JPS60260169A - Cryogenic temperature device - Google Patents

Abstract

PURPOSE:To enable to use a compressor of a very small quantity of flow by a method wherein a highly heat-insulated cryogenic temperature device having a little evaporative freezing mixture is applied. CONSTITUTION:The freezing mixture evaporated from a cryogenic vessel 1 cools the compressed freezing medium contained in compressure vessels 3 and 4 and the compressure vessels 3 and 4 themselves. The compressed freezing mixture of room temperature to be supplied from a compressor 9 is cooled by a heat exchanger 7, the heat exchanger 7 itself is brought to the temperature approximate to the room temperature, the freezing mixture returns to the sucking side of the compressor 9 through a buffer tank 8 again and compressed there, and these procedures are performed repeatedly. The valve 13 located on the outlet side of the pressure vessel 3 is cooled at first, evaporated gas is compressed by the compressor 9 operating a compressure switch and the like which are not shown in the diagram, and the cooled freezing mixture is compressed and stored in the compressure vessel 3. In the meantime, the pressure vessel 4 is brought in the state wherein compressed gas is not supplied by closing the outlet and inlet valves. When the pressure of the pressure vessel and its temperature reached the prescribed value, pressure is released by opening the bypass valve 14 located on the upstream side.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a cryogenic device using a cryogen that changes state between gas and liquid.

[Technical background of the invention and its problems]

Cryogenic equipment to achieve superconductivity uses liquid helium,
It has an insulated container called a cryostat that highly insulates cryogens such as nitrogen and hydrogen using vacuum insulation methods. In these devices, liquid helium evaporates due to the intrusion of heat, but to replenish it, it is either transferred from another container or the evaporated gas is recondensed using a helium refrigerator or the like.

In large superconducting equipment, a large refrigerator is directly connected to replenish liquid helium etc. continuously for a long period of time because of the large amount of heat that enters. Freezers cannot be used economically.

Large refrigerators have a good track record and their reliability has been increasing in recent years, but small helium refrigerators with a cooling capacity of several watts at 4.2 mm have little experience in use, and at present, It does not have the reliability to withstand continuous use for six months to one year.

This is partly due to low demand and a short history, but it is not possible to provide as many necessary equipment as possible with small equipment such as large refrigerators, which are aimed at simplicity, JN type, and low cost. It also depends on the fateful cause.

In addition, from a technical point of view, the valves that process gas-liquid two-phase flow are extremely small in small machines, making it impossible to follow the instability of the state peculiar to two-phase flow, which may impair the stability of the refrigerator. It will be done. In recent years, nuclear magnetic resonance tomography (hereinafter referred to as NMR-CT), which clearly shows cross-sectional views of the human body, has been attracting attention in the medical world. This device applies a high magnetic field to the human body (0.5~1.
5 Tesla), and a superconducting magnet is required. In order to maintain this magnet in a superconducting state and continue diagnosis, it is necessary to replenish the magnet with evaporated helium. NM
The cryostat requires a helium evaporation rate of 0.5/h or less, which is about ten times lower than conventional equipment. However, the better the insulation, the weaker the structure and the less able it will be to withstand transportation.

Therefore, a direct connection system with a small refrigerator is considered, but as mentioned above, highly reliable type 1 refrigerators are not available at present.

[Purpose of the invention]

An object of the present invention is to provide a cryogenic device that stably maintains a high cooling capacity, is robust, and is easy to handle.

[Summary of the invention]

In order to achieve the above object, the cryogenic apparatus of the present invention includes a cryogenic container containing a cryogenic liquid at a cryogenic temperature, a heat exchanger connected to the cryogenic container and through which cryogen gas from which the cryogen liquid has evaporated flows. A collection tank connected to the outlet of this heat exchanger,
A compressor that receives cryogen gas from the collection tank and pressurizes it into the pressure vessel through the heat exchanger, an adiabatic expansion valve provided at the upper part of the pressure vessel, and a lower part of the pressure vessel and the cryogenic vessel. The compressed cryogen gas cooled by the evaporated cryogen gas is adiabatically expanded intermittently according to the amount of cryogen evaporation in the cryogenic container, and a portion of the cryogen is liquefied. and return it to the cryogenic container.

[Embodiments of the invention]

FIG. 1 shows a cryogenic apparatus according to an embodiment of the present invention.

In this figure, reference numeral 1 denotes a superconducting coil or other cryogenic container containing a cryogen such as liquid helium, which is adiabatically supported in a vacuum insulation tank 2. 3 and 4 are pressure vessels containing a liquid or a cryogen such as compressed helium, which are arranged in parallel and can be switched by the pulp. These pressure vessels 3, 4 have heat exchangers 5, 6 in close contact with or built-in, respectively, to cool the cryogen in the pressure vessels 3.4. 7 is also a heat converter, which exchanges heat between the cryogens such as helium supplied and discharged from the pressure vessels 3 and 4 and the heat exchangers 5' and 6. 8
9 is a buffer tank that receives the evaporated cryogen such as helium, and 9 is a compressor that compresses the cryogen such as helium.

Each of the above-mentioned components 1 to 9 is connected to each other through the pipe lines and valves shown in the figure. Note that 10 is a liquefied cryogen, 11 is a check valve, and 12 is a warmer that brings the evaporated gas to room temperature.

The cooling principle in the cryogenic apparatus configured as described above will be explained next.

Figure 2 shows the temperature (T') entropy (S
Assume that a gas compressed to a pressure P in the l diagram is cooled along the vertical axis, undergoes adiabatic expansion (isentropic expansion) at a temperature T2, and reaches a temperature T2 and a pressure P2. At this time, T
If 1==4.2K and P2=1 atm, part of the expanding gas will liquefy. This is vacuum insulation, compression of gas,
This can be achieved by cooling and expanding, and was actually practiced in the early 19th century before the advent of the current liquefier, and is known as Simon's single expansion liquefaction method. This method was an intermittent patch method, which was later improved to include continuous cooling using the Gifford-McMahon cycle of small refrigerators. However, as mentioned above, in the case of helium refrigeration, highly reliable devices for cooling down to approximately 20K have been made with this small refrigerator, but those that perform helium liquefaction in 4.2 are still highly reliable. Gender is not guaranteed.

In cryogenic equipment with high thermal insulation, the amount of heat intrusion is 0.5
In the case of helium at W or less, there is a device with an evaporation rate of 0.51/h or less, and such a device may not require continuous cooling using a small refrigerator.

The present invention provides a highly reliable cooling device that performs intermittent liquid replenishment under such circumstances.

Now, the operation of the above embodiment will be explained. The cryogen evaporated from the cryogenic container 1 cools the compressed refrigerant in the pressure vessels 3 and 4 as well as the pressure vessels 3 and 4 themselves, and is further transferred to the heat exchanger 7 by the compressed refrigerant at room temperature supplied from the compressor 9. It is cooled down to a temperature close to room temperature, passes through the buffer tank 8, returns to the suction side of the compressor 9, is compressed, and repeats this process.

The valve 13 on the outlet side of the pressure vessel 3 is initially closed, and the evaporated gas is compressed by the compressor 9 using a pressure switch (not shown), and the cooled refrigerant is compressed and stored in the pressure vessel 3.

During this time, the valves at the inlet and outlet of the pressure vessel 4 are closed to prevent the supply of compressed gas.

When the pressure and temperature inside the pressure vessel 3 reach predetermined values, the bypass valve 14 on the upstream side is opened to release the pressure, and a portion of the refrigerant inside the pressure vessel 3 liquefies due to adiabatic expansion. remains. The expanded refrigerant that has passed through the bypass valve 14 is transferred to the heat exchanger 7
, passes through a buffer tank 8, is recompressed by a compressor 9, and is compressed and stored in a pressure vessel 4. When the pressure inside the pressure vessel 3 is sufficiently low and close to the pressure inside the cryogenic vessel 1, the outlet valve 13 is opened and liquefied cryogen is replenished into the vessel IVC.

By performing this cycle cyclically depending on the amount of evaporated gas from the cryogenic container 1, the evaporated gas is liquefied and recovered.

Note that a check valve 11 is provided to prevent the cryogen from flowing back into the compressor 9 side when the cryogen is supplied to the cryogenic container 1 when the pressure inside the pressure vessels 3 and 4 is high or when the compressor 9 is stopped. ing.

Further, the compressor 9 only needs to be operated depending on the amount of evaporated gas, and can be stopped within the allowable internal pressure range of the cryogenic container 1, so that the continuous operation time is shortened and reliability is improved.

In the above case, when the cryogen is helium, the pressure and temperature inside the pressure vessel are 150 atm, IOK, latm,
During adiabatic expansion to 4.2 K, the helium gas in the pressure vessel is liquefied, and liquefied helium is obtained that is approximately 80% of the internal volume of the vessel. Even when a gas at a pressure of 15 atm and a temperature of 8 is expanded to 1 atm and 4.2 K, about 20% liquid is obtained.

〔Effect of the invention〕

According to the present invention, by applying the present invention to a highly insulated cryogenic device with a small amount of evaporated refrigerant, a compressor with an extremely small flow rate can be used.

Furthermore, unlike small-sized refrigerators, it does not have a micronozzle Jouleton valve, and since the valve only opens and closes, there is no need to make adjustments in response to complex changes in the state of the cryogen. Even in long-term continuous operation, there are few mechanically moving parts and the operation is performed intermittently, so a cryogenic device with high reliability and high cold storage performance can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a cryogenic device according to an embodiment of the present invention;
The figure is a curve diagram illustrating the entire operation of the cryogenic apparatus of the present invention. 1 Cryogenic container 3, 4, pressure vessel 5.6.7 Heat exchanger 8 Buffer tank 9 Compressor 14 Pa-Ibus valve

Claims (1)

[Claims] a cryogenic container containing a cryogenic liquid at a very low temperature; a heat exchanger connected to the cryogenic container through which cryogen gas evaporated from the cryogen liquid flows; and a collection tank connected to an outlet of the heat exchanger. , a compressor that receives cryogen gas from the collection tank and pressurizes it into the pressure vessel through the heat exchanger; an adiabatic expansion valve provided in the upper part of the pressure vessel; and a lower part of the pressure vessel and the cryogenic vessel. A cryogenic device characterized by comprising a conduit connecting the two.