CN106679217B - A liquid helium recondensation cryogenic refrigeration system with mechanical vibration isolation - Google Patents

Abstract

The invention belongs to the technical field of low-temperature refrigeration equipment, and particularly relates to a mechanical vibration isolation liquid helium recondensation low-temperature refrigeration system. The system of the invention comprises: a closed-cycle refrigerator system, a liquid helium recondensation refrigeration vibration isolation system and a temperature feedback control system. The invention uses a closed-cycle refrigerator system to achieve low temperatures as low as 4.2K with almost no helium and liquid helium consumption. The invention generates and maintains the liquid helium through the liquid helium recondensation refrigeration vibration isolation system, thereby not only effectively isolating the low-frequency vibration generated during the operation of the closed-cycle refrigerator, but also solving the problem of large temperature fluctuation of the traditional closed-cycle refrigerator. The invention can not only control the liquid level of the liquid helium generated by recondensation through the temperature feedback control system, but also realize temperature change regulation and control. The invention is suitable for the ultrahigh vacuum environment needing high-temperature baking.

Description

A liquid helium recondensation cryogenic refrigeration system with mechanical vibration isolation

technical field

The invention belongs to the technical field of cryogenic refrigeration equipment, and in particular relates to a liquid helium recondensation cryogenic refrigeration system with mechanical vibration isolation.

Background technique

Low temperature environment refers to the environment below -180°C (93.15 K), which has important applications in the fields of physics, chemistry, materials, biology, national defense, and information. With the development of science and technology, cutting-edge precision scientific research and technical applications not only require an environment close to extremely low temperature (4.2 K), but also require a low vibration and ultra-high vacuum environment. At present, the vast majority of low-temperature refrigeration equipment that meets the above indicators need to consume scarce and expensive liquid helium, and the operating cost is relatively large. In order to get rid of the extreme dependence of cryogenic refrigeration equipment on liquid helium, there has recently been a cryogenic refrigeration system without liquid helium consumption with mechanical vibration isolation (ZL 201610002349.8). This low-temperature refrigeration system uses a closed-cycle refrigerator without liquid helium consumption for refrigeration, which solves the problem that traditional low-temperature equipment consumes a large amount of liquid helium; using helium heat exchange gas as a heat transfer medium, it can effectively isolate the refrigeration while cooling down. machine vibration. However, the working principle of the closed-cycle refrigerator causes the refrigeration power to change periodically, and the refrigeration vibration isolation technology using helium heat exchange gas still has limitations such as low refrigeration power and large temperature fluctuations on the vibration isolation interface. For these reasons, the refrigeration efficiency and temperature stability of cryogenic refrigeration systems without liquid helium consumption are still lower than those of cryogenic refrigeration systems that consume liquid helium. Therefore, it is of great significance to develop a cryogenic refrigeration system with high temperature stability and mechanical vibration isolation that consumes almost no liquid helium.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a low temperature refrigeration system with mechanical vibration isolation, small temperature fluctuation, high refrigeration power, and almost no consumption of helium and liquid helium, namely a liquid helium recondensation low temperature refrigeration system isolated by mechanical vibration . The operation of the system is compatible with low vibration environments and ultra-high vacuum environments.

The liquid helium recondensation cryogenic refrigeration system with mechanical vibration isolation provided by the present invention includes a closed-cycle refrigerator system, a liquid helium recondensation refrigeration vibration isolation system and a temperature feedback control system. Wherein, the closed-cycle refrigerator system includes: a refrigeration head, a compressor, and a helium gas transmission pipeline connecting the compressor and the refrigeration head; the liquid helium recondensation refrigeration vibration isolation system includes: a refrigeration vibration isolation interface, a helium Gas-heat exchange gas, liquid helium produced by recondensation, and soft rubber for sealing helium gas and isolating vibration, etc. The temperature feedback control system is composed of a temperature measuring element, a heating element and a feedback temperature control circuit.

In the liquid helium recondensation refrigeration vibration isolation system, the refrigeration head of the closed-cycle refrigerator extends into the refrigeration vibration isolation interface, and the helium heat exchange gas is filled between the refrigeration head and the refrigeration vibration isolation interface as a refrigeration and cooling medium; The soft rubber is connected to the upper end of the sealing refrigeration vibration isolation interface and the refrigeration head, which can isolate the low-frequency mechanical vibration of the refrigeration head while sealing the helium heat exchange gas; The exchange gas re-condenses to form liquid helium in the cooling vibration isolation interface. The liquid helium formed by recondensation has a large latent heat, which greatly improves the heat exchange capacity of the refrigeration head and the refrigeration vibration isolation interface, so that the liquid helium recondensation cryogenic refrigeration system provided by the present invention can be used for mechanical vibration isolation. While obtaining a low temperature and low vibration environment, it has excellent cooling capacity and temperature stability.

In the temperature feedback control system, the heating element is arranged at the low temperature end of the refrigeration vibration isolation interface, and the temperature measuring element is arranged on the refrigeration vibration isolation interface to cover the height of the liquid helium liquid level formed by recondensation in the height direction. The temperature measuring element is used to indirectly measure the liquid level of the recondensed liquid helium, and the feedback temperature control circuit is used to control the output power of the heating element. The height of the liquid helium level can be adjusted by the temperature feedback control system to avoid vibration caused by the direct contact between the liquid helium level and the refrigeration head; the temperature feedback control system can also achieve a wide range of temperature changes.

In the present invention, a heat radiation shielding cover may also be provided on the cooling vibration isolation interface to shield heat leakage caused by high temperature radiation.

In the present invention, in order to make the liquid helium recondensation cryogenic refrigeration system provided by the present invention compatible with the high temperature baking conditions required by the user's ultra-high vacuum environment, the liquid helium recondensation refrigeration vibration isolation system can be Materials such as stainless steel and oxygen-free copper as well as ultra-high vacuum compatible welding and sealing techniques.

In the present invention, the types of closed-cycle refrigerators include, but are not limited to, Gift-McMahon refrigerators, Stirling refrigerators, pulse-tube refrigerators, and improved refrigerators based on these principles. The cooling power and minimum temperature of closed-cycle refrigerators vary according to the working principle and model of the refrigerator.

The present invention has the following beneficial effects:

1. The operation of the closed-cycle refrigerator and the liquid helium recondensation refrigeration vibration isolation system adopted in the present invention is almost free of helium and liquid helium consumption. This solution solves the problem that traditional cryogenic refrigeration equipment needs to consume scarce and expensive liquid helium.

2. The present invention utilizes the recondensation technology to liquefy part of the helium heat exchange gas to generate liquid helium at the low temperature end, which greatly improves the refrigeration power and temperature stability of the system. This solution solves the problem of large temperature fluctuations in traditional closed-cycle refrigerators at low temperatures.

3. The helium heat exchange gas refrigeration vibration isolation interface used in the present invention effectively isolates the low-frequency mechanical vibration when the closed-cycle refrigerator works, and this solution provides a low-temperature and low-vibration working environment at the same time.

4. The temperature feedback control system adopted in the present invention can realize liquid helium level control, and can also realize a wide range of temperature changing operation.

5. The solution provided by the present invention to realize low temperature and low vibration under the condition of almost no consumption of helium and liquid helium can also work in an ultra-high vacuum environment, and can withstand the high temperature baking required to realize the ultra-high vacuum environment.

Description of drawings

FIG. 1 is a schematic diagram of the principle of the mechanical vibration isolation liquid helium recondensation cryogenic refrigeration system device proposed by the present invention.

FIG. 2 is a cross-sectional view of an embodiment of a refrigeration head component and a liquid helium recondensation refrigeration vibration isolation system in a closed-cycle refrigerator.

3 is a schematic diagram of an embodiment assembly of a temperature feedback control system.

Labels in the figure: 1-Closed cycle refrigerator system, 2-Liquid helium recondensation refrigeration vibration isolation system, 3-User's sample or equipment, 4-Temperature feedback control system, 5-Vacuum chamber, 6-Cooling head, 7--refrigeration vibration isolation interface, 8-helium heat exchange gas, 9-liquid helium formed by liquefaction or re-condensation, 10-experimental sample or equipment, 11-heat radiation shield, 12-soft rubber, 13-heating Elements, 14 - the first temperature measuring element, 15 - the second temperature measuring element.

Detailed ways

In order to make the use of the present invention clearer, the present invention will be further described in detail below with reference to the specific embodiments and the accompanying drawings.

The device of the present invention comprises: a closed-cycle refrigerator system 1 , a liquid helium recondensation refrigeration vibration isolation system 2 , and a temperature feedback control system 4 . in,

The closed-cycle refrigerator system 1 includes: a closed-cycle refrigeration head 6, a compressor, a helium gas delivery pipeline, and the like. The liquid helium recondensation refrigeration vibration isolation system 2 includes: a refrigeration vibration isolation interface 7, a helium heat exchange gas 8, a recondensed liquid helium 9, a heat radiation shield 11, a soft rubber 12, and the like.

The temperature feedback control system 4 includes a heating element 13 , a first temperature measuring element 14 and a second temperature measuring element 15 .

In the liquid helium recondensation refrigeration vibration isolation system, the refrigeration head 6 of the closed-cycle refrigerator system extends into the refrigeration vibration isolation interface 7, and the helium heat exchange gas 8 is filled between the refrigeration head and the refrigeration vibration isolation interface as a cooling device. Cooling and cooling medium. The soft rubber 12 is connected to the upper end of the sealed refrigeration vibration isolation interface and the refrigeration head, and can isolate the low-frequency mechanical vibration of the refrigeration head while sealing the helium heat exchange gas. The helium heat exchange gas will re-condensate in the refrigeration vibration isolation interface under the refrigeration action of the closed-cycle refrigeration head to form liquid helium, thereby greatly improving the refrigeration capacity and temperature stability between the refrigeration head and the refrigeration vibration isolation interface. The heat radiation shielding cover 11 is fixed on the cooling vibration isolation interface to shield heat leakage caused by high temperature radiation.

The temperature feedback control system is composed of a heating element 13, a first temperature measuring element 14, a second temperature measuring element 15 and a feedback temperature control circuit. Wherein, the first temperature measuring element 13 and the second temperature measuring element 14 are respectively disposed at the lower end and the upper end of the liquid helium horizontal projection surface. By measuring the temperature of the first and second temperature measuring elements, combined with feedback control, the height of liquid helium in the refrigeration vibration isolation interface can be controlled: when there is no liquid helium in the refrigeration vibration isolation interface, the first and second temperature measurement The temperature of the elements is higher than the phase transition point temperature of helium (about 4.2 K); when the liquid helium liquid level in the refrigeration vibration isolation interface is between the first and second temperature measuring elements, the temperature of the first temperature measuring element is equal to the phase transition point temperature, and the temperature of the second temperature measuring element is higher than the phase transition point temperature; when the liquid helium level is higher than the second temperature measuring element, the temperatures of the first and second temperature measuring elements are both equal to the phase transition point temperature . In addition, a wide range of temperature-variable operation can be achieved through the temperature feedback control system.

In this embodiment, the closed-cycle refrigerator system is used to solve the problem that a large amount of liquid helium is required for traditional low-temperature refrigeration operation; the use of helium heat exchange gas to cool the vibration isolation interface solves the problem of micron-level and above low frequency generated by the operation of traditional refrigerators. The problem of mechanical vibration; the use of liquid helium re-condensation technology to solve the problem of large temperature fluctuations in traditional closed-cycle refrigerators at low temperatures; the use of temperature feedback control system for feedback temperature control, not only can control the refrigeration vibration isolation interface. The height of the liquid helium liquid level can also realize a wide range of temperature-changing operation; stainless steel and oxygen-free copper and other materials are used to make the refrigeration vibration isolation interface in the vacuum environment, which is compatible with the high-temperature baking conditions required by the ultra-high vacuum environment.

The above-mentioned specific embodiments further describe and illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not limited to the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims (3)

1. A liquid helium recondensation cryogenic refrigeration system of mechanical vibration isolation is characterized in that, comprising: a closed cycle refrigerator system, a liquid helium recondensation refrigeration vibration isolation system and a temperature feedback control system; wherein, the closed cycle refrigeration system The machine system includes: a refrigeration head, a compressor, and a helium gas delivery pipeline connecting the compressor and the refrigeration head; the liquid helium recondensation refrigeration vibration isolation system includes: refrigeration vibration isolation interface, helium heat exchange gas, recondensation The generated liquid helium, and the soft rubber used to seal the helium heat exchange gas and isolate the vibration, are also provided with a heat radiation shield on the refrigeration vibration isolation interface to shield the heat leakage caused by high temperature radiation; the temperature feedback The control system is composed of a temperature measuring element, a heating element and a feedback temperature control circuit; the temperature measuring element is used to indirectly measure the liquid level of the re-condensation to form liquid helium, and the feedback temperature control circuit is used to control the output power of the heating element. The feedback control system adjusts the height of the liquid helium liquid level to avoid vibration caused by the direct contact between the liquid helium liquid level and the refrigeration head; In the liquid helium recondensation refrigeration vibration isolation system, the refrigeration head of the refrigerator extends into the refrigeration vibration isolation interface, and the helium heat exchange gas is filled between the refrigeration head and the refrigeration vibration isolation interface as a refrigeration and cooling medium; The soft rubber connects the upper end of the sealing refrigeration vibration isolation interface and the refrigeration head, which can isolate the low-frequency mechanical vibration of the refrigeration head while sealing the helium heat exchange gas; since the temperature of the lowest temperature end of the refrigeration head is lower than 4.2K, the helium heat exchange gas Re-condensed in the cooling vibration isolation interface to form liquid helium; In the temperature feedback control system, the heating element is arranged at the low temperature end of the refrigeration vibration isolation interface, the heating element is located directly under the liquid helium formed by recondensation, and the temperature measuring element is arranged on the refrigeration vibration isolation interface; The element is used to indirectly measure the height of the liquid helium re-condensed to form liquid helium, and the feedback temperature control circuit is used to control the output power of the heating element. The vibration introduced by the direct contact of the head; the temperature measuring element includes a first temperature measuring element and a second temperature measuring element, and the first temperature measuring element and the second temperature measuring element are respectively arranged at the lower end and the upper end of the liquid helium area where the liquid helium is located. Measure the temperature of the first and second temperature measuring elements, and combine with feedback control to control the height of liquid helium in the refrigeration vibration isolation interface: when there is no liquid helium in the refrigeration vibration isolation interface, the first and second temperature measuring elements The temperature is higher than the phase transition point temperature of helium by 4.2K; when the liquid helium liquid level in the refrigeration vibration isolation interface is between the first and second temperature measuring elements, the temperature of the first temperature measuring element is equal to the phase transition point temperature , the temperature of the second temperature measuring element is higher than the phase transition point temperature; when the liquid helium level is higher than the second temperature measuring element, the temperatures of the first and second temperature measuring elements are both equal to the phase transition point temperature. 2. The liquid helium recondensation cryogenic refrigeration system of mechanical vibration isolation according to claim 1 is characterized in that, the closed-cycle refrigerator is a Gifford-McMahon refrigerator, a Stirling refrigerator, a pulse tube refrigeration one of the machines. 3. The liquid helium recondensation cryogenic refrigeration system for mechanical vibration isolation according to claim 1, wherein the liquid helium recondensation refrigeration vibration isolation system adopts stainless steel and oxygen-free copper material, which is compatible with ultra-high vacuum environment .

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