JPS6341772A - Cryogenic refrigerator - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Objective of the Invention] (Industrial Application Field) The present invention is mainly applicable to liquid helium mixed food (V! Regarding cryogenic refrigerators that aim to cool down to extremely low temperatures, such as those listed below, especially cryogenic refrigerators that prevent a decrease in refrigerating capacity as cooling progresses? Leap into I1 machine.

(Prior Art) In a cryogenic refrigerator having an expansion bar in the cold head, for example, a Gifford-McMahon refrigerator Bl'S, the ability to generate low temperature t is expressed by the following equation.

W=η・■・△]]・n ・・・・・・・・・・・・・・・
... (1) In addition, W is the refrigerating capacity η is the efficiency (■) is the volume of the expansion chamber (expansion volume), ΔP is the pressure difference before and after the expansion n is the expansion recycle number.

Here, FIG. 3 shows the conventional configuration of the Gifford-McMahon type refrigerator.

A compressor 2 (e.g., a positive displacement compressor such as a U-type, a Suffle type, a reciprocating type, or a slurry set) driven by an electric motor 1 and an operation under back pressure from the compressor 2. A cold head 3 that generates low temperature by avoiding expansion of helium gas as a medium is connected to an open circuit by a high-pressure side pipe 4 and a low-pressure side pipe 5. cold head 3
Inside, a regenerator 6 having minute circulation holes is reciprocated up and down within the thin-walled cylinder 3a by an electric motor (not shown) via a drive unit 7. A high-pressure side inlet valve 8 and a low-pressure side outlet valve 9 that communicate the internal space of this cold head 3 with the n-pressure side pipe line 4 and the low-pressure side pipe line 5, respectively, are
It repeats opening and closing in synchronization with the movement direction and position of the regenerator 6.

That is, when the regenerator 6 passes the bottom dead center and begins to rise, the high pressure side inlet valve 8 opens. As a result, the ^-pressure helium gas flows into the cold head 3, passes through the fine circulation holes inside the regenerator 6, and flows into the lower expansion chamber 10 while being cooled. The inflow of high pressure gas continues until the regenerator 6 rises and reaches the vicinity of top dead center by 1J.

The high-pressure side artificial valve 8 closes when the cold storage *6 reaches near the top dead center, and the low-pressure side outlet valve 9 opens immediately after passing the top dead center.

As a result, the high pressure gas in the regenerator 6 and the expansion chamber 10 expands and flows out via the low pressure side outlet valve 9. Low pressure side outlet valve 9
is open while the regenerator 6 is descending, and opens near the bottom dead center.

In addition, in the figure, 11 is a cooler, 12 is Kufuiostat, and 13
14 is a vacuum section within the Kuhuiostat, and 14 is a bypass valve for preventing abnormally high pressure.

(Problems to be Solved by the Invention) In such a conventional machine, the pressure within the expansion chamber 10 fluctuates in a pressure range that is approximately the same as the discharge pressure and intake pressure of the compressor 2. The discharge pressure and intake pressure of the compressor 2 are determined from the relationship between the initial helium filling pressure into the closed loop and the theoretical compression ratio ε expressed by the following equation.

・・・・・・・・・(2) In addition, Vc is compressor displacement volume E is the cold head expansion chamber volume Nc is compression m rotation speed NE is cold head rotation speed ηC is compressor gas efficiency ηE is cold head gas efficiency TO is compressor intake gas temperature TE is the cold head expansion chamber gas temperature.

That is, the compression ratio ε is determined by the internal shape, rotation speed, and temperature of the compressor and the cold head, and if the operating conditions are the same, it decreases as the cooling progresses from immediately after startup. For example, referring to the design example of a conventional machine, the initial filling pressure in the system is 8 [Kg/cIi], the compression 1 displacement volume Vc is 30 (d/rev), and the compressor rotation speed TO is 30.
00 (r+oa), compressor gas efficiency ηC is 0.6
, the cold head expansion chamber volume VE is 300 (7/rev
], the cold head rotational speed NE is 60 [pI], and the cold head gas efficiency ηE is 0.85, the compression ratio ε immediately after startup ('r c-'r E-300°K) is 4.
．． It is about 5. On the other hand, cooling progresses and, for example, the expansion chamber gas tS! r! When iTE decreases to about 50'' (compressor absorbed gas temperature Tc = 300''K), compressor gas efficiency ηC slightly recovers to 0.9 ON degree,
Although the cold head gas efficiency ηE decreases to about 0.35, the compression ratio ε eventually decreases to about 2.3.

In other words, as the low-temperature side of the regenerator inside the cold head is cooled, the working medium gas helium in this part increases its density due to its low temperature, and the flow through the cold head per cycle; d increases. The pressure difference between the front and rear ends up decreasing.

This means that the pressure difference ΔP that determines the refrigerating capacity W11) of the refrigerator decreases, and the steady state operation is performed with less than half the refrigerating capacity at the start of initial operation.
This is an extremely costly situation.

FIG. 4 shows the pressure change in the IIi tensioner 10 of the conventional cryogenic refrigerator mentioned above over time from the start of operation to a steady state.

As can be understood from the fi1 diagram, the pressure difference Δ before and after expansion
P was about 11.5 (Kff/al) at the beginning of operation, but it dropped to about 7 (Kg/7) in steady state, and the basic refrigeration capacity decreased from about 270 (W) to about 160 (Kg/7).
(W), resulting in a decrease of about 40%.

In this way, in a cryogenic refrigerator whose cold head has an expansion chamber, its compression ratio decreases as cooling progresses.
This will be significantly lower than the possible refrigeration capacity.

In addition, the consumption of the drive electric motor of the compressor decreases by about 20 to 30% due to a decrease in the compression ratio ε, reducing the capacity of the electric machine to 100%.
% is not being utilized.

The above shows that although the actual cooling capacity of a cryogenic refrigerator is determined by the pressure when it reaches a cryogenic state6, the system design is based on the state immediately after startup, where the system internal pressure is highest. This is due to the fact that

Conventionally, the compression ratio decreases with the progress of cooling, and the pressure difference between before and after expansion in the expansion chamber decreases, so in advance, the volume or pressure of the expansion chamber of the cold head is expanded or the pressure is increased. I try to set my abilities high. However, this requires an increase in the wall thickness of the thin-walled cylinder 3a, which serves as a pressure vessel, and increases heat intrusion due to conduction. In addition, since the pressure on the high pressure side becomes very high at the beginning of operation, there is also the problem that it is uneconomical to keep the bypass valve 14 in a state where the amount of electricity is applied for a predetermined period of time to prevent abnormal high pressure [E].

The present invention was developed in view of the above-mentioned circumstances, and is designed to prevent a decrease in refrigerating capacity due to a decrease in compression ratio as cooling progresses, and to maintain the same refrigerating capacity even in a steady state as at the start of operation. The purpose of the present invention is to provide a cryogenic refrigerator that can demonstrate the following.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a cryogenic refrigerator in which a compressor and a cold head having an expansion chamber are connected in a closed circuit, in which the pressure of a working medium flowing through a predetermined part of the open circuit is controlled. A high pressure sensor connected to a closed circuit via a valve and a pressure detector to detect it.
The system is equipped with a high-pressure cylinder storing 114 bodies, and a control device that controls opening and closing of the valve based on a comparison between the pressure value detected by the pressure detector and a specified value.

(Function) As the temperature of the cryogenic part in the cold head decreases, the 1Mo compression ratio of the compressor decreases, the pressure difference before and after expansion decreases, and as a result, the pressure no. J in the closed circuit changes. do.

Therefore, the pressure at a predetermined point in the 111 circuit is detected, and the valve of the high-pressure cylinder connected to this open circuit is controlled to open and close so that the pressure is maintained at a specified value. Replenish the working medium and die.

This makes it possible to promptly detect and prevent a decrease in refrigerating capacity due to a decrease in compression ratio due to refrigerator operation.

(Example) The present invention will be explained below with reference to Examples.

FIG. 1 shows the configuration of an embodiment of the present invention. In addition, the above-mentioned No. 3
Components that are the same as those in the drawings are designated by the same reference numerals and their explanations will be omitted. A pressure detector 15 is connected to a high-pressure pipe line 4 connecting the discharge port of the compressor 2 and the intake port of the cold head 3 to detect the helium gas pressure within this pipe line. This pressure detector 15
The pressure signal output from the i, II t11 circuit 16 is input. III'! 11 circuit 16 compares the E[force value in the high pressure pipe 4 indicated by the pressure signal with a preset specified value, and if the pressure value is lower than the specified value, the electromagnetic valve An open signal is output to a solenoid valve 17, which will be described later.

A high-pressure cylinder 19 storing high-pressure helium gas is connected to the low-pressure pipe line 5 connecting the outlet of the cold head 3 and the inlet of the compression R2 through a solenoid valve 17 and a pressure reducing valve 18 in series.
is connected. The solenoid valve 17 is normally closed,
The solenoid valve opens when it receives an opening signal. As a result, the high pressure helium gas in the high pressure cylinder 19 flows into the low pressure side pipe line 5.

The set pressure of the pressure reducing valve 18 is set so that the pressure in the closed circuit does not exceed the filling pressure of helium gas at room temperature due to the inflow of gas from the high pressure cylinder 19.

Further, a safety valve 20 is provided in the high pressure side conduit 4. This safety valve 20 automatically opens when the pressure in the high-pressure side pipe 4 exceeds a predetermined safe pressure, releases helium gas in the closed circuit to the outside air, lowers the gas pressure, and reaches the safe pressure. When it returns, it automatically returns to the open state.

Next, the operation of this embodiment will be explained.

As described above, as the cold n1 advances f1, the compression ratio of the compressor 2 decreases, and the pressure within the closed circuit changes. This pressure change is caused by a buffer tank (not shown) in the low pressure side pipe line 5.
In a normal refrigerator into which a 100% cyclone is inserted, the most sensitive phenomenon appears as a 7J drop in pressure in the high-pressure side pipe 4. Now, the pressure in this high-pressure side pipe 4 is detected, and if it falls below the specified value, the heli-cum gas in the high-pressure cylinder 19 with the FTI magnetic valve magnet 17 is transferred from the low-pressure side pipe 5 to the system. I'll replenish it inside.

As a result, the gas pressure in the closed circuit rises to 4, and the pressure increases to 111 and 2.
The compression ratio of will increase. Then, when the pressure in the high-pressure side pipe line 5 reaches the specified value, the 7ti magnetic valve 17 is operated to stop gas replenishment.

As a result, the pressure difference between the discharge pressure and the intake pressure of the compressor 2 becomes almost constant, and therefore the pressure inside the expansion chamber 10 of the cold head 3 fluctuates with a nearly constant pressure difference ΔP as shown in FIG. become. In this way, by keeping the pressure difference ΔP before and after expansion in the expansion chamber 10 substantially constant, the refrigerating capacity is maintained at a value substantially equal to the initial value even in a steady state.

This is basically equivalent to increasing the refrigerating capacity of a refrigerator with the same general h1 as the conventional model, and specifically, it is equivalent to improving the refrigerating capacity by several tens of percent.

Furthermore, when the refrigerator is stopped or a large amount of heat is input into the cryogenic part of the cold head 3, the gas volume increases and the system pressure increases as the temperature rises. The pressure increase can be relieved by releasing gas from the safety valve 20, and safety is maintained.

In the above embodiment, the pressure detector 15 is installed in the high-pressure side pipe 4, but if pressure changes appear more sensitively in the low-pressure side pipe 5, the pressure detector 15 may be installed in the low-pressure m pipe 5. Alternatively, the valve may be provided in both the high-pressure side and low-pressure side conduits 4 and 5, and the opening/closing of the valve may be controlled based on the differential pressure therebetween. Further, the pressure cylinder 19 may be connected to the high-pressure side conduit instead of the low-pressure side conduit 5 as in the embodiment.

〔Effect of the invention〕

As explained above, according to the present invention, a decrease in the compression ratio is detected from the change in pressure in the closed circuit as cooling progresses, and by supplementing the working medium, the pressure difference before and after expansion is almost reduced. Since the cooling capacity is kept constant, it is possible to maintain a cooling capacity equivalent to that at the start of operation even in a steady state.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of a cryogenic refrigerator according to the present invention, Fig. 2 is a diagram showing the change in pressure in the expansion chamber over time of the same embodiment, and Fig. 3 is a diagram showing a conventional cryogenic refrigerator. A diagram showing the configuration of the machine,
FIG. 4 is a diagram showing changes over time in the pressure in the expansion chamber of the conventional machine. 2...Compressor, 3...Cold head, 4...High pressure side pipe line, 5...Low pressure side pipe line, 6...Regenerator, 1o
... Expansion chamber, 15... Pressure detector, 16 River control m+ device, 17... Solenoid valve, 18... Pressure reducing valve, 19...
High pressure cylinder, 20...safety valve. Applicant's agent: Mr. - Male Figure 1 Opening/closing Figure 2 U Figure 3 Old newspaper Figure 4

Claims (1)

[Claims] 1. A cryogenic refrigerator comprising a compressor and a cold head connected to a closed circuit, comprising: a pressure detector for detecting the pressure of a working medium flowing through a predetermined portion of the closed circuit; a high-pressure cylinder connected to a circuit via a valve and storing the high-pressure working medium; and a control device that controls opening and closing of the valve based on a comparison between a pressure value detected by the pressure detector and a specified value. A cryogenic refrigerator characterized by being equipped with. 2. A pressure reducing valve is provided in series with the valve between the closed circuit and the high pressure cylinder, and the set pressure of this pressure reducing valve is set so that the pressure in the closed circuit due to the inflow of working medium from the high pressure cylinder is at room temperature. 2. The cryogenic refrigerator according to claim 1, wherein the cryogenic refrigerator is set so as not to exceed the filling pressure in . 3. Connected to the high pressure side pipe line of the closed circuit, and when the pressure of the working medium in this pipe exceeds a predetermined safe pressure, it becomes open and releases the working medium in the closed circuit to the outside of the closed circuit; The cryogenic temperature control system according to claim 1, further comprising a safety valve that returns to a closed state and stops the discharge when the pressure of the working medium in the high-pressure side pipe decreases to the safe pressure. refrigerator.