Pulse tube refrigerator

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

Reexamination Certificate

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Details

Type

Reexamination Certificate

Status

active

Patent number

06393845

Description

ABSTRACT:

The entire disclosure of Japanese Patent Applications No. Hei 11-306895 filed on Oct. 28, 1999 including the specification, drawings and abstract, is incorporated herein by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pulse tube refrigerator and, more particularly, to a pulse tube refrigerator for cryogenic refrigeration.
2. Description of the Related Art
A pulse tube refrigerator is attractive as a cryogenic refrigerator. The pulse tube refrigerator refrigerates a working fluid by oscillating the working fluid therein, by shifting the phase of the pressure change and the position change.
Various structures for a pulse tube refrigerator of this kind have been proposed. For instance, the one introduced by M. David et al, in Cryogenics, Vol. 30, (1990), P. 262-266, and illustrated in the block diagram of
FIG. 4. A
pulse tube refrigerator
60
of this structure comprises a pressure oscillator
61
, a refrigerating portion
62
, a middle pressure buffer tank
63
and a middle pressure buffer side valve
64
.
The pressure oscillator
61
generating pressure oscillation to the working fluid filled in the pulse tube refrigerator
60
comprises a compressor
71
, a high pressure valve
72
and a low pressure valve
73
. An outlet port
71
a
of the compressor
71
is connected to the refrigerating portion
62
via the high pressure valve
72
. An inlet port
71
b
of the compressor
71
is connected to the refrigerating portion
62
via the low pressure valve
73
. The pressure oscillator
61
generates pressure oscillations in the working fluid in the refrigerating portion
62
of the pulse tube refrigerator
60
by controlling the opening and closing of the high pressure valve
72
and the low pressure valve
73
at a predetermined timing. The maximum pressure Ph which is an output pressure of the compressor
71
is set at 2 MPa, and the minimum pressure P
1
of an input pressure of the compressor
71
is set at 1 MPA.
The refrigerating portion
62
comprises a regenerator
74
, a low temperature heat exchanger
75
, a pulse tube
76
and a high temperature heat exchanger
77
connected in series, inline.
A hot end
74
a
of the regenerator
74
is connected to the pressure oscillator
61
. A cold end
74
b
is connected to the low temperature heat exchanger
75
. The regenerator
74
gradually refrigerates the working fluid while the working fluid moves therethrough towards the low temperature heat exchanger
75
side, and gradually heats the working fluid moving therethrough towards the pressure oscillator
61
side.
The low temperature heat exchanger
75
connected to the cold end
74
b
of the regenerator
74
generates a low temperature. In order to effectively remove the heat of a device to be refrigerated, such as an electronic device, in contact with the low temperature heat exchanger
75
, the low temperature heat exchanger
75
is provided with a number of holes regularly formed along the flow direction of the working fluid.
The pulse tube
76
connected to the low temperature heat exchanger
75
is formed by a hollow tube having a cold end
76
a
on the low temperature heat exchanger
75
side and a hot end
76
b
on the high temperature heat exchanger
77
side. The pulse tube
76
is made of a material with low heat conductivity in order to prevent the transfer of the heat generated by the oscillation from the hot end
76
b
side to the low temperature heat exchanger side.
The high temperature heat exchanger
77
connected to the pulse tube
76
includes a number of holes regularly arranged along the flowing direction of the working fluid. The high temperature heat exchanger
77
refrigerates the hot end
76
b
side by releasing the heat of the working fluid flowing therethrough to outside thereof. The high temperature heat exchanger
77
is connected to the middle pressure buffer side valve
64
.
The middle pressure buffer side valve
64
is provided between the high pressure heat exchanger
77
of the refrigerating portion
62
and the middle pressure buffer tank
63
. A phase lag (phase difference) between pressure oscillation and displacement of the working fluid in the pulse tube
76
is adjusted by opening and closing the middle pressure buffer side valve
64
at a predetermined timing. The volume of the middle pressure buffer tank
63
is much larger than that of the refrigerating portion
62
of the pulse tube refrigerator
60
. The pressure of the working fluid in the middle pressure buffer tank
63
is kept at an approximately average pressure (1.5 MPa) of the maximum pressure Ph (output pressure) and the minimum pressure P
1
(input pressure) of the compressor
71
.
Basic operation of the pulse tube refrigerator
60
will be explained as follows, referring to FIG.
5
. Operation in one cycle of the pulse tube refrigerator
60
consists of four stages (a) to (d), explained as follows. Each stage is defined in accordance with the respective opening and closing condition of the high pressure valve
72
, the low pressure valve
73
and the middle pressure buffer side valve
64
.
FIG. 5
is a diagram showing the opening and the closing conditions of the high pressure valve
72
, the low pressure valve
73
and the middle pressure buffer side valve
64
, and the pressure condition in the pulse tube
76
at each stage (a) to (d) in one cycle of the pulse tube refrigerator
60
. In
FIG. 5
, each bold line for the high pressure valve
72
, the low pressure valve
73
and the middle pressure buffer side valve
64
respectively shows the opening condition, and each fine line shows the closing condition of the valves
72
,
73
, and
64
. The operation of the pulse tube refrigerator at each stage (a) to (d) in one cycle will be explained as follows.
First stage (a) (First Half of Compression Stage)
The state in which the low pressure valve
73
is kept closed and the high pressure valve
72
is kept closed continuously from the previous stage (Second Half of Expansion Stage), whereas the middle pressure buffer control valve
64
is kept open. In this state, the pressure in the pulse tube
76
increases from the minimum pressure P
1
to the average pressure Pm (the pressure in the middle pressure buffer tank
63
).
Second stage (b) (Second Half of Compression Stage)
The state in which the middle pressure buffer side valve
64
is kept closed and the low pressure valve
73
is kept closed continuously from the previous stage (First Half of Compression Stage), whereas the high pressure valve
72
is kept open. In this state, the pressure in the pulse tube
76
increases from the average pressure Pm to the maximum pressure Ph.
Third stage (c) (First Half of Expansion Stage)
The state in which the high pressure valve
72
is kept closed and the low pressure valve
73
is kept closed continuously from the previous stage (Second Half of Compression Stage), whereas the middle pressure buffer side valve
64
is kept open. In this state, the pressure in the pulse tube
76
falls from the maximum pressure Ph to the average pressure Pm (the pressure in the middle pressure buffer
63
). Accordingly, the reduction of the pressure causes the adiabatic expansion of the working fluid in the pulse tube
76
to lower the temperature.
Fourth stage (d) (Second Half of Expansion Stage)
The state in which the middle pressure buffer control valve
64
is kept closed and the high pressure valve
72
is kept closed continuously from the previous stage (First Half of Expansion Stage), whereas the low pressure valve
73
is kept open. In this state, the pressure in the pulse tube
76
falls from the average pressure Pm to the minimum pressure P
1
. Accordingly, the pressure decrease causes further adiabatic expansion of the working fluid in the pulse tube
76
to further lower the temperature.
The foregoing stages (a) to (d) comprise one cycle, and by repetition of this cycle the working fluid repeats movement towards one side to release the heat at the high temperature heat exchanger
77
and towards the other side to absorb the h

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