JPH0650619A - Pulse tube refrigerator - Google Patents

Abstract

PURPOSE: To obtain a pulse pipe refrigerating machine the performance of which does not drop even when the flow rate is large although the machine requires a large flow rate in order to increase the generated refrigeration quantity per unit flow rate passing through a cold storage tank. CONSTITUTION: A pulse pipe refrigerating machine is provided with a compressor 1, a change-over valve 2, cooling water 9, and tubes 10. A pulse pipe 4 is composed of a multistage pipe which is constituted by successively connecting pipes from a small-diameter pipe to a large-diameter pipe and the diameter of the pipe 4 at its room-temperature end 7 is made smaller than that at its low-temperature end 8. Consequently, the quantity of the gas flowing in the pipe 4 through a cold storage tank 3 for compressing the gas in the pipe 4 can be reduced by reducing the volume of the pipe 4. On the other hand, when the diameter of the pipe 4 at the low-temperature end 8 is made equal to the conventional diameter, the same quantity of refrigeration can be generated, since the gas contributing to the generation of refrigeration accompanying expansion work is the gas which gets in and out the pipe 4 through the low- temperature end 8 when the gas is pushed and withdrawn by means of a piston 11 provided at the room-temperature end 7 of the pipe 4. Namely, the quantity of the generated refrigeration per unit flow rate can be improved.

Description

Detailed Description of the Invention

[0001]

[Industrial application] When used in an environment where maintenance is not possible, such as a refrigerator for cooling infrared detectors installed in artificial hygiene, magnetic resonance imaging equipment (MRI) / S
High reliability is required for cooling refrigerators for medical devices such as QUID brain (magnetocardiography) measuring devices and devices for continuous use such as superconducting computers. The pulse tube refrigerator, which has no moving parts in the low temperature part, is the refrigerator most suitable for such requirements. The present invention relates to improving the performance of this pulse tube refrigerator.

[0002]

2. Description of the Related Art FIG. 1 shows an orifice type pulse tube refrigerator having the highest performance among conventional pulse tube refrigerators. It is composed of a compressor 1 at room temperature, a valve 2 for switching between high pressure and low pressure, a regenerator 3 filled with wire mesh, a hollow pulse tube 4, an orifice or throttle valve 5 at room temperature, and a buffer container 6.

The principle of operation will be described below. When the switching valve 2 switches to the high-pressure side, the high-pressure working gas compressed by the compressor 1 passes through the regenerator 3 and its temperature drops, and enters the pulse tube 4. At this time, the gas originally present in the pulse tube is compressed and moves toward the room temperature end 7. as a result,
Since the pressure inside the pulse tube 4 becomes higher than the pressure inside the buffer container 6, the gas flows into the buffer container 6 through the orifice (throttle valve) 5. Next, when the switching valve 2 switches to the low pressure side, the temperature of the gas in the pulse tube 4 rises while passing through the regenerator 3 and flows toward the suction port of the compressor 1. At this time, on the contrary, the pressure in the pulse tube 4 becomes lower than the pressure in the buffer container 6, so that the gas in the buffer container 6 passes through the orifice (throttle valve) 5 and the pulse tube 4
It flows in. If there is no gas passing through the orifice (throttle valve) 5 and the heat exchange between the gas and the tube wall is negligible, the gas in the pulse tube simply adiabatically repeats compression and expansion. At this time, the pressure fluctuation and the gas displacement are in phase with each other. On the other hand, when there is gas passing through the orifice (throttle valve) 5, the phase changes and a component having a phase difference of 90 ° between the pressure fluctuation and the gas displacement is generated. Due to this component, an enthalpy flow is generated in the pulse tube 4, the expansion work of the gas at the low temperature end 8 is transmitted to the room temperature end 7, and is converted into heat at the orifice (throttle valve) 5 to cool the cooling water (9). Be carried away by. In this way, freezing occurs due to the expansion of the gas at the low temperature end 8 of the pulse tube.

[0004]

The greatest problem of the conventional pulse tube refrigerator is that the amount of refrigeration generated per unit flow rate passing through the regenerator 3 is small. For this reason, a large flow rate is required, and the heat capacity of the passing gas becomes larger than the heat capacity of the regenerator material, so that the performance of the regenerator 3 becomes low. Further, when the flow rate is large, the Reynolds number at the low temperature end 8 of the pulse tube becomes large and turbulent flow is likely to occur. Moreover, at the low temperature end 8, the Reynolds number tends to increase because the viscosity of the gas decreases as the temperature decreases. When turbulence occurs, the temperature distribution in the pulse tube 4 is disturbed,
This will reduce the performance of the refrigerator. An object of the present invention is to provide means for solving such a problem, and to realize a high performance pulse tube refrigerator.

[0005]

In order to achieve the above object, in the pulse tube refrigerator according to the present invention, pulses having different diameters are sequentially connected (FIG. 2) or a tapered tube is used. The diameter of the tube room temperature end 7 is set to
Is smaller than the diameter of. By doing so, the volume of the pulse tube 4 can be reduced and the amount of gas flowing through the regenerator 3 for compressing the gas in the tube can be reduced. On the other hand, what contributes to the generation of freezing due to the expansion work is the gas that enters and leaves the low temperature end 8 of the pulse tube by being pushed or pulled by the piston 11 provided at the room temperature end 7, which is the low temperature end 8. If the diameter of is the same as in the conventional case, the same amount of refrigeration is generated. That is, it is possible to improve the amount of refrigeration generated per unit flow rate and solve the above-mentioned problems. Further, it is effective to insert a thin tube 10 having a small diameter in the vicinity of the low temperature end 8 of the pulse tube to reduce the channel diameter to reduce the Reynolds number. This method is disclosed by the inventors of the present invention in Patent Application No. 02-17078.
This method is similar to the method described in No. 7. The above description relates to the pulse tube refrigerator of the type in which the piston (movable plug) 11 is provided at the room temperature end 7 of the pulse tube to recover the expansion work, but similarly, the present invention also applies to the orifice type pulse tube refrigerator. It is possible to apply the structure of pulse tubes and the insertion of capillaries.

[0006]

EXAMPLE The length of the three-stage pulse tube in FIG. 2 is 120 mm, 120 mm, 40 mm from the room temperature end 7 side, and the diameter is 6 mm, 1
6mm and 25mm. The performance of this pulse tube is compared with the conventional pulse tube of FIG. 1 (diameter 25 mm, length 280 mm).
For simplicity, the room temperature end 7 is 300K and the low temperature end 8 is 20K, and the temperature gradient is constant. The heat exchange between the gas and the tube wall is negligibly small. The working gas is helium gas. FIG. 3 shows a value obtained by dividing the Reynolds number in each part by the critical Reynolds number (2300 because it is a circular tube). In the conventional pulse tube of (a), turbulent flow exceeds the critical Reynolds number at a temperature lower than about 100K, but
In the three-stage pulse tube of (b), the value is below the critical Reynolds number up to around 60K.

Next, in the vicinity of the low temperature end 8, an outer diameter of 1 mm and a wall thickness of 10
A nickel capillary 10 of μm is inserted. The ratio of the heat capacity of the passing helium gas in this case divided by the heat capacity of the capillaries is shown in FIG. Since the heat capacity of helium gas is sufficiently large at about 60 K or less, heat exchange between the helium gas and the thin tube is sufficiently small, and therefore, the helium gas in the pulse tube 4 does not prevent the adiabatic cycle from being drawn. Here, the structure is such that three types of straight pipes having different diameters are connected, but it is clear that the same effect can be obtained by using a tapered pipe as described above.

[0008]

In the pulse tube refrigerator according to the present invention, the amount of gas flowing into and out of the pulse tube from the low temperature end can be reduced while maintaining the generated refrigeration amount, and the function of the thin tube near the low temperature end is also improved. In addition, the generation of turbulence in the pulse tube is prevented, the efficiency of the regenerator is improved, and a high-performance pulse tube refrigerator can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing a conventional orifice pulse tube refrigerator.

FIG. 2 shows a refrigerator equipped with a three-stage pulse tube according to the present invention.

FIG. 3 is a diagram showing an effect of the present invention by comparing Reynolds numbers in pulse tubes.

FIG. 4 is a diagram showing a heat capacity ratio between helium gas and a thin tube.

[Explanation of symbols]

 1 compressor 2 switching valve 3 regenerator 4 pulse tube 5 orifice or throttle valve 6 buffer container 7 room temperature end 8 low temperature end 9 cooling water 10 thin tube 11 piston

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 591100921 Kaya ▲ Chi ▼ All 2-1, Hirosawa, Wako City, Saitama Prefecture RIKEN A-101 (72) Inventor Junpei Yuyama 2 Morinosato, Atsugi City, Kanagawa Prefecture −28-2 (72) Inventor Masahiko Kasuya 1-15-52 Murota, Chigasaki City, Kanagawa Prefecture 1-202 Heights Kawabata (72) Inventor, Gaya ▲ Chi ▼ 64-2-304 Yahata, Chigasaki City, Kanagawa Prefecture Nunheim Inuki (72) Inventor Eiichi Goto 3-9 Tsujido East Coast, Fujisawa City, Kanagawa Shonanheim FE305

Claims (4)

[Claims] 1. The pulse tube comprises a tapered tube,
Alternatively, a pulse tube refrigerator characterized in that a diameter at a room temperature end is smaller than a diameter at a low temperature end by sequentially connecting pipes having different diameters from a small diameter to a large diameter. 2. The pulse tube refrigerator according to claim 1, wherein a large number of thin thin tubes having a heat capacity sufficiently smaller than that of the working fluid are inserted near the low temperature end of the pulse tube to prevent turbulence. . 3. The pulse tube refrigerator according to claim 2, wherein a piston is provided at the room temperature end of the pulse tube. 4. The pulse tube refrigerator according to claim 2, wherein the room temperature end of the pulse tube is connected to a large buffer container through an orifice or a throttle valve.