JP6320142B2 - Cryogenic refrigerator - Google Patents

Description

  The present invention relates to a cryogenic refrigerator that accumulates cold generated by Simon expansion of high-pressure refrigerant gas supplied from a compressor and generates desired cryogenic cold.

  There exists a thing of patent document 1 as a cryogenic refrigerator, for example. The displacer-type cryogenic refrigerator generates cold by expanding the refrigerant gas in the expansion space while reciprocating the displacer inside the cylinder. In addition, the pulse tube type cryogenic refrigerator generates cold by expanding the refrigerant gas in the expansion space while reciprocating the gas piston in the pulse tube. The refrigerant gas generated in the expansion space is transmitted to the cooling stage while being accumulated in the regenerator, reaches a desired cryogenic temperature, and cools the cooling target connected to the cooling stage.

JP 2013-2217517 A

  An object of this invention is to provide the technique which raises the efficiency of a cryogenic refrigerator.

  In order to solve the above problems, an aspect of the present invention is a cryogenic refrigerator including a regenerator. The regenerator is accommodated in the container, the nonmagnetic regenerator material accommodated in the first region on the high temperature side of the container, the magnetic regenerator material accommodated in the second region on the low temperature side of the container, and the first region. An insertion member. The thermal conductivity of the insertion member is 10 [W / (m · K)] or less at a temperature at which the cryogenic refrigerator is operating.

  Another embodiment of the present invention is also a cryogenic refrigerator. This cryogenic refrigerator is a cryogenic refrigerator including a high temperature side regenerator and a low temperature side regenerator. The low temperature side regenerator includes a container, a nonmagnetic regenerator material accommodated in the first region on the high temperature side of the container, and a magnetic regenerator material accommodated in the second region on the low temperature side of the container. The container has a cross-sectional area in a plane perpendicular to the axis of the container in at least a part of the first region that is smaller than a cross-sectional area in a plane perpendicular to the axis of the container in the second region, and the thermal conductivity of the container is It is 10 [W / (m · K)] or less at the temperature at which the cryogenic refrigerator is operating.

  According to the cryogenic refrigerator of the present invention, the regenerator material can be reduced while maintaining the refrigeration performance, and the efficiency of the refrigerator can be increased.

It is a figure which shows typically the whole structure of the cryogenic refrigerator which concerns on embodiment. It is a figure which shows typically the internal structure of the expander with which the cryogenic refrigerator which concerns on embodiment is provided. It is a figure which shows the temperature change of each density of helium gas of 2.2 MPa and helium gas of 0.8 MPa, and the temperature change of the density difference of both. It is a figure which shows an example of the temperature profile of the 2nd regenerator which concerns on embodiment. FIGS. 5A to 5D are diagrams showing the relationship between the size of the insertion member and the temperature of the first cooling stage and the temperature of the second cooling stage at that time. It is a figure which shows the temperature change of the cooling stage when the copper member is inserted in the high temperature side area of the second regenerator so as to be in thermal contact with the rectifier at the upper end. It is a figure which shows the thermal conductivity [W / (m * K)] of copper, stainless steel, and a fluorocarbon resin in 40K. It is a figure which shows typically the internal structure of the expander with which the cryogenic refrigerator which concerns on the modification of embodiment is provided.

A cryogenic refrigerator generally includes a compressor and an expander. For example, helium gas is used as the refrigerant gas of the cryogenic refrigerator. The compressor compresses low-pressure (for example, 0.8 MPa) helium gas and generates high-pressure (for example, 2.2 MPa) helium gas. The density difference between the density of the high-pressure helium gas and the density of the low-pressure helium gas has a large temperature dependence in the vicinity of extremely low temperatures, and the density difference becomes maximum especially when the temperature is around 8K. Therefore regenerator cryocooler provided according to the embodiment, in order to reduce the volume of the region where the density difference of helium gas in the regenerator is maximized substantially temperature during operation of the cryogenic refrigerator The insertion member is accommodated in a region near 8K. Further, in order to suppress the conduction of heat in the upper regenerator and the expansion space, the thermal conductivity of this insertion member is 10 [W / (m · K)] or less at the temperature at which the cryogenic refrigerator is operating. It is.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.

  First, the overall configuration of the cryogenic refrigerator of the embodiment will be described. FIG. 1 is a diagram schematically illustrating an overall configuration of a cryogenic refrigerator 100 according to an embodiment. As shown in FIG. 1, the cryogenic refrigerator 100 includes a compressor 1, an expander 10, a pipe 7, a power cable 8, and a cooling water pipe connection 9.

  The compressor 1 compresses the low-pressure refrigerant gas returned from the expander 10 and supplies the compressed high-pressure refrigerant gas to the expander 10. The expander 10 expands the high-pressure refrigerant gas supplied from the compressor 1 to generate cold. Details of the expander 10 will be described later.

  The pipe 7 is connected to the expander 10 and the compressor 1, and causes the refrigerant gas to flow between the expander 10 and the compressor 1. The pipe 7 includes a low pressure pipe 7a and a high pressure pipe 7b. The low-pressure piping 7a flows the low-pressure refrigerant gas from the expander 10 toward the compressor 1. On the other hand, high-pressure refrigerant gas from the compressor 1 toward the expander 10 flows through the high-pressure pipe 7b.

  The power cable 8 is connected to the compressor 1 and the expander 10. The power cable 8 is used to supply power from the compressor 1 as power for the expander 10. The cooling water pipe connection unit 9 connects a pipe (not shown) through which cooling water flows. The cooling water is used for cooling the compression heat generated by the compressor 1 compressing the refrigerant gas and exhausting the heat to the outside of the compressor 1.

  FIG. 2 is a diagram schematically illustrating an internal configuration of the expander 10 included in the cryogenic refrigerator 100 according to the embodiment. In the embodiment, a Gifford-McMahon (GM) refrigerator is taken as an example of the cryogenic refrigerator 100, and the expander 10 will be described. As shown in FIG. 2, the cryogenic refrigerator 100 according to the embodiment includes a two-stage expander 10. Therefore, the expander 10 includes two cylinders, a first cylinder 11 and a second cylinder 12.

  The first cylinder 11 and the second cylinder 12 are integrally formed, and each has a high temperature end and a low temperature end. The low temperature end of the first cylinder 11 and the high temperature end of the second cylinder 12 are connected at the bottom of the first cylinder 11. The second cylinder 12 is formed in a form extending in the same axial direction as the first cylinder 11, and is a cylindrical member having a smaller diameter than the first cylinder 11. The first cylinder 11 is a container for accommodating the first displacer 13 so as to be reciprocally movable in the longitudinal direction, and the second cylinder 12 is a container for accommodating the second displacer 14 so as to be reciprocally movable in the longitudinal direction. The first displacer 13 and the second displacer 14 are connected via, for example, a pin 15, a connector 16, and a pin 17.

  A scotch yoke mechanism (not shown) that reciprocates the first displacer 13 and the second displacer 14 is provided at the high temperature end of the first cylinder 11. For the first cylinder 11 and the second cylinder 12, for example, stainless steel is used in consideration of strength, thermal conductivity, helium blocking ability, and the like.

  The first displacer 13 is made of, for example, cloth-containing phenol from the viewpoint of specific gravity, strength, thermal conductivity, and the like. The second displacer 14 is a metal cylinder such as stainless steel. A film of an abrasion-resistant resin such as a fluororesin may be formed on the outer peripheral surface of the second displacer 14.

  The first displacer 13 has a cylindrical outer peripheral surface, and the inside of the first displacer 13 is filled with a first regenerator material made of a wire mesh or the like. The internal volume of the first displacer 13 functions as the first regenerator 18. A rectifier 19 is installed in the upper part of the first regenerator 18, and a rectifier 20 is installed in the lower part. The room temperature chamber 21 is a space formed by the first cylinder 11 and the high temperature end of the first displacer 13, and the volume changes as the first displacer 13 reciprocates. A first opening 22 through which the refrigerant gas flows from the room temperature chamber 21 to the first displacer 13 is formed at the high temperature end of the first displacer 13.

  The room temperature chamber 21 is connected to a common supply / exhaust pipe among the pipes connecting the intake and exhaust systems including the compressor 1, the supply valve 23, and the return valve 24. Further, a seal 25 is mounted between the portion of the first displacer 13 from the high temperature end and the first cylinder 11.

  The first expansion space 26 is a space formed by the first cylinder 11 and the first displacer 13, and the volume changes as the first displacer 13 reciprocates. A second opening 27 is formed at the low temperature end of the first displacer 13 for introducing the refrigerant gas into the first expansion space 26 via the first clearance C1.

  A first cooling stage 28 that is thermally connected to the object to be cooled is disposed at a position corresponding to the first expansion space 26 in the outer periphery of the first cylinder 11. The first cooling stage 28 is cooled by the refrigerant gas passing through the first clearance C1. The first expansion space 26 and the high temperature end of the second displacer 14 are communicated with each other through a communication path around the connector 16. The refrigerant gas flows from the first expansion space 26 to the second displacer 14 through this communication path.

The second displacer 14 has a cylindrical outer peripheral surface, and the inside of the second displacer 14 has two stages in the axial direction with a rectifier 29 at the upper end, a rectifier 30 at the lower end, and a partition member 31 positioned between the upper and lower sides. It is divided into. Of the internal volume of the second displacer 14, the high temperature side region 32 on the higher temperature (upper) side than the partition material 31 is filled with a second regenerator material made of a nonmagnetic material such as lead or bismuth. The low temperature side region 33 of the low temperature (lower) side of the partition member 31, different cold storage material, for example, the third cold accumulating material of a magnetic material such as HoCu ₂ is filled with the high temperature side region 32. Lead, bismuth, HoCu _{2 and the} like are formed in a spherical shape, and a plurality of spherical formations are gathered to form a cold storage material. The partition member 31 prevents the cold storage material in the high temperature side region 32 and the cold storage material in the low temperature side region 33 from mixing. The high temperature side region 32 and the low temperature side region 33 which are internal volumes of the second displacer 14 function as the second regenerator 34.

  The high temperature side region 32 accommodates an insertion member 42 that does not allow the refrigerant gas to pass therethrough. Details of the insertion member 42 will be described later.

  The second expansion space 35 is a space formed by the second cylinder 12 and the second displacer 14, and the volume changes as the second displacer 14 reciprocates. A third opening 36 is formed at the low temperature end of the second displacer 14. The third opening 36 allows the refrigerant gas to flow through the second expansion space 35 via the second clearance C2. The second clearance C <b> 2 is formed by the low temperature end of the second cylinder 12 and the second displacer 14.

  A second cooling stage 37 that is thermally connected to the object to be cooled is disposed at a position corresponding to the second expansion space 35 on the outer periphery of the second cylinder 12. The second cooling stage 37 is cooled by the refrigerant gas passing through the second clearance C2.

  The first displacer 13 and the second displacer 14 include a lid portion 38 and a lid portion 39 at the low temperature end, respectively. From the viewpoint of joining the first displacer 13 and the second displacer 14, the lid portion 38 and the lid portion 39 each have a two-stage cylindrical shape. The lid portion 38 is fixed to the first displacer 13 by a press-fit pin 40. Similarly, the lid portion 39 is fixed to the second displacer 14 by a press-fit pin 41.

  Next, the operation of the cryogenic refrigerator 100 according to the embodiment will be described.

  At a certain point in the refrigerant gas supply process, the first displacer 13 and the second displacer 14 are located at the bottom dead center of the first cylinder 11 and the second cylinder 12. When the supply valve 23 is opened at the same time or at a slightly shifted timing, high-pressure refrigerant gas is supplied into the first cylinder 11 from the supply / discharge common pipe through the supply valve 23. As a result, the high-pressure refrigerant gas flows into the first regenerator 18 inside the first displacer 13 from the first opening 22 located at the top of the first displacer 13. The high-pressure refrigerant gas that has flowed into the first regenerator 18 is cooled by the first regenerator material and enters the first expansion space 26 via the second opening 27 and the first clearance C1 that are located below the first displacer 13. Supplied.

  The high-pressure refrigerant gas supplied to the first expansion space 26 flows into the second regenerator 34 inside the second displacer 14 through the communication passage around the connector 16. The high-pressure refrigerant gas that has flowed into the second regenerator 34 is supplied to the second expansion space 35 through the third opening 36 and the second clearance that are positioned below the second displacer 14 while being cooled by the second regenerator. Is done.

  In this way, the first expansion space 26 and the second expansion space 35 are filled with the high-pressure refrigerant gas, and the supply valve 23 is closed. At this time, the first displacer 13 and the second displacer 14 are located at the top dead center in the first cylinder 11 and the second cylinder 12. When the return valve 24 is opened at the same time or slightly shifted timing, the refrigerant gas in the first expansion space 26 and the second expansion space 35 is decompressed and expanded. The refrigerant gas in the first expansion space 26 that has become low temperature due to expansion absorbs the heat of the first cooling stage 28 through the first clearance C1. Similarly, the refrigerant gas in the second expansion space 35 absorbs the heat of the second cooling stage 37 through the second clearance C2.

  The first displacer 13 and the second displacer 14 move toward the bottom dead center, and the volumes of the first expansion space 26 and the second expansion space 35 decrease. The refrigerant gas in the second expansion space 35 is returned to the first expansion space 26 via the second clearance C2, the third opening 36, the second regenerator 34, and the communication path. Further, the refrigerant gas in the first expansion space 26 is returned to the suction side of the compressor 1 through the second opening 27, the first regenerator 18, and the first opening 22. At that time, the first cold storage material and the second cold storage material are cooled by the refrigerant gas. This process is defined as one cycle, and the cryogenic refrigerator 100 cools the first cooling stage 28 and the second cooling stage 37 by repeating this cooling cycle.

  As described above, the cooling cycle in the cryogenic refrigerator 100 includes an operation in which the refrigerant gas repeatedly varies in pressure by repeatedly flowing in and out of the second regenerator 34. Hereinafter, when helium gas is used as the refrigerant gas, the temperature profile and mass change of the helium gas present in the second regenerator 34 will be described.

  FIG. 3 is a diagram showing a temperature change of each density of a 2.2 MPa helium gas and a 0.8 MPa helium gas, and a temperature change of a density difference between them. As shown in FIG. 3, the density difference between the 2.2 MPa helium gas and the 0.8 MPa helium gas becomes maximum when the temperature is about 9K. When the temperature of the helium gas is lower than 9K, the density difference between the 2.2 MPa helium gas and the 0.8 MPa helium gas monotonously increases with respect to the temperature, and when the helium gas temperature is higher than 9K, The density difference decreases monotonically with temperature.

Here, let M be the mass of helium gas present in the second regenerator 34. Further, the high temperature end of the second regenerator 34, i.e. the mass per unit time of the helium gas flowing to the rectifier 29 of the upper end and m _in, the mass per unit of the helium gas flowing out time from the rectifier 30 of the lower m _out And If helium gas flows into the second regenerator 34, the mass M of helium gas present in the second regenerator 34 increases. On the other hand, if helium gas flows out from the second regenerator 34, the mass M of helium gas present in the second regenerator 34 decreases. Thus, mass m _in per unit time of the helium gas flowing to the rectifier 29 at the upper end, the amount of change dM / dt and the lower end of the rectifier 30 per unit time of the mass M of the helium gas present in the second regenerator 34 The mass per unit time of the helium gas flowing out from the gas is the sum of m _out . From the above, the following relational expression (1) is obtained.
m _in = dM / dt + m _out (1)

As described above, the second regenerator 34 is inside the second displacer 14, and the second displacer 14 is configured by sandwiching a spherical second regenerator material such as lead or bismuth in the axial direction with a felt and a metal mesh. Composed. Accordingly, since the volume of the second regenerator 34 can be regarded as constant, the value is set to V. Further, if the average density of the helium gas in the second regenerator 34 is ρ, the mass M of the refrigerant gas existing in the second regenerator 34 can be expressed by the following equation (2).
M = Vρ (2)

Substituting equation (2) into equation (1) yields the following equation (3).
m _in = Vdρ / dt + m _out (3)
Here, dρ / dt represents a time derivative of the density ρ of helium gas.

In the formula (3), the density of the helium gas flowing into the second regenerator 34 is assumed not to change (dp / dt = 0) by the _time, and _m in ₌ m _out. This means that helium gas flows out of the second regenerator 34 by the amount that flows into the second regenerator 34. That is, it means that the mass M of the helium gas present in the second regenerator 34 does not change. However, in an actual system, when the supply valve 23 is opened, high-pressure helium gas is supplied through the supply valve 23. As a result, the high-pressure helium gas also flows into the second regenerator 34, and the low-pressure helium gas charged in the second regenerator 34 is pressurized to become high-pressure helium gas.

As shown in FIG. 3, there is a difference in density between high-pressure helium gas and low-pressure helium gas. Therefore, when the high-pressure helium gas flows into the second regenerator 34 and the low-pressure helium gas in the second regenerator 34 is boosted to become the high-pressure helium gas, the right side in Equation (3) has a positive value. More specifically, the right side in equation (3) is the density difference indicated by the solid line in FIG. From the above, the following inequality (4) is obtained.
_{Vdρ / dt = m in -m out} > 0 (4)

  As described above, the high-pressure helium gas that has flowed into the second regenerator 34 is expanded by the second expansion via the third opening 36 and the second clearance that are positioned below the second displacer 14 while being cooled by the second regenerator. It is supplied to the space 35. However, the inequality (4) indicates that the mass of helium gas flowing out from the second regenerator 34 into the second expansion space 35 is smaller than the mass of helium gas flowing into the second regenerator. This means that the second regenerator 34 functions like a helium gas buffer. As a result of the decrease in helium gas flowing out from the second regenerator 34 into the second expansion space 35, the pressure in the second expansion space 35 also decreases.

When the return valve 24 is opened, the high pressure helium gas in the second regenerator 34 is depressurized to become low pressure helium gas. At this time, the right side in Equation (3) is a negative value having the density difference indicated by the solid line in FIG. 3 as an absolute value. Therefore, the following inequality (5) is obtained.
_{Vdρ / dt = m in -m out} <0 (5)

  This indicates that the mass of helium gas flowing out from the second regenerator 34 is larger than the mass of helium gas flowing into the second regenerator 34 from the second expansion space 35. This means that the helium gas in the second regenerator 34 that has been reduced in pressure and reduced in density flows out from the second regenerator 34 to the first expansion space 26.

  Here, the amount of helium gas recovered by the compressor 1 is constant. For this reason, the amount of helium gas expanded in the second expansion space 35 is reduced by the amount of helium gas in the second regenerator 34 flowing out of the second regenerator 34. As a result, the helium gas that expands in the second expansion space 35 and passes through the second clearance C2 is reduced, so that the cooling efficiency of the second cooling stage 37 is lowered.

  FIG. 4 is a diagram illustrating an example of the temperature profile of the second regenerator 34 according to the embodiment, and the second regenerator when the distance from the high temperature end to the low temperature end of the second regenerator 34 is 1. 3 is a graph showing a temperature profile of the vessel 34.

  As shown in FIG. 4, in the second regenerator 34 of the two-stage refrigerator, the temperature profile from the high temperature end to the low temperature end has a shape that is inversely proportional to the distance from the high temperature end, It becomes a shape. In FIG. 4, the temperature gradient is greatest in the high temperature side region 32 of the second regenerator 34. The high temperature side region 32 includes a region where the temperature of the cryogenic refrigerator 100 is about 9K during operation. This temperature coincides with the temperature at which the density difference of helium gas is maximum in FIG.

  Based on the above, the second regenerator 34 according to the embodiment accommodates the insertion member 42 that inhibits the flow of helium gas in the high temperature side region 32 of the second regenerator 34. The insertion member 42 is fixed and arranged on the partition member 31 so as to be coaxial with the second regenerator 34.

When the insertion member 42 is accommodated in the high temperature side region 32 of the second regenerator 34, the region where the helium gas can exist in the second regenerator 34 is reduced by the volume V ₁ of the insertion member 42. Since the helium gas can not pass through the insertion member 42, the volume V of the second regenerator 34, the remaining volume is substantially minus the volume V ₁ of the insert member 42 from the volume V of the second regenerator 34 V ₂ (= V−V ₁ ). At this time, the above equation (3) becomes the following equation (6).
m _in = V ₂ dρ / dt + m _out (6)
However,
V ₂ <V (7)
It is.

When mass m _in per unit time of the helium gas flowing into the second regenerator 34 via a rectifier 29 from the first expansion space 26 is constant, equation (6) and the equation (7), a rectifier _Mout increases the mass per unit time of the helium gas flowing out from 30 to the second expansion space 35. However, in the actual system, mass m _in per unit time of the helium gas flowing from the first expansion space 26 to the second regenerator 34 is reduced. When the mass per unit time of the helium gas flowing from the first expansion space 26 to the second regenerator 34 and m _'in the case that houses the insertion member 42 to the high temperature side region 32 of the second regenerator 34, the formula (6) becomes the following formula (8).
m ′ _in = V ₂ dρ / dt + m _out (8)
However,
_{m 'in <m in (9} )
It is.

  The helium gas remains in the first expansion space 26 as much as the helium gas flowing into the second regenerator 34 from the first expansion space 26 decreases. The helium gas remaining in the first expansion space 26 expands in the first expansion space 26 and contributes to the generation of cold. For this reason, the temperature of the first cooling stage 28 can be further lowered.

From equation (8) and (9), the left-hand side m _'in the formula (8) is smaller than the left-hand side _{m in} the formula (3), also the right side _V 2 _dρ / dt _{+ m out} of Formula (8), equation (3 ) On the right side of Vdρ / dt + m _out . On the other hand, since V ₂ <V from Expression (7), the first term V ₂ dρ / dt on the right side of Expression (8) is smaller than the first term Vdρ / dt on the right side of Expression (3). Therefore, it is possible to suppress a decrease in the second term m _out on the right side of Equation (8).

From the above, the qualitative advantages of accommodating the insertion member 42 in the high temperature side region 32 of the second regenerator 34 can be summarized into the following three.
1. The helium gas flowing from the first expansion space 26 into the second regenerator 34 is reduced by the volume of the insertion member 42, and the helium gas expanding in the first expansion space 26 is increased. The increased helium gas expands in the first expansion space 26 and generates cold, contributing to a decrease in the temperature of the first cooling stage 28.
2. During the operation of the cryogenic refrigerator 100, the temperature of the high temperature side region 32 of the second regenerator 34 is in a temperature range in which the density difference between the high pressure helium gas and the low pressure helium gas becomes large. The volume of the region in which the above-described helium gas behaves like a buffer is reduced by the volume of the insertion member 42, and the flow rate of helium gas moving between the second regenerator 34 and the second expansion space 35 is reduced. To increase.
3. The cold storage material accommodated in the high temperature side region 32 of the second regenerator 34 is reduced by the volume of the insertion member 42.

  The qualitative effect of housing the insertion member 42 in the high temperature side region 32 of the second regenerator 34 has been described above. Next, a specific size of the insertion member 42 to be inserted into the high temperature side region 32 of the second regenerator 34 will be described.

  FIGS. 5A and 5B are diagrams showing the relationship between the size of the insertion member 42 and the temperature of the first cooling stage 28 and the temperature of the second cooling stage 37 at that time. More specifically, FIG. 5A is a graph showing a temperature change of each cooling stage when the insertion member 42 is a fluorocarbon resin, and FIG. 5B is a graph showing each temperature change when the insertion member 42 is stainless steel. It is a graph which shows the temperature change of a cooling stage.

  As described above, the second regenerator 34 is the internal volume of the second displacer 14 and has a cylindrical shape. The shape of the insertion member 42 is, for example, a cylinder or a prism. Since the insertion member 42 is disposed in the high temperature side region 32 of the second regenerator 34 so as to be coaxial with the second regenerator 34, the insertion member 42 is inserted when cut by a plane perpendicular to the axis of the second regenerator 34. The cross-sectional area of the member 42 is constant regardless of its axial position.

Now, the cross-sectional area of the second regenerator 34 when cut along a plane perpendicular to the axis of the second regenerator 34 and S _1, the cross-sectional area of the insert member 42 in the plane and S _2. Figure 5 (a) - the horizontal axis in the graph of (b), the difference to the cross-sectional area _{S 1} of the second regenerator 34, the cross-sectional area _{S 2} of the sectional area _{S 1} and the insertion member 42 of the second regenerator 34 It is the ratio of S ₁ -S ₂ . That is, the larger the sectional area _{S 2} of the insertion member 42, a difference _S 1 -S ₂ of the cross-sectional area _{S 2} of the sectional area _{S 1} and the insertion member 42 of the second regenerator 34 is small. Hereinafter, to the cross-sectional area _{S 1} of the second regenerator 34, the ratio of the difference _S 1 -S ₂ of the cross-sectional area _{S 2} of the sectional area _{S 1} and the insertion member 42 of the second regenerator 34, simply "sectional area ratio May be described. Also, in the vertical axis of the graphs of FIGS. 5A to 5B, “first stage temperature” represents the temperature of the first cooling stage 28, and “two stage temperature” represents the temperature of the second cooling stage 37. Represent.

As shown in FIG. 5A, when the insertion member 42 is not inserted into the high temperature side region 32 of the second regenerator 34, that is, when the cross-sectional area ratio is 1.0, the first stage temperature is approximately 36.2K. Yes, the two stage temperature is approximately 3.82K. When sectional area _{S 2} of the insertion member 42 is approximately 5% of the cross-sectional area _{S 1} of the second regenerator 34, i.e., when the cross-sectional area ratio is approximately 0.95, the first stage temperature is about 34.6K, and the 2 The plate temperature is approximately 3.83K.

The cross-sectional area _{S 2} is further increased in the insertion member 42, when the cross-sectional area _{S 2} of the insertion member 42 was set to approximately 10% of the cross-sectional area _{S 1} of the second regenerator 34, the first stage temperature is about 35.8K, and the The two-stage temperature is approximately 3.85K. Further increasing the sectional area S ₂ of the insertion member 42, both increase the first stage temperature and 2-stage temperature. When the sectional area S ₂ of the insertion member 42 of approximately 25% of the cross-sectional area S ₁ of the second regenerator 34, the same extent as if not inserted both insert member 42 and the first stage temperature and 2-stage temperature.

As shown in FIG. 5 (b), even if the insertion member 42 is stainless steel, when the cross-sectional area of the insert member 42 is S ₂ of approximately 5% of the cross-sectional area S ₁ of the second regenerator 34, the 2-stage temperature The first stage temperature is lowest while maintaining. When sectional area S ₂ of the insertion member 42 is approximately 25% of the cross-sectional area S ₁ of the second regenerator 34, the first stage temperature is the same extent as if not inserted insertion member 42.

Thus, the cross-sectional area S ₂ of the insertion member 42 accommodated in the high temperature side region 32 of the second regenerator 34 is equal to or more than 25% of the cross-sectional area S ₁ of the second regenerator 34, the first stage temperature While maintaining, the cool storage material accommodated in the high temperature side area | region 32 can be decreased. In particular, inserted in the case member 42 is fluorocarbon resin, when the cross-sectional area S ₂ of the insertion member 42 is 25% or less of the cross-sectional area S ₁ of the second regenerator 34, when no insert the insertion member 42 1 It is equal to or lower than the stage temperature and the stage temperature. Sectional area S ₂ of the insert member 42 when 5% of the cross-sectional area S ₁ of the second regenerator 34, the first stage temperature is most improved. Accordingly, the sectional area _{S 2} of the insert member 42 is preferably set to about 5% of the cross-sectional area _{S 1} of the second regenerator 34.

  By the way, in the example shown in FIG. 2, the insertion member 42 inserted into the high temperature side region 32 of the second regenerator 34 is in thermal contact with the rectifier 29 at the upper end. The temperature of the rectifier 29 at the upper end is equivalent to the temperature of the first expansion space 26, and is close to the maximum temperature in the temperature profile of the second regenerator 34 as shown in FIG. Therefore, if the insertion member 42 is a material that easily conducts heat, such as copper, the internal temperature of the second regenerator 34 rises. In this case, the first stage temperature or the second stage temperature may increase.

FIG. 6 is a diagram showing a temperature change of the cooling stage when a copper member is inserted into the high temperature side region 32 of the second regenerator 34 so as to be in thermal contact with the rectifier 29 at the upper end. As shown in FIG. 6, when a copper member having a diameter of 2 mm is inserted, both the first stage temperature and the second stage temperature rise. Here, the cross-sectional area of the copper member having a diameter of 2 mm is less than 1% of the cross-sectional area S ₁ of the second regenerator 34.

  FIG. 7 is a diagram showing the thermal conductivity [W / (m · K)] of copper, stainless steel, and fluorocarbon resin at 40K. As shown in FIG. 4, during operation of the cryogenic refrigerator 100, the rectifier 29 at the upper end is approximately 40K. Accordingly, FIG. 7 shows the thermal conductivity of each member when copper, stainless steel, and fluorocarbon resin are inserted into the high temperature side region 32 of the second regenerator 34 while the cryogenic refrigerator 100 is in operation. As shown in FIG. 7, the thermal conductivity of copper at 40K is 1850 [W / (m · K)]. This is 3 orders of magnitude larger than the thermal conductivity of 5 [W / (m · K)] for stainless steel at 40 K, and 0.2 [W / (m · K) for the thermal conductivity of fluorocarbon resin. ] 4 digits larger than

The qualitative advantage of housing the insertion member 42 in the high temperature side region 32 of the second regenerator 34 described above occurs regardless of the type of material of the insertion member 42. However, when the thermal conductivity of the insertion member 42 is large, the heat of the rectifier 29 at the upper end transmitted to the inside of the second regenerator 34 negates the above advantage. As a result, the first stage temperature and the second stage temperature rather increase. This is because the thermal conductivity of copper at 40K is an order of magnitude greater than that of stainless steel or fluorocarbon resin, so that the cross-sectional area S of the copper member inserted in the high temperature side region 32 of the second regenerator 34. _This is because even if it is less than 1% of 1, the first stage temperature and the second stage temperature will rise.

From the above, the thermal conductivity of the insertion member 42 is approximately the same as that of stainless steel or fluorocarbon resin at the temperature at which the cryogenic refrigerator 100 is operating, specifically 10 [W / (m · K )] It is preferable that: If the thermal conductivity of the insertion member 42 is about the same as that of stainless steel or fluorocarbon resin, the insertion member 42 is accommodated in the high temperature side region 32 of the second regenerator 34, so that the certain effect described above is achieved. Occurs. Thus, for example, the cross-sectional area _{S 2} of the insert member 42 may be any 25% or less than 1% of the cross-sectional area _{S 1} of the second regenerator 34, more preferably, long less than 15% 1% More preferably, it may be 1% or more and 10% or less.

  As described above, according to the cryogenic refrigerator 100 according to the embodiment of the present invention, the efficiency of the cryogenic refrigerator 100 can be increased.

  In particular, helium flowing from the first expansion space 26 into the second regenerator 34 is reduced by the volume of the insertion member 42 inserted into the high temperature side region 32 of the second regenerator 34. For this reason, helium gas expanding in the first expansion space 26 increases. As a result, more cold is generated in the first expansion space 26, and the temperature of the first cooling stage 28 can be lowered. Further, the helium gas present at a temperature at which the density difference of the helium gas becomes large is reduced by the volume of the insertion member 42 inserted into the high temperature side region 32 of the second regenerator 34. As a result, the flow rate of helium gas that moves between the second regenerator 34 and the second expansion space 35 can be increased. Furthermore, the regenerator material accommodated in the high temperature side region 32 of the second regenerator 34 can be reduced by the volume of the insertion member 42 inserted into the high temperature side region 32 of the second regenerator 34. As a result, the manufacturing cost of the cryogenic refrigerator 100 can be reduced.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions are made to the above-described embodiments without departing from the scope of the present invention. be able to.

  In the above, when the insertion member 42 made of a member having a low thermal conductivity is inserted into the high temperature side region 32 of the second regenerator 34 to reduce the substantial volume of the high temperature side region 32 of the second regenerator 34. explained. However, the method for reducing the volume of the high temperature side region 32 of the second regenerator 34 is not limited to the case where the insertion member 42 is inserted. Alternatively or in addition, the volume of the portion corresponding to the high temperature side region 32 of the second displacer 14 may be reduced.

  FIG. 8 is a diagram schematically illustrating an internal configuration of the expander 10 included in the cryogenic refrigerator 100 according to the modification of the embodiment. In FIG. 8, the same members as those of the cryogenic refrigerator 100 according to the above-described embodiment are denoted by the same reference numerals. Hereinafter, in the cryogenic refrigerator 100 according to the modified example, portions overlapping with the cryogenic refrigerator 100 according to the modified example of the embodiment will be described by omitting or simplifying them as appropriate.

  As shown in FIG. 8, in the cryogenic refrigerator 100 according to the modification, the insertion member 42 is not accommodated in the high temperature side region 32 of the second regenerator 34. Instead, in the second displacer 14 according to the modification, the portion corresponding to the high temperature side region 32 is a thicker container than the second displacer 14 according to the embodiment shown in FIG. For this reason, the cross-sectional area of the high temperature side region 32 of the second regenerator 34 according to the modification is smaller than the cross sectional area of the low temperature side region 33. Here, the “cross-sectional area of the high temperature side region 32” is a cross sectional area of the high temperature side region 32 when it is cut by a plane perpendicular to the axis of the second regenerator 34. The same applies to the “cross-sectional area of the low temperature side region 33”.

  More specifically, the cross-sectional area of the high temperature side region 32 is preferably 75% to 99% of the cross sectional area of the low temperature side region 33. As described above, the outer periphery of the second displacer 14 is a metal cylinder such as stainless steel. Therefore, the thermal conductivity of the wall portion of the high temperature side region 32 is 10 [W / (m · K)] or less at about 40 K, which is the temperature at which the cryogenic refrigerator 100 is operating.

  With the configuration as described above, according to the cryogenic refrigerator 100 according to the modified example, the volume of the high temperature side region 32 of the second regenerator 34 is reduced, and thus the second regenerator 34 from the first expansion space 26. The helium gas flowing into the gas is reduced. Thereby, helium gas expanding in the first expansion space 26 increases. As a result, more cold is generated in the first expansion space 26, and the temperature of the first cooling stage 28 can be lowered. Moreover, since the volume of the high temperature side region 32 of the second regenerator 34 is reduced, the helium gas present at a temperature at which the density difference of the helium gas is increased is reduced. As a result, the flow rate of helium gas that moves between the second regenerator 34 and the second expansion space 35 can be increased. Furthermore, since the volume of the high temperature side region 32 of the second regenerator 34 is reduced, the amount of cold storage material accommodated in the high temperature side region 32 of the second regenerator 34 can be reduced.

  FIG. 8 illustrates a case where the cross-sectional area in all portions of the high temperature side region 32 is smaller than the cross sectional area of the low temperature side region 33. The cross-sectional area in all parts of the high temperature side region 32 may not be smaller than the cross sectional area of the low temperature side region 33, and the cross sectional area in at least a part of the high temperature side region 32 is larger than the cross sectional area of the low temperature side region 33. Should be smaller.

  Further, FIG. 8 illustrates a case where the cross-sectional area in all portions of the high temperature side region 32 is constant, but this cross-sectional area may not necessarily be constant. For example, the cross-sectional area may continuously increase from the upper end side (high temperature side) to the lower end side (low temperature side) of the high temperature side region 32.

  Although the case where the number of stages is two in the cryogenic refrigerator 100 has been described above, the number of stages can be appropriately selected to be three or more. In the embodiment, the example in which the cryogenic refrigerator is a displacer type GM refrigerator has been described, but the invention is not limited thereto. For example, the present invention can be applied to a pulse tube refrigerator, a Stirling refrigerator, a Solvay refrigerator, and the like.

Above, the shape of the insertion member 42 is describes the Nitsu case of a cylindrical or prismatic. The shape of the insertion member 42 is not limited to a cylinder or a prism, and may be a cone or a pyramid, for example.

  Although the above has described the case where the insertion member 42 is in thermal contact with the rectifier 29 at the upper end, the insertion member 42 may not be in thermal contact with the rectifier 29. In this case, it is possible to further suppress the heat of the rectifier 29 from entering the second regenerator 34 through the insertion member 42.

  DESCRIPTION OF SYMBOLS 1 Compressor, C1 1st clearance, C2 2nd clearance, 7 piping, 7a Low pressure piping, 7b High pressure piping, 8 Power supply cable, 9 Cooling water piping connection part, 10 Expansion machine, 11 1st cylinder, 12 2nd cylinder, 13 First Displacer, 14 Second Displacer, 15 Pin, 16 Connector, 17 Pin, 18 First Regenerator, 19, 20 Rectifier, 21 Room Temperature Room, 22 First Opening, 23 Supply Valve, 24 Return Valve, 25 Seal, 26 first expansion space, 27 second opening, 28 first cooling stage, 29, 30 rectifier, 31 partition material, 32 high temperature side region, 33 low temperature side region, 34 second regenerator, 35 second expansion space, 36 second 3 openings, 37 second cooling stage, 38, 39 lid, 0,41 Compliant Pin, 42 insertion member, 100 cryogenic refrigerator.

Claims (8)

The supplied high-pressure refrigerant gas is expanded to generate cold and, a cryogenic refrigerator comprising an expander for exhausting low pressure refrigerant gas, and the high-pressure refrigerant gas and the low-pressure refrigerant gas and a regenerator that flows alternately And
The regenerator includes an axially extending container, an insertion member, a non-magnetic regenerator material, and a magnetic regenerator material,
The insertion member is accommodated in the first region on the high temperature side of the container, and reduces the volume in which the nonmagnetic cold storage material is accommodated in the first region,
The non-magnetic cold accumulating material is contained between Oite the container and the insertion member into the first region,
The magnetic regenerator material is accommodated in the second region on the low temperature side of the container ,
The thermal conductivity of the insert member 10 at a temperature in the cryogenic refrigerator is operating [W / (m · K) ] Ri Der below,
The first region on the high temperature side includes a temperature range in which a density difference between the high pressure refrigerant gas and the low pressure refrigerant gas is larger than a high temperature end of the regenerator,
The cross-sectional area of the plane perpendicular to the axial direction of the portion in which the nonmagnetic regenerator material is accommodated in the first region on the high temperature side is the cross section of the portion in which the magnetic regenerator material is accommodated in the second region on the low temperature side. A cryogenic refrigerator having a smaller cross-sectional area by a plane perpendicular to the axial direction .   The cryogenic refrigerator according to claim 1, wherein a cross-sectional area of the insertion member in a plane perpendicular to the axis of the container is 1% or more and 25% or less of a cross-sectional area of the container in the plane. The container further includes a partition material that partitions the non-magnetic regenerator material and the magnetic regenerator material,
The cryogenic refrigerator according to claim 1 or 2, wherein the insertion member is fixed to the partition member.   The cryogenic refrigerator according to any one of claims 1 to 3, wherein the container accommodates the insertion member in a coaxial arrangement.   The cryogenic refrigerator according to any one of claims 1 to 4, wherein the insertion member is made of resin. The cryogenic refrigerator according to any one of claims 1 to 5, wherein the temperature range is 8K to 9K. A cryogenic refrigerator having a high temperature side regenerator and a low temperature side regenerator,
The low temperature side regenerator is:
A container,
A nonmagnetic regenerator material housed in the first region on the high temperature side of the container;
A magnetic regenerator material housed in the second region on the low temperature side of the container,
The vessel cross-sectional area in a plane perpendicular to the axis of the container is constant, respectively in the second region and the first region, the cross-sectional area of the first region is smaller than the cross-sectional area before Symbol second region ,
A cryogenic refrigerator having a thermal conductivity of 10 [W / (m · K)] or less at a temperature at which the cryogenic refrigerator is operating. A cryogenic refrigerator having a high temperature side regenerator and a low temperature side regenerator,
The low temperature side regenerator is:
A container,
A nonmagnetic regenerator material housed in the first region on the high temperature side of the container;
A magnetic regenerator material housed in the second region on the low temperature side of the container,
The container has a cross-sectional area in a plane perpendicular to the axis of the container in at least a part of the first area that is smaller than a cross-sectional area in a plane perpendicular to the axis of the container in the second area,
The thermal conductivity of the container is 10 [W / (m · K)] or less at a temperature at which the cryogenic refrigerator is operating,
A cryogenic refrigerator having a cross-sectional area of the first region that continuously increases from a high temperature side to a low temperature side.

Images