CN101105345A - Stirling-type multistage pulse tube refrigerator in liquid helium temperature zone using helium 3-helium 4 duplex - Google Patents

Abstract

The invention discloses a liquid helium temperature zone Stirling multistage pulse tube refrigerator using helium 3-helium 4 duplex. The helium 4 compressor is connected to the second-stage regenerator through the first-stage regenerator, the first-stage regenerator is connected to the first-stage pulse tube and the first-stage phasing mechanism through the cold head, and the second-stage regenerator The cold head of the heater is connected to the second-stage phase adjustment mechanism through the second-stage pulse tube, the cold head of the second-stage pulse tube is connected to the middle part of the third-stage regenerator through a thermal bridge, and the hot end of the third-stage regenerator is connected to the middle part of the third-stage regenerator. The helium 3 compressor is connected, the cold head of the third-stage regenerator is connected with the cold head of the third-stage pulse tube, the hot end of the third-stage pulse tube is connected with the third-stage phasing mechanism, and the hot end of the third-stage pulse tube It is connected to the middle part of the third-stage regenerator through a heat bridge. In the present invention, the working fluid helium 4 is used in the first and second stages, and the working fluid helium 3 with better performance is used in the third stage with the lowest refrigeration temperature, thereby saving the amount of helium 3 and reducing the cost. At the same time, it achieves better results than the scheme that completely uses helium 4 as the working fluid.

Description

Stirling-type multistage pulse tube refrigerator in liquid helium temperature zone using helium 3-helium 4 duplex

technical field

The invention relates to a liquid helium temperature zone Stirling multistage pulse tube refrigerator using helium 3-helium 4 duplex. It is suitable for compact pulse tube refrigerators requiring to reach the temperature range of liquid helium.

Background technique

The pulse tube refrigerator is a recuperative refrigerator that has been researched by countries all over the world in the past ten years. Composition, due to the elimination of the ejector at low temperature, it is simpler and more reliable than the traditional G-M and Stirling type refrigerators, and the mean time between failures is greatly extended, so it has broader prospects in space applications.

According to the gas distribution type, pulse tube refrigerators are divided into G-M type pulse tube refrigerators and Stirling type pulse tube refrigerators. The former uses a switch valve connection between the mechanical compressor and the pulse tube refrigerator, and realizes the compression and expansion process of the gas in the pulse tube refrigerator through the control of the high and low pressure end valves, thereby generating a cooling effect at the cold end of the refrigerator. The frequency is generally 1-2Hz, which is currently the main method to obtain liquid helium temperature zone refrigeration. However, since the compressor part adopts an oil-lubricated structure and is equipped with an oil separation and adsorption device, it is relatively bulky and requires regular maintenance. At the same time, there is a large conversion loss in the pressure wave generated by the valve structure, so the efficiency is relatively low, so that it is difficult to obtain applications in space and military. In contrast, the Stirling-type pulse tube refrigerator provides high-frequency pressure waves (30-60Hz) through a valveless compressor, with leaf spring support, gap seals, and moving coil (or moving magnet) linear compression With the development of other technologies, the electric power conversion efficiency of the compressor can usually reach more than 80%. Generally speaking, the Stirling-type pulse tube refrigerator has the advantages of high efficiency (2 to 5 times), small size and light weight (less than 20%) compared with the G-M type, and has important application value in space and military aspects. Whether it is G-M type or Stirling type, it is necessary to use gas with superior thermodynamic properties as the working medium. At present, most of them use helium 4 as the working fluid, and some scholars use other gases or mixed working fluids for research in certain temperature ranges.

In order to achieve better refrigeration performance in the liquid helium temperature range and in this temperature range, recent theories and researches have shown that Helium 3 working fluid has better low temperature characteristics than Helium 4 working fluid. Jiang Ning of Zhejiang University has an independent On the G-M two-stage pulse tube refrigerator in the liquid helium temperature zone of the gas circuit, helium 3 was used as the second-stage refrigerant, and the lowest no-load refrigeration temperature of 1.27K was obtained. Compared with the case where both stages use helium 4 as the working fluid, under the same conditions (same compressor power consumption), the second stage uses helium 3 as the working fluid, so that the two-stage pulse tube refrigerator can operate at 4.2K Cooling capacity increased by 40.5%.

In the liquid helium temperature range, on the one hand, due to the influence of the non-ideality of the working medium at low temperatures - the sharp increase in the specific heat capacity accompanied by the λ phase transition will cause the regenerator to fail, and the nature of the working medium will become a bottleneck that limits the performance of the regenerative cryogenic refrigerator one. It is known that the 4λ phase transition temperature of helium is 2.171K, while the 3λ phase transition temperature of helium is in the mK temperature range. Below 20K, the specific heat capacity of helium 4 is significantly larger than that of helium 3. On the other hand, when the thermal expansion coefficient α _p of the working medium is 0, the adiabatic compression or expansion will not cause any temperature change, and the refrigerator will not be able to produce any cooling capacity. In fact, the temperature at which the thermal expansion coefficient α _p =0 of helium 4 is near its λ phase transition temperature, and the thermal expansion coefficient α _p of helium 3 becomes 0 at a lower temperature (around 1K). Therefore, the above two factors limit the performance of cryogenic refrigerators using helium 4 as the working fluid at low temperatures. The pulse tube refrigerator using helium 3 as the working medium is expected to achieve lower refrigeration temperature, greater refrigeration capacity and higher efficiency.

At present, the Stirling-type pulse tube refrigerator that can reach the temperature range of liquid helium, such as a four-stage pulse tube refrigerator ACTDP 4-stage designed and manufactured by The Lockheed Martin Advanced Technology Center (LMATC), is driven by a linear compressor. Using helium 3 as the working fluid, the lowest no-load refrigeration temperature is 3.8K.

Contents of the invention

The object of the present invention is to provide a Stirling type multi-stage pulse tube refrigerator in liquid helium temperature zone using helium 3-helium 4 duplex.

It includes the first-stage pulse tube refrigerator, the second-stage pulse tube refrigerator, and the third-stage pulse tube refrigerator. The first and second-stage pulse tube refrigerators include the second-stage pulse tube, the second-stage First stage regenerator, helium 4 compressor, first stage phase adjustment mechanism, first stage pulse tube, second stage regenerator, third stage pulse tube refrigerator including third stage pulse tube, third stage phase modulation Mechanism, third-stage regenerator, helium-3 compressor, helium-4 compressor is connected to the second-stage regenerator through the first-stage regenerator, and the first-stage regenerator is connected to the first-stage pulse tube through the cold head , The first-stage phase-modulating mechanism is connected, the cold head of the second-stage regenerator is connected with the second-stage phase-modulating mechanism through the second-stage pulse tube, and the second-stage pulse tube cold head is connected with the third-stage regenerator through the heat bridge The middle part of the regenerator is connected, the hot end of the third-stage regenerator is connected with the helium 3 compressor, the cold head of the third-stage regenerator is connected with the cold head of the third-stage pulse tube, and the hot end of the third-stage pulse tube is connected with the third-stage The third-stage phase modulation mechanism is connected, and the hot end of the third-stage pulse tube is connected with the middle part of the third-stage regenerator through a thermal bridge.

The first-stage pulse tube refrigerator and the second-stage pulse tube refrigerator use helium 4 as a working fluid. The third-stage pulse tube refrigerator uses helium 3 as the working fluid.

Both theory and practice have proved that helium 3 has better thermal performance than helium 4 in the liquid helium temperature range. Because helium 3 gas is very scarce and expensive, and in the higher temperature region, the difference in physical properties between the isotope helium 3 and helium 4 is very small. From the existing experimental results, the advantage of helium 3 over helium 4 is not obvious. In the third stage with a smaller volume and the lowest refrigeration temperature, helium 3 with better performance is used to improve the performance of the refrigerator. At the same time, in the front-end stage (pre-cooling stage), which is also a larger part, the relatively cheap working fluid helium 4 is used, thereby greatly saving the amount of helium 3 and reducing the cost.

Description of drawings

The accompanying drawing is a schematic diagram of a Stirling-type multi-stage pulse tube refrigerator system in the liquid helium temperature zone using helium 3-helium 4 duplex. In the figure: second-stage pulse tube 1, second-stage phase modulation mechanism 2, first-stage regenerator 3, helium 4 compressor 4, first-stage phase modulation mechanism 5, first-stage pulse tube 6, second-stage Regenerator 7 , thermal bridge 8 , third-stage pulse tube 9 , third-stage phase modulation mechanism 10 , third-stage regenerator 11 , and helium 3 compressor 12 .

Detailed ways

As shown in the attached figure, the Stirling-type multi-stage pulse tube refrigerator in the liquid helium temperature zone using helium 3-helium 4 duplex includes a first-stage pulse tube refrigerator, a second-stage pulse tube refrigerator, and a third-stage pulse tube refrigerator. The first and second stage pulse tube refrigerators include the second stage pulse tube 1, the second stage phase modulation mechanism 2, the first stage regenerator 3, the helium 4 compressor 4, the first stage phase modulation Mechanism 5, first-stage pulse tube 6, second-stage regenerator 7, and third-stage pulse-tube refrigerator including third-stage pulse tube 9, third-stage phase modulation mechanism 10, third-stage regenerator 11, helium 3. Compressor 12. Helium 4. Compressor 4 is connected to second-stage regenerator 7 via first-stage regenerator 3. First-stage regenerator 3 is connected to first-stage pulse tube 6 and first-stage regenerator 7 via cold head. The phase-modulating mechanism 5 is connected, the cold head of the second-stage regenerator 7 is connected with the second-stage phase-modulating mechanism 2 through the second-stage pulse tube 1, and the cold head of the second-stage pulse tube 1 is connected to the third-stage The middle part of the regenerator 11 is connected, the hot end of the third-stage regenerator 11 is connected with the helium 3 compressor 12, the cold head of the third-stage regenerator 11 is connected with the cold head of the third-stage pulse tube 9, and the third-stage The hot end of the pulse tube 9 is connected to the third-stage phase adjustment mechanism 10 , and the hot end of the third-stage pulse tube 9 is connected to the middle of the third-stage regenerator 11 through a thermal bridge.

The first-stage pulse tube refrigerator and the second-stage pulse tube refrigerator use helium 4 as a working fluid. The third-stage pulse tube refrigerator uses helium 3 as the working fluid.

The function of the thermal bridge 8 is to transfer the heat from the middle part of the regenerator of the third-stage pulse tube refrigerator and the radiator at the hot end of the pulse tube to the cold head of the second-stage pulse tube refrigerator through heat conduction, thereby realizing the precooling effect.

The specific assembly method is to first connect the helium 4 compressor 4 with the first and second stage Stirling type pulse tube refrigerator regenerators 3; secondly, connect the helium 3 compressor 12 and the third stage Stirling type pulse tube refrigerator The regenerator 11 of the tube refrigerator is connected; finally, a heat bridge 8 is used to connect the cold head of the second-stage pulse tube refrigerator with the middle part of the regenerator of the third-stage pulse tube refrigerator and the radiator at the hot end of the pulse tube.

After assembling the entire refrigeration system, turn on the helium-4 compressor, the first and second-stage pulse tube refrigerators start to refrigerate, the temperature of the cold head begins to drop, and pre-cool the third-stage pulse tube refrigerator; at the same time, turn on the helium-3 compression The third-stage pulse tube refrigerator starts to refrigerate. Since the middle part of the regenerator and the heat sink at the hot end of the pulse tube are connected to the cold head of the second-stage pulse tube refrigerator, the upper part of the regenerator drops from room temperature to the temperature of the second-stage The temperature of the cold head of the pulse tube refrigerator is similar, and generally the difference between the two is less than 10K. The lower half begins to drop from this intermediate temperature until it reaches the temperature of the cold head of the third-stage pulse tube refrigerator.

Claims (4)

1. liquid helium warm area stirling type multi vascular refrigerator that adopts helium 3-helium 4 duplexing matter, it is characterized in that it comprises first order vascular refrigerator, second level vascular refrigerator, third level vascular refrigerator, first, two stage pulse tube refrigerator comprises second level vascular (1), second level phase modulating mechanism (2), first order regenerator (3), helium 4 compressors (4), first order phase modulating mechanism (5), first order vascular (6), second level regenerator (7), third level vascular refrigerator comprises third level vascular (9), third level phase modulating mechanism (10), third level regenerator (11), helium 3 compressors (12), helium 4 compressors (4) are connected with second level regenerator (7) through first order regenerator (3), first order regenerator (3) is through first order vascular refrigerator cold head and first order vascular (6), first order phase modulating mechanism (5) is connected, second level regenerator (7) cold head is connected with second level phase modulating mechanism (2) through second level vascular (1), second level vascular (1) cold head is connected with third level regenerator (11) middle part through heat bridge (8), third level regenerator (11) hot junction is connected with helium 3 compressors (12), third level regenerator (11) cold head is connected with third level vascular (9) cold head, third level vascular (9) hot junction is connected with third level phase modulating mechanism (10), and third level vascular (9) hot junction is connected with third level regenerator (11) middle part through heat bridge.

2. a kind of liquid helium warm area stirling type multi vascular refrigerator that adopts helium 3-helium 4 duplexing matter according to claim 1 is characterized in that described first order vascular refrigerator, second level vascular refrigerator adopt helium 4 to be working medium.

3. a kind of liquid helium warm area stirling type multi vascular refrigerator that adopts helium 3-helium 4 duplexing matter according to claim 1 is characterized in that described third level vascular refrigerator adopts helium 3 to be working medium.

4. a kind of liquid helium warm area stirling type multi vascular refrigerator that adopts helium 3-helium 4 duplexing matter according to claim 1, it is characterized in that described first order vascular refrigerator and second level vascular refrigerator both can adopt the mode of gas coupled mode, also can adopt the mode of divergence type.For divergence type, both can distribute by gas to drive with helium 4 compressors, also can drive respectively with two helium 4 compressors.

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