JP6245991B2 - Pulse tube refrigerator - Google Patents

Description

  The present invention relates to a pulse tube refrigerator, and more particularly to a multistage multi-valve pulse tube refrigerator.

  A pulse tube refrigerator is known as one of refrigerators that generate cryogenic temperatures. The pulse tube refrigerator has an operation in which a refrigerant gas (for example, helium gas), which is a working fluid compressed by a compressor, flows into the cold storage tube and the pulse tube, and the working fluid flows out of the pulse tube and the cold storage tube. By repeating the operation collected in the above, cold is formed at the low temperature ends of the regenerator tube and the pulse tube. Moreover, heat can be taken from the cooling target by bringing the cooling target into thermal contact with these low-temperature ends. In particular, a multi-stage multi-valve pulse tube refrigerator has a feature of high cooling efficiency, and is expected to be applied in various fields.

JP 2011-094835 A

  The compressor compresses low-pressure (for example, 0.8 MPa) helium gas to generate 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 10K. For this reason, when helium gas is used as the refrigerant gas of the pulse tube refrigerator, the pressure difference of the refrigerant gas in the pulse tube refrigerator becomes small, and it is difficult to adjust the phase difference between the flow rate of the helium gas and the pressure fluctuation. For this reason, the refrigeration capacity of the pulse tube refrigerator can be a factor.

  This invention is made | formed in view of such a subject, The objective is to provide the technique which improves the refrigerating capacity of a pulse tube refrigerator.

  In order to solve the above problems, a pulse tube refrigerator according to an aspect of the present invention includes a compressor for compressing refrigerant gas, a first pulse tube having a low temperature end and a high temperature end connected to the compressor, A first regenerator tube having a low temperature end connected to the low temperature end of the pulse tube and a high temperature end connected to the compressor, a high temperature end connected to the compressor, and a low temperature end that is cooler than the low temperature end of the first pulse tube And a second regenerative tube having a high temperature end and a low temperature end connected to the low temperature end of the second pulse tube, and arranged side by side with the second pulse tube. The second pulse tube includes a constricted portion on the low temperature end side from the position corresponding to the high temperature end of the second regenerative tube.

  Another embodiment of the present invention is also a pulse tube refrigerator. This pulse tube refrigerator includes a compressor for compressing refrigerant gas, a first pulse tube having a low temperature end and a high temperature end connected to the compressor, a low temperature end connected to the low temperature end of the first pulse tube, and a compressor A first regenerator tube having a high temperature end connected to the compressor, a high temperature end connected to the compressor, a second pulse tube having a low temperature end that is cooler than the low temperature end of the first pulse tube, a high temperature end and a second A low temperature end connected to the low temperature end of the pulse tube, and a second regenerative tube arranged side by side with the second pulse tube. The second pulse tube includes a constricted portion in a region where the temperature of the refrigerant gas flowing through the second pulse tube is 8K to 30K.

  ADVANTAGE OF THE INVENTION According to this invention, the technique which improves the refrigerating capacity of a pulse tube refrigerator can be provided.

It is a figure which shows typically the outline of an example of a 4-valve type pulse tube refrigerator. It is a figure which shows the opening-and-closing state of six valves at the time of the action | operation of the 4-valve type pulse tube refrigerator shown in FIG. 1 in time series. 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. FIGS. 4A to 4B are diagrams schematically showing the configuration of the second pulse tube according to the embodiment. It is the figure which showed typically the outline of an example of the 4-valve type pulse tube refrigerator which concerns on the modification of this invention. It is a figure which shows the opening-and-closing state of eight valves in the time series at the time of the action | operation of the 4-valve type pulse tube refrigerator shown in FIG.

  Embodiments of the present invention will be described with reference to the drawings.

  Prior to the description of the pulse tube refrigerator according to the embodiment of the present invention, a general four-valve type pulse tube refrigerator will be described first. FIG. 1 is a diagram schematically illustrating an example of a general four-valve type pulse tube refrigerator 200. This pulse tube refrigerator 200 has a two-stage structure.

  As shown in FIG. 1, the pulse tube refrigerator 200 includes a compressor 212, a first regenerator tube 240 and a second regenerator tube 280, a first pulse tube 250 and a second pulse tube 290, a first pipe 256 and a second pipe. 286, the first flow path resistance 260, the second flow path resistance 261, and the opening / closing valves V1 to V6, which are configured by an orifice or the like.

  The first regenerator tube 240 has a high temperature end 242 and a low temperature end 244, and the second regenerator tube 280 has a high temperature end 244 (corresponding to the low temperature end 244 of the first regenerator tube 240) and a low temperature end 284. The first pulse tube 250 has a hot end 252 and a cold end 254, and the second pulse tube 290 has a hot end 292 and a cold end 294. A heat exchanger is installed at each of the high temperature ends 252 and 292 and the low temperature ends 254 and 294 of the first pulse tube 250 and the second pulse tube 290. Since the low temperature end 244 of the first regenerator tube 240 is common to the high temperature end 244 of the second regenerator tube 280, the first regenerator tube 240 and the second regenerator tube 280 are arranged so that the longitudinal axis is common. . Further, the first regenerator tube 240 and the first pulse tube 250 are arranged side by side so that the longitudinal axes are aligned. The second regenerative tube 280 and the second pulse tube 290 are also arranged side by side so that the longitudinal axes are aligned.

  The low temperature end 244 of the first regenerator tube 240 is connected to the low temperature end 254 of the first pulse tube 250 via the first pipe 256. Further, the low temperature end 284 of the second regenerator tube 280 is connected to the low temperature end 294 of the second pulse tube 290 via the second pipe 286. Therefore, the temperature of the refrigerant gas at the low temperature end 244 of the first regenerator tube 240 and the temperature of the refrigerant gas at the low temperature end 254 of the first pulse tube 250 are substantially equal. Further, the temperature of the refrigerant gas at the low temperature end 284 of the second regenerative tube 280 and the temperature of the low temperature end 294 of the second pulse tube 290 are also substantially equal.

  Since the low temperature end 244 of the first regenerator tube 240 is common to the high temperature end 244 of the second regenerator tube 280, the low temperature end 284 of the second regenerator tube 280 is further cooler than the low temperature end 244 of the first regenerator tube 240. Become. Therefore, the low temperature end 294 of the second pulse tube 290 is cooler than the low temperature end 254 of the first pulse tube 250.

  The refrigerant flow path on the high pressure side (discharge side) of the compressor 212 branches in three directions at point A in FIG. 1, and the first refrigerant supply path H1, the second refrigerant supply path H2, and the third refrigerant supply path H3. Is configured. The first refrigerant supply path H1 includes a high pressure side of the compressor 212 to a first high pressure pipe 215A to which a first opening / closing valve V1 is installed, a common pipe 220 to a first regenerative pipe 240. The second refrigerant supply path H2 is a common pipe 230 to a first pulse pipe 250 in which a high pressure side of the compressor 212 to a second high pressure pipe 225A to which a third on-off valve V3 is connected to a first flow path resistance 260 is installed. Composed. The third refrigerant supply path H3 is a high pressure side of the compressor 212 to a third high pressure pipe 235A to which the fifth open / close valve V5 is connected to a common pipe 299 to a second pulse pipe 290 in which a second flow path resistance 261 is installed. Composed.

  On the other hand, the refrigerant flow path on the low pressure side (suction side) of the compressor 212 branches in three directions: the first refrigerant recovery path L1, the second refrigerant recovery path L2, and the third refrigerant recovery path L3. The 1st refrigerant | coolant collection path L1 is comprised by the path | route of the 1st cool storage pipe 240-the common piping 220-the 1st low pressure piping 215B-B in which the 2nd on-off valve V2 was installed-the compressor 212. The second refrigerant recovery path L2 includes the first pulse pipe 250 to the common pipe 230 in which the first flow path resistance 260 is installed to the second low pressure pipe 225B to B point in which the fourth open / close valve V4 is installed to the compressor 212. Consists of routes. The third refrigerant recovery path L3 includes a common pipe 299 in which the second pulse tube 290 to the second flow path resistance 261 are installed, a third low pressure pipe 235B to a point B in which the sixth on-off valve V6 is installed, and the compressor 212. Consists of routes.

  Next, the operation of the pulse tube refrigerator 200 will be described.

  FIG. 2 is a diagram showing, in time series, the open / closed states of the six valves during the operation of the four-valve type pulse tube refrigerator 200 shown in FIG. 1, and the open / closed states of the six open / close valves V1 to V6. FIG. Hereinafter, the diagram shown in FIG. 2 is also referred to as a “timing chart”.

  As shown in FIG. 2, during the operation of the pulse tube refrigerator 200, the open / close states of the six open / close valves V1 to V6 periodically change as follows.

(First process: time 0 to t1)
First, at time t = 0, only the fifth on-off valve V5 is opened. As a result, the high-pressure refrigerant gas is supplied from the compressor 212 to the second pulse tube 290 via the third refrigerant supply path H3, that is, the path from the third high-pressure pipe 235A to the common pipe 299 to the high-temperature end 292. Thereafter, at time t = t1, the third opening / closing valve V3 is opened while the fifth opening / closing valve V5 is kept open. Accordingly, the high-pressure refrigerant gas is supplied from the compressor 212 to the first pulse tube 250 through the second refrigerant supply path H2, that is, the path from the second high-pressure pipe 225A to the common pipe 230 to the high temperature end 252.

(Second process: time t2 to t3)
Next, at time t = t2, the first on-off valve V1 is opened with the on-off valves V5, V3 being opened. As a result, the high-pressure refrigerant gas flows from the compressor 212 through the first refrigerant supply path H1, that is, in the path from the first high-pressure pipe 215A to the common pipe 220 to the high-temperature end 242. Introduced into tube 280. A part of the refrigerant gas flows into the first pulse tube 250 from the low temperature end 254 side through the first pipe 256. Further, another part of the refrigerant gas passes through the second regenerator 280 and flows into the second pulse tube 290 from the low temperature end 294 side via the second pipe 286.

(Third process: time t3 to t4)
Next, at time t = t3, the third on-off valve V3 is closed while the first on-off valve V1 is open, and then at time t = t4, the fifth on-off valve V5 is also closed. The refrigerant gas from the compressor 212 flows into the first regenerator tube 240 only through the first refrigerant supply path H1. Thereafter, the refrigerant gas flows into the first pulse tube 250 and the second pulse tube 290 from the low temperature end 254 and the low temperature end 294 side, respectively.

(Fourth process: time t4 to t5)
At the time t = t5, all the open / close valves V1 to V6 are closed. Due to the pressure increase in the first pulse tube 250 and the second pulse tube 290, the refrigerant gas in the first pulse tube 250 and the second pulse tube 290 is placed on the high temperature ends 252 and 292 side of both pulse tubes. The first reservoir 251 and the second reservoir 291 are moved.

(Fifth process: time t5 to t7)
Thereafter, at time t = t5, the sixth open / close valve V6 is opened, and the refrigerant gas in the second pulse tube 290 returns to the compressor 212 through the third refrigerant recovery path L3. Thereafter, at time t = t6, the fourth open / close valve V4 is opened, and the refrigerant gas in the first pulse tube 250 returns to the compressor 212 through the second refrigerant recovery path L2. Thereby, the pressures of the first pulse tube 250 and the second pulse tube 290 are reduced.

(Sixth process: time t7 to t8)
Next, at time t = t7, the second opening / closing valve V2 is opened while the opening / closing valves V6, V4 remain open. As a result, most of the refrigerant gas in the first pulse tube 250, the second pulse tube 290, and the second regenerator tube 280 passes through the first regenerator tube 240, and passes through the first refrigerant recovery path L1 to the compressor. Return to 212.

(Seventh process: time t8 to t10)
Next, at time t = t8, the fourth opening / closing valve V4 is closed with the second opening / closing valve V2 open, and then at time t = t9, the sixth opening / closing valve V6 is also closed. Thereafter, at time t = t10, the second opening / closing valve V2 is closed, and one cycle is completed.

  By repeating the above cycle as one cycle, cold is generated at the low temperature end 254 of the first pulse tube 250 and the low temperature end 294 of the second pulse tube 290, and the object to be cooled can be cooled.

  As described above, in the pulse tube refrigerator 200, refrigerant gas such as helium is compressed by a high pressure, and is expanded when the pressure is low, thereby causing cold. Here, the pressure of the high-pressure refrigerant gas supplied by the compressor 212 is about 2.2 MPa, and the pressure of the refrigerant gas at low pressure is about 0.8 MPa.

  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 8K. When the temperature of the helium gas is lower than 8K, the density difference between the 2.2 MPa helium gas and the 0.8 MPa helium gas increases monotonically with respect to the temperature, and when the helium gas temperature is higher than 8K, The density difference decreases monotonically with temperature.

  In the pulse tube refrigerator 200, the temperature of the refrigerant gas at the low temperature end 294 of the second pulse tube 290 is approximately 4K. The refrigerant gas in the second pulse tube 290 has a temperature of about room temperature at the high temperature end 292. Therefore, the refrigerant gas in the second pulse tube 290 has a temperature gradient of about 4 K to 300 K from the low temperature end 294 toward the high temperature end 292.

  Here, a gas piston is generated in the second pulse tube 290 by appropriately controlling the open / close states of the open / close valves V1 to V6. The second pulse tube 290 is divided into three regions by a gas piston: a low temperature region located on the low temperature side of the gas piston, a high temperature region located on the high temperature side of the gas piston, and a gas piston region where the gas piston exists. A cooling stage (not shown) attached to the low temperature end of the second pulse tube 290 is cooled mainly by expansion of the refrigerant gas existing in the low temperature region.

  Among the helium gases flowing into the low temperature end 294 of the second pulse tube 290, some helium gases remain in the low temperature region and contribute to refrigeration. The remaining helium gas flows from the low temperature region into the gas piston region and maintains the gas piston. Therefore, the refrigerating capacity of the refrigerator can be improved by reducing the amount of gas flowing from the low temperature region into the gas piston region.

The mass of the helium gas present in the low temperature region and M _e. Further, the mass per unit time of the helium gas flowing from the low temperature end to the low-temperature region and m _in, the mass per unit time of the helium gas flowing out of the low-temperature region to the gas piston region with m _out. If, when the helium gas flowing into the low temperature region, the mass M _e helium gas present in the low temperature region is increased. On the other hand, if the outflow helium gas from the low temperature region, the mass M _e helium gas present in the low-temperature region is reduced. Therefore, the variation _dM e / dt per unit time in the mass _{M e} helium gas present in the low temperature region can be expressed by the difference between the inflow mass _{m in} the outflow mass _{m out.} From the above, the following relational expression (1) is obtained.
_{m in = m out + dM e} / dt (1)
Here, _dM e / dt represents the derivative with time t of the mass _{M e} helium gas present in the low temperature region.

Similarly, let M _p be the mass of helium gas present in the gas piston region. Further, when the mass per unit time of helium gas flowing into the high temperature region from the gas piston region is m _h , it can be expressed by the following equation (2).
m _out = m _h + dM _p / dt (2)

Substituting equation (2) into equation (1) yields the following equation (3).
_{m in = m h + dM p} / dt + dM e / dt (3)

The volume change in the low temperature region of the second pulse tube 290 is negligible. Therefore, the volume in the low-temperature region of the second pulse tube 290 regarded as constant, and its value as V _e. Further, when the average density of the helium gas in the low temperature region and [rho _e, the mass M _e of the refrigerant gas present in the low temperature region can be expressed by the following equation (4).
M _e = Vρ _e (4)

Similarly, the change in volume in the gas piston region of the second pulse tube 290 is negligible. Therefore, the volume in the gas piston region of the second pulse tube 290 is assumed to be constant, and the value is set as V _p . Further, if the average density of helium gas in the gas piston region is ρ _p , the mass M _p of the refrigerant gas existing in the gas piston region can be expressed by the following equation (5).
M _p = V _p ρ _p (5)

Substituting Expression (4) and Expression (5) into Expression (3), the following Expression (6) is obtained.
m _in = m _h + V _p dρ _p / dt + V _e dρ _e / dt (6)
Here, dρ _p / dt represents the time derivative of the density ρ _p of helium gas in the gas piston region. Dρ _e / dt represents the time derivative of the density ρ _e of the helium gas in the low temperature region.

In equation (6), assuming that the density of helium gas in the low temperature region and the gas piston region does not change with time, m _in = m _h and the mass of helium gas existing in the low temperature region and the gas piston region does not change. become. That is, it means that helium gas flows out of the gas piston region by the amount that flows into the low temperature region. In the actual cooling cycle, high-pressure helium gas is supplied to the second pulse tube 290 in the second process and the third process. As a result, the low-pressure helium gas filled in the low-temperature region is pressurized and becomes 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 high-pressure helium gas flows into the low-temperature region and the low-pressure helium gas in the low-temperature region is boosted to become high-pressure helium gas, the second term and the third term on the right side in equation (6) are positive values. Become. More specifically, the right side in Equation (6) is the density difference indicated by the solid line in FIG. From the above, the following inequality (7) is obtained.
_{m in -m h = V p dρ} p / dt + V e dρ e / dt> 0 (7)

  The inequality (7) indicates that the mass of the helium gas flowing out from the gas piston region is smaller than the mass of the helium gas flowing into the low temperature region. This means that the low temperature region and the gas piston region act like a helium gas buffer. As a result, the pressure difference as a whole of the pulse tube refrigerator 200 is also reduced.

When the sixth open / close valve V6 is opened in the fifth process, the high-pressure helium gas in the second pulse tube 290 becomes low-pressure helium gas. At this time, the right side in Expression (6) is a negative value having the density difference indicated by the solid line in FIG. 3 as an absolute value. Therefore, the following inequality (8) is obtained.
_{m in -m out = V p dρ} p / dt + V e dρ e / dt <0 (8)

  This indicates that the mass of helium gas flowing out from the gas piston region is larger than the mass of helium gas flowing into the low temperature region. Since a large amount of helium gas flows out through the refrigerant flow path on the low pressure side (suction side) of the compressor 212, the pressure drop is suppressed, and as a result, the pressure difference as a whole of the pulse tube refrigerator 200 is reduced.

  As shown in FIG. 1, the second flow path resistance 261, which is a refrigerant gas phase adjustment mechanism, is provided on the high temperature end 292 side of the second pulse tube 290. For this reason, when helium gas is used as the refrigerant gas, it becomes difficult to adjust the flow rate of the refrigerant gas and the phase of the pressure fluctuation on the low temperature end 294 side of the second pulse tube 290. In the region where the temperature of the refrigerant gas is from 8K to 30K, the density difference between the high-pressure refrigerant gas and the low-pressure refrigerant gas increases, and as a result, the flow rate and input work of the refrigerant gas flowing into the second pulse tube 290 increase.

In the formula (6), if smaller second term of _{(V p dρ p / dt)} , if it is possible to increase the amount corresponding third term of _{(V e dρ e / dt)} , m in the m The mass of the helium gas in the low temperature region that contributes to refrigeration can be increased without changing _h . As a result, the refrigeration performance of the refrigerator can be improved. Further, helium gas in the gas piston region where the density difference between the high-pressure refrigerant gas and the low-pressure refrigerant gas becomes large can be reduced.

The basic configuration of the pulse tube refrigerator according to the embodiment is the same as that of the general pulse tube refrigerator 200 described above. Therefore, for convenience, the pulse tube refrigerator according to the embodiment is also referred to as “pulse tube refrigerator 200”. However, the pulse tube refrigerator 200 according to the embodiment reduces the second term (V _p dρ _p / dt) on the right side in the above-described formula (6), and the third term (V _e dρ _e / In order to increase dt), the configuration of the pulse tube (the second pulse tube 290 in the example shown in FIG. 1) having the lowest temperature end is different from that of the general pulse tube refrigerator 200 described above. Hereinafter, the pulse tube according to the embodiment will be described.

  FIGS. 4A to 4B are diagrams schematically showing the configuration of the second pulse tube 290 according to the embodiment. As shown in FIGS. 4A and 4B, the second pulse tube 290 according to the embodiment includes a constricted portion 293 in which a part of the refrigerant gas passage area is smaller than that of the other part.

  In FIG. 4 (a), a portion of the second pulse tube 290 is narrowed to form a constricted portion 293. Although not limited, the flow area of the refrigerant gas in the narrowed portion 293 is about 30% to 70%, more specifically about 60%, compared to the flow area of other portions. Yes. The narrowed portion 293 is provided in a region where the temperature of the refrigerant gas is approximately 8K to 30K in the second pulse tube 290, and corresponds to the above-described gas piston region. As a result, when helium is used as the refrigerant gas, the flow area of the second pulse tube 290 at the portion where the density difference between the 2.2 MPa helium gas and the 0.8 MPa helium gas increases is reduced. . That is, since the flow rate of the refrigerant gas flowing through the region where the temperature is about 8K to 30K in the second pulse tube 290 is reduced, the decrease in the pressure difference of the refrigerant gas in the pulse tube refrigerator 200 is suppressed, and the pressure of the refrigerant gas Fluctuation phase adjustment is appropriate. For this reason, the refrigerating capacity and the refrigerating efficiency of the pulse tube refrigerator 200 as a whole can be improved.

Here the volume of the constricted portion 293 and _{V c,} the mass of the helium gas in the constriction 293 and _{M c.} Since the narrowed portion 293 corresponds to the above-described gas piston region, the volume V _c of the narrowed portion 293 is smaller than the volume V _p of the gas piston region in Expression (6). On the other hand, the temperature distribution of helium gas in the narrowed portion 293 is the same as the temperature distribution of helium gas in the gas piston region described above. For this reason, the average density of helium gas in the constriction 293 is ρ _p . From the above, the following relational expression (9) is obtained.
M _c = V _c ρ _p <M _p (9)

From the equation (9), the following equation (10) is obtained.
| DM _c / dt | <| dM _p / dt | (10)

Expression (10) indicates that the absolute value of the mass change of the helium gas in the narrowed portion 293 is smaller than the absolute value of the mass change of the helium gas in the gas piston region before the narrowed portion 293 is provided. By narrowing the gas piston region where the contribution of helium gas to the buffering action is narrowed, the buffering action can be reduced. _{Moreover, |} dM p / dt _| only the small amount, since the third term on the right-hand side of equation (6) to _{(V e dρ e / dt =} dM e / dt) can be increased, helium gas contributes low-temperature region in refrigeration The mass of can be increased. As a result, the refrigeration capacity of the refrigerator can be improved.

  As shown in FIG. 4A, in the case of a two-stage pulse tube refrigerator, the first cold storage tube 240 on the high temperature side and the second cold storage tube 280 on the low temperature side are arranged sharing the central axis. . The second pulse tube 290 is arranged side by side so as to be substantially parallel to the first regenerative tube 240 and the second regenerative tube 280. The straight line connecting the low temperature end 294 of the second pulse tube 290 and the low temperature end 284 of the second regenerative tube 280 is substantially orthogonal to the central axis of the second pulse tube 290 and the central axis of the second regenerative tube 280. . That is, when the second pulse tube 290, the first regenerator tube 240, and the second regenerator tube 280 are installed so that the longitudinal directions thereof are vertical, the low-temperature end 294 of the second pulse tube 290 and the second regenerator tube 280 The low temperature end 284 has substantially the same height.

  For convenience of explanation, as shown in FIG. 4A, the longitudinal direction of the second pulse tube 290 from the low temperature end 294 of the second pulse tube 290 toward the high temperature end 292 with the low temperature end 294 of the second pulse tube 290 as the origin. Set the x coordinate axis in the direction. Since the first regenerative tube 240 and the second regenerative tube 280 are arranged side by side, the x coordinate in the second pulse tube 290 and the x coordinate in the first regenerative tube 240 and the second regenerative tube 280 may be associated with each other. It becomes possible. Therefore, in the present specification, for example, the position of the second pulse tube 290 corresponding to the second regenerative tube 280 means the position of the second pulse tube 290 having the same coordinate as the x coordinate of the second regenerative tube 280. To do. The position of the second pulse tube 290 corresponding to the low temperature end 284 of the second regenerator tube is the low temperature end 294 of the second pulse tube 290.

  Here, the temperature of the refrigerant gas at the high temperature end 242 of the first regenerator tube 240 is about room temperature, and the temperature of the refrigerant gas at the low temperature end 244 of the first regenerator tube 240 is approximately 50K. The temperature of the refrigerant gas at the high temperature end 244 of the second cold storage tube 280 is also about 50K, and the temperature of the refrigerant gas at the low temperature end 284 of the high temperature end 244 of the second cold storage tube 280 is about 4K. The temperature of the refrigerant gas at the low temperature end 294 of the second regenerator tube is also about 4K, and the temperature of the refrigerant gas at the high temperature end 292 is about room temperature. The temperature of the refrigerant gas at a predetermined position of the first cold storage tube 240 or the second cold storage tube 280 and the temperature of the refrigerant gas at the corresponding position of the second pulse tube 290 are substantially the same. Therefore, the temperature of the refrigerant gas in the second pulse tube 290 at the position corresponding to the high temperature end 244 of the second regenerator tube 280 is approximately 50K.

  As shown in FIG. 3, the density difference between the 2.2 MPa helium gas and the 0.8 MPa helium gas increases as the temperature decreases to about 8 K when the temperature is 50 K or less. Therefore, the narrowed portion 293 in the second pulse tube 290 is provided closer to the low temperature end 294 than the position corresponding to the high temperature end 244 of the second cold storage tube 280.

  The first regenerator tube 240 and the second regenerator tube 280 according to the embodiment each include a regenerator material. The 2nd cool storage pipe 280 is provided with two kinds of cool storage materials, the 1st cool storage material 281 arranged at the high temperature side, and the 2nd cool storage material 283 arranged at the low temperature side, the 1st cool storage material 281 and the 2nd cool storage material. Adjacent to the material. The narrowed portion 293 in the second pulse tube 290 is preferably provided on the high temperature end 292 side of the second cold storage tube 280 at a position corresponding to the boundary between the first cold storage material 281 and the second cold storage material 283. In addition, the temperature of the refrigerant gas on the low temperature side of the narrowed portion 293 is preferably about 8K. Thereby, in the 2nd pulse tube 290, it is provided in the area | region where the temperature of refrigerant gas becomes about 8K to 30K.

  Note that the constriction 293 in the second pulse tube 290 is about 60% compared to the flow path area of the other part. Therefore, if the flow path area changes suddenly at the boundary between the narrowed portion 293 and another region, turbulent flow may occur in the refrigerant gas, and pressure loss may occur. Therefore, it is preferable that the narrowed portion 293 has a tapered shape in which the flow path area continuously changes at the boundary portion with another region.

  More specifically, as shown in FIG. 4A, the constricted portion 293 is continuous at the boundary portion on the high temperature end side with another region until the channel area reaches the channel area in the other region. To increase. Similarly, the narrowed portion 293 continuously increases until the channel area reaches the channel area in the other region at the low temperature end side boundary with the other region.

  FIG. 4B is a diagram showing another configuration of the constriction 293 in the second pulse tube 290. The narrowed portion 293 shown in FIG. 4A is configured by narrowing the second pulse tube 290. On the other hand, in the example shown in FIG. 4B, the outer diameter of the second pulse tube 290 in the constricted portion 293 is not different from the outer diameter of other portions. Instead, the flow channel area is reduced by inserting a filling member into the second pulse tube 290. The filling member can be realized by appropriately using metal, resin, plastic, or the like.

  In the example shown in FIG. 4B, the function and effect of the narrowed portion 293 itself is the same as that in the example shown in FIG. The example shown in FIG. 4B is advantageous in that the strength of the constriction 293 in the second pulse tube 290 is improved as compared with the example shown in FIG.

  As described above, the pulse tube refrigerator 200 according to the embodiment includes the second pulse tube 290 partially provided with the narrowed portion 293, thereby reducing the flow rate of the refrigerant gas in the second pulse tube 290. And the fall of the pressure difference of the refrigerant gas in the pulse tube refrigerator 200 can be suppressed, and the phase between the flow velocity of the refrigerant gas and the pressure fluctuation can be optimized. As a result, the refrigeration capacity and refrigeration efficiency of the pulse tube refrigerator 200 can be improved.

  As mentioned above, although this invention was demonstrated based on embodiment, embodiment only shows the principle and application of this invention. In the embodiment, many modifications and arrangements can be made without departing from the spirit of the present invention defined in the claims.

(Modification)
In the above description, the pulse tube refrigerator 200 is assumed to have a two-stage structure. The pulse tube refrigerator 200 is not limited to a two-stage type, and the present invention can be applied to a multi-stage type. Hereinafter, a pulse tube refrigerator 201 having a three-stage structure will be described as an example of a multistage system.

  FIG. 5 is a diagram schematically showing an example of a four-valve pulse tube refrigerator 201 according to a modification of the present invention. The pulse tube refrigerator 201 has a three-stage structure. In FIG. 5, the same reference numerals as those in FIG. 1 are attached to the same members as those in FIG.

  The three-stage pulse tube refrigerator 201 has the same configuration as the two-stage pulse tube refrigerator 200 described above. However, the three-stage pulse tube refrigerator 201 further includes a third regenerator tube 440 and a third pulse tube 420.

  The third regenerator tube 440 has a high temperature end 284 (corresponding to the low temperature end 284 of the second regenerator tube 280) and a low temperature end 444. The third pulse tube 420 has a high temperature end 422 and a low temperature end 424, and a heat exchanger is installed at the high temperature end 422 and the low temperature end 424. The low temperature end 444 of the third regenerator tube 440 is connected to the low temperature end 424 of the third pulse tube 420 via the third pipe 416.

  The refrigerant flow path on the high-pressure side (discharge side) of the compressor 212 includes the first refrigerant supply path H1, the second refrigerant supply path H2, and the third refrigerant supply path H3 as shown in FIG. A supply path H4 is provided. In addition to the first refrigerant recovery path L1, the second refrigerant recovery path L2, and the third refrigerant recovery path L3 as shown in FIG. There are four refrigerant recovery paths L4.

  The fourth refrigerant supply path H4 includes a high pressure side of the compressor 212 to a fourth high pressure side pipe 245A to which the seventh open / close valve V7 is connected to a common pipe 455 to a third pulse pipe 420 provided with a flow path resistance 450. Is done. The fourth refrigerant recovery path L4 is a path from the third pulse pipe 420 to the common pipe 455 in which the flow path resistance 450 is installed to the fourth low pressure side pipe 245B to B in which the eighth open / close valve V8 is installed to the path of the compressor 212. Consists of. The channel resistance 450 is configured by an orifice or the like.

  Next, the operation of the 4-valve type pulse tube refrigerator 201 configured as described above will be described.

  FIG. 6 is a diagram showing, in time series, the open / closed states of the eight valves when the four-valve type pulse tube refrigerator 201 shown in FIG. 5 is operated, and shows the eight first open / close valves V1 to V8. It is the figure which showed the opening-and-closing state in time series. Hereinafter, the diagram illustrated in FIG. 5 is also referred to as a “second timing chart”. When the pulse tube refrigerator 201 is operated, the open / close states of the eight open / close valves V1 to V8 periodically change as follows.

(First process: time 0 to t3)
First, at time t = 0, only the seventh open / close valve V7 is opened. As a result, the high-pressure refrigerant gas is supplied from the compressor 212 to the third pulse tube 420 via the fourth refrigerant supply path H4, that is, the path from the fourth high-pressure side pipe 245A to the common pipe 455 to the high-temperature end 422. . Thereafter, at the time t = t1, the fifth opening / closing valve V5 is opened while the seventh opening / closing valve V7 remains open. As a result, the high-pressure refrigerant gas is supplied from the compressor 212 to the second pulse tube 290 via the third refrigerant supply path H3, that is, the path from the third high-pressure pipe 235A to the common pipe 299 to the high-temperature end 292.

  Next, at time t = t2, the third on-off valve V3 is opened with the on-off valves V7, V5 open. As a result, the high-pressure refrigerant gas is supplied from the compressor 212 to the first pulse tube 250 through the second refrigerant supply path H2, that is, through the second high-pressure pipe 225A to the common pipe 230 to the high-temperature end 252. .

  Next, at time t = t3, the first opening / closing valve V1 is opened with the opening / closing valves V7, V5, V3 being opened. Thereby, the high-pressure refrigerant gas is introduced into the first regenerator tube 240, the second regenerator tube 280, and the third regenerator tube 440. A part of the refrigerant gas flows into the first pulse tube 250 from the low temperature end 254 side through the first pipe 256. Another part of the refrigerant gas passes through the second regenerator 280 and flows into the second pulse tube 290 from the low temperature end 294 side via the second pipe 286. Yet another part of the refrigerant gas passes through the third regenerator tube 440 and flows into the third pulse tube 420 from the low temperature end 424 side via the third tube 416.

(Second process: time t4 to t7)
Next, at time t = t4, the third on-off valve V3 is closed while the on-off valves V1, V5, V7 are open, and then the on-off valves V5, V7 are also sequentially closed (time t = t5). And t = t6) Correspondingly, the refrigerant gas from the compressor 212 flows into the first regenerator tube 240 only through the first refrigerant supply path H1. Thereafter, the refrigerant gas flows into the first pulse tube 250, the second pulse tube 290, and the third pulse tube 420 from the respective cold ends 254, 294, 424.

  At time t = t7, all the open / close valves V1 to V8 are closed. Due to the pressure increase in the first pulse tube 250, the second pulse tube 290, and the third pulse tube 420, the refrigerant gas in the first pulse tube 250, the second pulse tube 290, and the third pulse tube 420 is respectively It moves toward a reservoir (not shown) installed on the high temperature end 252, 292, 422 side.

(Third process: time t7 to t10)
Thereafter, at time t = t7, the eighth on-off valve V8 is opened, and the refrigerant gas in the third pulse tube 420 returns to the compressor 212 through the fourth refrigerant recovery path L4. Thereafter, at time t = t8, the sixth open / close valve V6 is opened, and the refrigerant gas in the second pulse tube 290 returns to the compressor 212 through the third refrigerant recovery path L3. Thereby, the pressures of the third pulse tube 420 and the second pulse tube 290 are reduced. Thereafter, at time t = t9, the fourth open / close valve V4 is opened, and the refrigerant gas in the first pulse tube 250 returns to the compressor 212 through the second refrigerant recovery path L2. As a result, the pressure of the first pulse tube 250 decreases.

  Further, at time t = t10, the second on-off valve V2 is opened while the on-off valves V8, V6, V4 remain open. Accordingly, most of the refrigerant gas in the third pulse tube 420, the second pulse tube 290, the first pulse tube 250, the first regenerator tube 240, the second regenerator tube 280, and the third regenerator tube 440 is the first It passes through the cool storage tube 240 and returns to the compressor 212 through the first refrigerant recovery path L1.

(4th process: time t11-t14)
Next, at time t = t11, the fourth open / close valve V4 is closed with the open / close valves V2, V6, V8 being opened, and then the sixth open / close valves V6, V8 are sequentially closed (time t = t12). And t = t13).

  Finally, at time t = t14, the second opening / closing valve V2 is closed and one cycle is completed.

  By repeating the above cycle, cold occurs at the low temperature end 254 of the first pulse tube 250, the low temperature end 294 of the second pulse tube 290, and the low temperature end 424 of the third pulse tube 420, thereby cooling the object to be cooled. be able to.

  In the pulse tube refrigerator 201 according to the modification, the temperature of the refrigerant gas flowing through the low temperature end 444 of the third regenerator tube 440 is approximately 4K. For this reason, the temperature of the refrigerant gas flowing through the low temperature end 424 of the third pulse tube 420 is also about 4K. The refrigerant gas in the third pulse tube 420 reaches about room temperature at the high temperature end 422 of the third pulse tube 420.

  In the pulse tube refrigerator 201, the first regenerator tube 240, the second regenerator tube 280, and the third regenerator tube 440 are arranged so as to share the central axis in the longitudinal direction, and the third pulse tube 420 and the third regenerator tube are arranged. 440 is arranged side by side. Therefore, the position corresponding to the position in the 3rd cool storage tube 440 can be defined in the 3rd pulse tube 420 similarly to the relationship between the 2nd pulse tube 290 and the 2nd cool storage tube 280 shown in FIG.

  The pulse tube refrigerator 201 according to the modified example is provided with a constricted portion 493 in which the flow area of the refrigerant gas is reduced so that the temperature of the refrigerant gas flowing through the third pulse tube 420 is approximately 8K to 20K. . The narrowed portion 493 in the third pulse tube 420 is located on the lower temperature side than the position corresponding to the high temperature end 284 of the third regenerator tube 440 that is the last-stage regenerator tube.

  Thereby, the flow volume of the area | region where the density difference of 2.2 MPa helium gas and 0.8 MPa helium gas becomes large can be reduced, and the fall of the pressure difference of the refrigerant gas in the pulse tube refrigerator 200 can be suppressed. Further, the phase adjustment of the pressure fluctuation of the refrigerant gas can be optimized. As a result, the refrigeration capacity and refrigeration efficiency of the pulse tube refrigerator 200 can be improved.

  Similar to the two-stage pulse tube refrigerator 200 and the three-stage pulse tube refrigerator 201, even a refrigerator having a higher number of stages is constricted to a part of the pulse tube at the final stage on the warm side. By providing the part, the same effect can be achieved.

  H1 first refrigerant supply path, L1 first refrigerant recovery path, V1 first open / close valve, H2 second refrigerant supply path, L2 second refrigerant recovery path, V2 second open / close valve, H3 third refrigerant supply path, L3 third Refrigerant recovery path, V3 third open / close valve, H4 fourth refrigerant supply path, L4 fourth refrigerant recovery path, V4 fourth open / close valve, V5 fifth open / close valve, V6 sixth open / close valve, V7 seventh open / close valve, V8 first 8 open / close valve, 200, 201 pulse tube refrigerator, 212 compressor, 215A first high pressure piping, 215B first low pressure piping, 220 common piping, 225A second high pressure piping, 225B second low pressure piping, 230 common piping, 235A first 3 high pressure piping, 235B 3rd low pressure piping, 240 1st regenerative piping, 245A 4th high pressure piping, 245B 4th low pressure piping , 250 first pulse tube, 251 first reservoir, 254 low temperature end, 256 first piping, 260 first flow path resistance, 261 second flow path resistance, 280 second cold storage tube, 281 first cold storage material, 283 second Cold storage material, 286 second piping, 290 second pulse tube, 291 second reservoir, 293 constriction, 299 common piping, 416 third piping, 420 third pulse tube, 440 third cold storage tube, 450 channel resistance, 455 Common piping, 493 constriction.

Claims (6)

A compressor for compressing the refrigerant gas;
A first pulse tube having a cold end and a hot end connected to the compressor;
A first regenerative tube having a cold end connected to the cold end of the first pulse tube and a hot end connected to the compressor;
A second pulse tube having a hot end connected to the compressor and a cold end that is cooler than a cold end of the first pulse tube;
A second regenerator having a high temperature end and a low temperature end connected to the low temperature end of the second pulse tube, and being arranged alongside the second pulse tube;
The second pulse tube includes a constriction provided on the low temperature end side from a position corresponding to the high temperature end of the second regenerator, and a high temperature side boundary portion of the constriction on the high temperature end side of the second pulse tube. A high temperature side straight tube portion connecting the high temperature end of the second pulse tube, and a low temperature side straight tube portion connecting the low temperature side boundary portion of the narrowed portion on the low temperature end side of the second pulse tube to the low temperature end of the second pulse tube. A pulse tube refrigerator. A compressor for compressing the refrigerant gas;
A first pulse tube having a cold end and a hot end connected to the compressor;
A first regenerative tube having a cold end connected to the cold end of the first pulse tube and a hot end connected to the compressor;
A second pulse tube having a hot end connected to the compressor and a cold end that is cooler than a cold end of the first pulse tube;
A second regenerator having a high temperature end and a low temperature end connected to the low temperature end of the second pulse tube, and being arranged alongside the second pulse tube;
The second pulse tube includes a constricted portion on the cold end side from a position corresponding to the hot end of the second regenerator tube,
The second regenerator tube is
A first regenerator material disposed on the high temperature side;
It is arranged on the low temperature side, and includes the second cold storage material adjacent to the first cold storage material,
The narrowed portion is provided at a higher temperature end side than a position corresponding to a boundary between the first cold storage material and the second cold storage material in the second cold storage tube.   3. The pulse tube refrigerator according to claim 1, wherein the constriction is provided in a region where the temperature of the refrigerant gas flowing through the second pulse tube is 8K to 30K. 4.   2. The narrowed portion continuously increases at a high temperature side boundary portion of the narrowed portion until a flow channel area reaches a flow channel area in a high temperature side straight tube portion of the second pulse tube. 4. The pulse tube refrigerator according to any one of items 1 to 3.   2. The narrowed portion continuously increases at a low temperature side boundary portion of the narrowed portion until a flow channel area reaches a flow channel area in a low temperature side straight tube portion of the second pulse tube. To 4. The pulse tube refrigerator according to any one of items 1 to 4. The second pulse tube is a final-stage pulse tube on the low temperature side,
The pulse tube refrigerator according to any one of claims 1 to 5, wherein the second regenerator tube is a last-stage regenerator tube on a low temperature side.

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