JP3403446B2 - Gas pressure vibration generating method and apparatus, and refrigerator provided with pressure vibration generating apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a magnetic resonance imaging apparatus (MRI) and high resolution NMR spectroscopy (MR).
S) and other heat shield cooling, reliquefaction of helium gas in the cooling tank, or a refrigerator suitable for cooling elements such as superconducting quantum interference device (SQUID) and infrared detection sensor that require operation at low temperature, and The present invention relates to a method and an apparatus for generating pressure oscillation of gas in a refrigerator or the like.

[0002]

2. Description of the Related Art In order to generate cold in the above refrigerator, it is necessary to change the pressure of the working gas. Conventionally, a compressor is generally used as a means for that purpose.

For example, in a Gifford-McMahon (GM) refrigerator, which is often used for heat shield cooling such as MRI and reliquefaction of helium gas in a cooling tank, a mechanical compressor is arranged outside the refrigerator. This compressor continuously compresses low-pressure gas to high pressure, and by switching the rotary valve and solenoid valve provided between this compressor and the refrigerator,
High pressure gas is supplied into the refrigerator from the compressor, and low pressure gas is caused to flow out from the refrigerator.

In addition, SQUID, infrared detection sensor, etc.
In Stirling refrigerators that are often used to cool elements that require low-temperature operation, a compressor is placed near this refrigerator, and the piston and diaphragm are reciprocated in the compressor chamber to cycle the volume of the compressor chamber. The pressure oscillation of the working gas is generated by changing the pressure.

However, in a refrigerator using a piston type compressor, mechanical oil is indispensable for the seal portion of the piston, and it is impossible to completely prevent this oil from being mixed in the working gas. Therefore, when operating for a long time, the oil content may gradually solidify in the low temperature portion of the refrigerator, enter the sliding portion such as the displacer, and stop the movement. For this reason, maintenance such as periodical parts replacement and gas replacement is indispensable for this compressor, and there is an inconvenience that the refrigerator cannot be continuously operated for a long time. Further, since there are many moving parts in the compressor, metal fatigue is likely to occur, and the reliability of the refrigerator is likely to decrease.

Further, in the diaphragm type compressor, there is a possibility that mechanical vibration is generated from the compressor due to the movement of the diaphragm and is transmitted to the refrigerator. In particular, when the object to be cooled by the refrigerator is an infrared sensor, the infrared sensor is usually arranged on the microchip at intervals of about several tens of μm, and when mechanical vibration is transmitted to the infrared sensor, infrared rays are transmitted. It is practically impossible to use the diaphragm compressor for cooling such an infrared sensor because the element into which is incident is changed and the resolution of the sensor is lowered.

On the other hand, in a device that uses a solenoid valve or a rotary valve to generate pressure fluctuations, the solenoid valve and the like must be arranged in the vicinity of the refrigerator in order not to reduce the pressure vibration applied to the refrigerator. The electromagnetic noise generated directly from the rotary valve drive motor or the electromagnetic valve is apt to be applied to the cooled object. In particular, when the object to be cooled is MRI or MRS, if the detection signal (NMR signal) is mixed with the electromagnetic noise, the resolution of the device may be significantly reduced.

Therefore, in recent years, a so-called thermoacoustic oscillator has been proposed as a means for generating gas pressure oscillation. This thermoacoustic oscillator has a temperature gradient on a predetermined wall body and causes the gas to self-oscillate at a predetermined resonance frequency along the wall body due to the temperature gradient. It has the function of converting and increasing the amplitude of the small gas given as an initial investment.

By using such a thermoacoustic oscillator, sinusoidal pressure vibration can be generated in the working gas without using a mechanical compressor, a solenoid valve or the like.

[0010]

The pressure oscillation frequency of the working gas for operating the ordinary refrigerator efficiently is relatively low, generally 50 Hz or less. On the other hand, the thermoacoustic oscillator generally resonates sound waves in the tube,
The resonance frequency is determined by the tube length, and the tube length must be set large in order to obtain a low frequency. Therefore, when the thermoacoustic oscillator is used in the refrigerator requiring the gas pressure oscillation of 50 Hz or less as described above, the pipe length must be extended to several tens of meters, and as a result, for example, the thermoacoustic oscillator 40 shown in FIG. As described above, a special device such as forming the resonance tube in a loop shape is required, and it is unavoidable that the cost is high and the size of the entire apparatus is large.

In view of the above circumstances, the present invention provides a method, an apparatus, and a device capable of generating low-frequency gas pressure oscillation using the thermoacoustic oscillator without increasing the size of the thermoacoustic oscillator. It aims at providing the refrigerator provided with.

[0012]

As a method for solving the above problems, the present invention provides a first thermoacoustic oscillator for vibrating a gas pressure at a first frequency, and a gas pressure at a second frequency. A frequency equal to the frequency of this beat is obtained by connecting a second thermoacoustic oscillator to be oscillated, superimposing pressure vibrations generated from both thermoacoustic oscillators to generate a beat, and extracting and rectifying this beat component. A pressure oscillation of the gas having

The present invention also provides, as an apparatus for carrying out the above method, a first thermoacoustic oscillator for vibrating the gas pressure at a first frequency and a second thermoacoustic oscillator for vibrating the gas pressure at a second frequency. By connecting the thermoacoustic oscillator and the connecting pipe that connects both thermoacoustic oscillators and this pipe, and extracting and rectifying the beat component generated by the superposition of the pressure vibrations emitted from both thermoacoustic oscillators. The pressure vibration generating means for generating pressure vibration of the gas having a frequency equal to the beat frequency is provided (claim 2).

As the pressure vibration generating means, an internal pressure holding tank whose internal pressure is kept substantially constant, the internal pressure holding tank and the connecting pipe line are connected, and a connecting pipe is formed by a gas flow due to a difference in internal pressure between the two. Pressure vibration extracting means for extracting pressure vibration of gas having a frequency component equal to the beat frequency in the passage, and filter means for removing high frequency components of pressure vibration of gas extracted by the pressure oscillation extracting means Is preferred (claim 3).

By storing the hydrogen storage alloy in the internal pressure holding tank, the following advantageous effects can be obtained (claim 4).

The present invention also provides any one of the pressure vibration generators described above, and a refrigerator main body which is connected to the pressure vibration generation means of the pressure vibration generator and generates cold by utilizing the pressure vibrations of the working gas. A refrigerator provided with (Claim 5).

[0017]

According to the method of claim 1, the gas pressure oscillation of the first frequency oscillated from the first thermoacoustic oscillator, and the second
By superimposing it with the gas pressure oscillation of the second frequency oscillated from the thermoacoustic oscillator, it is possible to generate an oscillation (that is, beat) of an amplitude having a frequency equal to the difference between the two frequencies. Is taken out and rectified, it is possible to generate a pressure oscillation of the gas having a frequency equal to the beat frequency, that is, equal to the difference between the first frequency and the second frequency.

In the apparatus according to the second aspect of the present invention, the pressure vibrations of the gas oscillated from both thermoacoustic oscillators are superposed on each other in the connecting conduit, and the beat component generated thereby is taken out by the pressure vibration generating means and rectified. This produces a pressure oscillation of the gas with a frequency equal to the beat frequency.

More specifically, in the apparatus according to claim 3,
A gas flow occurs between the connection pipeline and the internal pressure holding tank due to the pressure fluctuation of the gas in the connection pipeline, and this flow causes a low frequency component equal to the frequency of the beat in the connection pipeline. The pressure oscillations of the gas contained therein are taken out and the high frequency components of this pressure oscillation are removed by the filter means.

Here, in the apparatus according to the fourth aspect, hydrogen gas is used as the gas, and this gas is appropriately stored and released by the hydrogen storage alloy in the internal pressure holding tank, so that the internal pressure in the internal pressure holding tank is Can be held substantially constant.

In the refrigerator according to the fifth aspect of the invention, the pressure vibration generated by the pressure vibration generator is used, so that the refrigerator body is not subjected to mechanical vibration or electromagnetic noise application. The main body can be continuously operated at a suitable frequency for a long time.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS.

The refrigerator shown in FIG. 1 has a first thermoacoustic oscillator 1
0A, second thermoacoustic oscillator 10B, pressure vibration generation device 2
0 and the refrigerator main body 30 are provided.

The thermoacoustic oscillators 10A and 10B are provided with resonance tubes 11a and 11b, and inside the resonance tubes 11a and 11b,
High temperature heat exchangers 12a, 12b, stacks 14a, 14
b and room temperature heat exchangers 16a and 16b are arranged in this order.

Resonance tube 11a of the first thermoacoustic oscillator 10A
Has a tube length set such that its resonance frequency becomes the first (oscillation) frequency f1. The resonance tube 11b of the second thermoacoustic oscillator 10B has a resonance frequency of the second (oscillation) frequency f2 (≠ The tube length is set to be f1), and both frequencies f1 and f2 are absolute values of the difference | f1-f2.
| Is set so as to match the operating frequency (several Hz) of the refrigerator body 30 described later.

Each of the high temperature heat exchangers 12a and 12b is composed of a large number of thin metal plates arranged at minute intervals, and is maintained at about 900 ° C. by a heater or the like. Stacks 14a, 14
In b, a large number of thin-walled stainless steel plates (several hundreds of μm) are arranged at minute intervals (several hundreds of μm) as in the high temperature heat exchangers 12a and 12b.
It is arranged in (degree). Room temperature heat exchanger 16a,
16b is also one in which a large number of thin metal plates are arranged at minute intervals, and the surroundings are cooled by water cooling or the like and kept near room temperature, and the stack 14a, together with the high temperature heat exchangers 12a, 12b, A temperature gradient is generated along the wall surface of 14b.

The thickness δ ₁ and the interval δ ₂ of the stainless steel plates in the stacks 14a and 14b are preferably set based on the following equation.

[0028]

## EQU1 ## δ ₁ = 2√ (κ ₁ / πf) δ ₂ = 2√ (κ ₂ / πf) where κ ₁ and κ ₂ are the thermal diffusion coefficients of stainless steel and working gas, and f is the target resonance frequency. (F1 in the stack 14a,
In the stack 14b, it is f2).

The pressure outlet 18a of the first thermoacoustic oscillator 10A and the pressure outlet 1 of the second thermoacoustic oscillator 10B.
8b is connected via a connection conduit 15. In this connection conduit 15, a valve 17A is provided at a portion from the pressure outlet 18a of the first thermoacoustic oscillator 10A,
A valve 17B is provided in a portion from the pressure outlet 18b of the second thermoacoustic oscillator 10B, and both valves 17A and 17B are provided.
The intermediate point Pm of B is connected to the pressure vibration generating device 2 via the conduit 19.
0 is connected to the third relay point P3.

The pressure oscillation generator 20 has a hollow first cavity.
A buffer tank (internal pressure holding tank) 21 and four check valves 22A, 22B, 22C and 22D are provided. The third relay point P3 is connected to the first relay point P1 and the second relay point P2 via the check valves 22A and 22C, respectively,
The first buffer tank 21 has the first relay point P1 and the second relay point P2 via the check valves 22B and 22D, respectively.
It is connected to the. Both relay points P1 and P2 have a conduit 24 between them.
And a valve 25 is provided in the middle of the conduit 24.

Here, the first buffer tank 21 has a sufficiently large volume, and as described later, the third relay point P
Even if the pressure p of 3 vibrates, the internal pressure is maintained at a substantially constant pressure (initial filling pressure) po. The check valve 22A is configured to restrict the flow of gas from the first relay point P1 toward the third relay point P3.
2B is configured to regulate the flow of gas from the first relay point P1 toward the first buffer tank 21. In addition, the check valve 22C is configured to restrict the flow of gas from the third relay point P3 toward the second relay point P2, and the check valve 22D is configured to move from the first buffer tank 21 to the second relay point. It is configured to regulate the flow of gas toward P2.

A second buffer tank 28 is connected to the first relay point P1 via a valve 26 (filter means), and the second buffer tank 28 is connected to the refrigerator main body 30.

In this embodiment, the refrigerator main body 30 is of a pulse tube type, that is, a refrigerator which produces cold due to pressure vibration of the gas along the wall. Specifically, the refrigerator main body 30 includes a pulse tube 32 and a regenerator 34, both of which are connected to the second buffer tank 28, and the pulse tube 32 has a valve 36.
It is connected to the first buffer tank 21 via.

As the refrigerator main body 30, various conventionally known refrigerators and the like can be applied in addition to the pulse tube type illustrated. Also, when using the pulse tube type, not only the double inlet type in which the pulse tube 32 and the regenerator 34 are connected as shown in the drawing but also the orifice type in which this connection is not performed can be used. .

Next, the operation of this refrigerator will be described.

In both thermoacoustic oscillators 10A and 10B, the high temperature heat exchangers 12a and 12b and the room temperature heat exchanger 14 are used.
The temperature difference between the stacks 14a and 14b
A temperature gradient occurs in the resonance tube 1 due to this temperature gradient.
The pressure oscillations of the gas in 1a and 11b are excited, the gas pressure oscillation having the first frequency f1 is output from the pressure extraction port 18a of the first thermoacoustic oscillator 10A, and the pressure extraction of the second thermoacoustic oscillator 10B is performed. The gas pressure oscillation having the second frequency f2 is output from the port 18b.

Both vibrations are superposed in the connecting line 15,
It is transmitted to the third relay point P3 through the conduit 19. The vibration of the pressure p at the third relay point P3 is caused by both frequencies f1,
The average frequency of f2 is (f1 + f2) / 2, and its amplitude fluctuates as shown by the waveform C3 in FIGS. More specifically, this amplitude oscillates at the frequency of the absolute value | f1-f2 | of the difference between the two frequencies f1 and f2 (that is, a beat occurs).

In this way, the gas pressure oscillates at the third relay point P3, while the gas pressure is maintained at a substantially constant pressure po in the first buffer tank 21, so that the internal pressure po of the first buffer tank 21 and the A difference occurs with the pressure p at the three relay points P3, and this difference fluctuates with time.

Here, during the period when the pressure p at the third relay point P3 exceeds the internal pressure po of the first buffer tank 21 (period A1 in FIG. 3), the gas is the third gas due to the regulation of the check valves 22C and 22B. The relay point P3 → the check valve 22A → the first relay point P1 → the valve 25 → the second relay point P2 → the check valve 22D → the first buffer tank 21 flows in this order, and conversely the pressure p at the third relay point P3 During the period below the internal pressure po of the 1-buffer tank 21 (period A2 in FIG. 3), the gas is regulated by the check valves 22D and 22A, and the gas is the first buffer tank 21 → the check valve 22B → the first relay point P1 → the valve. Flow is in the order of 25 → second relay point P2 → check valve 22C → third relay point P3. Therefore, in the conduit 24, the gas always flows only in the direction from the first relay point P1 to the second relay point P2 while the flow rate increases and decreases at the frequency equal to the beat frequency, and both relay points P1, P
The vibration waveform of the pressure in 2 is the waveform C shown in FIGS.
The waveforms are close to the envelope of 3, that is, the waveforms C1 and C2 having low frequency components equal to the beat frequency.

The valve 26 and the second buffer tank 28 connected to the first relay point P1 perform the same function as the low-pass filter in the electric circuit, so that the waveform C1 in the second buffer tank 28 is maintained. Therefore, the pressure oscillation from which the high frequency component is removed will be observed. Therefore, this gas pressure oscillation causes the pulse tube 3 of the refrigerator main body 30.
2 and the regenerator 34, it is possible to operate the refrigerator main body 30 at the optimum frequency | f1-f2 | as a result.

Strictly speaking, the vibration transmitted to the refrigerator main body 30 slightly includes a high frequency component which is an integral multiple of the optimum frequency │f1-f2│, but in reality, the higher the frequency component, the faster the damping. Therefore, the operation of the refrigerator main body 30 is not substantially affected.

According to such a method and apparatus, since the pressure vibration of the gas is generated by the thermoacoustic oscillators 10A and 10B, the mechanical vibration and electromagnetic waves are generated as in the case of using the mechanical compressor as in the conventional case. The refrigerator main body 30 can be continuously operated for a long period of time without being applied with noise. Moreover, since the vibrations oscillated from the two thermoacoustic oscillators 10A and 10B are overlapped with each other and the beat is used to generate the low frequency vibration, the oscillation frequencies of the thermoacoustic oscillators 10A and 10B themselves are high. Good, therefore dual thermoacoustic oscillator 10
A relatively short tube length can be used for A and 10B to reduce the size of the entire apparatus.

Although helium is used as the working gas in this embodiment, any kind of gas may be used in the present invention.
For example, when hydrogen gas is used as the working gas in the apparatus of the above-described embodiment, even if a tank containing a hydrogen storage alloy is installed in place of the first buffer tank 21 having a hollow interior, the gas will flow into this tank. When the gas flows in, the alloy occludes the same gas, and conversely, when the gas flows out of the tank, the alloy releases the gas. Therefore, the first buffer tank 21
Similar to, it is possible to obtain the effect of keeping the internal pressure constant. Moreover, in this case, there is an advantage that a smaller-sized buffer tank can be used as the above-mentioned tank.

[0044]

As described above, according to the present invention, the following effects can be obtained.

In the method and the apparatus according to claims 1 to 3, the first thermoacoustic oscillator and the second thermoacoustic oscillator having different oscillation frequencies are used, and the pressure vibrations oscillated from the first thermoacoustic oscillator and the second thermoacoustic oscillator are superposed to generate a beat. Since this beat is used to generate a pressure oscillation having a frequency equal to this beat frequency, both thermoacoustic oscillators with a high oscillation frequency, that is, a small one, are used, while a low frequency is used. There is an effect that the gas pressure oscillation can be easily generated.

More specifically, in the apparatus according to claim 3,
To obtain a desired pressure vibration with a simple configuration in which a connection pipe connecting both thermoacoustic oscillators and an internal pressure holding tank are connected, and the pressure vibration of gas is taken out by the flow of gas generated by the difference in internal pressure between the two. You can

Further, in the apparatus according to claim 4, a small-sized internal pressure holding tank is obtained by storing a hydrogen storage alloy in the internal pressure holding tank and appropriately storing and releasing hydrogen gas by the hydrogen storage alloy. There is an effect that the internal pressure can be maintained substantially constant while using.

In the refrigerating machine according to the fifth aspect, the pressure vibration generated by the pressure vibration generating device is utilized, so that mechanical vibration or electromagnetic noise is not applied to the refrigerating machine main body for a long period of time. Therefore, there is an effect that continuous operation can be performed at a suitable vibration frequency.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the overall configuration of a refrigerator in one embodiment of the present invention.

FIG. 2 is a graph showing a waveform of gas pressure oscillation at each relay point of the refrigerator.

FIG. 3 is a partially enlarged view of FIG.

FIG. 4 is a front view showing an example of a conventional thermoacoustic oscillator.

[Explanation of symbols]

10A 1st thermoacoustic oscillator 10B 2nd thermoacoustic oscillator 15 Connection pipelines 18a and 18b Pressure extraction port 20 Pressure vibration generator 21 1st buffer tank (internal pressure holding tank) 22A, 22B, 22C, 22D Check valve (pressure vibration) Taking out means) 24 Pipeline (constituting pressure vibration taking out means) 26 Valve (filter means) 28 Second buffer tank (filter means) 30 Refrigerator body

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) F25B 9/00 311 F25B 9/00

Claims (5)

(57) [Claims] 1. A first thermoacoustic oscillator that vibrates the gas pressure at a first frequency and a second thermoacoustic oscillator that vibrates the gas pressure at a second frequency are connected, and both thermoacoustic oscillators are connected. Pressure vibration of gas characterized by generating pressure vibration of gas having a frequency equal to the frequency of this beat by generating a beat by superimposing the generated pressure vibration and extracting and rectifying the component of this beat. Method of occurrence. 2. A first thermoacoustic oscillator that vibrates the gas pressure at a first frequency, a second thermoacoustic oscillator that vibrates the gas pressure at a second frequency, and both thermoacoustic oscillators are connected to each other. Pressure vibration of gas having a frequency equal to this beat frequency by extracting and rectifying the beat component generated by superposition of the pressure vibrations emitted from both thermoacoustic oscillators connected to this pipe line. A pressure vibration generator for gas, comprising: 3. The gas pressure vibration generator according to claim 2, wherein as the pressure vibration generating means, an internal pressure holding tank for keeping an internal pressure substantially constant, and the internal pressure holding tank and the connecting pipeline are connected. However, due to the difference in internal pressure between the two, the pressure vibration extracting means for extracting the pressure vibration of the gas having the frequency component equal to the frequency of the beat in the connecting conduit and the pressure of the gas extracted by this pressure vibration extracting means A gas pressure vibration generator comprising: a filter for removing high frequency components of vibration. 4. The gas pressure vibration generator according to claim 3, wherein a hydrogen storage alloy is stored in the internal pressure holding tank. 5. The method according to claim 2, wherein the pressure of the working gas is vibrated.
And a refrigerator main body that is connected to the pressure vibration generation means of the pressure vibration generation device and that generates cold by utilizing the pressure vibration of the working gas. A refrigerator equipped with a characteristic gas pressure oscillation generator.