Pulse tube cryocooler

Details Pulse tube cryocooler Pulse tube cryocooler

2002-11-01

2004-02-17

Doerrler, William C. (Department: 3744)

Refrigeration

Gas compression, heat regeneration and expansion, e.g.,...

Reexamination Certificate

active

06691520

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of Japanese Patent Application No. JP 2001-339174 filed on Nov. 5, 2001, and Japanese Patent Application No. JP 2002-082347 filed on Mar. 25, 2002, both in the Japanese Patent Office, and the disclosures of the above applications and Japanese Patent Application No. 2002-233114, filed on Aug. 9, 2002, in the Japanese Patent Office, are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cryocooler for forming a cryogenic temperature state. More particularly, the present invention relates to a pulse tube cryocooler using a Stirling cycle and including a pulse tube and a regenerator.
2. Description of the Related Art
Since a cryocooler using a Stirling cycle can obtain cryogenic temperatures by repeatedly compressing and expanding a working gas, it has become widely used in cooling operations, such as for cooling of superconducting elements, refining and separation of gases, infrared ray sensors, or the like.
The operation principle of a Stirling cryocooler, using this Stirling cycle, can be more fully explained using
FIGS. 2 and 3
.
FIG. 2
is an explanatory view showing the outline of a refrigeration cycle, and
FIG. 3
is a diagram showing a cycle of rising and falling of a compression piston and a displacer in accordance with a refrigeration cycle.
As illustrated in
FIG. 2
, a Stirling cryocooler
20
can include a compressor
21
having a compression piston
22
, a regenerator
23
having a regenerating agent, a displacer
24
forming an expansion chamber
25
and a compression chamber
28
, a cooling part
26
formed between the expansion chamber
25
and the regenerator
23
, and a heat radiation part
27
formed around the compression chamber
28
. A working gas is sealed under high pressure in a hermetically sealed flow passage constituted by these members, and the compression piston
22
, of the compressor
21
, and the displacer
24
are reciprocated with a phase difference therebetween.
In
FIG. 3
, a solid line
22
a
represents a rising and falling of the compression piston
22
, and a solid line
24
a
indicates rising and falling of the displacer
24
. Solid line
29
represents the total volume change in the cryocooler by the rising and falling of the compression piston
22
.
As is seen in the volume (P)—pressure (V) diagram illustrated in
FIG. 2
, the Stirling cycle encompasses a process having two isothermal changes and two constant-volume changes.
A process from “a” to “b,” illustrated in portion (A) of
FIG. 2
, is an isothermal expansion process, where the compression piston
22
goes down from a top dead point to a bottom dead point so that the working gas in the expansion chamber
25
is expanded, heat Qc is absorbed from the cooling part
26
, and cooling is performed.
A process from “b” to “c,” illustrated in portion (B) of
FIG. 2
, is a constant-volume heating process, where the displacer
24
goes up from the bottom dead point to the top dead point, so that the fluid in the expansion chamber
25
is pushed out and into a space at the side of the compression chamber
28
through the regenerator
23
and that pressure is raised.
A process from “c” to “d,” illustrated in portion (C) of
FIG. 2
, is an isothermal compression process, where the compression piston
22
goes up from the bottom dead point to the top dead point, so that the working gas is fed into the compression chamber
28
, and is isothermally compressed by radiating heat Qh at the heat radiation part
27
.
Finally, a process from “d” to “a,” illustrated in portion (D) of
FIG. 2
, is a constant-volume cooling process, where the displacer
24
goes down from the top dead point to the bottom dead point, such that the fluid in the compression chamber
28
is pushed out to the side of the expansion chamber
25
through the regenerator
23
, the pressure falls, and the cycle is ended.
In this cycle, as shown by the solid lines
22
a
and
24
a
of
FIG. 3
, the phase difference between the compression piston
22
and the displacer
24
is set to approximately 90 degrees.
As stated above, in the Stirling cryocooler, the compression piston is displaced by mechanical power, so that the pressure of the working gas in the sealed space is changed. The working gas in the expansion chamber is expanded, to cool, using the displacer moving in synchronization with the periodic change of this pressure. Therefore, a high heat efficiency can usually be achieved.
On the other hand, as a cryocooler using this Stirling cycle, a pulse tube cryocooler shown in
FIG. 4
is also known.
Pulse tube cryocooler
10
is provided with a compressor
11
to repetitively feed and suction a working gas, a regenerator
13
, coupled to the compressor
11
through a heat radiation part
12
and having a regenerating agent, a pulse tube
15
, coupled to the regenerator
13
through a cooling part
14
, and a buffer tank
18
coupled to this pulse tube
15
through a heat radiation part
16
and an inertance tube
17
.
A working gas such as helium, nitrogen or hydrogen can be sealed under high pressure in a hermetically sealed space of this pulse tube cryocooler
10
. Then, similarly to the foregoing Stirling cryocooler, expansion and compression of the working gas is repeated by the compressor
11
to form a pressure amplitude.
Here, in the pulse tube cryocooler
10
, the working gas
30
in the pulse tube
15
oscillates minutely in the flow passage, such that it functions as the displacer in the foregoing Stirling cryocooler example. Accordingly, the working gas
30
can be made to work by controlling the phase of the displacement of the oscillating working gas
30
and the pressure displacement. Heat Q
1
and Q
3
are radiated from the heat radiation parts
12
and
16
, heat Q
2
is absorbed in the cooling part
14
which becomes a cold head of the cryocooler, such that a cryogenic temperature state is formed. The inertance tube
17
and the buffer
18
serve to control the phases of the displacement of the oscillating working gas
30
and the displacement of the compression piston.
In this pulse tube cryocooler, the displacer installed in the Stirling cryocooler is not necessary, and instead of the displacer, the high pressure gas is minutely oscillated so that the working gas can be compressed and expanded. Therefore, there are no movable parts in the low temperature portion. Thus, since mechanical oscillation does not exist at a cooling head, an equipment structure becomes simple, resulting in high efficiency and reliability.
The output (cryocooler output) in the above pulse tube cryocooler is determined by a difference between an output (hereinafter referred to as an indicated cryocooler output) in proportion to the product of a pressure amplitude and a flow amplitude in the inner area of the pulse tube, and various heat losses generated inside the cryocooler. This is represented by the following relation.
(refrigeration output)=(indicated refrigeration output)−(heat loss)
In order to improve the cooling efficiency of the pulse tube cryocooler, an understanding of the following two desired results become important: (1) to increase the indicated refrigeration output by efficiently transmitting the pressure amplitude given by the compression piston of the compressor into the pulse tube, and (2) to reduce the heat loss due to heat conduction in respective structural units, especially in the regenerator.
First, with respect to the regenerator, in order to reduce the above heat loss, it becomes necessary to reduce heat conduction through the structure of the regenerator, due to the temperature difference between the heat radiation part
12
and the cooling part
14
, illustrated in FIG.
4
. That is, potential heat of the working gas supplied and exhausted from the compressor
11
is temporarily stored, and the inflow of heat from the heat radiation part
12
of the high temperature side to the cooling part
14
of the low temperature side through the working gas

Affiliated with

Also associated with

Rating

Pulse tube cryocooler does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Pulse tube cryocooler, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pulse tube cryocooler will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3336393