Title:
PULSE TUBE REFRIGERATOR
Kind Code:
A1


Abstract:
A pulse tube refrigerator, includes a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body, the laminated body including at least first and second metal gauzes; the first and second metal gauzes include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; and a side surface of the laminated body is diffusion-bonded to an internal wall forming the communicating path.



Inventors:
Takayama, Hirokazu (Tokyo, JP)
Xu, Mingyao (Tokyo, JP)
Application Number:
12/983913
Publication Date:
07/21/2011
Filing Date:
01/04/2011
Assignee:
SUMITOMO HEAVY INDUSTRIES, LTD. (Tokyo, JP)
Primary Class:
Other Classes:
62/467
International Classes:
F25B9/00; F25B23/00
View Patent Images:



Foreign References:
JP2008156701A
Primary Examiner:
MARTIN, ELIZABETH J
Attorney, Agent or Firm:
IPUSA, P.L.L.C (1054 31ST STREET, N.W. Suite 400, Washington, DC, 20007, US)
Claims:
What is claimed is:

1. A pulse tube refrigerator, comprising: a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body, the laminated body including at least first and second metal gauzes; the first and second metal gauzes include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; and a side surface of the laminated body is diffusion-bonded to an internal wall forming the communicating path.

2. The pulse tube refrigerator as claimed in claim 1, wherein the laminated body includes a third metal gauze, the third metal gauze being situated at a top of the laminated body, the third metal gauze including metal other than the copper or the copper alloy; the interfaces of the metal gauzes are diffusion-bonded to each other; and the laminated body is provided in the communicating path so that a side of the third metal gauze is situated furthest from the low temperature end of the regenerator.

3. The pulse tube refrigerator as claimed in claim 2, wherein the laminated body includes a fourth metal gauze, the fourth metal gauze being situated at a top of the laminated body, the fourth metal gauze including metal other than the copper or the copper alloy; the interfaces of the metal gauzes are diffusion-bonded to each other; and the laminated body is formed by laminating the third metal gauze, the first metal gauze, the fourth metal gauze, and the second metal gauze.

4. The pulse tube refrigerator as claimed in claim 3, wherein the laminated body is formed by laminating six or more of the metal gauzes; the laminated body has a structure where the metal gauzes made of metal other than the copper or the copper alloy and the metal gauzes made of the copper or the copper alloy are mutually and repeatedly provided; and the interfaces of the metal gauzes are diffusion-bonded to each other.

5. The pulse tube refrigerator as claimed in claim 3, wherein opening areas of the metal gauzes made of the metal other than the copper or the copper alloy are substantially equal to each other.

6. The pulse tube refrigerator as claimed in claim 3, wherein an opening area of the metal gauzes made of the metal other than the copper or the copper alloy is smaller than an opening area of the metal gauzes made of the copper or the copper alloy.

7. The pulse tube refrigerator as claimed in claim 3, wherein an opening area of the metal gauzes made of the metal other than the copper or the copper alloy is in a range between approximately 0.02 mm and approximately 0.58 mm.

8. The pulse tube refrigerator as claimed in claim 2, wherein the metal other than the copper or the copper alloy is stainless steel or nickel.

9. The pulse tube refrigerator as claimed in claim 1, wherein a rolling process is applied to the metal gauzes.

10. The pulse tube refrigerator as claimed in claim 1, wherein a thickness of the metal gauzes after a rolling process is applied is in a range between approximately 0.4 mm through approximately 0.99 mm when the thickness of the metal gauzes before the rolling process is applied is 1 mm.

11. The pulse tube refrigerator as claimed in claim 1, wherein an opening area of the metal gauzes made of the copper or the copper alloy is in a range between approximately 0.05 mm and approximately 1.14 mm.

12. The pulse tube refrigerator as claimed in claim 1, wherein opening areas of the metal gauzes made of the copper or the copper alloy are substantially equal to each other.

13. The pulse tube refrigerator as claimed in claim 1, wherein opening areas of the metal gauzes made of the copper or the copper alloy are continuously or gradually decreased from the metal gauze closest to the low temperature end of the regenerator toward a laminating direction of the laminated body.

14. A pulse tube refrigerator, comprising: a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body and a housing, the laminated body including at least first and second metal gauzes; the first and second metal gauzes and the housing include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; the laminated body is received in the housing; and a side surface of the laminated body is diffusion-bonded to an internal wall of the housing.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims the benefit of priority of Japanese Patent Application No. 2010-010447 filed on Jan. 20, 2010, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to pulse tube refrigerators.

2. Description of the Related Art

Conventionally, a pulse tube refrigerator has been used for cooling an apparatus requiring a cryogenic temperature environment, such as a MRI (magnetic resonance imaging) apparatus.

In the pulse tube refrigerator, a cryogenic state is formed at low temperature ends of a regenerator and a pulse tube by repeating operations where coolant gas (for example, helium gas) as operating fluid compressed by a compressor flows into the regenerator and into the pulse tube and operations where the operating fluid flows out from the regenerator and into the pulse tube and is received by the compressor.

A regenerator of the pulse tube refrigerator includes a cylindrical-shaped member (cylinder) in which a regenerator material is provided. A pulse tube includes a hollow cylindrical-shaped member (cylinder). Low temperature ends of the cylinder of the regenerator and the cylinder of the pulse tube are in fluid communication with each other via a communicating path. A cooling stage where a cooled body is connected is provided in this position.

It is a normal practice that a heat exchanger is provided at a low temperature end side of the pulse tube. The heat exchanger includes a laminated body formed of metal gauzes or the like made of copper.

the pulse tube refrigerator may be degraded.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention may be to provide a pulse tube refrigerator, including a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body, the laminated body including at least first and second metal gauzes; the first and second metal gauzes include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; and a side surface of the laminated body is diffusion-bonded to an internal wall forming the communicating path.

Another aspect of the embodiments of the present invention may be to provide a pulse tube refrigerator, including a pulse tube; and a regenerator having a low temperature end, the low temperature end being in communication with a low temperature end of the pulse tube via a communicating path, wherein a heat exchanger is provided at the low temperature end side of the pulse tube in the communicating path; the heat exchanger includes a laminated body and a housing, the laminated body including at least first and second metal gauzes; the first and second metal gauzes and the housing include copper or a copper alloy; interfaces of the metal gauzes are diffusion-bonded to each other; the laminated body is received in the housing; and a side surface of the laminated body is diffusion-bonded to an internal wall of the housing.

According to the embodiments of the present invention, it is possible to provide a pulse tube refrigerator including a heat exchanger having heat exchangeability better than that of the conventional art.

Additional objects and advantages of the embodiments are set forth in part in the description which follows, and in part will become obvious from the description, or may be learned by practice of the invention. The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a pulse tube refrigerator of an embodiment of the present invention;

FIG. 2 is a cross-sectional view of an example of a heat exchanger;

FIG. 3 is an exploded schematic structural view of a laminated body included in the heat exchanger;

FIG. 4 is a cross-sectional view of another example of a heat exchanger;

FIG. 5 is an exploded schematic structural view of another laminated body included in the heat exchanger; and

FIG. 6 is an exploded schematic structural view of yet another laminated body included in the heat exchanger.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

In a related art pulse tube refrigerator, the laminated body formed of the metal gauzes or the like made of copper, as the heat exchanger, is supplied at the low temperature end side of the pulse tube. The reason why the metal gauzes are used is for preventing a big difference of speeds of the coolant gas when the coolant gas flows from the regenerator to the pulse tube. In other words, a flow smoothening effect of the coolant gas is improved by using the metal gauzes.

However, in a case where such a laminated body is supplied at the low temperature end side of the pulse tube so that the heat exchanger is formed, it may be difficult to make efficient thermal contact between a side surface of the laminated body and an internal wall of a groove where the laminated body is received. Because of this, depending on a contact state of the side surface of the laminated body and the internal wall of the groove, thermal resistance of an interface may be drastically changed. As a result of this, an unstable state of the heat exchangeability may be generated so that the heat exchangeability of

Embodiments of the present invention may provide a novel and useful pulse tube refrigerator solving one or more of the problems discussed above.

More specifically, the embodiments of the present invention may provide a pulse tube refrigerator including a heat exchanger having heat exchangeability better than that of the conventional art.

A description is given below, with reference to the FIG. 1 through FIG. 6 of embodiments of the present invention.

FIG. 1 is a schematic view of a pulse tube refrigerator of an embodiment of the present invention.

As shown in FIG. 1, a pulse tube refrigerator 100 of an embodiment of the present invention includes a compressor 110, a regenerator 120, a pulse tube 140, a cooling stage 180, and a buffer tank 190. The regenerator 120 has a high temperature end 125a and a low temperature end 125b. The pulse tube 140 has a high temperature end 145a and a low temperature end 145b.

An exhaust valve 110a and an intake valve 110b are connected to the compressor 110. In addition, the compressor 110 is connected to the high temperature end 125a of the regenerator 120 via a gas flow path 112.

The regenerator 120 is formed of, for example, a hollow cylinder 121. A regenerator material 122 is supplied inside the cylinder 121. The cylinder 121 is made of, for example, stainless steel.

The pulse tube 140 is formed of, for example, a hollow cylinder 141 made of stainless steel. A heat exchanger 149a is provided at the high temperature end 145a side of the pulse tube 140. A heat exchanger 149b is provided at the low temperature end 145b side of the pulse tube 140.

The low temperature end 125b of the regenerator 120 and the low temperature end 145b of the pulse tube 140 come in contact with and are fixed to the cooling stage 180 made of, for example, copper. In addition, the low temperature end 125b of the regenerator 120 and the low temperature end 145b of the pulse tube 140 are in communication with each other by a communicating path 182 provided in the cooling stage 180. The cooling stage 180 is thermally connected to a cooled subject (not shown in FIG. 1) so that the cooled subject is cooled.

The buffer tank 190 is connected to the high temperature end 145a of the pulse tube 140 via a gas flow path 192 and an orifice 194.

The high temperature end 125a of the regenerator 120 and the high temperature end 145a of the pulse tube 140 are connected to a flange 115 so that the regenerator 120 and the pulse tube 140 are fixed.

Next, operations of the pulse tube refrigerator having the above-discussed structure are discussed.

First, in a state where the exhaust valve 110a is opened and the intake valve 110b is closed, coolant gas having a high pressure is supplied from the gas compressor 110 to the regenerator 120 via the exhaust valve 110a and the gas flow path 112. While the coolant gas flowing into the regenerator 120 is cooled by the regenerator material 122 so that a temperature of the coolant gas is decreased, the coolant gas passes through the communicating path 182 from the low temperature end 125b of the regenerator 120. The coolant gas is further cooled by the heat exchanger 149b provided at the low temperature end 145b side of the pulse tube 140 so as to flow into the pulse tube 140.

At this time, coolant gas having a low pressure which exists in the pulse tube 140 in advance is compressed by the flowing cooling gas with the high pressure. As a result of this, the pressure of the coolant gas situated in the pulse tube 140 becomes higher than a pressure of an inside of the buffer tank 190. The coolant gas passes through the orifice 194 and the gas flow path 192 so as to flow into the buffer 190.

Next, when the exhaust valve 110a is closed and the intake valve 110b is opened, the coolant gas in the pulse tube 140 passes through the low temperature end 145b so as to flow into the low temperature end 125b of the regenerator 120. Further, while the coolant gas cools the regenerator material 122, the coolant gas passes through the regenerator 120. The coolant gas passes from the high temperature end 125a through the gas flow path 112 and the intake valve 110b so as to be received by the compressor 110.

Here, the pulse tube 140 is connected to the buffer tank 190 via the orifice 194. Because of this, a phase of pressure change of the coolant gas and a phase of volume change of the coolant gas are changed with a constant phase difference. Due to this phase difference, a cryogenic state based on expansion of the coolant gas is formed at the low temperature end 145b of the pulse tube 140. By repeating the above-discussed operations, the pulse tube refrigerator 100 can cool the cooled subject connected to the cooling stage 180.

In the meantime, in the related art pulse tube refrigerator, a laminated body formed by metal gauzes made of copper is used as a heat exchanger provided at the low temperature end side of the pulse tube. The reason why such metal gauzes are used is to prevent generating big differences in the speed of the coolant gas when the coolant gas flows from the regenerator to the pulse tube. In other words, a flow smoothening effect of the coolant gas is improved by using the metal gauzes. This laminated body is supplied to the low temperature end side of the pulse tube, after members forming the laminated body are fixed in order to prevent shift of the members.

However, in the case where the heat exchanger has the above-mentioned structure, even if the laminated body is formed with high precision, a certain gap may be formed between a side surface of the laminated body and an internal wall of the groove receiving the laminated body (the communicating path 182 in an example shown in FIG. 1). Therefore, it may be difficult to always have precise thermal contact between the side surface of the laminated body and the internal wall of the groove receiving the laminated body. In addition, because of this, depending on the contact state of the side surface of the laminated body and the internal wall of the groove receiving the laminated body, the thermal resistance at an interface may be drastically changed. Hence, an unstable state of the heat exchangeability may be generated so that the heat exchangeability of the pulse tube refrigerator may be degraded.

In order to solve the above-mentioned problem, after the laminated body is supplied in the groove, a side part of the laminated body may be brazed at the internal wall of the groove.

However, in this way, even if the laminated body and the internal wall of the groove can be made to be in contact with each other at plural “points”, it may be difficult for the side part of the laminated body to entirely come in contact with the internal wall of the groove. Accordingly, this way cannot sufficiently achieve an inhibition effect of the thermal resistance and cannot solve the above-discussed problem.

On the other hand, according to the pulse tube refrigerator of the embodiment of the present invention, the heat exchanger 149b provided at the low temperature end side 145b of the pulse tube 140 is diffusion-bonded to the internal wall of the groove receiving the heat exchanger 149b.

With the above-mentioned structure of the heat exchanger 149b, the side part of the heat exchanger 149b always comes in contact with the internal wall of the groove. Therefore, a problem of the related art where the thermal resistance is drastically changed and the heat exchangeability of the pulse tube refrigerator is degraded can be reduced or solved.

Details of the embodiment of the present invention are further discussed with reference to FIG. 2 and FIG. 3.

FIG. 2 is a schematic cross-sectional view of the vicinity of a groove 189 of the cooling stage 180 where the low temperature end 145b of the pulse tube 140 is connected. In FIG. 2, a schematic cross section of an example of the heat exchanger 149b used for the embodiment of the present invention is used. FIG. 3 is an exploded schematic structural view of a laminated body 150 included in the heat exchanger 149b as earlier shown in FIG. 1.

As shown in FIG. 2, the heat exchanger 149b is formed in the groove 189 of the cooling stage 180. The heat exchanger 149b includes the laminated body 150. The side surface of the laminated body 150 is diffusion-bonded to an internal wall 184 of the groove 189.

As shown in FIG. 3, in a normal case, the laminated body 150 is made by laminating plural metal gauzes made of copper or a copper alloy (hereinafter “made of copper” in a lump). In the example shown in FIG. 3, the laminated body 150 is formed by laminating a first metal gauze 152A, a second metal gauze 152B, a third metal gauze 152C, . . . and an nth metal gauze 152N. Here, the laminated body 150 may be made of a single metal gauze 152A made of copper. Contact interfaces of the first metal gauze 152A, the second metal gauze 152B, the third metal gauze 152C, . . . , and the nth metal gauze 152N are diffusion-bonded. Therefore, thermal contact of the interfaces is improved so that the thermal resistance of the interfaces is made small.

The heat exchanger 149b is formed in the groove 189 of the cooling stage 180 in, for example, the following way.

First, the metal gauzes 152A, 152B, 152C, . . . , and 152N made of copper are laminated. Next, the formed laminated body 150 is provided in the groove 189 of the cooling stage 180. After that, a “diffusion bonding process” is applied for the cooling stage 180 so that the heat exchanger 149b is formed.

Here, the “diffusion bonding process” is a method where atomic interdiffusion is generated at the interfaces between the gauzes 152A-152N by heating so that the interface bonding is made. Normally, the diffusion bonding process of this embodiment is performed at a temperature in a range of between approximately 800° C. and approximately 1080° C. (for example, approximately 1000° C.).

By such a diffusion bonding process, at the same time when the interfaces of the metal gauzes 152A-152N are adhered and bonded, the side surface of the laminated body 150 is diffusion-bonded to the internal wall 184 of the groove 189.

The diffusion bonding process between the metal gauzes 152A-152N may be performed before the diffusion bonding process of the laminated body 150 and the internal wall 184 of the groove 189 (namely “two stages” of the diffusion bonding process).

With the structure of the heat exchanger 149b compared to a case where the laminated body 150 is supplied to the groove 189 later, contact between the heat exchanger 149b and the cooling stage 180 can be improved so that the thermal resistance between the heat exchanger 149b and the cooling stage 180 can be inhibited.

Here, in an example shown in FIG. 3, a mesh or an opening length of each of the metal gauzes 152A, 152B, 152C, . . . , and 152N made of copper may be substantially equal to the others or different from the others.

In this specification, the “mesh” means the number of stitches situated in a length of approximately 1 inch (approximately 25.4 mm.) The “opening length” means a length between neighboring wires of the metal gauze (the length of a gap).

In a case where the opening lengths of the metal gauzes 152A, 152B, 152C, . . . , and 152N are different, the opening lengths may be greater continuously or gradually (for example, in a step manner) in the order from the first metal gauze 152A to the Nth metal gauze 152N. In this case, the first metal gauze 152A having short opening lengths, compared to the Nth metal gauze 152A having long opening lengths, is provided at a side far from the low temperature end 125b of the regenerator 120 (a side near the pulse tube 140). As a result of this, when the coolant gas flows from the regenerator 120 to the pulse tube 140, a big change of the flow speed of the coolant gas may not be generated so that a more effective flow smoothening effect can be achieved.

A total number of the metal gauzes 152A-152N may differ depending on the thickness of each of the metal gauzes. The total number of the metal gauzes 152A-152N may be in a range between 2 and 200 (for example, 100).

The mesh of each of the metal gauzes made of copper is normally in a range between #16 and #300, By converting the opening length of the metal gauzes 152A-152N, this is in a range between approximately 1.14 mm and approximately 0.05 mm. It may be preferable that the meshes of the metal gauzes made of copper be in a range between #60 and #150 (which is the opening length in a range between approximately 0.303 mm and approximately 0.104 mm).

A rolling process may be applied to the metal gauzes 152A-152N. A case where the rolling process is applied to the metal gauzes is discussed at, for example, Japanese Patent Application Laid-Open Publication No. 2003-28526. As shown in FIG. 2(A) of Japanese Patent Application Laid-Open Publication No. 2003-28526, by applying the rolling process to the metal gauzes, a contact area of the metal gauzes is increased. As a result of this, thermal contact resistance of the metal gauzes becomes small so that the heat exchange efficiency rate is improved. The thickness of the metal gauzes after the rolling process is applied is in a range between approximately 0.4 mm through approximately 0.99 mm when the thickness of the metal gauze before the rolling process is applied is 1 mm. It is preferable that the thickness be in a range between approximately 0.6 mm through approximately 0.8 mm.

In the example shown in FIG. 2, the side surface of the heat exchanger 149b is diffusion-bonded to the internal wall 184 of the groove 189 of the cooling stage 180. However, the present invention is not limited to this structure. For example, the side surface of the heat exchanger 149b may be diffusion-bonded to the internal wall 184 at the low temperature end 145b of the cylinder 141 forming the pulse tube 140.

Next, a structure of another heat exchanger 149b-2 is discussed with reference to FIG. 4. FIG. 4 schematically shows a cross section of the vicinity of the groove 189 of the cooling stage 180 where the low temperature end 145b of the pulse tube 140 is connected. A schematic cross-section of an example of the heat exchanger 149b-2 used for the embodiment of the present invention is shown in FIG. 4.

As shown in FIG. 4, the heat exchanger 149b-2 is formed in the groove 189 of the cooling stage 180. The heat exchanger 149b-2 includes a laminated body substantially the same as that of the heat exchanger 149b. However, the heat exchanger 149b-2 further includes a housing 159 receiving the laminated body 150 formed of metal gauzes. The housing 159 is made of copper or a copper alloy. In addition, openings are formed in an upper surface and a lower surface of the housing 159. A size of a side surface of the housing 159 substantially corresponds to an internal diameter of the groove 189. A side surface of the laminated body 150 formed of the metal gauzes is diffusion-bonded to the internal wall 184 of the side surface of the housing 159.

The heat exchanger 149b-2 can be formed by laminating the metal gauzes 152A, 152B, 152C, . . . , and 152N and supplying the metal gauzes 152A, 152B, 152C, . . . , and 152N into the housing 159, and then by applying the diffusion bonding process to the metal gauzes 152A, 152B, 152C, and 152N together with the housing 159. After that, the housing 159 is provided in the groove 189 of the cooling stage 180 and the housing 159 is brazed to the internal wall 184 of the groove 189 of the cooling stage 180.

In a case where the housing 159 and the internal wall 184 are brazed to each other, compared to a case where the laminated body and the internal wall are directly brazed to each other, degrees of adhesion and contact of the housing 159 and the internal wall 184 at the contact interface are better. Since end parts of plural members exist at the side surface of the laminated body, it may be difficult to sufficiently smooth the side surface of the laminated body with high precision. On the other hand, since the housing 159 is formed of a single member, it is relatively easy to smooth the side surface of the housing with high precision.

Accordingly, with the structure shown in FIG. 4, compared to the related art heat exchanger, it is possible to improve the thermal contact-ability between the heat exchanger 149b-2 and the cooling stage 180 so that the thermal resistance between the heat exchanger 149b-2 and the cooling stage 180 can be effectively inhibited.

In the example shown in FIG. 4, the heat exchanger 149b-2 is directly provided in the groove 189 of the cooling stage 180. However, the present invention is not limited to this structure. For example, the outside of the heat exchanger 149b-2 may come in contact with the low temperature end 145b side of the cylinder 141 forming the pulse tube 140. In this case, the housing 159 of the heat exchanger 149b-2 is brazed to the internal wall of the cylinder 141.

In the above-discussed example, the cases where the heat exchanger 149b and the heat exchanger 149b-2 includes the laminated body 150 formed of the metal gauzes made of copper is explained. However, the present invention is not limited to this structure.

FIG. 5 shows a structure of another laminated body used for the heat exchanger 149b and the heat exchanger 149b-2.

In the example shown in FIG. 5, the laminated body 150A is formed by laminating a first metal gauze 153A, a second metal gauze 153B, a third metal gauze 153C, a fourth metal gauze 153D, . . . and an nth metal gauze 153N in this order. In the laminated body 150A, as well as the laminated body 150 discussed above, contact interfaces of the first metal gauze 153A, the second metal gauze 1538, the third metal gauze 153C, the fourth metal gauze 153D, . . . and the nth metal gauze 153N are diffusion-bonded.

While the second metal gauze 153B, the third metal gauze 153C, the fourth metal gauze 153D, . . . and the nth metal gauze 153N are made of copper, the first metal gauze 153A is made of metal or an alloy excluding copper. For example, the first metal gauze 153A may be made of stainless steel (SUS 304, 316, or the like), nickel, or the like. Stainless steel or nickel has rigidity higher than that of copper. Therefore, in a case where the first metal gauze 153A is made of stainless steel or nickel, it is possible to improve rigidity of the laminated body 150A being finally formed. Hence, the likelihood is small of the laminated body 150A being deformed due to a pressure of the coolant gas when the pulse tube refrigerator 100 is formed.

In addition, the first metal gauze 153A may have meshes relatively larger than those of other metal gauzes (opening lengths relatively shorter than those of other metal gauzes). In this case, the laminated body 150A is provided in the groove 189 so that the first metal gauze 153A is provided at a far side from the low temperature end 125b of the regenerator 120 (an upper side in the examples shown in FIG. 2 and FIG. 4). As a result of this, a more effective flow smoothening effect relative to the coolant gas reciprocating between the regenerator 120 and the pulse tube 140 can be achieved.

Normally, it is difficult to manufacture the metal gauze made of copper and having large meshes and short opening lengths due to limitations of manufacturing techniques and costs. For example, in the case of the metal gauze made of copper, a maximum value of the mesh is approximately #100 and a minimum value of the opening length is approximately 0.134 mm through approximately 0.154 mm. However, it is relatively easy to manufacture the metal gauze made of non-copper metal such as stainless steel and having large meshes and short opening lengths. Therefore, by combining two kinds of materials, it is possible to perform a wide range of design relative to flow smoothening of the heat exchangers 149b and 149b-2.

The mesh of the first metal gauze 153A is in a range between #30 and #500. By converting the opening length of the metal gauze, this is in a range between approximately 0.577 mm and approximately 0.026 mm. It may be preferable that the mesh of the first metal gauzes 153A be in a range between #60 and #400 (which is the opening length in a range between approximately 0.253 mm and approximately 0.034 mm). The mesh of the second metal gauzes 153B through the nth metal mesh 153N may be in a range between #16 and #300. By converting the opening length of the metal gauze, this is in a range between approximately 1.14 mm and approximately 0.05 mm. It may be preferable that the mesh of the second metal gauze 153B through the nth metal mesh 153N is in a range between #60 and #150 (which is the opening length in a range between approximately 0.303 mm and approximately 0.104 mm). As discussed above, the meshes or the opening lengths of the second metal gauzes 153E through the nth metal mesh 153N may be equal to or different from each other.

A total number of the metal gauzes may differ depending on the thicknesses of the metal gauzes. The total number of the metal gauzes may be in a range between 2 and 200 (for example, 100).

As discussed above, the laminated body 150A is provided in the groove 189 of the cooling stage 180 and then the diffusion bonding process is applied, so that the heat exchanger 149b is formed. Alternatively, the laminated body 150A is provided in the housing 159 and then the diffusion bonding process is applied. After that, the housing 159 is provided in the groove 189 of the cooling stage 180 and the housing 159 and the internal wall 184 are brazed to each other, so that the heat exchanger 149b-2 is formed. The diffusion bonding process is performed at a temperature in a range between approximately 800° C. and approximately 1080° C. (for example, approximately 1000° C.).

FIG. 6 shows a structure of another laminated body used for the heat exchanger 149b and the heat exchanger 149b-2.

In the example shown in FIG. 6, a laminated body 150B is formed by laminating a first metal gauze 154A, a second metal gauze 154B, a third metal gauze 154C, a fourth metal gauze 154D, . . . and an nth metal gauze 154N in this order. In the laminated body 150B, as well as the laminated body 150 and the laminated body 150A discussed above, contact interfaces of the first metal gauze 154A, the second metal gauze 154B, the third metal gauze 154C, the fourth metal gauze 154D, . . . and the nth metal gauze 153N are diffusion-bonded.

The second metal gauze 154B, the fourth metal gauze 154D, and a sixth metal gauze 154F through the nth metal gauze 154N are made of copper. On the other hand, three metal gauzes, namely, the first metal gauze 154A, the third metal gauze 154C, and a fifth metal gauze 154E are made of metal or an alloy excluding copper. For example, the first metal gauze 153A, the third metal gauze 154C, and the fifth metal gauze 154E are made of stainless steel (SUS 304, 316, or the like), nickel, or the like. The first metal gauze 154A, the third metal gauze 154C, and the fifth metal gauze 154E may be made of the same material or different materials.

In a structure shown in FIG. 6, a cycle where a metal gauze made of non-copper and a metal gauze made of copper are mutually laminated is repeated three times.

Three metal gauzes, namely, the first metal gauze 154A, the third metal gauze 154C, and the fifth metal gauze 154E have meshes relatively larger than those of other metal gauzes (opening lengths relatively shorter than those of other metal gauzes).

For example, the meshes of the first metal gauze 154A, the third metal gauze 154C, and the fifth metal gauze 154E are in a range between #30 and #500. By converting the opening length of the metal gauze, this is in a range between approximately 0.577 mm and approximately 0.026 mm. It may be preferable that the meshes of the first metal gauzes 154A, the third metal gauzes 154C, and the fifth metal gauzes 154E be in a range between #60 and #400 (which is the opening length in a range between approximately 0.253 mm and approximately 0.034 mm). On the other hand, the meshes of the metal gauzes 154B, 154D, and 154F through 154N are in a range between #16 and #300. By converting the opening length of the metal gauze, this is in a range between approximately 1.14 mm and approximately 0.05 mm. It may be preferable that the meshes of the metal gauzes 154B, 154D, and 154F through 154N are in a range between #60 and #150 (which is the opening length in a range between approximately 0.303 mm and approximately 0.104 mm). The meshes or the opening lengths of the metal gauzes made of copper may be equal to or different from each other. In a case where the opening lengths of the metal gauzes 154B through 154N are different, the opening lengths may be greater continuously or gradually (for example, in a step manner) in the order from the second metal gauze 154B to the Nth metal gauze 154N.

A total number of the metal gauzes may differ depending on the thickness of each of the metal gauzes. The total number of the metal gauzes may be in a range between 2 and 200 (for example, 100).

The laminated body 150B shown in FIG. 6 is provided in the cooling stage groove 189 so that the first metal gauze 154A is provided at a side far from the communicating path 182 of the cooling stage 180 (an upper side in the examples shown in FIG. 2 and FIG. 4).

The laminated body 150B, where there are three metal gauzes made of non-copper and the cycle number C is three, is discussed in the example shown in FIG. 6. However, in the laminated body 150B, there is no limitation of the number of the metal gauzes made of non-copper and the cycle number C. The number of the metal gauzes may be, for example, two, four or equal to or greater than six. In addition, the cycle number C may be, for example, two, four or equal to or greater than six. For example, mutual arrangement of the metal gauzes made of non-copper and the metal gauzes made of copper may be repeated from the first metal gauze to the nth metal gauze (in the entirety of the laminated body 150B).

Other objects, features, and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. For example, in the above-discussed example, the pulse tube refrigerator 100 is a single-stage type pulse tube refrigerator. However, the present invention can be applied to a multi-stage type pulse tube refrigerator such as two-stage type or three-stage type pulse tube refrigerator.

In the meantime, inventors of the present invention actually operated the pulse tube refrigerator, with normal conditions, where the heat exchanger 149b shown in FIG. 2 is formed in the groove of the cooling stage 180, so as to measure the temperature of the cooling stage 180. In addition, the laminated body 150A shown in FIG. 5 was used as the laminated body of the heat exchanger 149b. A metal gauze, made of SUS 304, whose mesh is #250 was used as the metal gauze 153A situated at the top. In addition, metal gauzes, made of copper, whose meshes are #80 were used as the metal gauzes situated at second and subsequent stages.

As a result of the measurement, it was found that the temperature of the cooling stage 180 was approximately 36.4 K. On the other hand, the same measurement was made of a pulse tube refrigerator where a conventional heat exchanger (the laminated body made of copper and having meshes of #80 provided, where the side part of the laminated body is not diffusion-bonded to the internal wall of the groove) was provided in the groove of the cooling stage. It was found that the temperature of the cooling stage was approximately 40.2 K in this case.

As a result of the measurements, it was confirmed that cooling abilities are improved in the pulse tube refrigerator 100 of the embodiment of the present invention compared to the conventional pulse tube refrigerator.

All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority or inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

The present invention can be applied to a single-stage type or a multi-stage type pulse tube refrigerator which is applied to a low temperature system such as a nuclear magnetic resonance diagnostic apparatus, a superconducting magnet apparatus, or a cryopump.