JPS6246782B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cryogenic generator, and more particularly to a cryogenic generator suitable for preventing a drop in intake pressure of an expansion engine employed as an expansion means.

A conventional cryogenic temperature generator will be explained with reference to FIG. FIG. 1 is a system diagram of a cryogenic generator using a Claude cycle helium refrigerator as an example of a cryogenic cooler. In Figure 1, compressor 1
The helium gas, which is a high-pressure and high-temperature process gas discharged from the tank, passes through the high-pressure channel of the first heat exchanger 2 and reaches point A of the high-pressure line 3. At point A, a part of the high-pressure helium gas is divided, and after passing through a filter 4 to remove impurities such as dust, it is supplied to the first expansion engine 5, where it undergoes isentropic expansion to become low pressure and low temperature, and is passed through the low pressure line. After merging at point C of 6, it passes through the low-pressure flow path of the second heat exchanger 7 and the first heat exchanger 2, and while exchanging heat with the helium gas in the high-pressure flow path, its temperature rises and returns to the compressor 1. .
On the other hand, most of the remaining high-pressure helium gas that was not diverted at point A passes through the high-pressure flow path of the second heat exchanger 7, and then passes through the high-pressure flow path of the third heat exchanger 8 to point B of the high-pressure line 3. leading to. At point B, a part of the high-pressure helium gas is further divided, and after filtering out impurities such as dust through the filter 9, it is supplied to the second expansion engine 10, where it undergoes isentropic expansion to become low pressure and low temperature. After joining at point D of the low pressure line 6, it passes through the low pressure flow path of the fourth heat exchanger 11 and the third heat exchanger 8, and while exchanging heat with the helium gas in the high pressure flow path, its temperature rises and reaches point C. reach. on the other hand,
Most of the remaining high-pressure helium gas that was not diverted at point B is transferred to the fourth heat exchanger 11 and the fifth heat exchanger 1.
After passing through the high-pressure channels 2 and 2, impurities such as dust are filtered out by the filter 13, and then entering the Joel-Thomson valve 14, where it undergoes isenthalpic expansion to become a low pressure and low temperature. Enter Tatsuto 15. After that, cryostat 1
The low-pressure helium gas that exits the fifth heat exchanger 12
The low pressure line 6 merges with point D through the low pressure flow path of
It returns to compressor 1 via . Note that, in order to prevent heat from entering from the outside, all other equipment except the compressor 1 is housed in a vacuum cold storage tank 16.

Next, the details of the operation of the expansion engine will be explained with reference to FIG. Generally, an expansion engine is a low cycle (about 2 to 4 Hz) reciprocating type, and helium gas is intermittently sucked into the expansion engine. Therefore, in order to suppress fluctuations in the gas flow rate in the entire refrigeration system, the pistons 17 and 18 of the first expansion engine 5 and the second expansion engine 10 are set at a crank angle relative to each other, as shown in FIG. 2a.
They are connected to a common crank mechanism 19 so as to reciprocate 180 degrees apart. In this case, the change in gas flow rate with respect to the crank angle of the first expansion engine 5 is as shown in FIG. 2b, and the change in pressure in the cylinder of each expansion engine is as shown in FIG. 2c. In addition, in FIG. 2b, G ₁ is the gas flow rate of the first expansion engine 5, G ₂ is the gas flow rate of the second expansion engine, and G ₃ is the gas flow rate of the Joel-Thomson valve 14.
The gas flow rate through and G _T is the gas flow rate of the entire system. In this case, due to pressure loss in the filter 4 installed at the inlet of the first expansion engine 5 and the filter 9 installed at the inlet of the second expansion engine 10, helium gas is not inhaled during the short intake stroke. As a result, the gas flow rates G ₁ and G ₂ of each expansion engine become smaller than the designed values, as shown in FIG. 2b. In particular, in the second expansion engine 10, since the gas flow rate _G2 is large, the pressure loss in the filter 9 is also large, and the pressure in the intake stroke of the second expansion engine becomes smaller than the designed value as shown in Fig. 2c. Therefore, the pressure drop (=pressure at the end of the intake stroke - pressure at the end of the expansion stroke) is also small, and the enthalpy drop, which is proportional to the pressure drop, is small.

In this way, the gas flow rate of the expansion engine is low,
Furthermore, if the enthalpy drop is small, the cooling ability determined by the gas flow rate and the enthalpy drop decreases, which ultimately results in a decrease in the refrigerating ability or liquefaction ability of the helium refrigerator.

As a solution to the above problem, filters 4 and 9
It is common to make the mesh coarser or to increase the cross-sectional area of the filters 4 and 9 to reduce the gas flow rate passing through the filters 4 and 9. However,
In the former solution, more impurities such as dust enter the expansion engine without being filtered out, and there is a risk of damaging the sliding parts of the expansion engine.In addition, in the latter solution, the filter becomes redundant and extremely This had the disadvantage that it was contrary to the miniaturization of low temperature generators.

The present invention aims to solve the above-mentioned problems and eliminate the above-mentioned drawbacks, and focuses on the fact that the process gas intake in the expansion engine takes about 1/6 of one cycle, and the remaining time is about 1/6. The present invention provides a compact and high-performance cryogenic generator characterized by installing a gas tank on the intake side of each expansion engine to store process gas for 5/6 of the time.

An embodiment of the present invention will be described with reference to FIG. In FIG. 3, the same equipment as in FIG. 1 is denoted by the same reference numerals and the explanation thereof will be omitted. 20 is a first gas tank installed between the intake side of the first expansion engine 5 and the filter 4;
21 is the intake side of the second expansion engine 10 and the filter 9
This is the second gas tank installed between the two. Here, the internal volume of each gas tank is selected as follows.

First, regarding the selection of the internal volume of the second gas tank 21, in this case, the pressure at the end of the intake stroke in the second expansion engine 10 is approximated as shown in equation (1).

Here, P ₂ : Pressure at the end of the intake stroke (however, P ₂ P ₁ ) P ₁ : Pressure before the start of the intake stroke V: Internal volume between the filter and the second expansion engine △V: Cylinder at the end of the intake stroke Internal volume G: mass of gas between the filter and the second expansion engine △G: mass of the gun that passes through the filter and is supplied to the second expansion engine during the intake stroke As is clear from equation (1), P ₂ ≒ P To set it to ₁ ,
It is effective to reduce △V/V, for example, △
If V/V=1, when △G/G=0.8, P ₂ =0.9P ₁ , whereas if △V/V=0.2, △G/G=
Even when 0.16, P ₂ = 0.967P ₁ , and △G/G is
It can be seen that the decrease in P ₂ is small even if it becomes small like ΔV/V. That is, in order to make the decrease in P ₂ practically negligible, the internal volume of the second gas tank 21 should be selected so that ΔV/V becomes 5 or more.

On the other hand, the first gas tank 2 of the first expansion engine 5
Regarding the internal volume of 0, as shown in FIG. 2b, the gas flow rate _G1 of the first expansion engine 5 is smaller than the gas flow rate _G2 of the second expansion engine 10, so the pressure loss of the filter 4 is also small. , the pressure in the intake stroke hardly decreases from the design value as shown in Fig. 2c, but considering the same as the case of the second expansion engine 10, △V/V should be 5 or more. It is more sufficient if the internal volume of the first gas tank 20 is selected. Therefore, in practice, it is sufficient to select the internal volume of each gas tank to be at least five times the internal cylinder volume at the end of the intake stroke of each corresponding expansion engine.

In this way, if a gas tank is installed between the filter and the expansion engine intake side with an internal volume that is 5 times or more the cylinder internal volume at the end of the expansion engine's intake stroke, the pressure during the expansion engine's intake stroke will be reduced. Since the decrease with respect to the design value is almost negligible, the pressure drop and furthermore the enthalpy drop become large, and a decrease in the cooling generation ability can be prevented. In addition, since there is no need to use a redundant filter, the cryogenic temperature generator can be made smaller.
There is no need to make the filter mesh coarser,
There is no risk of damage to the sliding parts of the expansion engine due to impurities such as dust.

FIG. 4 shows another embodiment of the gas tank structure, in which filters 4 and 9 are installed inside a first gas tank 20 and a second gas tank 21, respectively.

When the gas tank structure is configured in this way, a container containing only the filter is not required, and the piping can be simplified, so that the cryogenic temperature generator can be downsized. Also,
Heat intrusion due to radiation can also be suppressed compared to when the filter and gas tank are installed separately.

Furthermore, the first gas tank 20 and the second gas tank 21 may be directly provided at the tip of each cylinder of the first expansion engine 5 and the second expansion engine 10, respectively.

When the gas tank is directly installed at the cylinder end of the expansion engine in this way, there is no need for piping connecting the gas tank and the intake side of the expansion engine, so the cryogenic generator can be further downsized.

As explained above, the present invention has a gas tank installed between the filter and the intake side of the expansion engine, thereby suppressing a decrease in the cold generation ability of the expansion engine, and eliminating the need for a redundant filter. ,
This has the effect of providing a high-performance, compact cryogenic generator.

[Brief explanation of the drawing]

Figures 1 and 2a to 2c explain a conventional cryogenic generator. Figure 1 is a system diagram of a cryogenic generator using a Claude cycle helium refrigerator. Figure 2a is an explanatory diagram of the operation of the expansion engine, Figure 2b is a diagram of changes in gas flow rates of the first expansion engine and the second expansion engine with respect to the crank angle of the first expansion engine, and Figure 2c is a diagram illustrating the operation of the expansion engine.
is also a pressure change diagram. FIG. 3 is a system system diagram illustrating an embodiment of a cryogenic temperature generator using a Claude cycle helium refrigerator according to the present invention, and FIG. 4 is a sectional view showing another embodiment of the gas tank structure. 4, 9... Filter, 5... First expansion engine, 10... Second expansion engine, 20... First gas tank, 21... Second gas tank.

Claims (1)

[Claims] 1. A gas tank is provided on the intake side of the expansion engine to store the process gas at times other than the intake time of the process gas in the expansion engine that expands the process gas that has been filtered to remove impurities to generate cold. A cryogenic generator characterized by: