JPH0932965A - Adaptive joule thomson cryostat having servo control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stably operated throttle valve mechanism for cryostat used in the cryostat of a Joule Thomson effect in needle valve control for cooling a heat load. SOLUTION: A device has a flow control means of coolant like a bellows 31 connected to a needle valve 19 to control flow of the coolant, heat sensor 51 connected to a heat load 15 to detect a temperature in the vicinity of this heat load to give a signal showing the detected temperature and adjusting means 41, 45 like a biometal rod receiving this signal in response thereto adjusting the flow control means of the bellows 31 or the like.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to Joule-Thomson cryostats, and more particularly to systems and techniques for improving the performance of Joule-Thomson cryostats.

[0002]

While the present invention is described herein with reference to specific application embodiments, it should be understood that the invention is not limited thereto. Persons of ordinary skill in the art and those who have access to the technology given herein will recognize additional modifications, applications, and examples within the highly applicable technical scope of the present invention and in additional fields.

A cryostat is a device that provides a localized low temperature environment in which operation or measurement is performed under controlled temperature conditions. Cryostats are also used, for example, to cool infrared detectors of guided missiles where the detector and associated electronics are packed in a small storage package. Cryostats are also used in superconducting systems where controlled very low temperatures are required for superconducting operation.

The Joule-Thomson cryostat is a valve (known in the art as the "Joule-Thomson valve") that allows high-pressure gas to expand through an irreversible throttle process in which the enthalpy is preserved and reduces the temperature. ) Is a cooling device.

The simplest form of the common Joule Thomson cryostat typically has an orifice sized to be fixed to the heat exchange device at the cooling end of the cryostat,
As a result, the cryostat cooling is not regulated.
The dynamics of input pressure and internal gas flow set the coolant flow parameters through the cryostat. The usual Joule-Thomson cryostat is a simple device in that there are no moving parts, but the inherent uncontrolled flow characteristics require rapid cooling from a gas source of limited size and long cooling periods. It makes fixed orifice type cryostats unsuitable for many applications. Rapid cooling requires high velocity gas flow and large size orifices, while long cooling periods require low velocity gas flow and small size orifices. These two
The two conditions cannot be met simultaneously with a fixed orifice cryostat.

In the 1950s, demand-flow Joule Thomson cryostats with internal passive thermostat control at variable orifice sizes were used. These cryostats have the ability to initiate cooling at the maximum orifice size, thereby providing freezing with rapid cooling due to high velocity gas flow. After achieving cooling, the orifice size is reduced for the minimum gas flow rate and refrigeration required for heat loading. A thermostat element in the mandrel of the device self regulates the gas flow based on the temperature in or around the gas filled chamber. The cooling rate is proportional to the rate of gas mass flow through the cryostat. A thermostatic element, which is a gas-filled bellows or segment of material that contracts or expands based on temperature, is coupled to a demand flow needle valve mechanism. As the temperature decreases, the bellows contract, bringing the needle closer and partially adjacent to the Joule-Thomson orifice. At a predetermined critical temperature, Bellow's thermostat mechanism can completely close the needle valve. As the temperature rises, the bellows expand again, energizing the valve mechanism and allowing fresh coolant flow to eventually flow through the orifice to the heat load.

Self-regulating demand flow cryostats provide control over coolant flow, and there are still limits that make it unacceptable in systems where temperature fluctuations are critical to operation. Thermostatic bellows mechanisms (and similar alternative devices that rely on expansion and contraction materials such as some plastics) inherently suffer from large performance tolerances. This causes instability and fluctuations at the critical on-off temperature point of the needle bubble. Therefore, it has been discovered that such cryostats are not proportional in gas flow regulation in the expected full operating range.

Additionally, the same cryostat reacts differently when using different coolants. Therefore, system performance depends on the particular coolant used during a single operating period. If another coolant is used instead of the coolant for which the heat shrink link is designed, the cryostat will pursue the designed setpoint and repeat the failure.

Further, the temperature wave in the expansion chamber causes thermal cycling of the bellows mechanism. Moreover, in a rocket environment, the mechanism is subject to acceleration and deceleration. In infrared detector cooling, detector instability due to fluctuations in cryostat refrigeration results in thermal noise of the type known as thermophones generated in coupled video displays.

When the liquid pool operates under the influence of environmental forces when the filling chamber reaches saturation, the liquid gas pool seriously affects the performance of the cryostat needle valve operation. This causes a rapid vaporization or impedance in the gas flow on the low pressure side of the heat exchanger resulting in a change in liquid vapor pressure and a sudden opening of the needle valve. Another operating limit is encountered when long-term heat loads are used. The temperature of the gas-filled chamber drops to the far end of the heat load,
Allow the needle valve to close early before the load is totally cooled.

Any of these exemplary conditional aspects cause premature closure or unwanted changes in needle valve positioning and gas flow rate. This allows the cumulative manufacturing design of Joule Thomson cryostat components to be adjusted for both thermal load elements and coolant parameters.

[0012]

Therefore, in order to adjust the size of the gas expansion valve orifice, which is set from the maximum opening during the cooling period, to the reduced minimum opening for continuous cooling of the heat load, the mere gas-filled chamber temperature is required. Rather, there is a need for a cryostat activation mechanism that can use the sensed temperature of the heat load. In addition, there is a need for an active mechanism for the cryostat to provide stable time-averaged proportional control of gas expansion valve orifice dimensions for stable gas flow and stable refrigeration rate and temperature control. . Ideally, this control would be a continuous, gradual, rather than sudden, method of maintaining a stable cooling temperature.
It should be possible to adjust to changing thermal environments and changing heat loads and input pressure conditions. Ideally, this control should work with multiple coolant gases to provide stable cooling temperatures and optimal performance. Further, there is a need for an activation mechanism for the cryostat that minimizes sensitivity to temperature fluctuations or internal heat waves caused by external environmental effects such as inertial acceleration, or pressure changes in the filling chamber.

[0013]

SUMMARY OF THE INVENTION The need for such a technique is to provide an active gas throttle mechanism for a cryostat using a Joule-Thomson effect cryostat with needle valve control to cool the heat load. It is solved by the invention. The device of the present invention includes a biasing device connected to the needle valve to control the flow of coolant therethrough. The temperature sensor is connected to the heat load adjacent thereto. The sensor provides a signal indicative of the sensed temperature. The servo controller receives the signal and in response regulates the flow of coolant to the energizer.

In operation, the present invention (a) senses the approximate temperature of the heat load, (b) sends a first signal for the approximate temperature, and (c) regulates the flow of coolant in the cryostat. Closed loop for controlling the refrigeration of a heat load by means of a Joule-Thomson cryostat including the step of converting the signal into a second signal for the purpose of: (d) adjusting the flow of the coolant in direct relation to the first signal. Give way.

[0015]

DETAILED DESCRIPTION OF THE INVENTION A typical general Joule Thomson cryostat 10 is shown in FIGS. A coolant such as high pressure argon or nitrogen gas or air is introduced through the gas inlet 1 into the recoverable heat exchanger 3 surrounding the support mandrel 5 in the cooling fingers 7 of the dewar package 9. The heat exchanger 3 is wrapped around a mandrel 5 and is based on a counter-flow fin metal tube 4 which makes it possible to cool the high pressure gas particularly strongly as it moves towards the lower end of the cooling finger 7. It is equipped with The heat exchanger tubes 4 terminate in an orifice 16 at the lower end of the mandrel 5, commonly referred to as the cryostat cooling end.
Orifice 16 operates as a Joule Thomson gas throttle valve. As the gas passes through the orifice 16 and enters the surrounding gas-filled chamber 29, it expands to a low pressure gas to create a liquid form. The vaporized liquid and low pressure gas are used to cool a heat load 15 located adjacent to the dewar window 11. Cooling of the load is achieved by a liquid coolant spray from the orifice 16 to the part of the cooling finger 7 located in contact with the heat load 15. The gas from chamber 29 is recycled through another low pressure branch of heat exchanger 3 before exiting to the atmosphere through outlet port 13 at the upper end of cryostat 10.

As mentioned above, the simplest form of a typical Joule-Thomson cryostat typically has an orifice 16 sized to be fixed to the heat exchanger 3 at the cooling end of the cryostat, so that cooling by the cryostat is regulated. Not done. The input pressure and internal gas flow dynamics set the coolant flow parameters through the cryostat. A simple device with no moving parts and inherently uncontrolled flow characteristics requires a fixed orifice type cryostat with rapid cooling from a gas source of limited size and long cooling periods. Make it unsuitable for many applications. Rapid cooling requires high gas flow rates and large size orifices, and long cooling periods require low gas flow rates and small size orifices. These two conditions cannot be met simultaneously by a fixed orifice cryostat.

Since the 1950's, internally, a demand-flow Joule-Thomson cryostat with a passive thermostatically controlled variable orifice size has been used, as shown in FIG. 1b. These cryostats initiate cooling at the maximum orifice size, thereby having high velocity gas flow and refrigeration capacity for rapid cooling. After achieving cooling, the orifice size is reduced due to the minimum gas flow rate and refrigeration required under heat load.

The thermostat element in the mandrel 5 self-regulates the gas flow based on the temperature in and around the gas-filled chamber 29. The cooling rate is proportional to the gas mass flow rate through the cryostat. A thermostat element, which may be a gas filled bellows or a material segment that contracts or expands based on temperature, is coupled to the demand flow needle valve mechanism 19. As the temperature decreases, the bellows are adapted to contract, extending the needle to the Joule-Thomson orifice 16 for partial proximity. At a predetermined critical temperature, the bellows thermostat mechanism 17
Can be completely close to the needle valve 19. As the temperature rises, the bellows expand again, energizing the valve mechanism 19 and allowing new coolant flow through the orifice and ultimately to the heat load 15.

As noted above, self-regulating demand flow cryostats provide additional control over coolant flow, making it unacceptable in systems where temperature fluctuations are critical to operation.

The thermostat bellows mechanism 17 (and similar alternative devices that rely on expanding and contracting materials such as some plastics) are inherently subject to significant performance differences. This causes instability and fluctuations in the critical on-off temperature point of the needle valve. Therefore, it has been discovered that such cryostats are not proportional in gas flow regulation over the expected full operating range.

Moreover, the same cryostat reacts differently when using different coolants. Therefore, system performance depends on the particular coolant used during a single operating period. If another coolant is used instead of the coolant for which the heat shrink link is designed, the cryostat will pursue the designed setpoint and repeat the failure to reach it.

Further, the temperature wave in the expansion chamber causes thermal cycling of the bellows mechanism. Moreover, in a rocket environment, the mechanism is subject to acceleration and deceleration. In the cooling of infrared detectors, the instability of the detectors due to fluctuations in cryostat refrigeration causes thermal noise of the type known as thermophones, which is generated in combined video displays.

When the liquid pool operates under the influence of atmospheric forces when the inside of the filling chamber 29 has reached saturation,
The liquid gas pool seriously affects the performance of the cryostat needle valve operation. This is the heat exchange device 3
On the low pressure side of the gas flow there is a rapid vaporization or impedance in the gas flow, resulting in a change in liquid vapor pressure and a sudden opening of the needle valve.

Another operating limit is encountered when the heat load 15 is used in the extended position. The temperature of the gas-filled chamber drops to the far limit of the heat load 15 and closes the needle valve 19 early before the load is totally cooled.

Any of these exemplary conditions will cause premature closure or unwanted changes in needle valve positioning and gas flow rates. This allows various manufacturing designs of Joule-Thomson cryostat components to be adjusted for both thermal load elements and coolant parameters.

Therefore, in order to adjust the gas expansion valve orifice size set from the maximum opening during the cooling period to the minimum opening reduced for sustained cooling of the heat load, rather than just the gas filled chamber temperature, the heat load There is a need for a cryostat activation mechanism that can use the sensing temperature of.

In addition, there is a need for a stable, time-averaged proportional control of the gas expansion valve orifice size for stable gas flow and an active mechanism for the cryostat to provide stable refrigeration rate and temperature control. To do. Ideally, this control should be able to adjust the changing thermal environment and changing heat load and input pressure conditions in a continuous rather than sudden, gradual manner that maintains a stable cooling temperature. Ideally, this control should work with multiple coolant gases to provide stable cooling temperatures and optimum performance.

Further, there is a need for an activation mechanism for the cryostat that minimizes sensitivity to temperature fluctuations or internal heat waves caused by external environmental effects such as inertial acceleration, or pressure changes in the filling chamber.

The present invention solves these needs. The invention can be adapted to the construction of a cryostat of the type shown in Figure 1a. FIG. 2a shows the present invention when incorporated in such a Joule Thomson cryostat.

The present invention is contained within the cooling finger 7 of a vacuum dewar container 9 similar to the prior art method of FIG. 1a. Referring to FIG. 2A, the mandrel cap member 21
Seals the mandrel chamber 23. Cap member 21 typically includes a foamed thermal insulation 25 encapsulated in polyurethane to prevent heat leakage from chamber 23.

A sealed sheath 27, preferably made of stainless steel or the like, extends the length of the cap member 21 to the mandrel chamber 23 and connects into a coolant filled chamber 29 at the cooling end of the cryostat. To be done. The coolant-filled chamber 29 houses a bellows spring 31 which is fixedly mounted. In the preferred embodiment, a low mass, high spring rate device is used for bellows spring 31.

Cap chamber of mandrel cap 21
Located within 33 is an electrical feedthrough connector 35. In the preferred embodiment, this is a glass metal feedthrough connector.
35. The through conductor connector 35 has a mandrel cap 21.
Has a conductor 55 terminating outside thereof. The bellows spring biasing mechanism terminates at a first end 39 of the feedthrough connector 35. The bellows spring biasing device comprises a first portion, which in the preferred embodiment is a biometal wire rod 41. The rod 41 has a length from the mandrel cap 21 to the sheath tube 27, and the electrical return coupling 43 connects the wire rod.
45, which in the preferred embodiment is connected to a steel wire rod. Note that the relatively sturdy rod 45, sheath 27 may be removed. Electrical return wire that joins to joint 43
The 55 'is also guided outside the mandrel cap 21.

The biometal rod 41 operates as a transducer. In the preferred embodiment, the biometal wire rod 41 is a type of memory alloy in the form of titanium nickel that shrinks during heating when an electric current passes through it (Martensite AA phase conversion). Either a small percentage of direct current or pulse width modulated current may be provided through rod 41 via a pair of conductors 55, 55 '. The rod 41 thus acts as a miniature transducer for converting movement to the needle valve 19 of the coolant filled chamber 29 using the attached steel wire rod 45. Alternatives to biometals are solid state electromagnetic devices such as solenoids or magnetostrictive alloys or other solid state electromechanical devices such as piezoelectric transducers. The cryostat application represents the most suitable substitute. In FIG. 2a, the current is through conductor connector 35.
(FIG. 3) and is supplied to the wire rod 41. Current is also supplied to heating element 64 by wires 62,63.

Referring to FIG. 2b, the electrical return coupling 43
The length of the steel wire rod 45 connected to the biometal wire rod 41 extends through the sheath tube 27 to the bellows compression plate 47 connected to the movable end of the bellows spring 31.

The bellows spring 31 is connected to the needle valve mechanism 19 in the cooling filling chamber 29 via the bellows pressure plate 47. The connection of the pressure plate with the spring 31 connected through the steel wire rod 45 to the biometal rod 41 forms a valve biasing device. As shown in FIG. 2b, the needle valve mechanism 19 and the connecting bellows spring 31 are shown in FIG.
Similar to or identical to springs recognized by those skilled in the art as indicated by b.

Returning to FIG. 2a, the thermal sensor 51 is mounted on or adjacent to the thermal load mounting platform 15 '(which may be integrated with a particular load). In the preferred embodiment, the silicon diode temperature sensor 51 is a load
It is fixedly attached to the heat load platform 15 'adjacent to 15.

Commercially available sensors such as the IN914 diode manufactured and sold by Texas Instruments Incorporated are suitable for use in the present invention. Transistor type sensors may alternatively be used in the present invention. The sensor 51 is mounted so that it is more sensitive to the ambient temperature of the load environment than the temperature in the filling chamber 29.

Referring to FIG. 3, there is shown a schematic diagram that helps understand the operation of the apparatus of the present invention. A heat load 15, which requires temperature control of, for example, an infrared detector of a missile or a focal plane array, is fixedly mounted on a heat load platform 15 '. Platform 15 'is shown in Figure 2
It is located adjacent to the cryostat near the orifice 16 as indicated by a.

The servo control device 53 is provided with conductors 55 and 55 '(return).
Is connected to the bellows spring urging device 57 and the temperature sensor 51. There are various heat sources that make up the load, as indicated by the Qx arrows. Load 15 and its platform 15 ', Qfpa, its Qrad, Qcond,
Another load environment heat-providing device, shown as Qvalve, represents the heat generated from the valve energizer.
The heat extracted by the cryostat is indicated by -Qcryo. The temperature sensor 51 provides feedback from the load 15, 15 'environment to the servo controller 53 of the valve control biasing device 57. The operating parameters of servo controller 53 are designed to control the length of biometal rod 41 based on the sensed temperature. Servo controller biasing device 53, which is currently coupled to biometal wire rod 41 by conductors 55, 55 ', drives the transducer action of biometal wire rod 41. Thereby, the steel wire rod 45 attached to the biowire rod 41 controls the flow of the coolant to the bellows spring 31, the Joule-Thomson orifice of the needle valve 19, and the load 15.

The method of operation is illustrated by the block diagram shown in FIG. As indicated by reference numeral 101, the servo control device 53 of the valve control activation device 57 is activated when the coolant gas is input to the heat exchanger 3 through the gas inlet 1. The current to the biometal rod 41 is switched on to reach a predetermined temperature just below the phase conversion temperature of the preselected biometal material used in the rod 41. During the cooling phase of the refrigeration cycle, needle valve 19 is normally wide open to maximize gas flow and refrigeration effects. When the load temperature approaches its predetermined reference value, as indicated by reference numeral 103,
The temperature sensor 51 sends a temperature error feedback signal to the valve control energizer 57 as indicated by reference numeral 105.
To the servo control device 59. Servo controller 59 also begins to generate additional current to biometal wire rod 41 via conductor 55 and feedthrough connector 35. When the rod 41 is heated, the biometal material contracts. This contraction is transmitted through the steel wire rod 37 and the bellows pressure plate 47 to insert the connected needle into the valve orifice, reducing gas flow and, consequently, the refrigerating effect of the Joule-Thomson cryostat.

The reduction of gas flow continues until the load temperature rises above the reference level detected by the thermal sensor 51. As a result, the current to the biometal wire 41 is reduced, creating a reverse reaction to generate further refrigeration and opening the orifice of the needle valve 19. Temperature fluctuates,
The oscillations cause the temperature error signal to be properly zeroed when feedback through the valve control bias 57 adjusts the orifice of the needle valve 19 to a size where the refrigeration rate matches the thermal load within the desired reference temperature range. Until.

FIG. 5 shows another embodiment of the valve control biasing device 57 which includes a fine servo controller 61 which is coupled to the temperature sensor 51 by a wire pair 56. As also shown, the fine servo controller element 61 drives a heating element 64 located within the cooling end of the cryostat chamber 23, or alternatively, as shown in FIG. Installed. The function of the second fine servo controller element 61 is to add the additional heat required to maintain the load temperature within a fine error reference temperature range for a particular load.

Similarly, the operation of the embodiment of FIG. 5 is illustrated by the block diagram of FIG. That is, the secondary servo loop with feedback uses a small amount of electrical heating power added to the thermal load to keep the temperature constant within tighter tolerances.

In this way, active, servo-controlled cryogenic refrigeration for maintaining a constant temperature environment for the heat load is achieved in an unsaturated cryogenic operating mode.
In the non-saturated cryogenic mode of operation, no excess liquid coolant is produced and therefore there is no pool of liquid coolant in the filling chamber 29. Since the present invention operates in a non-saturated mode, it does not depend so much on the boiling pressure or temperature of the coolant as long as the reference temperature is above the boiling range of the coolant, so the present invention covers a wide range of ambients, including vacuum spaces. Must operate at ambient pressure.

The present invention also has the ability to operate in a nearly saturated mode of operation. For example, a mode that uses a servo control reference temperature slightly higher than the liquid coolant boiling temperature but transmits a predetermined output current that locks the servo controller from a zero search mode when the threshold temperature is reached. By converting to, the cryostat is operated with a reduced but fixed orifice during a sustained cooling period to generate a slight excess of liquid coolant.

These features make the present invention useful, for example, in a Joule-Thomson cooling system that provides fast cooling and long term cooling from a gas supply system of minimum size and weight in a missile system, for example.

The present invention has been described herein with reference to a particular embodiment for a particular application. Those skilled in the art and those who have access to the method of the present invention will recognize additional variations, applications, and embodiments within the scope of the present invention. Therefore, all these applications are within the scope of the present invention by the claims.
It is intended to include modifications and examples.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a typical conventional cryostat and a typical demand flow needle valve used therein.

FIG. 2 is a sectional view of a device of the present invention incorporated in a Joule Thomson cryostat and a detailed view of a part thereof.

FIG. 3 is a schematic view of the device of the present invention shown in FIG.

FIG. 4 is a flow chart of the operation of the apparatus of the present invention shown in FIGS.

5 is a schematic view of another embodiment of the apparatus of the present invention shown in FIG.

6 is a flowchart of the operation of the apparatus of the embodiment shown in FIG.

Front Page Continuation (72) Inventor Joseph El Haraba, California 92677, USA, Laguna Niger, Dover Place 47 (72) Inventor Daniel W. Brunton, Arizona, USA 85730, Taxon, E.E. Golf Links Road 11650

Claims (5)

[Claims] 1. A throttle valve mechanism for a cryostat using a needle valve controlled Joule-Thomson effect cryostat for cooling a heat load, comprising first means connected to the needle valve to control a flow of a coolant. Second means connected to a heat load for sensing a temperature in the vicinity of the load and providing a signal indicative of the sensed temperature; and receiving the signal and responsively adjusting the first means. And a third means for controlling the throttle valve mechanism. 2. A means for controlling the flow of the coolant is connected to a transducer means for receiving a regulated signal, and a tip of the transducer means for imparting movement to the needle of the needle valve. The mechanism of claim 1, further comprising a needle valve biasing means. 3. The mechanism of claim 1, wherein the means for sensing temperature further comprises a silicon diode temperature sensor. 4. A servo controller configured to receive the signal from the temperature sensing means and provide an output signal in response thereto, the adjusting means further comprising: And a transducer energizing means configured to receive the energizing signal and to provide an energizing signal to the means for responsively controlling the flow of the coolant. 5. The transducer means further comprises: a transducer element that expands or contracts in response to the adjustment signal; a first end connected to the transducer means and a remote end connected to the needle valve biasing means. 3. The mechanism of claim 2 further comprising a transmission means connected to transmit expansion and contraction of the transducer to the needle valve.