space. The heat sink 3 and the electron emitting element 4 are connected to the power supply 5. The power supply 5 thus applies a voltage between the heat sink 3 and the electron emitting element 4. This voltage causes the electron emitting element 4 to emit electrons. These electrons collide with air molecules present in the space between the heat sink 3 and the electron emitting element 4. This collision then ionizes the air molecules. The air molecules thus ionized move along directions indicated by arrows shown in FIG. 1 (i.e., through an electric field generated between the heat sink 3 and the electron emitting element 4). This generates an ionic wind. The ions arrive at the heat sink 3, and thus stir air molecules which are present along the surface of the heat sink 3 and which have been heated by heat from the heating element 2. The arrival of the ions at the heat sink 3 will cause the heat sink 3 to be charged up. To prevent the heat sink 3 from being charged up, the heat exchanger 1 is connected to ground 6.
FIG. 2 is an enlarged view illustrating respective main portions of the heat sink 3 and the electron emitting element 4 of the heat exchanger 1 illustrated in FIG. 1. As illustrated in FIG. 2, the electron emitting element 4 includes: an electrode substrate 7; an electron acceleration layer 8; a thin-film electrode 9; and a power supply (first voltage applying means) 10. The electron acceleration layer 8 is sandwiched between the electrode substrate 7 and the thin-film electrode 9. The power supply 10 applies a voltage between the electrode substrate 7 and the thin-film electrode 9. The electron acceleration layer 8 is made at least partially of an insulating material. The electron emitting element 4 accelerates electrons between the electrode substrate 7 and the thin-film electrode 9 (i.e., in the electron acceleration layer 8) in response to the voltage applied between the electrode substrate 7 and the thin-film electrode 9. The electron emitting element thus emits electrons from the thin-film electrode 9.
As described above, the heat exchanger 1 includes the two power supplies 5 and 10. The power supply 10 is used to accelerate electrons in the electron acceleration layer 8 of the electron emitting element 4 so that the electrons are emitted from the thin-film electrode 9. On the other hand, the power supply 5 is used to provide the electrons from the thin-film electrode 9 to the heat sink 3.
The heat sink 3 may be separated from the thin-film electrode 9 by any distance, provided that it is possible to provide the electrons from the thin-film electrode 9 to the heat sink 3. The distance, for example, falls preferably within a range from 100 μm to 50 cm, more preferably within a range from 100 μm to 10 mm, or particularly preferably within a range from 100 μm to 1 mm.
According to the heat exchanger 1, the electrode substrate 7 of the electron emitting element 4 may be (i) a substrate made of a metal such as SUS, Ti, and Cu, or (ii) a substrate made of a semiconductor such as Si, Ge, and GaAs. Alternatively, in a case where an insulator substrate such as a glass substrate is used as the electrode substrate 7, a conductive material such as a metal may be attached to the insulator substrate along an interface between the insulator substrate and the electron acceleration layer 8 so as to serve as an electrode.
The thin-film electrode 9 is used to apply a voltage across the electron acceleration layer 8. The thin-film electrode 9 may thus be made of any material, provided that the material allows the voltage to be applied. However, the electrons accelerated through the electron acceleration layer 8 and thus having a high energy are desirably transmitted through the thin-film electrode and emitted therefrom with a smallest possible energy loss. In view of this, it is preferable to use a material which has a low work function and of which a thin film can be made. This can achieve a greater effect. Examples of such a material encompass gold, carbon, titanium, nickel, and aluminum.
The electron acceleration layer 8 is simply required to include: conductive particles each made of an electric conductive material and surrounded by a first dielectric material; and a second dielectric material larger than the conductive particles. The present embodiment describes (i) the first dielectric material as a coating material which coats the conductive particles and (ii) the conductive particles as insulatively coated metal particles 12. Further, the present embodiment describes the second dielectric material as insulator particles 11 having an average diameter larger than an average diameter of the metal particles 12, which are insulatively coated. However, an arrangement of the electron acceleration layer 8 is not limited to this. The electron acceleration layer may, for example, be arranged as follows: The second dielectric material takes the form of a sheet, and is provided on the electrode substrate 7. The second dielectric material has a plurality of openings which penetrate the second dielectric material in a direction from the electrode substrate to the second dielectric material. These openings contain the conductive particles, which are dielectrically coated with the coating material.
FIG. 3 is an enlarged cross-sectional view illustrating a main portion of the electron acceleration layer 8 in the heat exchanger 1. As illustrated in FIG. 3, the electron acceleration layer 8 includes: the insulator particles 11 which serve as the second dielectric material; and the metal particles 12 which serve as the conductive particles and which are made of the electric conductive material surrounded by the first dielectric material. The electron acceleration layer 8, as described above, includes two kinds of particles, namely the insulator particles 11 and the metal particles 12.
The insulatively coated metal particles 12 may be of any kind of metal, provided that an operating principle of generating ballistic electrons can be realized. However, to prevent oxidative degradation occurring when the heat exchange is performed under an atmospheric pressure, it is preferable to use a metal which is not easily oxidized. Examples of such a metal encompass gold, silver, platinum, nickel, and palladium. Also, the insulating coating for the insulatively coated metal particles 12 may be any insulating coating, provided that the operating principle of generating ballistic electrons can be realized. However, if the insulating coating is formed with a coating made of oxidized metal particles, such an oxide coating may be subject to oxidative degradation in an atmosphere, and in turn have a thickness larger than a desired thickness. Thus, to prevent oxidative degradation occurring when the atmospheric pressure is changed, the insulating coating is preferably made of an organic material. Examples of such an organic material encompass alcoholate, aliphatic acid, and alkanethiol. According to the principle (described below in detail) of generating ballistic electrons, it is important that the insulatively coated metal particles 12 each have a diameter not larger than 10 nm, and also the insulating coating is more effective when having a smaller thickness.
The insulator particles 11 may be made of any material, provided that the material is an insulating material. The insulator particles 11 desirably make up 80 w % to 95 w % of all materials included in the electron acceleration layer 8. To achieve an appropriate resistivity and heat dissipation effect, it is necessary to include 2 to 300 metal particles 12 for every insulator particle 11. In other words, the insulator particles 11 and the metal particles 12 need to be present at a number ratio of 1:2-300. Also, the insulator particles 11 each preferably have a diameter of 5 to 1000 nm. Thus, the insulator particles 11 are practically made of a material such as SiO₂, Al₂O₃, and TiO₂. The insulator particles may alternatively be made of an organic polymer.
A thinner electron acceleration layer 8 allows a stronger electric field to be applied thereto. Hence, a thin electron acceleration layer only requires a low voltage to be applied thereto in order to accelerate electrons. The electron acceleration layer cannot have a thickness smaller than the average diameter of the insulator particles 11. Thus, the electron acceleration layer preferably has a thickness within a range from 5 to 1000 nm.
The following describes a principle of electron emission. As illustrated in FIG. 3, some insulatively coated metal particles 12 in the electron acceleration layer 8 are present continuously in contact with one another. This translates into an insulating material and an electric conductive material present alternately. FIG. 4 is an energy band diagram for a voltage applied to such a portion.
As illustrated in FIG. 4, an electron enters the electron acceleration layer 8 from the electrode substrate 7 due to an electric field. The electron enters an insulating material due to a tunnel effect. A strong electric field applied across the insulating material accelerates the electron, and causes the electron to increase its energy. The electron passes through the insulating material, and then enters an electric conductive material, which is formed with a metal. While electrons have a mean free path of 10 nm or longer in a metal, the insulatively coated metal particles 12 each have a radius of 10 nm or smaller. Thus, the electron collides with no metal atoms, and passes through the electric conductive material without being scattered. The electron then tunnels through another insulating material. Repetition of this process causes the electron to have a high energy and thus to turn into a ballistic electron. The electron finally arrives at the thin-film electrode 9. If the electron has an energy not lower than a work function of the thin-film electrode 9, the electron passes through the thin-film electrode 9, and then is emitted therefrom. The electron emitting element 4 can emit electrons on the basis of the principle described above.
As described above, the heat exchanger 1 causes the electron emitting element 4 to generate a gas flow under an atmospheric pressure, and also uses an electric field to cause the gas to arrive at the heat sink 3, which is in contact with the heating element 2. As such, the heat exchanger 1 does not generate a gas flow in vacuum. This increases a speed of the gas flow of the ionic wind, and in turn increases a cooling effect.
The heat sink 3 of the heat exchanger 1 includes, in at least a portion thereof, a concavity or a convexity. Such a concavity or a convexity included in at least a portion of the heat sink allows heat to be transferred to a larger number of gas molecules. This increases a heat dissipation effect. The electron emitting element 4 is placed in parallel with the heat sink 3. This allows the ionic wind to arrive at the heat sink 3 while preventing concentration of the electric field in the electron emitting element. This in turn allows heated gas molecules to be removed entirely from a heat dissipation surface of the heat sink 3, and consequently increases the heat dissipation effect.
The voltage applied by the power supply 5 between the heat sink 3 and the thin-film electrode 9 of the electron emitting element 4 may be any voltage, provided that the voltage causes negatively charged ions to arrive at the heating element 2. The voltage preferably has a lower limit of higher than 0 V. For example, the lower limit is preferably +10 V or higher, more preferably +100 V or higher, or particularly preferably +200 V or higher. Further, the applied voltage may have any upper limit. Practically, in consideration of a limit (described below) on an electric field strength, the upper limit is preferably +10 kV or lower, or more preferably +1 kV or lower.
The electric field applied between the heat sink 3 and the thin-film electrode 9 of the electron emitting element 4 may have any strength. For example, the strength is 1 V/m or greater, preferably 10 V/m or greater, or more preferably 1000 V/m or greater. To prevent generation of ozone, the electric field strength has an upper limit of preferably 10⁷V/m or lower, or more preferably 10⁶V/m. This prevents generation of hazardous substances such as ozone and nitrogen oxides.
According to the present invention, it is preferable to connect the heat sink 3 to ground before the gas from the electron emitting element 4 is blown toward the heat sink 3, which is in contact with the heating element 2. This prevents the heating element 2 from being charged up.
The gas flow generated by the electron emitting element 4 may be used in combination with an airflow generated by a rotary-blade airflow generator. Alternatively, such a rotary-blade airflow generator may not be used.
According to the heat exchanger 1, the heat sink 3 may face an electron emission surface of the thin-film electrode 9 in the electron emitting element 4 at any angle. For example, the angle falls preferably within a range from 0° to 90°, more preferably within a range from 0° to 45°, or particularly preferably within a range from 0° to 10°. This prevents concentration of lines of electric force between the heat sink 3 and the electron emitting element 4, and in turn eliminates a risk of flowing a current between the terminals of the electron emitting element 4 serving as an electron source element.

Example 1

With reference to FIGS. 5 and 6, the following describes, as an example, experiments for verifying the heat dissipation effect achieved by the heat exchanger according to the present invention. Note that these experiments merely serve as example embodiments, and that the description of the experiments does not limit the scope of the present invention.
The experiments of the present example were conducted with use of a heat exchanger illustrated in FIG. 5. The heat exchanger illustrated in FIG. 5 was equipped with a fan 14 (airflow generator) so that the fan would blow air toward the heat sink 3. The heating element 2 serving as the heat source was arranged to start or stop generating heat in response to an on-off action of a switch. When the switch was turned off, the heating element would stop generating heat. In the present example, the heat generation by the heating element 2 was stopped (i.e., the switch was turned off) simultaneously with a start of temperature measurement with use of a temperature measuring terminal 15. The temperature measuring terminal 15 included a thermocouple which would be in contact with a surface of the heat sink 3, and which would thus measure a surface temperature of the heat sink.
In the present example, after the heat generation by the heating element 2 was stopped, first and second experiments described below were conducted, in which a temperature of the heating element 2 was measured over time. The heat dissipation effect was verified by making a comparison between respective temporal changes in the temperature of the heating element 2 of the two experiments.
In the first experiment, the heating element 2 was cooled only with use of air blown by the fan (airflow generator) 14, while the power supply 5 generated no applied voltage (i.e., no voltage was applied between the heat sink 3 and the electron emitting element 4). In the second experiment, the heating element 2 was cooled, while the power supply 5 generated an applied voltage, with use of a combination of (i) air blown by the fan 14 and (ii) ions 30 emitted from the electron emitting element 4.
The heat exchanger used in the first and second experiments was equipped with an air pipe 13 so that a rate of gas flow was identical between the experiments, even in the case where the air blown by the fan 14 was mixed with a wind of ions 30. In the first and second experiments, the rate of gas flow was 9 L/min. Further, in the second experiment, a current recovered at the heat sink 3 due to the electron emission caused by the voltage application was within a range from 10 to 14 μA.
FIG. 6 shows a result of measuring the temporal changes in the temperature of the heating element 2 in the first and second experiments. FIG. 6 shows that the temperature of the heating element 2 for the second experiment was lowered more rapidly than that of the heating element for the first experiment. FIG. 6 further shows that, 60 seconds after the start of the temperature measurement, a temperature drop caused by the cooling of the second experiment was approximately 767% of a temperature drop caused by the cooling of the first experiment.

Embodiment 2

Another embodiment of the present invention is described below with reference to FIG. 7.
A heat exchanger of the present embodiment has an arrangement and a drive principle which are basically identical to those of the heat exchanger according to Embodiment 1. Such identical parts of the arrangement and the drive principle are not described here. The heat exchanger of the present embodiment differs from the heat exchanger of Embodiment 1 in how the electron emitting element is arranged. FIG. 7 is a view illustrating the arrangement of the electron emitting element and its surroundings of the heat exchanger according to the present embodiment.
As illustrated in FIG. 7, the electron emitting element 16 is characterized by its flexibility. The electron emitting element 16 includes: a flexible substrate 18; a substrate thin-film electrode 17; the electron acceleration layer 8; and the thin-film electrode 9. The substrate thin-film electrode 17 and the thin-film electrode 9 are connected to the power supply 10. The electron emitting element 16 accelerates electrons between the substrate thin-film electrode 17 and the thin-film electrode 9 (i.e., in the electron acceleration layer 8) in response to a voltage applied between the substrate thin-film electrode 17 and the thin-film electrode 9. The electron emitting element thus emits electrons from the thin-film electrode 9.

Embodiment 3

Still another embodiment of the present invention is described below with reference to FIG. 8.
A heat exchanger of the present embodiment has an arrangement and a drive principle which are basically identical to those of the heat exchanger according to Embodiment 1. Such identical parts of the arrangement and the drive principle are not described here. The heat exchanger of the present embodiment differs from the heat exchanger of Embodiment 1 in that the electron emitting element is provided to a rotary-blade airflow generator. FIG. 8 is a view illustrating the rotary-blade airflow generator 19 included in the heat exchanger according to the present embodiment.
As illustrated in FIG. 8, the rotary-blade airflow generator 19 includes a blade 20, and is designed to rotate the blade 20 so as to blow air toward the heating element (target of heat exchange). The blade 20 is designed to be rotated along a rotation direction R (i.e., along a direction indicated by an arrow in FIG. 8) so as to blow air from a rear side toward a front side of the drawing (i.e., toward a viewer of the drawing). FIG. 8 indicates the air blow direction by S.
According to the heat exchanger of the present embodiment, the heat sink 3 is provided so as to face a surface 20 a of the blade 20 included in the rotary-blade airflow generator 19. The heat sink 3 is in contact with the heating element 2.
According to the heat exchanger of the present embodiment, the rotary-blade airflow generator 19 is provided with the electron emitting element 4 of Embodiment 1 or the electron emitting element 16 of Embodiment 2. In other words, the electrode substrate 7 or the flexible substrate 18 is placed on the surface 20 a of the blade 20.
This allows (i) the air from the rotary-blade airflow generator 19 and (ii) the charged gas (ions) from the electron emitting element 4 (or 16) to be simultaneously blown toward the heat sink 3, which is attached to the heating element 2.

Embodiment 4

Yet another embodiment of the present invention is described below with reference to FIG. 9.
A heat exchanger of the present embodiment has an arrangement and a drive principle which are basically identical to those of the heat exchanger according to Embodiment 1. Such identical parts of the arrangement and the drive principle are not described here. The heat exchanger of the present embodiment differs from the heat exchanger of Embodiment 1 in that the electron emitting element takes the form of a mesh. FIG. 9 is a view illustrating the electron emitting element included in the heat exchanger according to the present embodiment. Air is blown from a rear side toward a front side of FIG. 9 (i.e., toward a viewer of the drawing). FIG. 9 indicates an air blow direction by S′.
As illustrated in FIG. 9, the electron emitting element 21 takes the form of a mesh. The electron emitting element 21 includes a mesh substrate 22. The mesh substrate 22 has a plurality of openings 22 b which penetrate the mesh substrate in the air blow direction S′. According to the heat exchanger of the present embodiment, the heat sink 3 is provided so as to face a surface 22 a of the mesh substrate 22. The heat sink 3 is in contact with the heating element 2. The air is thus blown along the air blow direction S′ through the openings 22 b toward the heat sink 3.
According to the heat exchanger of the present embodiment, the mesh substrate 22 is provided with the electron emitting element 4 of Embodiment 1 or the electron emitting element 16 of Embodiment 2. In other words, the electrode substrate 7 or the flexible substrate 18 is placed on the surface 22 a of the mesh substrate 22.
As described above, the heat exchanger of the present invention can stably blow an ionic wind even with a reduced interelectrode distance. This allows for downsizing of a cooling device.
The electron emitting element serving as an electron source element can be formed by a coating method on a surface which is flexible or which has irregularities. This allows a TV set to include a cooling function in its cabinet section. As a result, it is possible to simultaneously reduce the thickness of a liquid crystal display TV and cool a high-temperature portion of the TV.
In addition, since the reduced distance allows no electric discharge, no ozone or nitrogen oxide is generated. Thus, the heat exchanger can be mounted in household electric appliances. For example, increasing the cooling effect, achieved through spontaneous heat dissipation, of a refrigerant for a refrigerator allows for a reduction in power consumption and for downsizing of a compressor. Further, as illustrated in FIG. 5, the heat exchanger can rapidly remove heat from the vicinity of a heat source. This advantage can be used to provide an ionic wind to a heat source of an air conditioner or a fan heater. This allows for quickly serving warm air to a user. In addition, since warm air can be provided efficiently, it is possible to reduce a heater output and consequently to reduce power consumption. Furthermore, in a case where the heat exchanger is included in a washer-dryer, the washer-dryer can also blow strong warm air toward wet clothes. Therefore, it is possible to reduce power consumption by reducing a heater output, and also to downsize the device (washer-dryer). In the case of the washer-dryer, the heat exchanger blows an ionic wind toward clothes. This prevents the clothes from being tangled up due to their triboelectricity. As a result, it is possible to improve a drying efficiency and in turn to reduce a drying time.
As described above, a heat exchanger of the present invention includes: a contact member which is electrically conductive and which is for contacting with a target of heat exchange; and an electron emitting element which is provided so as to be separated from the contact member by a space and which provides electrons to the contact member via air in the space, the electron emitting element including: an electrode substrate; a thin-film electrode; first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and an electron acceleration layer which accelerates electrons inside itself by the voltage applied from the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode, the electron acceleration layer being formed at least partially from an insulating material.
The heat exchanger of the present invention may preferably be arranged such that the electron acceleration layer includes: conductive particles formed from an electric conductive material and surrounded by a first dielectric material; and a second dielectric material larger than the conductive particles.
According to the above arrangement, the electron acceleration layer creates a multilayer MIM structure by an assembly of the conductive particles each formed with the electric conductive material and surrounded by the first dielectric material. In addition, applying the voltage between the electrode substrate and the thin-film electrode accelerates electrons passing through the electron acceleration layer, and thus turns the electrons into ballistic electrons so that these ballistic electrons pass through the thin-film electrode, whereby the electrons can be emitted.
The second dielectric material can serve to adjust a resistance of the electron acceleration layer. Further, the second dielectric material can also serve to dissipate, e.g., heat generated in the process during which electrons sequentially tunnel through the insulatively coated metal particles. As a result, it is possible to prevent the electron emitting element from being broken due to heat.
The heat exchanger of the present invention, which includes the electron acceleration layer having the above arrangement, can stably emit electrons in response to a low voltage and can thus cause air molecules to be ionized even if the interelectrode distance is small. Hence, the above arrangement allows for downsizing of a heat exchanger. In addition, the above arrangement causes planar emission of electrons. This prevents electric field concentration, and thus improves stability. Furthermore, since no electric field concentration occurs, no damage arising from arc discharge is caused to the contact member or to the target of heat exchange.
The heat exchanger of the present invention may preferably be arranged such that the electric conductive material, from which the conductive particle is formed, includes at least one of gold, silver, platinum, nickel, and palladium.
The above inclusion of at least one of gold, silver, platinum, nickel, and palladium in the electric conductive material, with which the conductive particle is formed, prevents the conductive particle from deteriorating due to, e.g., oxidization caused by atmospheric oxygen. As a result, it is possible to extend a lifetime of the electron emitting element.
The heat exchanger of the present invention may preferably be arranged such that the first dielectric material includes at least one of alcoholate, aliphatic acid, and alkanethiol.
The above inclusion of at least one of alcoholate, aliphatic acid, and alkanethiol in the first dielectric material prevents the conductive particle from deteriorating due to, e.g., growth of the first dielectric material, the growth arising from oxidization caused by atmospheric oxygen. As a result, it is possible to extend the lifetime of the electron emitting element more effectively.
The heat exchanger of the present invention may preferably be arranged such that the second dielectric material includes either at least one of SiO₂, Al₂O₃, and TiO₂, or an organic polymer.
In the case where the second dielectric material includes either at least one of SiO₂, Al₂O₃, and TiO₂, or an organic polymer, since these substances are highly insulating, it is possible to adjust the resistance of the electron acceleration layer so that the resistance falls within a certain range.
The heat exchanger of the present invention may preferably be arranged such that the thin-film electrode includes at least one of gold, carbon, nickel, titanium, and aluminum.
In the case where the thin-film electrode includes at least one of gold, carbon, nickel, titanium, and aluminum, since each of these substances has a low work function, it is possible to (i) cause the electrons accelerated in the particle layer to efficiently tunnel through the particles, and thus to (ii) cause more electrons having a high energy to be emitted from the electron emitting element.
The heat exchanger of the present invention may preferably be arranged such that the first dielectric material is a coating material for coating the conductive particle; the coating material has a thickness smaller than an average diameter of the conductive particles; the second dielectric material takes a form of particles having an average diameter larger than the average diameter of the conductive particles, coated dielectrically with the coating material. In this case, the particles of the second dielectric material preferably have an average diameter which falls within a range from 30 nm to 1000 nm. In the case where the average diameter of the particles of the second dielectric material is set to 30 nm to 1000 nm, it is possible to efficiently dissipate heat generated when electrons sequentially tunnel through the dielectrically coated conductive particles, and thus to prevent the electron emitting element from being broken due to heat. Further, it is also possible to facilitate adjusting the resistance of the electron acceleration layer.
The heat exchanger of the present invention may preferably be arranged such that the first dielectric material is a coating material for coating the conductive particle; the coating material has a thickness smaller than an average diameter of the conductive particles; the second dielectric material takes a form of a sheet, and is placed on the electrode substrate; the second dielectric material has a plurality of openings which penetrate the second dielectric material in a thickness direction; and the openings contain the conductive particles, which are dielectrically coated with the coating material.
The conductive particles, which are dielectrically coated, preferably have an average diameter of 10 nm or smaller. In the case where the dielectrically coated conductive particles have an average diameter of 10 nm or smaller, this average diameter of the conductive particles is equal to or smaller than the mean free path of electrons in electric conductive being scattered. As a result, the electrons are turned into ballistic electrons, and are thus caused to have a high energy.
The heat exchanger of the present invention may preferably be arranged such that the second dielectric material accounts for 80 w % to 95 w % of the electron acceleration layer.
In the case where the second dielectric material makes up from 80 w % to 95 w % of the electron acceleration layer, it is possible to appropriately increase the resistance of the electron acceleration layer, and thus to prevent the electron emitting element from being broken due to a large number of electrons simultaneously flowing through the electron emitting element.
The heat exchanger of the present invention may preferably be arranged such that the electron acceleration layer has a thickness which falls within a range from 30 nm to 1000 nm.
In the case where the electron acceleration layer has a thickness which falls within the range from 30 nm to 1000 nm, it is possible to (1) cause electrons to perform tunneling an appropriate number of times, and thus to (ii) cause the electrons to be emitted more efficiently.
The heat exchanger of the present invention may be arranged such that the heat exchanger is a cooling device for cooling a heating element as the target of heat exchange.
The heat exchanger of the present invention may preferably be arranged such that the contact member is a heat sink having an up-and-down surface which faces the electron emitting element. Further, the electron emitting element is favorably provided in parallel with the irregularity of the heat sink.
In view of device downsizing, the above arrangement allows a device having a certain size to include more projections of the irregularities than a conventional ionic wind generator. This consequently improves the heat exchange capability.
The heat exchanger of the present invention may preferably be arranged such that the electron emitting element is configured to generate a gas flow under an atmospheric pressure.
According to the above arrangement, the electron emitting element is designed to generate a gas flow under an atmospheric pressure, but not in vacuum. As a result, it is possible to increase a speed of the gas flow of the ionic wind, and in turn to increase the heat exchange effect.
The heat exchanger of the present invention may preferably further include: a substrate having a plane surface or a rounded surface, wherein the electron emitting element is formed on the substrate. In addition, the electron emitting element is preferably flexible.
For example, in a case where the target of heat exchange, i.e., a heat exchange target, has a rounded surface, the above arrangement allows the electron emitting element to be provided in parallel with the rounded surface. This prevents electric field concentration from occurring inside the element, and thus prevents electrification from occurring within the element. In addition, the above arrangement allows the electron emitting element to emit electrons from a plane surface, and thus causes electrically charged gas (ionic wind) to be blown from the plane surface. This consequently increases the heat exchange effect.
The heat exchanger of the present invention may preferably further include: a rotary-blade airflow generator which includes a blade provided so as to face the contact member and which rotates the blade so as to blow air toward the contact member, wherein the electron emitting element is provided on a surface of the blade which surface faces the contact member.
According to the above arrangement, the electron emitting element is provided on the surface of the blade of the rotary-blade airflow generator which surface faces the contact member. This causes ions generated due to collision of electrons emitted from the electron emitting element to be carried by the air blown toward the contact member, and consequently to arrive at the contact member. In other words, the ions travel without being resisted by an air current, and then arrive at the contact member. The above arrangement increases wind power, and consequently improves the heat exchange effect achieved by the electrically charged gas. The above arrangement further allows for device downsizing and for a reduction in power consumption.
The heat exchanger of the present invention may preferably be arranged such that the electron emitting element takes a form of a mash.
The above arrangement causes air to be readily drawn from behind the electrode substrate, and thus causes gas to be readily blown from the entire surface of the electron emitting element toward the contact member. This increases an amount of the gas, and consequently improves the heat exchange effect.
The heat exchanger of the present invention may preferably further include: second voltage applying means for applying a voltage between the contact member and the electron emitting element, wherein the voltage applied by the second voltage applying means is higher than 0 V and not higher than +10 kV.
According to the above arrangement, the heat exchanger includes the second voltage applying means for applying the voltage between the contact member and the electron emitting element. Further, the voltage applied by the second voltage applying means is higher than 0 V and not higher than +10 kV. In other words, the voltage applied by the second voltage applying means is higher than the voltage applied by the first voltage applying means. Consequently, the above arrangement causes negatively charged ions to arrive at the contact member, and thus dissipates heat generated by the heating element.
The heat exchanger of the present invention may preferably be arranged such that a strength of an electric field generated between the contact member and the electron emitting element falls within a range from 1 V/m to 10⁷V/m.
The above arrangement allows electrons to be provided to oxygen molecules included in the air molecules with use of an energy lower than 6 electron volts, which is an energy of dissociation for oxygen. This prevents generation of hazardous substances such as ozone and nitrogen oxide. In other words, since the mean free path for electrons in an atmosphere is 0.1 μm, in the case where, for example, the electric field strength is 10⁷μm, the energy of an electron reaches 1 electron volt before the electron collides with an air molecule. Hence, setting the electric field strength to lower than 10⁷V/m prevents generation of ozone and nitrogen oxide.
The heat exchanger of the present invention may preferably be arranged such that the contact member is grounded.
This prevents charging of the target of heat exchange.
The heat exchanger of the present invention may preferably be arranged such that the contact member is provided to make an angle with an electron emission surface of the thin-film electrode of the electron emitting element, the angle falling within a range from 0° to 90°.
According to the above arrangement, the contact member is provided so as to face the thin-film electrode of the electron emitting element at an angle which falls within the range from 0° to 90°. This prevents concentration of lines of electric force between the contact member and the electron emitting element. This can in turn eliminate a risk of electrification occurring in the electron emitting element serving as an electron source element.
The heat exchanger of the present invention may preferably be arranged such that the contact member is separated from the electron emitting element by a distance which falls within a range from 100 μm to 50 cm.
This causes the electron emitting element to be close to the contact member, which is in contact with the target of heat exchange. This in turn improves the heat exchange effect. Further, making the electron emitting element of a material that is not easily oxidized allows the heat exchanger to be driven for an extended period of time even in a case where the heat exchanger is placed close to a heating element.
The embodiments and concrete examples of implementation discussed in the foregoing detailed description of the invention serve solely to illustrate the technical details of the present invention, which should not be narrowly interpreted within the limits of such embodiments and concrete examples. The present invention may rather be applied in many variations within the spirit of the present invention, provided that such variations do not exceed the scope of the patent claims set forth below. Further, the scope of the present invention naturally encompasses embodiments involving numerical ranges other than the numerical ranges presented in the present specification, provided that such other numerical ranges are reasonable and consistent with the spirit of the present invention.

INDUSTRIAL APPLICABILITY

The heat exchanger of the present invention can stably blow an ionic wind even with a reduced interelectrode distance. This allows for downsizing of a cooling device. The heat exchanger of the present invention is applicable to liquid crystal display TVs and laptop personal computers, both of which require efficient cooling within a small space and prevention of wind noise caused by a fan.

Claims

1. A heat exchanger, comprising:

a contact member which is electrically conductive and which is for contacting with a target of heat exchange; and

an electron emitting element which is provided so as to be separated from the contact member by a space and which provides electrons to the contact member via air in the space,

the electron emitting element including:

an electrode substrate; a thin-film electrode;

first voltage applying means for applying a voltage between the electrode substrate and the thin-film electrode; and

an electron acceleration layer which accelerates electrons inside itself by the voltage applied from the first voltage applying means so that the electrons thus accelerated are emitted from the thin-film electrode,

the electron acceleration layer being formed at least partially from an insulating material.

2. The heat exchanger according to claim 1, wherein the electron acceleration layer includes:

conductive particles formed from an electric conductive material and surrounded by a first dielectric material; and

a second dielectric material larger than the conductive particles.

3. The heat exchanger according to claim 2, wherein the electric conductive material, from which the conductive particle is formed, includes at least one of gold, silver, platinum, nickel, and palladium.

4. The heat exchanger according to claim 2, wherein the first dielectric material includes at least one of alcoholate, aliphatic acid, and alkanethiol.

5. The heat exchanger according to claim 2, wherein the second dielectric material includes either at least one of SiO₂, Al₂O₃, and TiO₂, or an organic polymer.

6. The heat exchanger according to claim 1, wherein the thin-film electrode includes at least one of gold, carbon, nickel, titanium, and aluminum.

7. The heat exchanger according to claim 2,

wherein:

the first dielectric material is a coating material for coating the conductive particle;

the coating material has a thickness smaller than an average diameter of the conductive particles;

the second dielectric material takes a form of particles having an average diameter larger than the average diameter of the conductive particles, coated dielectrically with the coating material.

8. The heat exchanger according to claim 2,

wherein:

the second dielectric material takes a form of a sheet, and is placed on the electrode substrate;

the second dielectric material has a plurality of openings which penetrate the second dielectric material in a thickness direction; and

the openings contain the conductive particles, which are dielectrically coated with the coating material.

9. The heat exchanger according to claim 7, wherein the particles of the second dielectric material have an average diameter which falls within a range from 30 nm to 1000 nm.

10. The heat exchanger according to claim 7, wherein the conductive particles, which are dielectrically coated, have an average diameter of 10 nm or smaller.

11. The heat exchanger according to claim 2, wherein the second dielectric material accounts for 80 w % to 95 w % of the electron acceleration layer.

12. The heat exchanger according to claim 2, wherein the electron acceleration layer has a thickness which falls within a range from 30 nm to 1000 nm.

13. The heat exchanger according to claim 1, wherein the heat exchanger is a cooling device for cooling a heating element as the target of heat exchange.

14. The heat exchanger according to claim 1, wherein the contact member is a heat sink having an up-and-down surface which faces the electron emitting element.

15. The heat exchanger according to claim 1, wherein the electron emitting element is configured to generate a gas flow under an atmospheric pressure.

16. The heat exchanger according to claim 1, further comprising:

a substrate having a plane surface or a rounded surface,

wherein the electron emitting element is formed on the substrate.

17. The heat exchanger according to claim 1, wherein the electron emitting element is flexible.

18. The heat exchanger according to claim 1, further comprising:

a rotary-blade airflow generator which includes a blade provided so as to face the contact member and which rotates the blade so as to blow air toward the contact member,

wherein the electron emitting element is provided on a surface of the blade which surface faces the contact member.

19. The heat exchanger according to claim 1, wherein the electron emitting element takes a form of a mash.

20. The heat exchanger according to claim 1, further comprising:

second voltage applying means for applying a voltage between the contact member and the electron emitting element,

wherein the voltage applied by the second voltage applying means is higher than 0 V and not higher than +10 kV.

21. The heat exchanger according to claim 20, wherein a strength of an electric field generated between the contact member and the electron emitting element falls within a range from 1 V/m to 10⁷V/m.

22. The heat exchanger according to claim 1, wherein the contact member is grounded.

23. The heat exchanger according to claim 1, wherein the contact member is provided to make an angle with an electron emission surface of the thin-film electrode of the electron emitting element, the angle falling within a range from 0° to 90°.

24. The heat exchanger according to claim 1, wherein the contact member is separated from the electron emitting element by a distance which falls within a range from 100 pm to 50 cm.