JP2005127633A - Pulse pipe refrigerating machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inhibit the impairing of the performance when a pulse pipe refrigerating machine is mounted in a state of keeping a high-temperature side of a pulse pipe down. <P>SOLUTION: In this pulse pipe refrigerating machine comprising a compressor, a cold storage unit 2, the pulse pipe 3 and a phase control part, and provided with a heat exchanger 6 at a low-temperature end 5 formed between the cold storage unit 2 and the pulse pipe 3, a straightening unit 12 is inserted between the heat exchanger 6 and the pulse pipe 3 for straightening the flow of a working gas flowing into the pulse pipe 3 through the heat exchanger 6. Whereby a distribution of a speed of the working gas flowing into the pulse pipe 3 is unified, the generation of the natural convection and vortex of the working gas in a case of keeping the high-temperature side of the pulse pipe down, can be minimized, and the impairing of the performance can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

    The present invention relates to a pulse tube refrigerator that generates a cryogenic temperature by a piston action of a working gas in a pulse tube.

  The pulse tube refrigerator is described in, for example, Patent Document 1 and Patent Document 2, and FIG. 9 shows a schematic configuration of a conventional pulse tube refrigerator. In FIG. 9, the pulse tube refrigerator includes a compressor 1, a regenerator 2, a pulse tube 3, and a phase controller 4, and a heat exchanger at a low temperature end 5 formed between the regenerator 2 and the pulse tube 3. 6 is arranged. The phase control unit 4 includes an inertance tube 7 and a buffer tank 8, and a heat transfer body 9 is provided around the heat exchanger 6. For example, helium is enclosed as a working gas (refrigerant gas) in the system of the pulse tube refrigerator.

  As the operation principle of the pulse tube refrigerator having such a configuration is already known, when the piston 1a reciprocates by the operation of the compressor 1 and the working gas is repeatedly compressed and expanded, the working gas is compressed into the compressor 1. From the regenerator 2 and the pulse tube 3 to the phase control unit 4 as a reciprocating flow. At that time, the working gas flows in the phase control unit 4 composed of the inertance tube 7 and the buffer tank 8 with a substantially sinusoidal pressure amplitude, and the phase difference between the pressure change and the flow rate change of the working gas. Will occur.

  If this is compared to an electric circuit, the inertance tube 7 corresponds to an inductance, resistance, capacitance component, and the buffer tank 8 corresponds to a capacitance component, and the phase difference of the flow rate with respect to the pressure of the working gas is changed from −90 ° to + 90 °. . As a result, a phase difference occurs between the pressure and the flow rate in the pulse tube 3 during operation of the refrigerator, and cold is generated at the low temperature end 5 due to the PV work due to this pressure and flow rate. This cold work is called a low-temperature PV work.

  Here, the working gas sent out in the compression process of the compressor 1 becomes a low temperature in the regenerator 2 and flows into the pulse tube 3, absorbs heat by adiabatic expansion therein, and flows out to the phase controller 4. On the other hand, in the process where the working gas passes through the pulse tube 3 from the phase control unit 4 and recirculates to the low temperature end 5, heat is not generated or absorbed because it moves at a substantially constant volume. In that case, in order for the working gas to perform the PV work efficiently, it is necessary to act as a piston (so-called gas piston) 10 in which the working gas moves as a fixed surface at least on the low temperature end side in the pulse tube. . It is ideal that the gas piston 10 behave as solidly as possible. For this purpose, the flow of the fluid inside the pulse tube 3 is only the flow according to the operation cycle of the compressor 1, and other secondary flows. Desirably no flow exists.

JP 11-248279 A Japanese Patent Laid-Open No. 2002-235932

  Incidentally, as shown in FIG. 9, the pulse tube refrigerator is usually installed upright so that the end of the pulse tube 3 on the high temperature side (upper side in FIG. 9) is on the upper side (hereinafter referred to as “upward”). "Installation"). In fact, it has been confirmed that when the end of the pulse tube 3 on the low temperature side (the lower side in FIG. 9) is placed on the upper side (hereinafter referred to as “downward installation”), the performance is greatly reduced. The reason for this is that when the end of the high-temperature side of the pulse tube 3 is positioned downward due to the downward installation, the high-temperature working gas having a small specific gravity on the lower side rises by natural convection in the pulse tube, while the low-temperature having a large specific gravity on the upper side. This is thought to be because the working gas is lowered due to the influence of gravity, and as a result, a vortex is generated and smooth heat transfer is hindered, and the rising of the hot gas hinders cooling of the cold end.

  Here, FIG. 10 is a plan view of the heat exchanger 6 in FIG. The heat exchanger 6 shown in FIG. 10 is made of a metal having a good thermal conductivity, such as a copper disk, and a large number of through holes 11 are formed in the disk 6a in the axial direction. The low-temperature working gas that flows into the pulse tube 3 from the regenerator 2 passes through the through hole 11, exchanges heat with the heat transfer body 9 through the heat exchanger 6, and is to be cooled (not shown) that contacts the heat transfer body 9. Cool down. The heat exchanger 6 also serves as a rectifier and rectifies the working gas flowing into the pulse tube 3. The illustrated heat exchanger 6 made of a porous disk has good adhesion to the heat transfer body 9 and is also used in the pulse tube refrigerator disclosed in Patent Document 1. In addition, a mesh structure with a metal mesh is also used as a heat exchanger. This mesh structure heat exchanger has a large rectifying effect and a large heat transfer surface area compared with a porous disk, but heat transfer Adhesion with the body is inferior.

  FIG. 11 shows the velocity distribution of the working gas flowing into the pulse tube 3 through the heat exchanger 6 in the conventional pulse tube refrigerator using the heat exchanger 6 made of a porous disk. As shown in FIG. 11, the speed at the center of each through hole 11 is substantially uniform in the cross section of the pulse tube 3, but the speed is distributed in a mountain shape in the cross section of each through hole 11, and the cross section of the pulse tube 3. The distribution is uneven and uneven as a whole.

  However, the non-uniform velocity distribution does not significantly affect the refrigeration performance (hereinafter simply referred to as “performance”) in the conventional upward installation, but the inventors have a large influence on the performance in the downward installation. It became clear by experiment. As described above, when the pulse tube refrigerator is installed downward, natural convection occurs due to unstable conditions of the temperature and density of the working gas, but the working gas having a high density at a low temperature has a non-uniform velocity distribution. As shown in the figure, when blown from the top to the bottom, the working gas with a large velocity component is accelerated by the action of gravity and rushes into the working gas at the high temperature side end, generating convection of the working gas and generation of vortices It is judged that it promotes.

  The subject of this invention is suppressing the fall of the performance when a pulse tube refrigerator is installed downward, and improving the usability of a pulse tube refrigerator.

  In order to solve the above problems, the present invention includes a compressor, a regenerator, a pulse tube, and a phase control unit, and a heat exchanger is disposed at a low temperature end formed between the regenerator and the pulse tube. In the pulse tube refrigerator, a rectifier that rectifies the flow of the working gas flowing through the heat exchanger and flowing into the pulse tube is inserted between the heat exchanger and the pulse tube. 1).

  According to the first aspect of the present invention, the velocity of the working gas flowing into the pulse tube is provided by providing a rectifier separately from the heat exchanger and rectifying the flow of the working gas flowing through the heat exchanger and flowing into the pulse tube. The distribution can be made uniform, and the natural convection and vortex generation of the working gas when the pulse tube refrigerator is installed downward can be minimized.

  In the first aspect of the present invention, a gap may be provided between the heat exchanger and the rectifier (second aspect). As a result, the working gas that has passed through the heat exchanger spreads over the entire cross section of the pulse tube within the gap before the rectifier, and the velocity distribution becomes more uniform.

  The ratio d / M [m · s / kg] between the inner diameter d [m] of the pulse tube and the mass flow rate M [kg / s] of the working gas may be 260 to 315. (Claim 3).

  In any one of claims 1 to 3, the ratio L / d between the length L [m] of the pulse tube and the inner diameter d [m] may be selected in the range of 7.5 to 10 (invention). Item 4).

  According to the present invention, the rectifier is inserted between the heat exchanger and the pulse tube, and the velocity distribution of the working gas flowing through the heat exchanger and flowing into the pulse tube is made uniform. When the machine is installed downward, natural convection and vortex generation due to the lower end of the high-temperature side of the pulse tube are minimized, and performance degradation due to the downward installation of the pulse tube refrigerator is reduced. be able to.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

  1 is a longitudinal sectional view of a heat exchanger portion of a pulse tube refrigerator showing Embodiment 1 of the present invention. In FIG. 1, a rectifier 12 that rectifies the flow of the working gas flowing through the heat exchanger 6 and flowing into the pulse tube 3 is inserted between the heat exchanger 6 at the low temperature end 5 and the pulse tube 3. The heat exchanger 6 is obtained by opening a large number of through holes 11 in the axial direction in a copper disk. The rectifier 12 has a mesh structure in which metal nets punched into a circle are stacked. The rectifier 12 having a mesh structure can form a uniform velocity distribution while suppressing an increase in pressure loss by adjusting the number of meshes and the number of stacked layers. In the experiment, the number of meshes is 100, the wire diameter is 110 μm, and the number of stacked layers is 23. (Height 5 mm) was used. The rectifier 12 is not limited to a mesh structure, and other structures such as a honeycomb structure can be used.

  As shown in FIG. 1, the velocity distribution of the working gas flowing into the pulse tube 3 through the rectifier 12 eliminates the mountain shape for each through hole 11 (see FIG. 11), and is uniform over the entire cross section of the pulse tube 3. . As a result, the natural convection of the working gas and the generation of vortices when the pulse tube refrigerator is installed downward as shown in the figure are suppressed, and as a result, the performance degradation is reduced.

  FIG. 3 is a diagram showing the results of confirming this effect by experiment. When the pulse tube refrigerator is installed in the downward direction, the reduction rate of how much the performance is reduced with respect to the installation in the upward direction. [%] Is compared for the presence or absence of the rectifier 12. In the experiment conditions, L / d is the ratio of the length L [m] of the pulse tube 3 to the inner diameter d [m], and d / m is the inner diameter d [m] and the working gas mass flow rate M [ kg / s]. According to the result of FIG. 3, it can be seen that the decrease rate without the rectifier is about 87%, whereas the decrease rate with the rectifier is reduced to about 62%.

  FIG. 2 shows a second embodiment in which a gap 13 is provided between the heat exchanger 6 and the rectifier 12 in the first embodiment. As a result, the working gas that has passed through the heat exchanger 6 spreads over the entire cross section of the pulse tube 3 in the air gap 13 in front of it due to the fluid resistance of the rectifier 12. As a result, the rectification action by the rectifier 12 becomes higher, and the velocity distribution becomes smoother as compared with the embodiment as shown.

By the way, in the pulse tube refrigerator of Example 1 or Example 2, the operational effects of the present invention can be further enhanced by appropriately selecting the inner diameter of the pulse tube. As shown in FIG. 4, the average flow velocity of the pulse tube 3 having a small inner diameter in FIG. 4B is larger than that of the pulse tube 3 having a large inner diameter in FIG. In the reciprocating motion of the working gas in the pulse tube refrigerator, a high working gas flow velocity means that the amplitude of movement of the fluid element in one cycle is large. That is, when the mass m [kg] of the fluid element reciprocates at the position amplitude r [m] and the angular frequency ω, the force F _X applied to the fluid element is expressed as follows by the equation of motion.

F _X = mrω ² sin (ωt)
Here, when operating at the same angular frequency ω, if the working gas flow rate Q [m ³ / s] flowing into the pulse tube is always constant, the inner diameter of the pulse tube 3 is defined as d [m]
Q = r · (1/2 · πd ² )
r = Q / (1/2 · πd ² )
Thus, the position amplitude r is inversely proportional to the square of the inner diameter d of the pulse tube. Since the force F _X is affected only by the position amplitude r from the above equation, the force F _X is inversely proportional to the square of the inner diameter d of the pulse tube. For example, if the inner diameter d is halved, the force F _X Is quadrupled.

The force F _X is a driving force that causes the fluid element to reciprocate. On the other hand, the natural convection of the working gas that causes the performance deterioration of the pulse tube refrigerator installed in the downward direction is caused by the gravity acting on the working gas. That is, the driving force F _X and the gravity act simultaneously on the working gas. At this time, if the driving force F _X is large, the influence of the gravity on the working gas is relatively lowered, and the natural convection of the working gas is suppressed. Therefore, from the viewpoint of suppressing natural convection, it is better that the inner diameter of the pulse tube is smaller.

  FIG. 5 shows the deterioration in performance due to the orientation of the installation, using three types of inner diameter d [m] of the pulse tube and taking the ratio d / M [m · s / kg] to the mass flow rate M [kg / s] as a parameter. The experimental result which compared rate [%] is shown. As shown in the figure, the rate of decrease in performance takes a local minimum when the ratio d / M is 275 [m · s / kg]. From this result, it can be seen that if the mass flow rate M is the same, the smaller the inner diameter d of the pulse tube, the smaller the performance degradation rate. However, if the inner diameter d is made too small, the viscous resistance due to the working gas increases, so the performance is considered to deteriorate. As described above, there is an optimum range for the ratio d / M between the inner diameter d [m] of the pulse tube and the mass flow rate M. When the upper limit of the performance degradation rate is 10%, 260 to 315 [m · s / kg] range. That is, if it is selected within this range, the performance deterioration rate can be kept within 10%.

  On the other hand, FIG. 6 schematically shows the natural convection of the working gas in the pulse tube 3 in FIG. 6A, and shows the temperature gradient in the longitudinal direction of the pulse tube 3 in FIG. 6B. . As illustrated, the temperature gradient dT / dL [K / m] can be moderated by increasing the length L [m] of the pulse tube 3 (L1 → L2). Generally, the amount of heat transfer by convection is determined by the temperature gradient. Therefore, by increasing the length L of the pulse tube 3, it is possible to reduce the heat brought in by natural convection from the high temperature side (phase control unit side) of the pulse tube 3 to the low temperature end.

  In general, natural convection found in a vertical pipe such as a pulse tube is greatly affected by the ratio L / d between the length L and the inner diameter d. FIG. 7 shows the experimental results of the change in the performance degradation rate depending on the installation direction when the ratio L / d is changed while keeping the inner diameter d constant. From FIG. 7, it can be seen that the performance degradation rate can be greatly reduced only by changing the ratio L / d from 6.9 to 7.9.

  Based on the experimental results described above, the configuration of Example 2 (FIG. 2) was adopted, the ratio L / d was selected as 9.6, and the refrigeration performance for both the upward and downward installation states in FIG. The experimental results compared with the conventional configuration are shown in FIG. The display “before countermeasure” in the figure represents the conventional configuration, and “after countermeasure” represents the configuration of the second embodiment. According to FIG. 8, there is almost no difference between before and after the countermeasure in the upward installation, but in the downward installation, before the countermeasure, the cold end temperature is 70K and the refrigeration output is reduced from 2.8 [W] to 0. On the other hand, after the measure, it is only about 8% decrease from 2.7 [W] to 2.5 [W], and it can be seen that the performance deterioration rate due to the installation direction is greatly reduced. In the above embodiment, the heat exchanger has a porous disk structure. However, the present invention can be applied to other structures such as a mesh structure.

It is a longitudinal cross-sectional view of the heat exchanger part of the refrigerator which shows Example 1 of this invention. It is a longitudinal cross-sectional view of the heat exchanger part of the refrigerator which shows Example 2 of this invention. It is a figure explaining the effect of Example 1. FIG. It is a figure explaining the difference of the average flow velocity of the working gas by the inside diameter of a pulse tube. It is a figure explaining the difference of the performance fall rate by the pulse tube internal diameter at the time of downward installation of the refrigerator of FIG. It is a figure explaining the difference of the temperature gradient by the natural convection of the working gas in a pulse tube, and pulse tube length. It is a figure explaining the difference by the pulse tube length of the performance fall rate by direction for installation of a refrigerator. It is a figure explaining the difference of the freezing output before and behind the countermeasure by this invention. It is a figure which shows the structure of the conventional pulse tube refrigerator. It is a top view of the heat exchanger in FIG. It is an enlarged view of the heat exchanger part in the pulse tube refrigerator of FIG.

Explanation of symbols

2 Regenerator 3 Pulse tube 5 Low temperature end 6 Heat exchanger 9 Heat transfer body 12 Rectifier 13 Air gap

Claims (4)

A pulse tube refrigerator comprising a compressor, a regenerator, a pulse tube, and a phase control unit, wherein a heat exchanger is disposed at a low temperature end formed between the regenerator and the pulse tube, wherein the heat exchanger and the A pulse tube refrigerator, wherein a rectifier for rectifying the flow of the working gas flowing through the heat exchanger and flowing into the pulse tube is inserted between the pulse tube and the pulse tube. The pulse tube refrigerator according to claim 1, wherein a gap is provided between the heat exchanger and the rectifier. The ratio d / M [m · s / kg] between the inner diameter d [m] of the pulse tube and the mass flow rate M [kg / s] of the working gas is selected in the range of 260 to 315. The pulse tube refrigerator according to claim 1 or 2. 4. The ratio L / d between the length L [m] and the inner diameter d [m] of the pulse tube is selected in the range of 7.5 to 10. 5. Pulse tube refrigerator.

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