Patent Application
20070220903
The present invention relates to a thermoacoustic apparatus capable of cooling or heating an object through the use of thermoacoustic effect.
Known technologies of a heat exchange apparatus through the use of thermoacoustic effect include the technologies described in the following Patent Document 1, Non-Patent Document 1, and the like.
The apparatus described in Patent Document 1 relates to a cooling apparatus through the use of thermoacoustic effect. This apparatus is configured to include a first stack sandwiched between a high-temperature-side heat exchanger and a low-temperature-side heat exchanger and a regenerator sandwiched between a high-temperature-side heat exchanger and a low-temperature-side heat exchanger in the inside of a loop tube, in which helium, argon, or a mixed gas thereof is enclosed, where the low-temperature-side heat exchanger on the regenerator side is cooled by a standing wave and a traveling wave generated through self excitation by heating the high-temperature-side heat exchanger on the first stack side.
Likewise, Non-Patent Document 1 discloses an experimental study of a cooling apparatus through the use of thermoacoustic effect. The cooling apparatus used in this experiment is also configured to include a loop tube enclosing helium, argon, or a mixed gas thereof in the inside, a first stack sandwiched between a heater (high-temperature-side heat exchanger) and a low-temperature-side heat exchanger, and a second stack disposed at a position opposite to the first stack. A temperature gradient is generated in the first stack by heating the heater (high-temperature-side heat exchanger) disposed on the first stack side and, in addition, circulating running water in the low-temperature-side heat exchanger, and an acoustic wave is generated through self excitation in a direction opposite to the temperature gradient. The resulting acoustic energy is transferred to the regenerator side through the loop tube, and on the second stack side, thermal energy is transferred in the direction opposite to the direction of the acoustic energy on the basis of the energy conservation law, so as to cool the vicinity of a thermometer disposed on the other end side of the second stack. According to this document, a temperature reduction of about 16° C. has been ascertained under a predetermined condition at the portion where the thermometer has been disposed.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2000-88378
Non-Patent Document 1: Shinichi SAKAMOTO, Kazuhiro MURAKAMI, and Yoshiaki WATANABE, “Netsuonkyou Koukao Mochiita Onkyoureikyaku Genshouno Jikkenteki Kentou (Experimental Study of Acoustic Cooling Phenomenon Through the Use of Thermoacoustic Effect)”, The Institute of Electronics, Information and Communication Engineers, TECHNICAL REPORT OF IEICE. US2002-118 (2003-02)
In the apparatus through the use of the above-described thermoacoustic effect, efficient energy conversion is required as in general heat exchange apparatuses and the like. In order to improve the efficiency of the energy conversion of the apparatus through the use of this thermoacoustic effect, the time period from heating to generation of the standing wave and the traveling wave must be reduced. Furthermore, after the acoustic wave is generated, the efficiency of energy conversion must be improved. Therefore, with respect to known apparatuses, helium having a small Prandtl number, argon having a large Prandtl number, or a mixed gas thereof is enclosed in the inside of the loop tube and, thereby, a reduction of the time until the standing wave and the traveling wave are generated and an improvement in acoustic energy and thermal energy conversion efficiencies are intended.
However, if helium having a small Prandtl number is used as in the above-described known apparatus, although the time until the generation of an acoustic wave can be reduced, the sound velocity of the resulting acoustic wave is increased, and there is a problem in that heat exchange with a stack inner wall cannot be performed smoothly. If a working fluid, e.g., argon, having a relatively large Prandtl number is used, although the sound velocity can be decreased due to the viscosity thereof, there is a problem in that the time until the generation of an acoustic wave is increased conversely. On the other hand, when a mixed gas of helium and argon is enclosed, there is a problem in that the sound velocity may become too high or, conversely, the time until the generation of an acoustic wave may be excessively increased depending on the mixing ratio. Furthermore, even when the ratio of the mixed gas is in an optimized condition, the mixed gas may be separated into upper and lower portions after the loop tube is stood for a long time, and there are problems in that, for example, the same effect as in the initial homogeneously mixed state may not be exerted.
The present invention has been made in consideration of the above-described problems. Accordingly, it is an object to provide a thermoacoustic apparatus and the like capable of reducing the time until an acoustic wave is generated and performing heat exchange smoothly in a stack.
In order to overcome the above-described problems, a thermoacoustic apparatus according to an aspect of the present invention includes a first stack sandwiched between a first high-temperature-side heat exchanger and a first low-temperature-side heat exchanger and a second stack sandwiched between a second high-temperature-side heat exchanger and a second low-temperature-side heat exchanger in the inside of a loop tube, wherein a standing wave and a traveling wave are generated through self excitation by heating the above-described first high-temperature-side heat exchanger, the above-described second low-temperature-side heat exchanger is cooled by the standing wave and the traveling wave, or/and a standing wave and a traveling wave are generated by cooling the above-described first low-temperature-side heat exchanger, and the above-described second high-temperature-side heat exchanger is heated by the standing wave and the traveling wave, while the thermoacoustic apparatus includes a mixing device for injecting and mixing a working fluid different from a first working fluid after the first working fluid is enclosed in the inside of the loop tube.
According to this configuration, since the first working fluid is enclosed, and the working fluid different from the first working fluid is injected, for example, immediately before a sound is generated, immediately after the sound is generated, or after the sound rises suddenly, the working fluid in the loop tube can be brought into a homogeneous state during the use, and the gases can be mixed into an optimum state in consideration of a balance between the generation of sound and the output of heat.
When the working fluid is mixed, the working fluid, which has a low sound velocity, is injected afterward into the working fluid, which has a high sound velocity, enclosed in the loop tube in advance.
According to this configuration, the acoustic wave can be generated rapidly, and after the acoustic wave is generated, transition to a state, in which the efficiency of heat exchange is high, is possible.
With respect to forms thereof, for example, the working fluid having a small specific gravity is enclosed in advance and the working fluid having a large specific gravity is injected afterward.
For another form, the working fluid having a large Prandtl number is injected afterward into the working fluid having a small specific gravity enclosed in the loop tube in advance.
According to this configuration, under a predetermined condition, an acoustic wave can be generated rapidly by using the working fluid having a small Prandtl number (that is, a working fluid having a small kinematic viscosity coefficient relative to a thermal diffusion coefficient), and a state most suitable for the efficiency of heat exchange can be brought about by injecting the working fluid having a large Prandtl number (that is, a working fluid having a small thermal diffusion coefficient relative to a kinematic viscosity coefficient).
The loop tube including a plurality of linear tube portions, which stand relative to the ground, and connection tube portions connected between the plurality of linear tube portions is used, and the mixing device is disposed above the center of the loop tube.
According to this configuration, in the case where working fluids having different weights relative to each other are mixed, working fluids can be mixed homogeneously in the loop tube by injecting a heavier working fluid afterward from above.
Alternatively, the loop tube is configured to be bilaterally symmetric and include a plurality of linear tube portions, which stand relative to the ground, and connection tube portions connected between the plurality of linear tube portions, and the mixing device is disposed at the center of the upper connection tube portion.
According to this configuration, since the working fluid is injected from the center of the upper side of the loop tube configured to be bilaterally symmetric, the injected working fluid is uniformly divided into the right and the left, and the entire loop tube can be mixed homogeneously.
Furthermore, a sound detection device for detecting generation of a sound is disposed, and injection of the working fluid is started when the generation of a sound in the loop tube is detected by this sound detection device or when a variation in the state of sound is detected.
According to this configuration, since the working fluid is injected after the sound is generated or after the sound rises suddenly, a state, in which the efficiency of heat exchange is high, can be brought about rapidly after the sound is generated or after the sound rises suddenly.
In addition, a pressure measuring device for measuring a pressure in the loop tube is disposed, and injection of the working fluid is stopped when a predetermined pressure is measured by this pressure measuring device.
According to this configuration, the pressure in the loop tube can be kept at a constant value, and it becomes possible to prevent a problem in that, for example, the efficiency of heat exchange varies due to pressure variation in each use.
The injection of the working fluid is stopped on the basis of the variation over time of heat output from the second high-temperature-side heat exchanger or the second low-temperature-side heat exchanger.
According to this configuration, it becomes possible to prevent a problem in that the working fluid is continued being injected even when the variation in the heat output from the second high-temperature-side heat exchanger is terminated.
When the working fluid composed of a working fluid lighter than air and a working fluid heavier than air is used, an opening portion for releasing the working fluid heavier than air is disposed at the lower end portion of the loop tube.
According to this configuration, for example, when helium, which is lighter than air, and argon, which is heavier than air, are used, argon can simply be released from the opening portion disposed at the lower end and, therefore, it is not necessary to replace the entire working fluid.
The thermoacoustic apparatus according to an aspect of the present invention includes the first stack sandwiched between the first high-temperature-side heat exchanger and the first low-temperature-side heat exchanger and the second stack sandwiched between the second high-temperature-side heat exchanger and the second low-temperature-side heat exchanger in the inside of the loop tube, wherein a standing wave and a traveling wave are generated through self excitation by heating the above-described first high-temperature-side heat exchanger, the above-described second low-temperature-side heat exchanger is cooled by the standing wave and the traveling wave, or/and a standing wave and a traveling wave are generated through self excitation by cooling the above-described first low-temperature-side heat exchanger, and the above-described second high-temperature-side heat exchanger is heated by the standing wave and the traveling wave, while the thermoacoustic apparatus includes the mixing device for injecting and mixing the working fluid different from the first working fluid after the first working fluid is enclosed in the inside of the loop tube. Consequently, the working fluids in the loop tube can be mixed homogeneously and, in addition, an optimum mixing state can be achieved while the generation of sound and output of heat are adjusted.
A first embodiment of a thermoacoustic apparatus 1 according to an aspect of the present invention will be described below with reference to drawings.
As shown in
In the present embodiment, in order to reduce the time from the start of heating of the first high-temperature-side heat exchanger 4 until the standing wave and the traveling wave are generated and increase the efficiency of energy conversion due to the generated standing wave and the traveling wave, initially a first working fluid having a high sound velocity, a small Prandtl number, and a small specific gravity is enclosed in the loop tube 2, and after a standing wave and a traveling wave are generated, a second working fluid having a low sound velocity, a large Prandtl number, and a large specific gravity is injected.
In general, the Prandtl number Pr is represented as described below.
Pr=ν(kinematic viscosity coefficient)/κ(thermal diffusion coefficient)=Cpμg/λ
Cp: specific heat at constant pressure, μ: viscosity, g: acceleration of gravity, λ: thermal conductivity
Therefore, when the thermal diffusion coefficients κ of different working fluids are the same, the working fluid having a smaller Prandtl number exhibits a smaller kinematic viscosity coefficient ν. Consequently, the time until an acoustic wave is generated is reduced, and the sound velocity of the resulting acoustic wave is increased. On the other hand, the working fluid having a larger Prandtl number exhibits a relatively larger kinematic viscosity coefficient ν (thermal diffusion coefficient κ is decreased), and it takes a time until an acoustic wave is generated. However, when the Prandtl number is large, the efficiency of heat exchange is improved. With respect to the relationship between the specific gravity and the sound velocity, when the specific gravity is small, the sound velocity tends to be increased. Therefore, in the present embodiment, a working fluid, e.g., helium, having a high sound velocity, a small Prandtl number, and a small specific gravity is enclosed in the loop tube 2 initially and, thereby, a standing wave and a traveling wave are generated rapidly. Thereafter, a working fluid, e.g., argon, having a low sound velocity, a large Prandtl number, and a large specific gravity is injected appropriately so as to improve the efficiency of heat exchange. The thermoacoustic apparatus 1 in the present embodiment will be described below in detail.
The loop tube 2 constituting the thermoacoustic apparatus 1 includes a pair of linear tube portions 2a opposite to each other, which are disposed along the vertical direction relative to the ground, and connection tube portions 2b connected between these linear tube portions 2a, and is composed of a metal pipe or the like. The material for this loop tube 2a is not limited to the metal or the like, and may be transparent glass, a resin, or the like. When the loop tube 2a is composed of a material, such as the transparent glass, the resin, or the like, positions of the first stack 3a and the second stack 3b can be checked and the status in the tube can easily be observed in an experiment or the like.
For the lengths of the thus disposed linear tube portion 2a and the connection tube portion 2b, when the length of the linear tube portion 2a is assumed to be La and the length of the connection tube portion 2b is assumed to be Lb,
La and Lb are set within the range satisfying
1:0.01≦La:Lb<1:1.
However, it is preferable that the linear tube portion 2a is made as long as possible, and
La and Lb are set within the range satisfying
1:0.01≦La:Lb≦1:0.5.
When the length of the linear tube portion 2a is set at a large value, the surface wavefront of an acoustic wave generated from the first stack 3a can be stabilized as rapid as possible.
In the inside of the thus configured loop tube 2, the first stack 3a sandwiched between the first high-temperature-side heat exchanger 4 and the first low-temperature-side heat exchanger 5 and the second stack 3b sandwiched between the second high-temperature-side heat exchanger 6 and the second low-temperature-side heat exchanger 7 are disposed.
This first stack 3a is configured to take on a cylindrical shape which touches the inner wall of the loop tube 2, and is formed from a material, e.g., ceramic, sintered metal, gauze, or nonwoven metal fabric, which has a large heat capacity. The first stack 3a is configured to have multiple holes penetrating in the axis direction of the loop tube 2. As shown in
Both the first high-temperature-side heat exchanger 4 and the first low-temperature-side heat exchanger 5 are composed of a thin metal, and are configured to include through holes for transmitting the standing wave and the traveling wave in the inside thereof. Among these heat exchangers, the first high-temperature-side heat exchanger 4 is configured to be heated by an electric power supplied from the outside, waste heat, unused energy, or the like. On the other hand, the first low-temperature-side heat exchanger 5 is set at a temperature relatively lower than that of the first high-temperature-side heat exchanger 4 by circulating water around it.
The first stack 3a sandwiched between the first high-temperature-side heat exchanger 4 and the first low-temperature-side heat exchanger 5, as described above, is disposed below the center of the linear tube portion 2a while the first high-temperature-side heat exchanger 4 is disposed on the upper side. The first stack 3a is disposed below the center of the linear tube portion 2a, as described above, on the grounds that an acoustic wave is generated rapidly through the use of an updraft generated when the first high-temperature-side heat exchanger 4 is heated and that a warm working fluid generated when the first high-temperature-side heat exchanger 4 is heated is prevented from entering the first stack 3a. A large temperature gradient is formed in the first stack 3a by preventing the warm working fluid from entering the first stack 3a, as described above.
With respect to the condition for the generation of the acoustic wave through self excitation in the first stack 3a, in the case where the working fluid flows in the first stack 3a, when a flow path radius of the parallel channels is assumed to be r, an angular frequency of the working fluid is assumed to be ω, a temperature diffusion coefficient is assumed to be α, and a temperature relaxation time is assumed to be τ (=r2/2α), the acoustic wave can be generated through self excitation most efficiently when ωτ is within the range of 0.2 to 20. Therefore, r, ω, and τ are set in such a way as to satisfy these relationships. Furthermore, when one end of the linear tube portion 2a in the upper left of the loop tube 2 is connected to one end of the connection tube portion 2b in
On the other hand, similarly to the first stack 3a, the second stack 3b is configured to take on a cylindrical shape which touches the inner wall of the loop tube 2, and is formed from a material, e.g., ceramic, sintered metal, gauze, or nonwoven metal fabric, which has a large heat capacity. The second stack 3b is configured to have multiple holes penetrating in the axis direction of the loop tube 2. This second stack 3b is disposed in such a way that when a first peak of the pressure variation of the working fluid along the loop tube 2 is present in the vicinity of the first stack 3a, and a second peak is present at a position corresponding to about one-half the entire length of the circuit, the center of the second stack 3b is positioned past the second peak. With respect to the structure of this second stack 3b, as shown in
Likewise, both the second high-temperature-side heat exchanger 6 and the second low-temperature-side heat exchanger 7 disposed on the second stack 3b side are composed of a thin metal, and are configured to include through holes for transmitting the standing wave and the traveling wave in the inside thereof. Water is circulated around the second high-temperature-side heat exchanger 6 and, in addition, an object of cooling is connected to the second low-temperature-side heat exchanger 7. It is believed that the object of cooling is outside air, a heat-producing household electric appliance, a CPU of a personal computer, and the like. However, objects other than them may be cooled.
In the inside of the thus configured loop tube 2, helium serving as the first working fluid having a small Prandtl number and argon serving as the second working fluid having a Prandtl number larger than that of the first working fluid are enclosed.
When these working fluids are enclosed, if helium having a high sound velocity, a small Prandtl number, and a small specific gravity is used, the time until an acoustic wave is generated can be reduced. However, the sound velocity is increased and the heat exchange with the stack inner wall cannot be performed smoothly. Conversely, if argon or the like having a low sound velocity, a large Prandtl number and a small specific gravity is used, the viscosity is increased and an acoustic wave cannot be generated rapidly. Consequently, in the present embodiment, in order to generate an acoustic wave rapidly, helium is enclosed in the inside of the loop tube 2a initially, and argon is injected after a standing wave and a traveling wave are generated. In the case where the above-described second working fluid is injected, the procedure is as described below.
As shown in
The following method can be used as the method in the case where argon is injected as described above.
As shown in
The injection from the argon gas injection apparatus 9b is stopped as described below.
A pressure measuring device 90, e.g., a pressure gauge, for measuring the pressure in the loop tube 2 is disposed, and the valve 9c of the argon gas injection apparatus 9b is closed when a predetermined pressure value is measured with this pressure measuring device 90. This pressure is set within the range of, for example, 0.01 MPa to 5 MPa. In the case where the loop tube 2 is configured to be relatively small, the pressure is set at a small value in order to reduce the influence of viscosity.
Furthermore, not only the valve 9c of the argon gas injection apparatus 9b is controlled by the pressure measuring device 90, but also a heat variation control device 91 for controlling the closing and opening of the valve 9c on the basis of the variation in heat output from the second low-temperature-side heat exchanger 7 may be disposed. In the case where this heat variation control device 91 is used, for example, the control is performed in such a way that the valve 9c of the argon gas injection apparatus 9b is closed and the injection is stopped when the variation over time of the heat output from the second low-temperature-side heat exchanger 7 becomes a predetermined value or less. According to this configuration, needless injection of argon is avoided, and the gas can be saved. In the case where the closing and opening of the valve 9c is controlled on the basis of the variation over time of heat, the above-described control of the closing and opening of the valve 9c by the pressure may be performed in combination therewith. According to this configuration, unlimited pressurization is avoided, and breakage and the like of the apparatus 1 can be prevented.
Moreover, in the case where the above-described apparatus 1 is used, a closable opening portion 2c is disposed in the loop tube 2 in such a way that degasification operation and fresh mixing can be performed in each use. It is preferable that this opening portion 2c is disposed in the lower end portion of the loop tube 2. After the use of apparatus 1 is finished, this opening portion 2c is opened, so that the working fluid having a relatively heavier specific gravity is released into air. According to this configuration, argon having a relatively heavier specific gravity is settled in a lower portion of the loop tube 2 when a certain time has elapsed after the use is finished, and argon heavier than air is simply released into air from the opening portion 2c. In the case where helium is filled in again from the upper side in the next use, the air entered into the loop tube 2 can be pushed out and released from the lower opening portion 2c and, thereby, the density of helium in the loop tube 2 can be increased.
According to the above-described embodiment, the gas injection apparatus 9b is disposed, the standing wave and the traveling wave are generated through self excitation under the condition in which one working fluid is enclosed in the inside of the loop tube 2 and, thereafter, another working fluid different from the above-described working fluid is injected with the apparatus. Consequently, it becomes possible to set at a state in best balance from the view point of the generation of acoustic wave and the efficiency of energy conversion.
In the present embodiment, helium having a high sound velocity, a small Prandtl number, and a small specific gravity is enclosed in advance and, thereafter, argon having a low sound velocity, a large Prandtl number, and a large specific gravity is injected. Consequently, an acoustic wave is generated rapidly by helium and, in addition, after the acoustic wave is generated, it is possible to bring about a state most suitable for the efficiency of heat exchange by argon.
The loop tube 2 including a plurality of linear tube portions 2a, which are disposed vertically relative to the ground, and connection tube portions 2b connected between these linear tube portions 2a is used, and the argon gas injection apparatus 9b is disposed above the center of the loop tube 2. Consequently, the working fluids can be mixed homogeneously by injecting argon heavier than helium from above.
Since the loop tube 2 is configured to be bilaterally symmetric and the injection hole 9d of the gas injection apparatus 9b is disposed at an upper side of the center portion of the loop tube 2, argon injected from the injection hole 9d is divided into the right and the left, and the working fluid can be injected into the loop tube uniformly. Consequently, variations in acoustic wave generation and variations in heat exchange can be eliminated.
Furthermore, a sound detection device 8a for detecting generation of a sound is disposed, and the working fluid having a large Prandtl number is injected when the sound generated in the loop tube is detected by this sound detection device. Consequently, the generation time of acoustic wave can be reduced and, in addition, the efficiency of heat exchange can be improved.
Moreover, the pressure measuring device 90 is disposed, and injection of the working fluid is stopped when the pressure in the loop tube 2 reaches a predetermined value. Consequently, the pressure in the loop tube can always be kept at a constant value, and it becomes possible to prevent a problem in that the efficiency of heat exchange varies due to pressure variation in each use.
In another form of the case where the injection of the working fluid is stopped, the injection of the working fluid is stopped on the basis of the variation over time of heat output from the second high-temperature-side heat exchanger 6. Consequently, it becomes possible to avoid waste, such that the injection of the working fluid is continued needlessly.
In the case where argon, which is heavier than air is injected into helium, which is lighter than air, since the opening portion 2c for releasing argon is disposed at the lower end portion of the loop tube 2, argon can simply be released into air by opening the opening portion 2c and, therefore, it is not necessary to replace the entire working fluid.
The present invention is not limited to the above-described embodiments, and can be carried out in various forms.
For example, in the above-described thermoacoustic apparatus 1, the acoustic wave is generated through self excitation by the temperature gradient provided in the first stack 3a. In order to facilitate the acoustic wave through self excitation, an acoustic wave generator 8b may be disposed on the outer perimeter portion or in the inside of the loop tube 2. This acoustic wave generator 8b is composed of a speaker, a piezoelectric element, or other devices which forcedly vibrate the working fluid from the outside. It is preferable that the acoustic wave generator 8b is attached with a distance of one-half or one-quarter the wavelength of the standing wave and the traveling wave generated. Preferably, the acoustic wave generator 8b is disposed in such a way as to forcedly vibrate the working fluid in the axis direction of the loop tube 2 in correspondence with the movement direction of the standing wave and the traveling wave. When the acoustic wave generator 8b is disposed as described above, the generation time of the standing wave and the traveling wave can be reduced, and the second low-temperature-side heat exchanger 7 can be cooled.
In the case where satisfactory cooling effect cannot be attained by the above-described thermoacoustic apparatus 1 alone, a thermoacoustic system 100, in which a plurality of thermoacoustic apparatuses 1 are connected, as shown in
In the above-described embodiment, the explanation is conducted with reference to the thermoacoustic apparatus 1 in which the first stack 3a side is heated and the second stack 3b side is cooled. Conversely, the first stack 3a side may be cooled and the second stack 3b side may be heated.
In
In the present embodiment as well, in order to facilitate the generation of the standing wave and the traveling wave, an acoustic wave generator 8b may be disposed on the outer perimeter surface or in the inside of the loop tube 2. Alternatively, the above-described thermoacoustic apparatuses 1 may be connected as shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-91686 | Mar 2004 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP05/05221 | 3/23/2005 | WO | 9/26/2006 |
