JP2000018746A - Stirling chiller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress pressure rise of a water circuit by providing means for stopping operation of the water circuit with a specified time lag after stopping a driver. SOLUTION: When an operating switch 72 is turned off, a controller 71 actuates a delay timer 75 based on an operation stop signal from a relay 73 and the contact 76 thereof is opened by a delay timer 75 upon elapsing a predetermined time thus stopping a cooling water pump P1 and a cooling tan 70. At the time of stopping operation of a Stirling chiller, a decision is made at first whether an operation stop signal is inputted by the switch 72 or not and control operation is sustained as it is if the operation stop signal is not inputted otherwise a motor 16 is stopped and the delay timer 75 begins to measure the time. Subsequently, a decision is made whether the cooling water pump P1 and the cooling fan 70 are operated continuously for a predetermined time or not and continuous operation control is performed again if the predetermined time has not yet elapsed otherwise the operation is stopped. Cooling can be performed even after stopping operation of a refrigerating machine and pressure rise of water circuit can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides an expansion chamber having a low temperature and a compression chamber having a high temperature. The compression chamber is cooled by a water circuit in which a water pump and a radiator are connected in a ring. And a Stirling cooling device.

[0002]

2. Description of the Related Art A Stirling cooling apparatus is configured to compress and expand a working gas to thereby lower the temperature of an expansion chamber and raise the temperature of a compression chamber. For example, there is one described in Japanese Patent Laid-Open No. 5-118687.

Such a Stirling cooler has a compression section provided with a compression piston for compressing the working gas in the compression chamber, an expansion section provided with an expansion piston for expanding the working gas in the expansion chamber, and the like. The expansion chamber is connected to the expansion chamber by a gas flow path.

The gas flow path is provided with a heat-radiating heat exchanger for cooling the working gas which has been compressed to a high temperature, and lowers the temperature of the working gas flowing from the compression chamber to the expansion chamber to reduce the Stirling cooling. Increases the refrigeration efficiency of the device.

[0005] In order to enhance the heat radiation efficiency of the heat radiation heat exchanger, the present applicant has prototyped a device provided with a radiator for exchanging heat with, for example, cooling water. Then, the heat radiating heat exchanger and the radiator are connected by a cooling water pipe so that the cooling water is circulated by being pumped by the cooling water pump, and when the operation of the cooling device is stopped, each piston is driven. The drive circuit and the pump are simultaneously stopped.

[0006]

However, in the above-described Stirling cooling apparatus, even after the operation is stopped, the compression chamber and its vicinity remain at a high temperature, and this temperature is transmitted to the water circuit to reduce the temperature of the entire water circuit. The pressure in the water circuit also increased with this temperature increase. The water circuit uses a hose, and although it is firmly connected, it is not welded like a refrigerant pipe of an air conditioner,
It is also conceivable that the pressure rises and comes off. Also,
If the temperature of the compression chamber and its vicinity is forever high, there is no undeniable possibility that the cooling may become uneven and may be thermally deformed.

The present invention provides a Stirling cooling device that suppresses a rise in the pressure of a water circuit.

[0008]

In order to solve the above-mentioned problems, the present invention provides a compression chamber in which a compression piston is accommodated in a compression cylinder, and an expansion piston or a displacer is accommodated in an expansion cylinder and both ends thereof are provided. Along with forming the expansion chamber and the buffer chamber, each chamber is in a communicating state, and the working gas is sealed therein, and the driving device drives the compression piston and the expansion piston, so that the space between the compression chamber and the expansion chamber is formed. In a Stirling cooling device configured to cool the expansion chamber by reciprocating the working gas and to cool the compression chamber by a water circuit configured by connecting a water pump and a radiator in a ring, the driving device may include: When the operation is stopped, the water circuit is provided with delay means for delaying the operation of the water circuit for a predetermined time and stopping the operation.

The Stirling cooling apparatus further includes delay means for delaying and stopping the operation of the water circuit for a predetermined time so that the temperature of the expansion chamber decreases to a predetermined temperature.

Further, in the Stirling cooling device, there is provided delay means for delaying and stopping the operation of the water circuit until the temperature of the expansion chamber reaches a predetermined temperature.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a Stirling cooling device according to the present invention. In this Stirling cooling device 1, a Stirling refrigerator 3 is disposed in a box-shaped case 2.

Further, a cooling head 4 is provided in the Stirling refrigerator 3, and a cooling / cooling refrigerant pipe line 5 is connected to the cooling head 4 so that the cooling / cooling refrigerant circulates. In addition,
The cold refrigerant refers to a refrigerant for transporting cold generated by the Stirling refrigerator 3 to a cold utilization device 8 such as a freezer.

[0013] Both ends of the cold refrigerant pipe 5 are connected to an inlet plug 6 and an outlet plug 7 fixed to the case 2. The end 9 and the inlet end 10 are each detachably connected.

In the middle of the cold refrigerant pipe 5, a cold refrigerant pump P2 is arranged so that the cold refrigerant circulates between the cooling head 4 and the cold heat utilization equipment 8.

In addition to the refrigerator, a refrigerator, a throw-in type cooler, a low-temperature liquid circulator, a low-temperature constant temperature device for various temperature characteristic tests, a constant-temperature bath, a heat shock test device, a freeze dryer and a cold A cooler or the like is applicable.

A cylinder 12 is formed at the top of the housing in the Stirling refrigerator 3, and a motor chamber 14 and a crank chamber 1 are formed inside the housing by a partition wall 13.
5 is divided.

A motor (drive device) 16 capable of normal and reverse rotation is disposed in the motor chamber 14, and a rotary reciprocating conversion mechanism 17 for converting the rotation of the motor 16 into reciprocating motion is disposed in the crank chamber 15. ing.

The opening 18 of the motor chamber 14 and the crank chamber 1
The opening 19 of 5 is closed by lids 20 and 21, respectively, and the inside of the housing is held in a semi-sealed state.

In the housing, the partition wall 13 is penetrated,
Bearing part 2 of housing wall, partition wall 13 and lids 20 and 21
A crankshaft 23 pivotally supported by 2 is rotatably arranged.

The motor 16 includes a stator 24a and a rotatable rotor 24 on the inner peripheral side of the stator 24a.
The crankshaft 23 is fixed to the center of the rotor 24b.

The rotary reciprocating conversion mechanism 17 includes the crank chamber 1
5, a crank portion 25 of the crankshaft 23 extending into
Connecting rods 26, 2 connected to the crank 25
7. It is composed of cross guide heads 28 and 29 attached to the tips of the connecting rods 26 and 27, and functions as a driving means of the Stirling refrigerator 3.

The cross guide heads 28, 29 are provided with cross guide liners 30, 3 provided on the inner wall of the cylinder 12.
1 are reciprocally movable.

The crank portion 25 is formed with a phase difference so that the crank 25b moves ahead of the crank 25a when the motor 16 rotates forward. As this phase difference, a phase difference of 90 degrees is generally adopted.

A compression cylinder 32 and an expansion cylinder 33 slightly above the compression cylinder 32 are disposed above the crank chamber 15. A working gas such as helium, hydrogen, or nitrogen is sealed in the housing including the compression cylinder 32 and the expansion cylinder 33.

The compression cylinder 32 has a compression cylinder block 34 fixed to the housing with bolts or the like. A compression piston 36 provided with a piston ring 35 reciprocates in the space of the compression cylinder block 34, The upper part (compression space) of this space is the high temperature chamber 37,
The working gas therein is compressed to a high temperature.

The compression piston rod 38 has one end fixed to the compression piston 36 and the other end extended through an oil seal 39, and is rotatably connected to the cross guide head 28 by a pin.

Since the sliding direction of the reciprocating compression piston 36 is reversed at the top dead center and the bottom dead center, the speed becomes zero.
The velocity is slow near the top dead center and the bottom dead center, and the amount of change in volume per unit time is small, and at the respective middle points when moving from the bottom dead center to the top dead center and from the top dead center to the bottom dead center. The maximum speed is reached, and the amount of change in volume due to the movement of the piston per unit time is also maximized.

On the other hand, the expansion cylinder 33 has an expansion cylinder block 40 fixed to the upper part of the compression cylinder 32 by bolts or the like, and an expansion piston 42 provided with a piston ring 35 'in the space of the expansion cylinder block 40. Slides back and forth, and the upper part (expansion chamber) of this space is the low-temperature chamber 41, in which the working gas expands to a low temperature.

One end of an expansion piston rod 43 is fixed to the expansion piston 42, and the other end of the expansion piston rod 43 extends through an oil seal 44 and is connected to the cross guide head 29. The expansion piston (which is made of synthetic resin and is sometimes called a displacer) 42 moves ahead of the compression piston 36 by 90 degrees.

The expansion cylinder block 40 is provided with a manifold 45 through which working gas flows in and out of the compression chamber of the compression cylinder 32 from below in the drawing.
Further, the heat exchanger 46 for heat radiation, the animal cooler 47 and the high temperature chamber 37
Passages 48 are arranged in an annular shape so as to communicate with each other sequentially.

Near the upper end of the compression cylinder block 34, a communication hole 4 for communicating the high temperature chamber 37 and the manifold 45 is provided.
Thus, the high temperature chamber 37 (compression chamber) and the low temperature chamber 41 (expansion chamber) are connected to the communication hole 49, the manifold 45, the heat exchanger 46 for heat radiation, the cooler 47, and the passage 4
8 so as to sequentially communicate with each other.
The passage 48 may be provided with a heat exchanger in this portion to serve as a cooler.

The heat-radiating heat exchanger 46 is an annular type heat exchanger, for example, a shell-and-tube type heat exchanger 50 (a working gas in an annular heat exchange chamber 51) as shown in FIGS. (A heat exchanger that cools the working gas by flowing cooling water into the heat exchange chamber 51 by providing a number of tubes 52 through which heat flows in the axial direction). FIG. 3 is a sectional view taken along the line AA in FIG.

Alternatively, as shown in FIG. 4, an annular jacket 53 may be arranged around the annular working gas flow path, and cooling water may flow through the jacket 53 to cool the working gas.

The heat-exchanging heat exchanger 46 is connected to the cooling water pipe 5.
4 and the radiator 55 via the cooling water pump (water pump) P1, the cooling water circulates, and the radiating heat exchanger 46
The cooling water heated by the heat exchange is cooled by the cooling fan of the radiator 55. That is, a water circuit is formed by connecting the heat radiation heat exchanger 46, the cooling water pump P 1, and the radiator 55 in a ring shape with the cooling water pipe 54.

The cooling water pump P1 is provided with a radiator 55
Is disposed in a cooling water pipe 54 connecting the lower end portion K1 of the heat-radiating heat exchanger 46 and the lower end portion K4.

Thus, for some reason, the cooling water pipe 5
Even if air enters the cooling water pump 4, the air is located at a position higher than the inlet K2 of the cooling water pump P1, so that the air biting of the cooling water pump P1 can be suppressed.

At this time, the inlet K2 of the cooling water pump P1
Is provided at a position appropriately lower than K1, the outlet K3 of the cooling water pump P1 is provided at a position appropriately lower than K4, and
If K1 is provided so as to be lower than K4, the air can be substantially prevented from entering the cooling water pump P1, so that the cooling water pump P1 can surely suppress the air bite. it can.

The cooling water piping 54 is branched and connected to a piping. A water reservoir tank 57 is connected to the piping via a reservoir valve 56.

The radiator 55 is connected to an air vent 58 and a drain valve 59.

The cooling head 4 is formed above the expansion cylinder block 40. For example, as shown in FIGS. 5 and 6, the cooling head 4 is provided with a top wall 62 having a large thickness at the top of the expansion cylinder block 40, and a heat exchange channel 63 for a cryogen is formed on the top wall 62. Configuration.

Alternatively, as shown in FIG. 4, a structure may be adopted in which a jacket wall 64 is provided on the top of the expansion cylinder block 40, and a cooling / cooling refrigerant flows through the jacket wall 64.

As described above, the cooling head 4 is connected to the cold heat utilization device 8 through the cold refrigerant pipe 5 and the cold refrigerant pump P2 to circulate the cold refrigerant. A suction tank 65 is disposed in the cold refrigerant line 5.

A cryogenic refrigerant reservoir tank 67 is connected to the suction tank 65 via a reservoir valve 66. A drain valve 68 is connected to the suction tank 65. In the cold / hot refrigerant line 5,
An air vent 69 is connected.

As the cold refrigerant, ethyl alcohol, HFE, PFC, nitrogen, helium and the like are used.

Next, the operation of the Stirling cooling device 1 of the above embodiment of the present invention will be described. The motor 16 rotates the crankshaft 23 in the forward direction, and the cranks 25a and 25b in the crank chamber 15 rotate with a phase shift of 90 degrees.

Via connecting rods 26, 27 rotatably connected to the crank portions 25a, 25b, cross guide heads 28, 29 attached to the tips of the connecting rods 26, 27 are connected to cross guide liners 30, 31. Slides back and forth inside.

A compression piston 36 and an expansion piston 42 connected to the cross guide heads 28 and 29 via a compression piston rod 38 and an expansion piston rod 43, respectively.
Reciprocate with a phase difference of 90 degrees from each other.

While the expansion piston 42 moves slowly near the top dead center 90 degrees ahead of it, the compression piston 36 moves rapidly toward the top dead center near the middle to compress the working gas. The compressed working gas flows into the heat-radiating heat exchanger 46 through the communication hole 49 and the manifold 45.

The working gas radiated to the cooling water in the heat radiating heat exchanger 46 is cooled by the storage cooler 47 and flows into the low temperature chamber 41 (expansion chamber) through the passage 48.

When the compression piston 36 moves slowly near the top dead center, the expansion piston 42 moves rapidly toward the bottom dead center, and the working gas flowing into the low temperature chamber 41 (expansion chamber) expands rapidly. Cold heat is generated.

Thus, the top of the expansion cylinder block 40 in the cooling head 4 surrounding the expansion chamber is cooled to a low temperature.

Then, in the cooling head 4, the cold refrigerant circulating through the cold refrigerant pipe 5 is cooled.

When the expansion piston 42 moves from the bottom dead center to the top dead center, the compression piston 36 moves from the intermediate position to the bottom dead center, and the working gas flows from the expansion chamber into the animal cooler 47 through the passage. The cold heat of the working gas is stored in the animal cooler 47.

The cold heat stored in the animal cooler 47 is reused to re-cool the working gas sent from the high-temperature chamber 37 through the heat-exchanging heat exchanger 46 as described above.

Then, the cryogen cooled in the cooling head 4 flows from the cryogen line 5 and the outlet plug 7, for example,
It is sent to the cold refrigerant pipe in the cold utilization equipment 8 such as a freezer,
Freezing or cooling action is performed in the cold heat utilization device 8.

In the cold utilization device 8, the cold refrigerant absorbs heat and performs a cooling action, is sent from the cold refrigerant pipe to the inlet plug 6, passes through the cold refrigerant pipe 5, and is returned to the cooling head 4; There it is cooled.

In this way, the cold refrigerant circulates between the cooling head 4 of the Stirling refrigerator 3 and the cold heat utilization device 8,
The cryogenic refrigerant is cooled by the Stirling refrigerator 3, and the cryogenic refrigerant performs a cooling function in the cryogenic heat utilization device 8. Less than,
A similar cycle is repeated.

On the other hand, the cooling water heat-exchanged in the heat radiating heat exchanger 46 flows from the cooling water pipe 54 to the radiator 55, where it is cooled by the cooling fan, and again.
Circulates to

At this time, the cooling water pipe 5
Even if air is stored in the cooling water pump 4, the cooling water pump P1 is provided between the lower end portion K1 of the radiator 55 and the lower end portion K4 of the heat radiating heat exchanger 46. Can be suppressed, and the cooling water can be circulated to the heat exchanger 46 for heat radiation stably. Therefore, it is possible to prevent the efficiency of the Stirling cooling device from decreasing.

Next, a defrosting action of frost generated in the cold heat exchanger of the cold heat utilizing device 8 will be described. When defrosting is performed, frost formation is detected by a frost formation sensor (not shown) provided on the cold heat utilization device 8, and the motor 16 of the Stirling refrigerator 3 is rotated in the reverse direction.

As a result, the compression piston 36 and the expansion piston 42 have a phase difference of 90 degrees, and the compression piston 36 acts as an expansion piston and the expansion piston 42 To act as. Therefore, the expansion cylinder 33
The working gas in the expansion chamber is compressed by the expansion piston 42 and becomes high in temperature. Therefore, the cold refrigerant is heated by circulating through the cooling head 4 and supplied to the cold heat utilization device 8.
The frost generated in the heat exchanger of the heat utilization device 8 can be removed.

Thus, defrosting can be effectively performed even with the cold heat utilization equipment 8 in which the heat exchanger is not provided with defrosting means such as a heater wire.

In the case where the cold heat utilizing device 8 is a cooling constant temperature bath, a cooling operation by reverse rotation of the motor 16 can be used.

That is, the temperature of the thermostatic chamber is measured while performing the normal cooling operation of the Stirling cooling device of the present invention, and based on the result, the motor 16 is sequentially controlled to rotate in reverse by the temperature control circuit of the temperature control device. Heating operation to maintain a constant temperature.

Although the two-piston type Stirling refrigerator 3 is used in the above embodiment, it is needless to say that another type of Stirling refrigerator 3 such as a displacer type may be used.

FIG. 7 is an electric circuit diagram showing a main part of the Stirling cooling device. Reference numeral 75 denotes a delay timer (delay means). The controller 71 is a delay timer 75
The contact 76 is opened by a delay timer 75 after a predetermined time (for example, one hour), and the cooling water pump P1 and the cooling fan 70 are stopped.

Next, control when the operation of the Stirling cooling device is stopped will be described with reference to the flowchart of FIG.

First, it is determined whether an operation stop signal has been input from the switch 72 (S1). The operation stop signal is, for example, when the operation switch 72 is operated by the user.

If no operation stop signal has been input,
The operation control is performed as it is (S2). When the operation stop signal is input, the motor 16 is stopped (S3), and the delay timer starts measuring time (S4).

The operation of the cooling water pump P1 and the cooling fan 70 is continued without stopping (S5).

It is determined whether a predetermined time has elapsed (S
6) If the predetermined time has not elapsed, the control of (S5) is performed again. If the predetermined time has elapsed, the operation of the cooling water pump P1 and the cooling fan 70 is stopped (S6).

In the operation control of the present invention, the temperature of the compression chamber (the temperature of the cooling water becomes lower than this temperature) gradually decreases after the motor stops, as shown by the solid line A in FIG. However, it does not rise above the dangerous temperature X (the temperature corresponding to the pressure at which the hose is likely to come off). However, as described in the section of the prior art, in the prototype in which the operation of the cooling water pump and the cooling fan is stopped at the same time as the motor is stopped, as shown by the dotted line B in the related art, the temperature is temporarily reduced. Since the temperature rises and approaches the dangerous temperature, it is not always possible to prevent danger such as disconnection of the hose.

In this embodiment, the operation of the water circuit is delayed and stopped for a predetermined period of time so that the temperature of the expansion chamber drops to the predetermined temperature. The operation can be terminated by cooling the vicinity to a predetermined temperature, maintenance can be performed immediately at the time of maintenance, even if there is a risk of touching the cooling water like removing the hose, It is unlikely to cause burns.

[0074]

【Example】

Next, different embodiments will be described. The difference from the above-described embodiment is that the water circuit is provided with a temperature detector for detecting the temperature (water temperature) of the water circuit, The configuration is such that the circulating pump and the cooling fan are stopped when the detection is made. Of course, in this case, it is not necessary to provide the above-mentioned delay timer in the control means.

In the Stirling cooling apparatus thus configured, when the operation of the motor is stopped, the cooling is performed until the water temperature drops to a predetermined temperature (for example, 50 degrees, and about 55 degrees during operation). The water pump and the cooling fan are continuously operated. For this reason, since the water temperature that is directly correlated with the pressure is detected as compared with the above-described embodiment using the delay timer, the continuous operation of the cooling water pump and the cooling fan can be shortened, and the electricity bill can be saved. And the time during which noise is generated and the time during which vibration occurs (time during which driving is not completely completed) can be shortened.

[0077]

As described above, according to the first aspect of the present invention, when the driving device is stopped, the operation of the water circuit is delayed for a predetermined time to stop the operation of the water circuit. The compression chamber and its vicinity can also be cooled afterwards, and the pressure rise in the water circuit can be suppressed.

According to the second aspect of the present invention, the water circuit is provided with delay means for delaying and stopping the operation of the water circuit for a predetermined time so that the temperature of the expansion chamber decreases to the predetermined temperature. The operation can be terminated by cooling the vicinity of the compression chamber to a predetermined temperature.

According to the third aspect of the present invention, since the temperature which is correlated with the pressure in the water circuit in which the pressure is not to be increased is detected, the continuous operation of the water pump and the cooling fan can be shortened, and the electric power can be shortened. In addition to saving money, the noise and vibration time can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall conceptual diagram of a Stirling refrigerating apparatus applied to an embodiment of the present invention.

FIG. 2 is a plan view illustrating an example of a heat radiation heat exchanger.

FIG. 3 is a sectional view taken along the line AA of FIG. 2;

FIG. 4 is a side sectional view illustrating another example of the cooling head of the Stirling refrigerating apparatus.

FIG. 5 is a side sectional view illustrating an example of a cooling head of the Stirling refrigerating apparatus.

FIG. 6 is a view showing the front of the cooling head of FIG. 5;

FIG. 7 is an electric circuit diagram showing a main part of the Stirling refrigerating apparatus.

FIG. 8 is a flowchart showing a control operation of the Stirling refrigerating apparatus.

FIG. 9 is a diagram showing a change in temperature of a compression chamber.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Stirling cooling device 3 Stirling refrigerator 16 Motor (drive device) 36 Compression piston 37 High-temperature chamber (compression chamber) 41 Low-temperature chamber (expansion chamber) 42 Expansion piston 46 71 Controller (delay means) P1 Cooling water pump (water pump)

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shinhachiro Uehara 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Shinji Yamamoto 2 Keihan-hondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Kenichi Kagawa 2-5-5, Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (3)

[Claims] 1. A compression cylinder is accommodated in a compression cylinder to form a compression chamber, an expansion cylinder is accommodated in an expansion cylinder, and an expansion chamber and a buffer chamber are formed at both ends of the compression cylinder. A working gas is sealed inside, and the compression piston and the expansion piston are driven by a driving device to reciprocate the working gas between the compression chamber and the expansion chamber, thereby cooling the expansion chamber. Along with heating the compression chamber, in a Stirling cooling device that further cools the compression chamber with a water circuit configured by connecting a water pump and a radiator in a ring, the drive device is stopped when the drive device is stopped. A Stirling cooling device comprising a delay means for delaying the operation of the water circuit by a predetermined time and stopping the operation. 2. A compression chamber is formed by accommodating a compression piston in a compression cylinder, an expansion piston is accommodated in an expansion cylinder, and an expansion chamber and a buffer chamber are formed at both ends of the compression cylinder. Enclosing the working gas therein, driving the compression piston and the expansion piston with a driving device, and cooling the expansion chamber by reciprocating the working gas between the compression chamber and the expansion chamber, In a Stirling cooling device configured to cool the compression chamber by a water circuit configured by connecting a water pump and a radiator in a ring, the water is cooled for a predetermined time so that the temperature of the expansion chamber decreases to a predetermined temperature. A Stirling cooling device comprising delay means for delaying and stopping operation of a circuit. 3. A compression chamber is formed by accommodating a compression piston in a compression cylinder, an expansion piston is accommodated in an expansion cylinder, and an expansion chamber and a buffer chamber are formed at both ends of the compression cylinder. Enclosing the working gas therein, driving the compression piston and the expansion piston with a driving device, and cooling the expansion chamber by reciprocating the working gas between the compression chamber and the expansion chamber, In a Stirling cooling device configured to cool the compression chamber with a water circuit configured by connecting a water pump and a radiator in a ring, the operation of the water circuit is delayed and stopped until the temperature of the expansion chamber reaches a predetermined temperature. A Stirling cooling device comprising a delay means for causing a delay.