Hybrid dual inlet valve for vascular cryocooler

Abstract

A dual inlet valve for a Gifford-McMahon (GM) type dual inlet pulse tube cryocooler system for providing cooling at cryogenic temperatures, the dual inlet valve including a fixed restrictor and a needle valve coupled in parallel with the fixed restrictor. The needle valve creates an asymmetric flow. The combination of the fixed restrictor and the needle valve with asymmetric flow provides improved alternating current (AC) flow characteristics and tunability of direct current (DC) flow to increase available cooling.

Description

[0001] Cross-referencing of related patent applications

[0002] This application claims priority to U.S. Provisional Application Serial No. 63 / 064,528, filed August 12, 2020, the entire contents of which are hereby incorporated herein by reference. Technical Field

[0003] The present invention relates to an improved dual-inlet valve for Gifford-McMahon (GM) type pulse tube cryogenic coolers, which improves performance primarily by advantageously controlling direct current (DC) flow. Background Technology

[0004] Gifford-McMahon (GM) pulse tube refrigerators are cryogenic coolers, similar to GM refrigerators, that achieve cooling through gas compression in a compressor connected to an expander via supply and return hoses. The expander typically uses a rotary valve to circulate gas through inlet and outlet valves to a cold expansion space via a regenerator. While GM expanders generate this cold expansion space through the reciprocating motion of a solid piston in a cylinder (often referred to as a displacement valve when the displacement volume above and below the piston is connected via the regenerator), pulse tube expanders generate it through the reciprocating motion of a "gas piston." Pulse tube refrigerators have no moving parts in their cold heads; instead, an oscillating column of gas within the pulse tube acts as a compressible piston. This piston contains the gas retained in the pulse tube during pressurization and depressurization. Eliminating moving parts at the cold end of a pulse tube refrigerator significantly reduces vibration and improves reliability and lifespan. To further reduce vibration, the rotary valve is typically connected to the expander via a flexible hose. Two-stage GM-type pulse tube refrigerators typically use oil-lubricated compressors to compress helium and consume 5 to 15 kW or more of input power. Their primary applications today are cooling MRI (Magnetic Resonance Imaging) and NMR (Nuclear Magnetic Resonance Imaging) magnets, which cool insulation at approximately 40 K and recondense helium at approximately 4 K. They were also used in the early development of quantum computers. These applications require low levels of vibration and low levels of electromagnetic interference (EMI).

[0005] GM-type pulse tube coolers were developed in parallel with Stirling-type pulse tube coolers, which provide a pressure cycle directly from the reciprocating compressor piston to the accumulator and pulse tube. These coolers are widely used to cool infrared detectors approaching 70K in terrestrial and space systems. They are typically much smaller and operate at higher speeds, such as 60Hz, while GM-type pulse tubes operate at 1 to 2Hz. Stirling-type pulse tubes are more efficient than GM-type pulse tubes because they recover most of the expansion work, but they control the flow between the warm end and the buffer volume differently, and they are less efficient at low temperatures.

[0006] WEGifford, a co-inventor of the GM circulating refrigerator, also conceived of an expander that replaced the solid piston with a gas piston, which he called a “pulse tube” refrigerator. This expander was first described in his U.S. Patent 3,237,421 (“'421 Patent”), which showed a pulse tube connected to a valve, much like in early GM refrigerators. Early developments of the pulse tube expander showed that gas entered a vertical tube at the bottom and flowed through a flow leveler, forming a stratified column of gas that heated up as it was compressed and pushed to the top. The top of the tube had a copper cap that absorbed some of the heat, so that as the gas flowed out of the tube and cooled during expansion, it cooled the flow leveler and the adjacent copper at the so-called cold end. As reported in 1984, Mikulin et al. made significant improvements to the basic GM-type pulse tube by adding a buffer volume at the warm end of the pulse tube and by using throttling valves for gas inflow and outflow. This is now known as the basic orifice pulse tube or single-inlet valve pulse tube. Subsequent development work designed several different throttling methods, thereby improving the performance of the pulse expander. Most Stirling pulse expanders employ a single-inlet design.

[0007] For GM-type pulse tubes, it was found that adding a second small orifice between the warm end of the pulse tube and the inlet towards the accumulator improved performance and made it possible to operate below 4K in both stages of the pulse tube. This is now called a dual-inlet pulse tube, and the second throttling device is called a dual-inlet valve. Similar to the different forms used with single-inlet valves, dual-inlet valves also take different forms. This invention is a novel dual-inlet valve that exhibits improved performance.

[0008] Gifford's U.S. Patent 3,205,668 ("'668 Patent") describes a GM expander with a solid piston having a rod connected to the warm end. This piston drives the displacement valve up and down by circulating pressure opposite to the pressure cycle of the expansion space. A rotary valve is the most common device for circulating pressure between a high pressure (Ph) and a low pressure (P1). If the cold end of the gas piston follows essentially the same pattern as the cold end of the solid piston, then flow control at the warm end of the pulse valve can be considered optimized. The cycle of the expander described in the '668 Patent begins by depressing the displacement valve when the inlet valve is open, increasing the pressure to Ph. The piston then moves upward, and the pressure decreases as the piston moves to the top when the inlet valve is closed for approximately 3 / 4 of the way. The outlet valve then opens, and the pressure drops to P1. The piston then moves downward, and the pressure increases as the piston moves to the bottom when the outlet valve is closed for approximately 3 / 4 of the way. The area of ​​the pressure-volume (PV) is a measure of the amount of cooling produced per cycle. There is a significant difference between solid and gas pistons. These differences include: 1) Length and stroke depend on the pressure ratio and how much gas is allowed to flow into and out of the cold end of the pulse tube; 2) Asymmetry in valve timing and flow resistance can cause more gas to flow into or out of one end of the pulse tube per cycle than out, known as direct current (DC) flow; 3) It is difficult to simultaneously balance the flow into and out of the cold and warm ends to establish a cold boundary (known as alternating current (AC) flow), simulating the motion of a solid piston and the PV relationship. Because the compressor piston has a fixed displacement, a Stirling cycle pulse tube with a single inlet valve avoids the first problem; and because the amount of gas flowing out of the buffer volume is the same as the amount flowing into the buffer volume, it avoids the second problem.

[0009] While this analogy of a gas piston to a solid piston provides a physical description of the process, it is more common to find flow patterns described by the phase relationship between the pressure cycle and the mass flow cycle. U.S. Patent Application Publication No. 2011 / 0100022 (“022 Publication”) by Yuan et al. provides a good description of a phase control device for a Stirling-type single-inlet pulse tube refrigerator. '022 Publication… Figure 2 A resistive device is shown, which is described as comprising a small hole, a short tube, and a closely spaced plate. Figure 2An inertial tube is shown, which is a long, small-diameter tube that acts as an inductor in electrical analogues. Figure 8 of the '022 disclosure illustrates how these devices can be combined using circuit analogues to optimize the phase relationship between the pressure cycle and the mass flow rate cycle that provides maximum cooling. Figure 7 of the '022 disclosure is a schematic diagram of a single intake valve consisting of a resistive device and an inertial device connected in parallel. It is important to note that in Stirling-type pulse tubes, the inertial device is practical because it is capable of operating at high frequencies. In GM-type pulse tubes, only the resistive device is practical at low frequencies. It is also important to note that all the devices described in the '022 disclosure have the same flow characteristics in either direction.

[0010] Efforts to improve the cooling capacity of the 4K two-stage GM cooler include the development of a four-valve design. Xu's U.S. Patent 10,066,855 (“'855 Patent”) describes a four-valve pulse tube. The name derives from the phase-shifting mechanism, which includes a pair of inlet and outlet valves connected to the warm end of the accumulator and a second pair of inlet and outlet valves connected to the warm end of the pulse tube. The '855 Patent describes a flow control mechanism for balancing the gas flow to the second and third stage pulse tubes, each requiring an additional pair of valves. The four-valve pulse tube does not utilize a buffer volume, and the current design performs slightly better than current dual-inlet pulse tube designs. However, their disadvantage is that the void volume in the hoses reduces pressure oscillations and performance when the valve motors and rotary valves must be disconnected from the accumulator. While dual-inlet pulse tubes require only one hose between the valve assembly and the pulse tube / accumulator assembly, called the cold end, the four-valve pulse tube requires one hose connected to the accumulator and smaller diameter hoses connected to the warm end of each pulse tube in the multi-stage pulse tube. The improved performance of the dual-inlet pulse tube of this invention makes it possible to achieve performance comparable to that of a four-valve pulse tube in a component with a remote valve assembly and a single connecting hose. A patent application for an improved connecting hose was recently filed. This hose reduces vibration transmitted from the valve motor assembly to the cold head and reduces void volume, thereby improving efficiency.

[0011] Ogura's Japanese Patent No. 3917123 describes a dual-intake valve using a needle valve, with the first intake valve employing a replaceable bushing with a through-hole. Under the same flow conditions, the through-hole of the bushing provides the same flow restriction in either direction, making it a symmetrical flow restrictor. On the other hand, as shown, the needle valve has a port at its end facing the needle tip and a port on its side facing the valve stem. Since the flow restriction differs in different directions under the same conditions, this flow restriction is asymmetrical. The degree of asymmetry depends on many factors, such as the inclination of the intake and the port, and the length of the hole in the port. Phase shift can be improved by simplifying adjustment methods.

[0012] In addition to optimizing the phase shift mechanism for controlling the PV relationship in GM-type pulse tubes operating near 4K, controlling the DC flow rate was also found to be important. Xu's U.S. Patent No. 9,157,668 (“'668 Patent”) describes a dual-intake pulse tube in which an exhaust pipe is added between the buffer volume and the compressor return pipe. '668 Patent… Figure 1 The basic dual-inlet pulse tube of the prior art is shown, and the flow pattern via the dual-inlet valves is described, resulting in excessive DC flow from the warm end to the cold end of the pulse tube. A discharge line returning the flow from the buffer volume to the compressor return side reduces the DC flow to an optimized cooling rate. A disadvantage of this is the need for additional piping when the valve assembly is far from the cold end. A two-stage dual-inlet pulse tube has two parallel pipes extending from room temperature to the first and second stage temperatures. Each warm end is connected to its own buffer volume and has its own dual-inlet valve. The second-stage accumulator is an extension of the first-stage accumulator, so the pressure drop through the first-stage accumulator to the cold end of the first-stage pulse tube is less than the pressure drop to the cold end of the second-stage pulse tube. Optimizing the DC flow in the two-stage pulse tube may require an upward DC flow in the second stage and a downward DC flow in the first stage. Summary of the Invention

[0013] This invention relates to a dual-inlet valve with good AC flow characteristics and adjustable DC flow to increase available cooling. This dual-inlet valve also requires only a single connecting hose between the remote valve assembly and the cold head.

[0014] The dual-inlet valve includes a fixed flow restrictor connected in parallel with an adjustable needle valve. The flow rate through the needle valve is asymmetrical, meaning that when gas enters one port under given conditions, the pressure drop is greater compared to entering the other port. The fixed flow restrictor can be a short orifice with the same symmetrical pressure drop in either direction, or a tapered orifice with asymmetrical flow. This combination provides good AC flow characteristics and DC flow adjustability to increase available cooling. The dual-inlet valve also requires only a single connecting hose between the remote valve assembly and the cold head.

[0015] These and other advantages are achieved through the Gifford-McMahon (GM) dual-inlet pulse tube cryogenic cooler system for providing cooling at cryogenic temperatures. The GM dual-inlet pulse tube cryogenic cooler system includes: a compressor that supplies gas at a supply pressure via a supply line and receives gas at a return pressure via a return line; a valve assembly connected to the supply line and the return line; and a pulse tube cold head connected to the valve assembly. The valve assembly circulates gas between the supply and return pressures to the pulse tube cold head and through the connecting lines. The pulse tube cold head includes: at least one accumulator having a warm end and a cold end; at least one pulse tube having a warm end and a cold end; at least one dual-inlet valve; a buffer volume connected to the warm end of the pulse tube; a first conduit extending from the connecting conduit to the warm end of the accumulator and the dual-inlet valve; a second conduit connecting the cold end of the accumulator to the cold end of the pulse tube; and a third conduit extending from the warm end of the pulse tube to the dual-inlet valve and the buffer volume, and passing through a single-inlet valve. Attached Figure Description

[0016] The accompanying drawings depict one or more implementations consistent with the present concept and are intended as examples rather than limitations. In the drawings, the same reference numerals refer to the same or similar elements.

[0017] Figure 1 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system is shown, which has dual-inlet valves according to the first embodiment disclosed in this invention.

[0018] Figure 2 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system is shown, which has dual-inlet valves according to the second embodiment disclosed in this invention.

[0019] Figure 3 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system is shown, which has dual-inlet valves according to the third embodiment disclosed in this invention.

[0020] Figure 4 A schematic diagram of a two-stage GM-type dual-inlet pulse tube refrigerant system is shown, which has dual-inlet valves according to an embodiment of the present invention.

[0021] Figures 5A-5C Schematic diagrams of the first, second, and third embodiments of the dual intake valve are shown. Detailed Implementation

[0022] In this section, some embodiments of the invention will be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. However, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be more thorough and complete, and will convey the scope of the invention to those skilled in the art. Similar numerals refer to similar elements throughout, and apostrophes are used to indicate similar elements in alternative embodiments. Identical or similar portions in the drawings have the same numbering and are generally not described repeatedly.

[0023] refer to Figure 1 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system 100 is shown, featuring a dual-inlet valve 1a according to the first embodiment disclosed in this invention. (See reference...) Figure 5A A schematic diagram of the dual intake valve 1a according to the first embodiment is shown. The dual intake valve 1a is shown in the context of the entire system. Reference Figure 1 and Figure 5A A single-stage GM-type dual-inlet pulse tube cryogenic cooler system 100 includes: a compressor 10, a valve assembly 12 including valves 12a and 12b, and a pulse tube cold head 101. The compressor 10 is connected to supply valves 12a and V1 via a supply line 11a and to return valves 12b and V2 via a return line 11b. Lines 11a and 11b are typically flexible metal hoses 5 to 20 meters long, and valves 12a and 12b are typically slotted, electrically driven rotary valves that rotate at ports on a fixed base. Gas, typically helium, circulates at a pressure between a supply pressure and a return pressure (typically 2.2 MPa and 0.6 MPa), flowing through a connecting line 13 to the warm end 16a of the accumulator 16 and the warm end of the pulse tube 17, and then through the dual-inlet valves 1a. The compressor 10 supplies gas at the supply pressure via the supply line 11a and receives gas at the return pressure via the return line 11b. Valves 12a and 12b are connected to supply line 11a and return line 11b, respectively, thereby circulating gas between supply and return pressures to pulse head 101 via connecting line 13. If valves 12a and 12b are integral parts of pulse head 101, connecting line 13 may be a few millimeters long; or if the valves are remote, connecting line 13 may be up to one meter long.

[0024] The pulse tube cold head 101 includes: a cold accumulator 16 having a warm end 16a and a cold end 16b; a pulse tube 17 having a warm flow leveler 17a at the warm end and a cold flow leveler 17b at the cold end; a conduit 18 for connecting the cold end 16b of the cold accumulator 16 to the cold flow leveler 17b of the pulse tube 17; a conduit 7 extending from a connecting conduit 13 to the warm end 16a of the cold accumulator 16; conduits 6a and 9a extending from conduit 7 to a dual intake valve 1a; a conduit 5 extending from the warm flow leveler 17a of the pulse tube 17 to a buffer volume 15 and through a single intake valve 4; and conduits 8a and 9b extending from the dual intake valve 1a to conduit 5 and the warm flow leveler 17a of the pulse tube 17. A circulating flow continues to flow to the warm end 16a of the cold accumulator 16 and through conduit 7, and continues to flow to conduit 5 and through the dual intake valve 1a. One end of pipe 5 is connected to the warm end of pulse tube 17, which includes warm flow leveler 17a, and the other end is connected to single air inlet valve 4, which in turn is connected to buffer volume 15. The cold end 16b of cold accumulator 16 is connected to the cold end of pulse tube 17, which includes cold flow leveler 17b, via pipe 18.

[0025] refer to Figure 1 and Figure 5A The dual-inlet valve 1a includes a fixed flow restrictor 3a and a needle valve 2a, which is adjustable to regulate flow from both directions. The needle valve 2a and the fixed flow restrictor 3a are connected in parallel. The needle valve 2a includes a base 30 and a needle 31 extending from the base 30, both disposed within a cavity 32 formed in the needle valve 2a. The needle valve 2a includes a needle tip port 33 connected to a conduit 7 via a conduit 6a, and a valve stem port 34 connected to a conduit 5 via a conduit 8a. The needle 31 protrudes into the needle tip port 33, while the base 30 seals the cavity 32, creating a fluid flow path through the cavity 32 between the needle tip port 33 and the valve stem port 34. Moving the needle 31 toward or away from the needle tip port 33 alters the opening of the flow path, thereby changing the flow velocity in both directions and the degree of asymmetry in the bidirectional flow. It should be noted that the size and shape of the needle 31 and the needle end port 33 can change the flow velocity and asymmetry in both directions of the needle valve 2a, thereby changing the AC and DC flow characteristics.

[0026] The fixed flow restrictor 3a has an orifice (flow path) 35a connecting to pipes 9a and 9b, with pipe 9a connected to pipe 7 and pipe 9b connected to pipe 5. The orifice 35a can have the same cross-sectional area throughout its length, thus the flow rate through the flow restrictor 3a is symmetrical. Symmetrical flow means that the airflow in one direction has the same flow resistance as the airflow in the opposite direction. Asymmetrical flow means that the airflow in one direction has different flow resistances than the airflow in the opposite direction. In asymmetrical flow, the flow resistance of the gas flowing in one direction is greater than or less than the flow resistance of the gas flowing in the opposite direction. The flow rate through the needle valve 2a is asymmetrical. The gas flow rate entering the needle tip port 33 through pipe 6a is more restricted than the gas flow rate entering the valve stem port 34 through pipe 8a. Therefore, the airflow from the needle tip port 33 to the valve stem port 34 has higher flow resistance than the airflow from the valve stem port 34 to the needle tip port 33. In other words, the flow in the direction from the needle 31 to the base 30 has higher resistance than the flow in the opposite direction.

[0027] refer to Figure 2 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system 200 is shown, featuring a dual-inlet valve 1b according to the second embodiment disclosed in this invention. (See reference...) Figure 5B A schematic diagram of the dual-inlet valve 1b according to the second embodiment is shown. The dual-inlet valve 1b differs from the dual-inlet valve 1a in that the needle valve 2b is flipped so that the needle tip port 33 is connected to the pipe 5 via the pipe 6b, and the valve stem port 34 is connected to the pipe 7 via the pipe 8b. The length of the orifice 35a through which the fixed flow restrictor 3a passes can have the same cross-sectional area; therefore, the flow rate through the flow restrictor 3a is symmetrical. The flow rate through the needle valve 2b is asymmetrical. The gas flow rate entering the needle tip port 33 via the pipe 6b is more restricted than the gas flow rate entering the valve stem port 34 via the pipe 8b. Therefore, the airflow from the needle tip port 33 to the valve stem port 34 has higher flow resistance than the airflow from the valve stem port 34 to the needle tip port 33.

[0028] The single-stage GM type dual-inlet pulse tube cryogenic cooler system 200 includes: a compressor 10, a valve assembly 12 including valves 12a and 12b, and a pulse tube cold head 201. The compressor 10 supplies gas at a supply pressure via a supply line 11a and receives gas at a return pressure via a return line 11b. Valves 12a and 12b are connected to the supply line 11a and the return line 11b, respectively, thereby circulating the gas between the supply pressure and the return pressure via a connecting line 13 to the pulse tube cold head 201. The pulse tube cold head 201 includes: a cold storage unit 16 having a warm end 16a and a cold end 16b; a pulse tube 17 having a warm flow leveler 17a at the warm end and a cold flow leveler 17b at the cold end; a conduit 18 for connecting the cold end 16b of the cold storage unit and the cold flow leveler 17b of the pulse tube 17; a conduit 7 extending from a connecting conduit 13 to the warm end 16a of the cold storage unit 16; conduits 8b and 9a extending from conduit 7 to a dual intake valve 1b; a conduit 5 extending from the warm flow leveler 17a of the pulse tube 17 to a buffer volume 15 and through a single intake valve 4; and conduits 6b and 9b extending from the dual intake valve 1b to conduit 5 and to the warm flow leveler 17a of the pulse tube 17.

[0029] refer to Figure 3 A schematic diagram of a single-stage GM-type dual-inlet pulse tube cryogenic cooler system 300 is shown, featuring a dual-inlet valve 1c according to the third embodiment disclosed in this invention. (See reference...) Figure 5C A schematic diagram of the dual-intake valve 1c according to a third embodiment is shown. The dual-intake valve 1c differs from 1a in that it has a fixed flow restrictor 3b with a tapered orifice 35b, producing an asymmetric flow pattern. In this embodiment, the cross-sectional area of ​​the orifice 35b is increased from the connection point of pipe 9a to the connection point of pipe 9b. In this configuration, the fixed flow restrictor 3b has lower flow resistance in the flow from pipe 9a to pipe 9b than in the opposite direction. It is understood that the asymmetric flow restrictor 3b, combined with the adjustable flow restrictor 2a or 2b, can be oriented in either direction. For example, if the fixed flow restrictor 3b is combined with… Figure 2 In the needle valve 2b assembly of the illustrated embodiment, the cross-sectional area of ​​the orifice 35b may be reduced from the connection point of pipe 9a to the connection point of pipe 9b.

[0030] The single-stage GM type dual-inlet pulse tube cryogenic cooler system 300 includes: a compressor 10, a valve assembly 12 including valves 12a and 12b, and a pulse tube cold head 301. The compressor 10 supplies gas at a supply pressure via a supply line 11a and receives gas at a return pressure via a return line 11b. Valves 12a and 12b are connected to the supply line 11a and the return line 11b, respectively, thereby circulating gas between the supply pressure and the return pressure through a connecting line 13 to the pulse tube cold head 301. The pulse tube cold head 301 includes: a cold accumulator 16 having a warm end 16a and a cold end 16b; a pulse tube 17 having a warm flow leveler 17a at the warm end and a cold flow leveler 17b at the cold end; a conduit 18 for connecting the cold end 16b of the cold accumulator and the cold flow leveler 17b of the pulse tube 17; a conduit 7 extending from a connecting conduit 13 to the warm end 16a of the cold accumulator 16; conduits 6a and 9a extending from conduit 7 to a dual intake valve 1c; a conduit 5 extending from the warm flow leveler 17a of the pulse tube 17 to a buffer volume 15 and through a single intake valve 4; and conduits 8a and 9b extending from the dual intake valve 1c to conduit 5 and to the warm flow leveler 17a of the pulse tube 17.

[0031] refer to Figure 4 The diagram shows a schematic of a two-stage GM-type dual-inlet pulse tube cryogenic cooler system 400, comprising two pulse tubes 17 and 21. A dual-inlet valve 1a is connected to the first-stage pulse tube system 17, and a dual-inlet valve 1d is connected to the second-stage pulse tube 21. The dual-inlet valve 1d is structurally equivalent to 1a, but with a different arrangement. Specifically, the dual-inlet valves 1a and 1d are arranged in a mirror-symmetric manner relative to pipe 7. The circulating flow continues to the warm end 16a' of the first-stage accumulator 16' and the second-stage accumulator 20 through pipe 7, and continues to pipe 5 through dual-inlet valve 1a, and then to pipe 5a through the second-stage dual-inlet valve 1d. One end of pipe 5 is connected to the warm end of pulse tube 17, which includes a warm flow leveler 17a, and the other end is connected to a single-inlet valve 4, which in turn is connected to a buffer volume 15. One end of the pipe 5a is connected to the warm end of the second-stage pulse 21, which includes the warm flow leveler 21a, and the other end is connected to the single air intake valve 4a, which in turn is connected to the second-stage buffer volume 15a.

[0032] like Figure 4As shown, the two-stage GM-type dual-inlet pulse tube cryogenic cooler system 400 includes a second-stage regenerator 20, which is an extension of the first-stage regenerator 16'. The second-stage pulse tube 21 is separate from the first-stage pulse tube 17, with its warm end at room temperature. The cold end 16b' of the first-stage regenerator 16 is connected via pipe 18 to the cold end of the first-stage pulse tube 17, which includes a cold flow leveler 17b. The cold end 20b of the second-stage regenerator 20 is connected via pipe 22 to the cold end of the pulse tube 21, which includes a flow leveler 21b. The warm end of the first-stage pulse tube 17 has a flow leveler 17a and is connected to pipe 5, which is connected via a single inlet valve 4 to a first dual inlet valve 1a and a buffer volume 15. The warm end of the second-stage pulse tube 21 has a flow leveler 21a and is connected to pipe 5a, which is connected via a single inlet valve 4a to a dual inlet valve 1d and a buffer volume 15a.

[0033] The two-stage GM type dual-inlet pulse tube cryogenic cooler system 400 includes: a compressor 10, a valve assembly 12 including valves 12a and 12b, and a pulse tube cold head 401. The compressor 10 supplies gas at a supply pressure via a supply line 11a and receives gas at a return pressure via a return line 11b. Valves 12a and 12b are connected to the supply line 11a and the return line 11b, respectively, thereby circulating the gas between the supply pressure and the return pressure via a connecting line 13 to the pulse tube cold head 401. The pulse cold head 401 includes: a first-stage cold accumulator 16' having a warm end 16a' and a cold end 16b'; a second-stage cold accumulator 20 connected to the cold end 16b' of the first-stage cold accumulator 16' and having a cold end 20b; a first-stage pulse tube 17 having a warm flow leveler 17a at the warm end and a cold flow leveler 17b at the cold end; a second-stage pulse tube 21 having a warm flow leveler 21a at the warm end and a cold flow leveler 21b at the cold end; a pipe 18 for connecting the cold end 16b' of the cold accumulator and the cold flow leveler 17b of the pulse tube 17; a pipe 22 for connecting the cold end 20b of the cold accumulator and the cold flow leveler 21b of the pulse tube 21; and a pipe 7 connecting the pipe 1... 3 extends to the warm end 16a' of the cold storage 16; pipes 6a and 9a extend from pipe 7 to the double inlet valve 1a; pipes 6a' and 9a' extend from pipe 7 to the double inlet valve 1d; pipe 5 extends from the warm flow leveler 17a of the pulse tube 17 to the buffer volume 15 and through the single inlet valve 4; pipe 5a extends from the warm flow leveler 21a of the pulse tube 21 to the buffer volume 15a and through the single inlet valve 4a; pipes 8a and 9b extend from the double inlet valve 1a to pipe 5 and to the warm flow leveler 17a of the pulse tube 17; and pipes 8a' and 9b' extend from the double inlet valve 1d to pipe 5a and to the warm flow leveler 21a of the pulse tube 21.

[0034] It has been found that dual inlet valve 1a provides optimal results for this design. For other designs with different pulse tube and accumulator sizes, dual inlet valves 1b and 1c may be preferred. Dual inlet valves 1a or 1d can be used alone in the first or second stage of the two-stage GM type dual inlet pulse tube cold head 401, in combination with another stage of conventional dual inlet valve 2a.

[0035] The terminology and descriptions used herein are set forth by way of illustration only and are not intended to be limiting. Those skilled in the art will recognize that many variations are possible within the spirit and scope of the invention and within the embodiments described herein.

Claims

1. A dual inlet valve for a Gifford-McMahon (GM) type dual inlet pulse tube cryocooler system for providing cooling at cryogenic temperatures, comprising: a fixed restrictor comprising an orifice or a conical orifice having a constant cross-sectional area; and a needle valve coupled in parallel to the fixed restrictor, wherein the needle valve is configured to allow and regulate flow from both directions and such that the flow resistance in one direction is different from the flow resistance in the opposite direction. The flow through the fixed restrictor is symmetrical.

2. The dual intake valve of claim 1, wherein, The flow through the fixed restrictor is asymmetrical.

3. The dual intake valve of claim 1, wherein, The needle valve defines a cavity having a needle end port and a stem end port, and wherein the needle valve comprises:

4. The dual intake valve according to any of the preceding claims, wherein, a base sealing the cavity; and a needle extending from the base toward the needle end port, wherein the flow of gas from the needle end port to the stem end port has a higher flow resistance than the flow of gas from the stem end port to the needle end port. The needle valve is adjustable for adjusting the flow between the needle end port and the stem end port.

5. The dual intake valve of claim 4, wherein, 6. A Gifford-McMahon (GM) type dual inlet pulse tube cryocooler system for providing cooling at cryogenic temperatures, comprising: a compressor for supplying gas at a supply pressure through a supply line and receiving gas at a return pressure through a return line; a valve assembly connected to the supply line and the return line; and a pulse tube cold head connected to the valve assembly, wherein the valve assembly circulates gas between the supply pressure and the return pressure through a connecting line to the pulse tube cold head, the pulse tube cold head comprising: at least one cold accumulator having a warm end and a cold end; at least one pulse tube having a warm end and a cold end; at least one dual inlet valve comprising: a fixed restrictor comprising an orifice or a conical orifice having a constant cross-sectional area; and a needle valve coupled in parallel to the fixed restrictor, wherein the needle valve is configured to allow and regulate flow from both directions and such that the flow resistance in one direction is different from the flow resistance in the opposite direction; a buffer volume connected to the warm end of the pulse tube; a first line extending from the connecting line to the warm end of the cold accumulator, wherein one end of the fixed restrictor and the needle valve of the dual inlet valve are both connected to the first line; a second line connecting the cold end of the cold accumulator with the cold end of the pulse tube; and a third line extending from the warm end of the pulse tube to the buffer volume and through a single inlet valve, wherein the other end of the fixed restrictor and the needle valve of the dual inlet valve are both connected to the third line at a location between the warm end of the pulse tube and the single inlet valve. The flow through the fixed restrictor is symmetrical.

7. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 6, wherein, The flow through the fixed restrictor is asymmetrical.

8. The Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 6, wherein, The needle valve defines a cavity having a needle end port and a stem end port, and wherein the needle valve comprises:

9. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to any one of claims 6-8, wherein, a base sealing the cavity; and a needle extending from the base toward the needle end port, wherein the flow of gas from the needle end port to the stem end port has a higher flow resistance than the flow of gas from the stem end port to the needle end port. ​ 10. The Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 9, wherein, The needle valve is adjustable to adjust flow between the needle end port and the valve stem port.

11. The Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 9, wherein, The needle end port is connected to the first line and the valve stem port is connected to the third line.

12. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 11, wherein, The fixed restrictor has a lower flow resistance in flow from the first line to the third line than in flow from the third line to the first line.

13. The Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to claim 9, wherein, The needle end port is connected to the third line and the valve stem port is connected to the first line.

14. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to any one of claims 6-8, wherein, The pulse tube cold head further comprises: a second stage cold accumulator connected to the cold end of the cold accumulator; a second stage pulse tube having a warm end and a cold end; a second stage dual inlet valve connected to the first line; a second stage buffer volume connected to the warm end of the second stage pulse tube; a fourth line connecting the cold end of the second stage pulse tube to the cold end of the second stage cold accumulator; and a fifth line extending from the warm end of the second stage pulse tube to the second stage dual inlet valve and to the second stage buffer volume and through a single inlet valve.

15. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to any one of claims 6-8, wherein, The connecting lines between the valve assembly and the pulse tube cold head are single flexible hoses.

16. A Gifford-McMahon (GM) type dual-inlet-pulse-tube cryogenic cooler system for providing cooling at low temperatures according to any one of claims 6-8, wherein, The connecting lines between the valve assembly and the pulse tube cold head are at least 0.5 meters long.

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