WO2022024426A1 - Dispositif thermoacoustique - Google Patents

Dispositif thermoacoustique Download PDF

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Publication number
WO2022024426A1
WO2022024426A1 PCT/JP2021/005872 JP2021005872W WO2022024426A1 WO 2022024426 A1 WO2022024426 A1 WO 2022024426A1 JP 2021005872 W JP2021005872 W JP 2021005872W WO 2022024426 A1 WO2022024426 A1 WO 2022024426A1
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gas
temperature gradient
temperature
waveguide
medium
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PCT/JP2021/005872
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English (en)
Japanese (ja)
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道明 西村
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京セラ株式会社
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Priority to JP2022539999A priority Critical patent/JPWO2022024426A1/ja
Publication of WO2022024426A1 publication Critical patent/WO2022024426A1/fr

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point

Definitions

  • thermoacoustic device relates to a thermoacoustic device.
  • thermoacoustic device that converts heat energy into acoustic energy by the thermoacoustic effect, which is an interaction between heat and sound, and converts the acoustic energy into other energy such as electric energy is known.
  • thermoacoustic generator in which a generator that responds to generate power is provided in a loop tube is disclosed (see, for example, Japanese Patent Application Laid-Open No. 2003-324932).
  • the thermoacoustic device includes a loop-shaped waveguide and a heat exchanger.
  • the loop-shaped waveguide is filled with a medium.
  • the heat exchanger is provided in the waveguide and has a low temperature part and a high temperature part.
  • the heat exchanger is provided between the low temperature portion and the high temperature portion, and further has a temperature gradient holding portion for holding the temperature gradient generated between the low temperature portion and the high temperature portion.
  • the temperature gradient holding unit has a plurality of heat conductive members that transfer heat according to the temperature gradient to the medium.
  • the spacing between the plurality of heat transfer members is created in the medium by the temperature gradient, and the phase velocity of the amplified sound wave is set to correspond to the temperature rise or fall rate of the medium caused by the temperature gradient.
  • the length of the waveguide corresponds to the phase velocity of the sound wave.
  • FIG. 1 is a diagram showing an example of a thermoacoustic device according to an embodiment.
  • FIG. 2 is a diagram showing an example of a high temperature portion of a heat exchanger included in the thermoacoustic device according to the embodiment.
  • FIG. 3 is a diagram showing an example of a temperature gradient holding portion of a heat exchanger included in the thermoacoustic device according to the embodiment.
  • FIG. 4 is a diagram illustrating a physical quantity relating to a relational expression between the phase velocity of a sound wave and the rate of temperature increase or decrease of a gas in the thermoacoustic device according to the embodiment.
  • FIG. 5 is a diagram illustrating several examples of the shape of the heat conductive member in the partial cross section of the temperature gradient holding portion according to the embodiment.
  • the efficiency of converting thermal energy into sound energy may be low.
  • the efficiency of converting heat energy into sound energy becomes low.
  • thermoacoustic device that improves the efficiency of converting thermal energy into acoustic energy.
  • thermoacoustic apparatus disclosed in the present application will be described in detail with reference to the attached drawings.
  • the present invention is not limited to the embodiments shown below.
  • FIG. 1 is a diagram showing an example of a thermoacoustic device 1 according to an embodiment.
  • the front side is the positive direction in the Z-axis direction in the direction orthogonal to the paper surface
  • the longitudinal direction and the lateral direction of the thermoacoustic device 1 are the X-axis direction and the Y-axis direction, respectively. Shows a three-dimensional Cartesian coordinate system.
  • the thermoacoustic device 1 is a device that converts thermal energy into acoustic energy of sound waves and converts acoustic energy of sound waves into other energy such as electric energy by a thermoacoustic effect.
  • the thermoacoustic effect is the interaction between heat and sound waves.
  • the thermoacoustic device 1 according to the embodiment includes a waveguide 2, a heat exchanger 3, an exciter 7, and a converter 8.
  • the waveguide 2 is filled with gas G.
  • the gas G is, for example, air, nitrogen (N 2 ), helium (He), argon (Ar), hydrogen (H 2 ), carbon dioxide (CO 2 ), or the like.
  • the waveguide 2 is configured to seal the gas G inside.
  • the pressure of the gas G filled in the waveguide 2 is, for example, 1 atm (1013.25 hPa) or more and less than 30 atm (30397.5 hPa). As will be described later, the pressure of the gas G filled in the waveguide 2 may be less than 1 atm.
  • the waveguide 2 is a loop-shaped waveguide without a reflective wall.
  • the waveguide 2 has, for example, the shape of a single loop as shown in FIG.
  • the waveguide 2 resonates the sound wave generated in the gas G.
  • the phase of the temperature change of the gas G caused by the heat conduction between the heat exchanger 3 and the gas G is the phase of the temperature change of the medium with respect to the movement (transfer) of the gas G by the sound wave generated in the gas G. It is delayed by the amount corresponding to the rate of temperature increase or decrease. Accordingly, the phase of the pressure change of the sound wave of the gas G is delayed by 0 ° to 90 ° from the phase of the pressure change of the sound wave of the gas G when there is no temperature change of the gas G.
  • thermoacoustic device 1 when the waveguide 2 has a reflective wall, the resonance of the sound wave whose pressure phase is delayed due to the temperature change generated in the gas G is not stabilized, and the amplitude of the sound wave generated in the gas G is not stabilized. Will be reduced.
  • the waveguide 2 has the shape of a loop without a reflection wall, so that the resonance of the sound wave generated in the gas G can be stabilized. Accordingly, the thermoacoustic device 1 according to the embodiment can improve the output of the acoustic energy of the sound wave.
  • the length of the loop-shaped waveguide 2 is an integral multiple of the wavelength of the sound wave generated in the gas G.
  • the length of the waveguide 2 can be set, for example, so that the wavelength of the sound wave generated in the gas G by the exciter 7 is 1 m or less.
  • the wavelength of the sound wave is determined according to the sound velocity of the gas G, and the length of the waveguide 2 is set.
  • the waveguide 2 is, for example, a hollow waveguide having a circular or rectangular cross section.
  • the waveguide 2 is made of, for example, a metal such as stainless steel (SUS) or a plastic such as vinyl chloride.
  • SUS stainless steel
  • plastic such as vinyl chloride.
  • the heat exchanger 3 transfers heat to the gas G filled in the waveguide 2.
  • the heat exchanger 3 heats or cools the gas G according to the phase of advection of sound waves.
  • the length of the heat exchanger 3 in the direction in which the waveguide 2 extends is, for example, equal to or larger than the amplitude of the sound wave generated in the gas G and 1/20 or less of the wavelength of the sound wave, for example, about 1 to 8 cm.
  • the heat exchanger 3 is provided in the waveguide 2.
  • the heat exchanger 3 has a low temperature section 4, a high temperature section 5, and a temperature gradient holding section 6.
  • the low temperature section 4 is a member included in the heat exchanger 3 that maintains a relatively low temperature.
  • the high temperature unit 5 is a member included in the heat exchanger 3 that maintains a relatively high temperature.
  • the relatively low temperature and the relatively high temperature are based on the contrast between the temperature of the low temperature portion 4 and the temperature of the high temperature portion 5. That is, the temperature of the high temperature portion 5 is higher than the temperature of the low temperature portion 4.
  • a temperature gradient is generated between the low temperature portion 4 and the high temperature portion 5. The configuration of the low temperature section 4 and the high temperature section 5 will be described later.
  • the low temperature section 4 and the high temperature section 5 are connected to a heat source having a relatively low temperature and a heat source having a relatively high temperature, respectively.
  • the heat source at a relatively low temperature may be, for example, a refrigerant such as water supplied to a pipe.
  • the heat source at a relatively high temperature may be a heating medium such as hot water supplied to the pipe.
  • One of the relatively low temperature heat source and the relatively high temperature heat source may be, for example, air at room temperature.
  • the temperature gradient holding portion 6 is a member that holds the temperature gradient generated between the low temperature portion 4 and the high temperature portion 5 of the heat exchanger 3.
  • the temperature gradient holding portion 6 is provided between the low temperature portion 4 and the high temperature portion 5 of the heat exchanger 3.
  • the temperature gradient holding unit 6 generates and amplifies a sound wave in the gas G by the temperature gradient generated between the low temperature unit 4 and the high temperature unit 5.
  • the configuration of the temperature gradient holding unit 6 will be described later.
  • the exciter 7 generates a sound wave in the gas G at a predetermined frequency.
  • the exciter 7 is provided in the waveguide 2 so as to seal the gas G.
  • the pressure of the gas G is caused by the reciprocating motion of the piston inserted in the cylinder provided so as not to change the acoustic impedance of the waveguide 2. Is configured to vibrate.
  • the sound wave can be excited by environmental noise of about 200 Hz existing in the natural world, and the exciter 7 may be omitted when generating such a low frequency audible sound wave.
  • the converter 8 converts the acoustic energy of the sound wave generated in the gas G into a predetermined energy and extracts the predetermined energy.
  • the converter 8 may be, for example, a generator that generates electricity by converting the acoustic energy of the sound wave generated in the gas G into electric energy.
  • the thermoacoustic device 1 can generate electricity by using, for example, the heat supplied from the heat source to the heat exchanger 3.
  • the converter 8 is, for example, a cooler (heat exchanger for cooling) that lowers the temperature of the medium in contact with the converter 8 by converting the acoustic energy of the sound wave generated in the gas G into cooling energy. You may.
  • the thermoacoustic device 1 can cool the medium by using, for example, the heat supplied from the heat source to the heat exchanger 3.
  • thermoacoustic device 1 for example, the gas G filled in the waveguide 2 is vibrated at a predetermined frequency by the exciter 7. For example, this vibration causes the gas G to move from the low temperature side to the high temperature side of the temperature gradient holding portion 6 in the heat exchanger 3.
  • the gas G is heated and expanded by the temperature gradient held by the temperature gradient holding unit 6.
  • the gas G moves from the high temperature side to the low temperature side of the temperature gradient holding portion 6 in the heat exchanger 3.
  • the gas G is cooled and contracted by the temperature gradient held by the temperature gradient holding unit 6.
  • the sound wave of the gas G filled in the waveguide 2 is amplified by the repeated expansion and contraction of the gas G in the heat exchanger 3, and the heat energy is converted into the sound energy of the sound wave of the gas G.
  • the sound wave generated in the gas G filled in the waveguide 2 by the exciter 7 can be excited at a predetermined frequency.
  • the sound wave generated in the gas G is amplified and resonates by the heat exchanger 3 in the waveguide 2.
  • the converter 8 can convert the acoustic energy of the sound wave generated in the gas G into a predetermined energy and extract the predetermined energy.
  • FIG. 2 is a diagram showing an example of a high temperature portion 5 of the heat exchanger 3 included in the thermoacoustic device 1 according to the embodiment.
  • the high temperature portion 5 of the heat exchanger 3 has a substantially cylindrical shape as shown in FIG. 2, for example, when the cross section of the waveguide 2 is circular.
  • the thickness of the high temperature portion 5 of the heat exchanger 3 in the direction of the central axis (X-axis direction) is, for example, 0.5 cm or more and 3 cm or less.
  • the high temperature portion 5 of the heat exchanger 3 has, for example, a plurality of fins 5a and 5b having planes whose normals are orthogonal to the direction of the central axis (X-axis direction) and orthogonal to each other.
  • the high temperature portion 5 of the heat exchanger 3 has grid-shaped fins 5a and 5b.
  • the high temperature portion 5 of the heat exchanger 3 may be a superposition of grid-like fin structures at different intervals, and a parallel flat plate fin structure is provided as a part of the superposition of the grid-like fin structures of the high temperature portion 5. May be.
  • the plurality of fins 5a and 5b are formed of, for example, metal. In this case, the thermal conductivity of the plurality of fins 5a and 5b can be improved.
  • the metal forming the plurality of fins 5a and 5b is, for example, copper. In this case, the cost of the plurality of fins 5a and 5b can be reduced, and the heat conduction amount of the plurality of fins 5a and 5b can be set high.
  • the distance between the plurality of fins 5a and 5b is, for example, 0.4 mm or more and 15.0 mm or less.
  • the plurality of fins 5a and 5b may be configured by superimposing fin structures having different intervals in the direction of the central axis (X-axis direction).
  • the thicknesses of the plurality of fins 5a and 5b can be changed according to the fin spacing so that the heat conduction amounts are the same.
  • the thickness of the plurality of fins 5a and 5b is, for example, 100 ⁇ m or more and 2.0 mm or less.
  • the low temperature portion 4 of the heat exchanger 3 has the same or similar structure as the structure of the high temperature portion 5 of the heat exchanger 3.
  • FIG. 3 is a diagram showing an example of the temperature gradient holding unit 6 of the heat exchanger 3 included in the thermoacoustic device 1 according to the embodiment.
  • the temperature gradient holding portion 6 of the heat exchanger 3 has a substantially cylindrical shape as shown in FIG. 3, for example, when the cross section of the waveguide 2 is circular.
  • the length of the temperature gradient holding portion 6 of the heat exchanger 3 in the direction of the central axis (X-axis direction) is, for example, 1 cm or more and 3 cm or less. In this case, by obtaining the amplitude of the effective magnitude of the sound wave, it is possible to obtain the effective output of the acoustic energy of the sound wave converted from the thermal energy of the temperature gradient holding unit 6.
  • the temperature gradient holding portion 6 of the heat exchanger 3 has, for example, a plurality of fins 6a having surfaces whose normals are orthogonal to the direction of the central axis (X-axis direction) and parallel to each other.
  • the temperature gradient holding portion 6 of the heat exchanger 3 has, for example, a plurality of partitions 6b provided between the plurality of fins 6a.
  • the plurality of fins 6a (and the plurality of partitions 6b) are a plurality of members for partitioning a space provided so that the gas G is advected between the low temperature portion 4 and the high temperature portion 5.
  • the plurality of fins 6a (and the plurality of partitions 6b) function as a heat conductive member that transfers heat corresponding to the temperature gradient held by the temperature gradient holding portion 6 (heat of the temperature gradient holding portion 6) to the gas G.
  • the plurality of fins 6a can be supported by the fin structure of the high temperature portion 5 and / or the low temperature portion 4.
  • the plurality of fins 6a and the plurality of partitions 6b are formed of, for example, ceramic and / or glass having low thermal conductivity. In this case, the thermal conductivity of the plurality of fins 6a and the plurality of partitions 6b can be reduced. Therefore, it is possible to suppress the reduction of the temperature gradient in the temperature gradient holding portion 6 of the heat exchanger 3. Accordingly, the temperature gradient holding portion 6 can satisfactorily hold the temperature gradient generated between the low temperature portion 4 and the high temperature portion 5 of the heat exchanger 3.
  • the ceramic forming the plurality of fins 6a and the plurality of partitions 6b is, for example, zirconia, titania, or steatite.
  • the thermal conductivity of the plurality of fins 6a and the plurality of partitions 6b can be satisfactorily reduced with respect to the thermal conductivity of the plurality of fins 6a and the plurality of partitions 6b to the gas G. Therefore, the temperature gradient holding portion 6 can improve the heat conduction from the plurality of fins 6a and the plurality of partitions 6b to the gas G. Accordingly, the temperature gradient holding section 6 can easily hold a desired temperature gradient between the low temperature section 4 and the high temperature section 5 of the heat exchanger 3.
  • the thickness of the plurality of fins 6a is, for example, 100 ⁇ m or less.
  • the distance d F between the plurality of fins 6a as shown in FIG. 3 is, for example, 0.25 mm or more and 1.5 mm or less.
  • the thickness of the plurality of partitions 6b and the spacing between the plurality of partitions 6b are appropriately determined.
  • the plurality of fins 6a and the plurality of partitions 6b may be integrally shaped and manufactured.
  • the plurality of partitions 6b are unnecessary.
  • FIG. 4 is a diagram illustrating a physical quantity relating to a relational expression between the phase velocity of a sound wave and the temperature rising or falling rate of the gas G in the thermoacoustic device 1 according to the embodiment.
  • the density, specific heat, thermal conductivity, viscosity coefficient, and speed of sound of the gas G filled in the waveguide 2 are determined by ⁇ G , c G , ⁇ G , ⁇ G , and v G , respectively. show.
  • the wavelength of the sound wave generated in the gas G is represented by ⁇ .
  • the temperatures of the low temperature section 4 and the high temperature section 5 of the heat exchanger 3 are represented by T 1 and T 2 , respectively.
  • T 1 and T 2 satisfy the relationship T 2 > T 1 .
  • the temperature difference held by the temperature gradient holding portion 6 of the heat exchanger 3 is represented by ⁇ T.
  • the temperature rise or fall rate of the gas G in the temperature gradient holding portion 6 of the heat exchanger 3 is the temperature of the gas G (x, y, z, t) when the temperature of the gas G is expressed as TG (x, y, z, t).
  • x, y, and z represent a position in the X-axis direction, a position in the Y-axis direction, and a position in the Z-axis direction with respect to the center of the temperature gradient holding portion 6, respectively.
  • the temperature gradient can be obtained by dividing the temperature difference ⁇ T by the length of the temperature gradient holding portion 6 in the X-axis direction.
  • the temperature of the plurality of fins 6a at the position x with respect to the center in the X-axis direction of the temperature gradient holding portion 6 can be expressed by g ⁇ x.
  • the particles constituting the gas G vibrate as sound waves.
  • the position x of the particles constituting the gas G at time t is represented by the displacement A ⁇ sin ( ⁇ t) of the sound wave
  • the temperature of the plurality of fins 6a in the temperature gradient holding portion 6 causes the transfer vibration of the gas G.
  • it is vibrating at gA ⁇ sin ( ⁇ t).
  • A is the amplitude of the sound wave
  • ⁇ is the phase velocity of the sound wave obtained by multiplying the vibration frequency f of the sound wave by 2 ⁇ .
  • T G (y, z) i ⁇ G / ( ⁇ G c G ⁇ ) ⁇ 2 T G (y, z) ...
  • i an imaginary unit
  • ⁇ is a nabla in the plane stretched by the Y-axis and the Z-axis
  • ⁇ 2 is the Laplacian in the plane stretched by the Y-axis and the Z-axis).
  • ⁇ G / ( ⁇ G c G ⁇ r 02 ) is a dimensionless quantity, and if this is written as 1 / ( 2 ⁇ ), the equation (3) is written as follows.
  • Equation (4) means that the temperature TG of the gas G sandwiched between the plurality of fins 6a is determined by the value of ⁇ alone.
  • ⁇ means the time constant of the time required for the ascending / descending temperature of the gas G.
  • ⁇ is written as ⁇ G c G r 0 2 / ( 2 ⁇ G ).
  • the heat of the temperature gradient holding unit 6 can be converted into the sound wave most efficiently. That is, the length of the waveguide 2 is designed, and the phase velocity ⁇ of the sound wave is set so that the length of the waveguide 2 is an integral multiple of the wavelength ⁇ of the sound wave in consideration of the sound velocity v G of the gas G. ..
  • r 0 is adjusted so that ⁇ ⁇ represented by ⁇ G / ( ⁇ G c G ) for the gas G and r 0 which is half of the interval d F of the plurality of fins 6a satisfies the equation (5).
  • ⁇ ⁇ represented by ⁇ G / ( ⁇ G c G ) for the gas G and r 0 which is half of the interval d F of the plurality of fins 6a
  • FIG. 5 is a diagram illustrating several examples of the shape of the heat conductive member in the partial cross section of the temperature gradient holding portion 6 according to the embodiment.
  • the heat conductive member included in the temperature gradient holding portion 6 surrounding the gas G on a plane perpendicular to the X-axis direction is (a) a heat conductive member in the shape of a honeycomb air column tube, as shown in FIG.
  • Table 1 shows ⁇ when heat can be most efficiently transferred from the temperature gradient holding unit 6 obtained as a result to the gas G as f P defined by the following equation.
  • f P 1 / ⁇ ... (6)
  • f P depends on the ratio R 0 / d F of the distance d F between the radius R 0 of the linear heat conductive member and the linear heat conductive member as shown in FIG. Has changed, and Table 1 shows three cases where this ratio is 0.17, 0.33, 0.5, etc. as an example.
  • the gas G has viscosity, and a viscous resistance is generated in the sound wave advected in the temperature gradient holding portion 6. For this reason, a viscous loss is generated in the sound wave, and the sound energy is reduced.
  • the advection velocity of the sound wave generated in the gas G is u G
  • the following equation regarding the advection velocity u G can be obtained from the equation of motion of the gas (Navier-Stokes equation).
  • u G (y, z) i / (2 ⁇ ⁇ ) ⁇ 0 2 u G (y, z) ...
  • Equation (7) is the same equation as equation (4) except for the coefficient, and the advection rate uG of the gas G at the position in contact with the heat conduction member of the temperature gradient holding portion 6 is set to the heat conduction member as in equation (4). Since Eq.
  • the Prandtl number ⁇ does not depend substantially on the pressure P, but only slightly depends on the temperature.
  • 1 / ⁇ ⁇ needs to be at least one tenth, preferably one hundredth or less (insulation region). Therefore, when the heat conduction from the temperature gradient holding portion 6 to the gas G is optimized, there is a problem that the energy dissipation of the sound wave vibration due to the viscosity becomes very large even if 1 / ⁇ ⁇ is slightly smaller than f P. be.
  • the equation of motion regarding the advection displacement S including the resistance to the gas G on the surface of the heat conductive member of the temperature gradient holding portion 6 is written as the following equation (9).
  • the advection velocity uG of the sound wave is written as dS / dt using the advection displacement S.
  • ⁇ G d 2 S / dt 2 ⁇ G Pd 2 S / dx 2 - ⁇ W dS / dt ⁇ ⁇ ⁇ ⁇ (9)
  • P is the pressure of the gas G
  • ⁇ G is the specific heat ratio of the gas G
  • ⁇ W is the resistance coefficient due to the surface roughness of the surface of the heat conductive member of the temperature gradient holding portion 6.
  • ⁇ G0 is the density ⁇ G of the gas G when the atmospheric pressure is 1 atm. From the equation (11), in order to increase the sliding distance of the gas G, reduce ⁇ W (proportional to the surface roughness of the surface of the heat conductive member of the temperature gradient holding portion 6) or reduce the gas G at 1 atm. It can be seen that increasing the density ⁇ G0 (proportional to the molecular weight of the gas G) and / or increasing the pressure P of the gas G is effective.
  • the surface of the heat conductive member in contact with the gas G of the temperature gradient holding portion 6 is preferably a mirror surface.
  • the surface roughness (arithmetic mean roughness Ra) is preferably, for example, 30 nm or less. It is more preferable that the surface roughness (Ra) is at the level of several nm.
  • the surface roughness (Ra) is at the sub ⁇ m level.
  • the distance of the gas G sliding on the surface of the heat conductive member of the temperature gradient holding portion 6 can be increased.
  • the molecular weight of air (the average molecular weight of air) is about 29, the molecular weight of nitrogen is 28, the molecular weight of He is 4, and the molecular weight of Ar is 40.
  • the sliding distance can be increased by about 2.7 times. If He is replaced with Ar, the sliding distance can be increased by about 3.2 times.
  • the average molecular weight of air decreases slightly as the humidity increases, it is preferable to select air because it is easy to manufacture and maintain the thermoacoustic device 1 that uses air as the gas G.
  • the slip of the gas G on the surface of the heat conductive member of the temperature gradient holding portion 6 can be increased.
  • the slip of the gas G can be increased by several tens of times by increasing the pressure P from 1 atm.
  • the thermoacoustic system can be driven by increasing the pressure of the gas to 10 atm (10132.5 hPa) to 30 atm.
  • the waveguide needs to have high compressive strength and / or increased sealing accuracy for the gas, which is costly, including maintenance of the thermoacoustic system as well as the waveguide. It will be a factor to raise.
  • FIG. 1 shows an example in which an exciter 7 is provided so as to excite a sound wave at the resonance frequency of the waveguide 2.
  • the wavelength ⁇ of the sound wave is determined according to this frequency region and the sound velocity v G of the gas G, and the waveguide that resonates this sound wave.
  • the length of the tube 2 is determined as an integral multiple of the wavelength ⁇ .
  • the speed of sound v G of the gas G does not depend on ⁇ G and is only slightly changed with temperature.
  • Table 2 shows the speed of sound v G of some kinds of gases G near room temperature.
  • the speed of sound v G of air, nitrogen, and Ar is about the same magnitude, and the speed of sound v G of He is about three times the speed of sound v G of air.
  • the speed of sound v G of carbon dioxide is the smallest. Since the wavelength ⁇ of the sound wave increases in proportion to the speed of sound v G of the gas G under the same frequency, in order to create a compact waveguide 2 system under the same frequency, the gas G is used. Air, nitrogen, and / or carbon dioxide, etc., which have a low sound velocity vG , are preferable.
  • the wavelength ⁇ of the sound wave is about 1.65 m, and when designing the length of the waveguide 2 with one wavelength, this is used.
  • a waveguide 2 of a size loop will be provided.
  • the shape of the surface of the loop is a substantially elliptical shape having a major axis and a minor axis
  • the size of the surface of the loop is about 60 cm (major axis) x 15 cm (minor axis), and one loop is twisted and overlapped.
  • the waveguide 2 is manufactured with an elliptical double loop, the size of the surface of the loop is about 25 cm (long axis) ⁇ 12 cm (short axis).
  • the wavelength ⁇ of the sound wave is 4.85 m, which shows that it is not suitable for constructing a compact system.
  • thermoacoustic system can be achieved by, for example, providing an exciter 7 of 700 to 1 kHz to excite a sound having a frequency several times higher than the frequency of environmental noise.
  • the wavelength ⁇ is changed by using the exciter 7 to make a compact design is described below.
  • ⁇ / P ⁇ f P r 0 2 ⁇ G0 c G v G / ⁇ G ... (12)
  • Table 2 shows the values of ⁇ G0 c G v G / ⁇ G on the right side of the equation (12) for various gases G.
  • the length of the waveguide 2 is set to an integral multiple of the wavelength ⁇ of the sound wave. Therefore, it can be seen that the method of reducing the viscous loss by increasing the pressure P is not appropriate for the design of the compact waveguide 2. For example, in order to raise the pressure P to about 10 atm and maintain the size of the waveguide 2, it is necessary to reduce dF to about 1/3.
  • Table 2 shows d F satisfying equation (6) for several types of gas G at a frequency of 200 Hz, where the pressure P of the gas G is 1 atm and the f P is 1.
  • dF is about 0.4 mm, which is within the practical design range.
  • the wavelength ⁇ of the sound wave is 1.29 m, and d F is about 0.3 mm. This d F is a practical value capable of manufacturing a compact temperature gradient holding portion 6.
  • the pressure P of the gas G such as air and / or nitrogen from the equation (12) in order to keep dF within the range of practical design. It can be seen that it is preferable to change the design according to the frequency of the environmental noise that can be used, such as setting the pressure to 1 atm to 5 atm (5066.25 hPa).
  • ⁇ G0 c G v G / ⁇ G is about 1/2 of that in the case of air, and it can be seen that the pressure P cannot be greatly increased while the wavelength ⁇ is kept constant.
  • the original purpose is to increase the pressure P in order to reduce the viscous loss, at the same time, using a light element such as He and / or hydrogen having a small ⁇ G0 is as shown in the formula (11). It can be seen that the effect opposite to the effect of reducing the viscous loss is brought about.
  • thermoacoustic device is operated by environmental noise.
  • the gas is He
  • environmental noise is used as the excitation source
  • the wavelength that is, the size of the waveguide becomes large, and the size becomes at least about 5 m. ..
  • the pressure is increased for the purpose of operating the thermoacoustic device by using the honeycomb-shaped temperature gradient holding portion, it is necessary to adopt a sealing structure for maintaining the gas pressure by using, for example, stainless steel (SUS) or the like. Therefore, it is inevitable that the thermoacoustic device will have high device cost and maintenance cost.
  • SUS stainless steel
  • the size of the waveguide 2 that resonates the sound and the temperature gradient holding portion 6 is designed according to the physical property values such as the thermal conductivity and / or the heat capacity of the gas G, and the viscous loss is reduced to reduce the acoustic energy conversion efficiency.
  • the surface of the heat conductive member in contact with the gas G of the temperature gradient holding portion 6 is made a mirror surface, or the molecular weight of the gas G is increased so as to be equal to or more than the average molecular weight of air or the molecular weight of nitrogen. , It is preferable to increase the pressure P of the gas G (about 30 atm).
  • the surface of the heat conductive member of the temperature gradient holding portion 6 is made a mirror surface, or the molecular weight of the gas G is set to be equal to or higher than the average molecular weight of air or the molecular weight of nitrogen. It is preferable to select a means for increasing the pressure so as to be as high as possible and lowering the pressure P so as to be about 1 atm. When the pressure P is set to 1 atm, the wavelength ⁇ can be reduced and the waveguide 2 can be made compact.
  • the waveguide 2 can be formed of a plastic such as vinyl chloride, and has a loop shape.
  • the waveguide 2 can be easily manufactured, and the maintenance cost of the waveguide 2 can be reduced.
  • the pressure P should be about 1 atm to 5 atm. It is preferable to select a means for lowering the temperature, making the surface of the heat conductive member of the temperature gradient holding portion 6 a mirror surface, and increasing the molecular weight of the gas G so as to be equal to or higher than the average molecular weight of air or the molecular weight of nitrogen.
  • the pressure P is set to about 1 atm so that the wavelength ⁇ of the sound wave, which becomes long due to the low frequency of the environmental noise, does not become longer, and at the same time, the viscous loss is reduced.
  • a temperature gradient holding portion 6 having a mirror surface on the surface of the heat conductive member is adopted.
  • the wavelength ⁇ becomes about 1/2 of that of air.
  • d F is made smaller by selecting a gas G with a small molecular weight such as He, the value ⁇ G0 c G v G / ⁇ G is about 1/2 smaller than that of air or the like, so d F is made too small.
  • the temperature gradient holding portion 6 is relatively easy to design and manufacture.
  • thermoacoustic device 1 in order to design a more compact thermoacoustic device 1 in the above, a sound wave is excited at a frequency higher than the frequency of environmental noise by using an exciter 7, and the pressure P is lowered to about 1 atm. It is more preferable to select a means for making the surface of the heat conductive member of the temperature gradient holding portion 6 a mirror surface and making the gas G a gas such as He and / or hydrogen having a small value ⁇ G0 c G v G / ⁇ G. By doing so, even if the resonance frequency is higher than the frequency of the environmental noise, it is possible to prevent the distance dF between the plurality of components constituting the heat conductive member from becoming extremely small, and the temperature gradient holding unit. It is avoided that the production of 6 becomes difficult.
  • the pressure P is lowered to about 1 atm, and the temperature gradient. It is preferable to select a means for making the surface of the heat conductive member of the holding portion 6 a mirror surface and reducing the distance d F between a plurality of components constituting the heat conductive member. By doing so, even if the wavelength ⁇ of the gas G is reduced by making the resonance frequency higher than the frequency of the environmental noise, the gas G in which ⁇ G0 c G v G / ⁇ G in the equation (12) is small.
  • the need to select a gas G is reduced, and thus it is possible to avoid making the gas G a gas such as He and / or hydrogen having a small molecular weight, so that the viscosity loss due to the gas G having a large molecular weight represented by the formula (11) is reduced.
  • the temperature gradient holding portion 6 that maintains the effect can be manufactured.
  • the pressure P is lowered to about 1 atm and the temperature gradient is applied.
  • a means for reducing d F by making the surface of the heat conductive member of the holding portion 6 a mirror surface and selecting a gas such as He and / or hydrogen having a small value ⁇ G 0 c G v G / ⁇ G for the gas G. It is preferable to choose. By doing so, even if the wavelength ⁇ of the gas G is reduced by making the resonance frequency higher than the frequency of the environmental noise, the value of the gas G such as He and / or hydrogen ⁇ G0 c G v G /. Since ⁇ G is smaller than that of air or the like, the degree to which the value of d F is reduced is reduced, and the design and fabrication of the temperature gradient holding portion 6 becomes relatively easy.
  • thermoacoustic device 1 In order to design a compact thermoacoustic device 1 by exciting a sound wave at a frequency higher than the frequency of environmental noise using an exciter 7, a method of further lowering the pressure P to 1 atm can be mentioned. As can be seen from the equation (12), by lowering the pressure P further than 1 atm, the wavelength ⁇ can be changed without changing the distance d F or the gas G between the plurality of components constituting the heat conductive member on the right side.
  • the thermoacoustic device 1 can be made smaller and more compact. In this case, it is necessary to keep the airtightness high by using a stainless steel (SUS) material or the like for the waveguide 2 as in the case of increasing the pressure P.
  • SUS stainless steel
  • thermoacoustic device 1 it is necessary to design the thermoacoustic device 1 on the premise of these things. ..
  • Table 1 shows the sound waves in the case of the shape of each heat conductive member (the shape of the air column tube of the honeycomb, the shape of the square column tube, the shape of the parallel fins, the shape of the line) in the space where the gas G of the temperature gradient holding portion 6 flows as a sound wave.
  • ⁇ and f P depend on the ratio of the radius R 0 of the linear heat conductive member and the distance d F between the plurality of linear heat conductive members, so that there are three cases (R).
  • Table 2 Physical characteristics of various gases and design examples of thermoacoustic device 1.
  • Table 2 shows the physical quantities of various gases G (air, nitrogen, helium (He), argon (Ar), hydrogen, or carbon dioxide) when the pressure P is 1 atm, and the environmental noise of 200 Hz at 1 atm.
  • G air, nitrogen, helium (He), argon (Ar), hydrogen, or carbon dioxide
  • f P was set to 1.0.
  • the waveguide 2 is filled with the gas G, but the waveguide 2 may be filled with a medium other than the gas G.
  • the waveguide 2 may be filled with a liquid in a range in which sound waves are effectively generated and amplified.
  • thermoacoustic device 1 it is assumed that the waveguide 2 has the shape of a single loop, but the waveguide 2 has, for example, the shape of a plurality of loops connected by at least one tube. You may have.
  • the thermoacoustic device 1 may have a plurality of heat exchangers 3 and / or a plurality of converters 8 in the same loop or different loops of the waveguide 2.
  • thermoacoustic device 1 the gas G filled in the waveguide 2 is vibrated or excited by the exciter 7, but the thermoacoustic device 1 does not include the exciter 7. You may.
  • thermoacoustic device 1 uses, for example, the heat energy supplied to the heat exchanger 3 as the acoustic energy of the sound wave generated in the gas G. Can be converted.
  • the efficiency of converting thermal energy into sound energy can be improved.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)

Abstract

L'invention concerne un dispositif thermoacoustique qui comprend un guide d'ondes en forme de boucle et un échangeur de chaleur. Le guide d'ondes en forme de boucle est rempli d'un milieu. L'échangeur de chaleur est disposé à l'intérieur du guide d'ondes et comprend une partie basse température et une partie haute température. L'échangeur de chaleur comprend aussi une partie de maintien de gradient qui est disposée entre la partie basse température et la partie haute température, et qui maintient le gradient de température généré entre la partie basse température et la partie haute température. La partie de maintien de gradient de température présente une pluralité d'éléments de conduction de chaleur qui transfèrent de la chaleur au milieu selon le gradient de température. L'espacement entre la pluralité d'éléments de conduction thermique est réglé de telle sorte que la vitesse de phase des ondes sonores générées et amplifiées dans le milieu par le gradient de température correspond à la montée en température ou à la vitesse de chute du milieu provoqué par le gradient de température. La longueur du guide d'ondes correspond à la vitesse de phase des ondes sonores.
PCT/JP2021/005872 2020-07-31 2021-02-17 Dispositif thermoacoustique WO2022024426A1 (fr)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005351224A (ja) * 2004-06-11 2005-12-22 Toyota Motor Corp 熱音響エンジン
JP2013148282A (ja) * 2012-01-19 2013-08-01 Honda Motor Co Ltd 熱音響機関
WO2019026217A1 (fr) * 2017-08-02 2019-02-07 北海道特殊飼料株式会社 Système thermoacoustique
WO2020045600A1 (fr) * 2018-08-31 2020-03-05 京セラ株式会社 Dispositif thermoacoustique

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2005351224A (ja) * 2004-06-11 2005-12-22 Toyota Motor Corp 熱音響エンジン
JP2013148282A (ja) * 2012-01-19 2013-08-01 Honda Motor Co Ltd 熱音響機関
WO2019026217A1 (fr) * 2017-08-02 2019-02-07 北海道特殊飼料株式会社 Système thermoacoustique
WO2020045600A1 (fr) * 2018-08-31 2020-03-05 京セラ株式会社 Dispositif thermoacoustique

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