GB2168799A - Cyrogenic cooling apparatus - Google Patents
Cyrogenic cooling apparatus Download PDFInfo
- Publication number
- GB2168799A GB2168799A GB08432059A GB8432059A GB2168799A GB 2168799 A GB2168799 A GB 2168799A GB 08432059 A GB08432059 A GB 08432059A GB 8432059 A GB8432059 A GB 8432059A GB 2168799 A GB2168799 A GB 2168799A
- Authority
- GB
- United Kingdom
- Prior art keywords
- compressor
- pressure
- inlet
- cooler
- outlet
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
- F25B9/02—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point using Joule-Thompson effect; using vortex effect
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
- F25B49/022—Compressor control arrangements
Landscapes
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Thermal Sciences (AREA)
- General Engineering & Computer Science (AREA)
- Compressors, Vaccum Pumps And Other Relevant Systems (AREA)
- Devices That Are Associated With Refrigeration Equipment (AREA)
Abstract
Cyrogenic cooling apparatus of closed circuit type includes a compressor 2 whose outlet 4 is connected to the inlet 6 of a Joule-Thomson cooler 8 whose outlet 10 is connected to the inlet 12 of the compressor. The apparatus includes means arranged to maintain pressure at the inlet 12 of the compressor substantially within a predetermined range. These means preferably comprise a pressure sensor 16 arranged to sense the pressure at the inlet 12 of the compressor and connected to a controller 14 to increase the speed of the compressor when the said pressure exceeds a first value and to decrease the speed of the compressor when the said pressure is less than a second value which is lower than the first value. <IMAGE>
Description
SPECIFICATION
Cryogenic cooling apparatus
The present invention relates to cryogenic cooling apparatus and is concerned with that type of apparatus which is adapted to cool a load, such as the active element of an infrared detector, to a cryogenic temperature. The invention is concerned with that type of cooling apparatus which incorporates a Joule-Thomson cooler, i.e. a cooler including two pathways through one of which refrigerant gas is supplied under pressure to a Joule-Thomson expansion nozzle whereafter the gas flows through the other pathway which is in heat exchange relationship with the first pathway thereby cooling the incoming gas.Such Joule-Thomson coolers may be supplied with gas from a reservoir or pressurised gas, e.g. a flask containing nitrogen at 400 bar, in which event the cooler is operated on open circuit, that is to say the gas is exhausted to atmosphere after passing through the cooler. Alternatively the cooler may be supplied with gas by a compressor, in which event it may be operated on open circuit or on closed circuit, that is to say the outlet from the cooler is connected to the compressor inlet.
The present invention is concerned with that type of cooling apparatus which includes a compressor connected in a closed circuit to the cooler.
The cooler is frequently of self-regulating type that is to say it includes a throttling valve arranged automatically to vary the flow rate of gas through it in dependence on the thermal load to which it is subjected, but in any event it is necessary to control the rate of output of the compressor so as substantially to match this output to the throughput of the cooler and to ensure that the supply pressure to the cooler does not vary outside a predetermined range. The compressor output is normally controlled by varying the compressor speed in dependence on the compressor output pressure.
Whilst this form of control may be satisfactory for cooling apparatus which operates in known, substantially unvarying ambient conditions, the thermal load may constitute the active element of an infrared detector which is used in airborne applications and may thus be in operation in an ambient temperature which can vary by up to 1000C or more e.g. from +70 C to -400C. A temperature variation of this magnitude results in substantial variations in the average system pressure, even if mass flow rate is maintained substantially constant.
The cooling rate thus varies substantially and in order to ensure that the cooling rate is adequate at even high ambient temperatures at which the gas is considerably less dense buffer volumes may have to be incorporated upstream and/or downstream of the cooler or it may have to be accepted that the cooler will produce a greater amount of liquid refrigerant than is actually required at low ambient temperature. All of these measures can result in an increase in the complexity, weight and size of the cooling apparatus, all of which are extremely undesirable when the apparatus is to be used in airborne applications.Accordingly, it is an object of the present invention to provide a cryogenic cooling apparatus of the type referred to above which substantially overcomes the above problems and in particular to provide a method of controlling the compressor so that the apparatus inherently includes at least a degree of automatic compensation for changes in ambient temperature.
According to the present invention cryogenic cooling apparatus includes a compressor whose outlet is connected to the inlet of a Joule-Thomson cooler, the outlet of which is connected to the inlet of the compressor, and means to maintain the pressure at the inlet to the compressor substantially within a predetermined range. The apparatus preferably incudes means to sense the pressure at the inlet to the compressor and means to vary the speed of the compressor in dependence on the magnitude of the said pressure.
Preferably the compressor includes a controller connected to the pressure sensor and arranged to increase the speed of the compressor when the said pressure exceeds a first value and to decrease the speed of the compressor when the said pressure is less than a second value which is lower than the first value.
Thus in the apparatus in accordance with the present invention the compressor inlet pressure is maintained within a predetermined range or substantially constant and the outlet pressure is thus permitted to be at its natural value. Since the apparatus constitutes a closed system and thus contains a fixed mass of refrigerant gas the outlet pressure of the compressor varies substantially with ambient temperature and is very much higher at high ambient temperatures than at low ambient temperatures.The cooler is very much more efficient at lower temperatures rather than high temperatures due to the fact that the Joule-Thomson coefficient varies inversely with temperature but this coefficient also rises with increasing pressure and thus the variation of the pressure on the outlet side of the compressor with ambient temperature automatically at least partially compensates for the variation in cooling efficiency of the cooler at differing ambient temperatures. It is therefore not necessary to include buffer volumes or the like on the inlet or outlet side of the compressor or to oversize the orifice in the Joule-Thomson expansion nozzle to ensure that the cooler can produce at least the minimum required cooling effect at all ambient temperatures. This results in a considerable decrease in the complexity, weight and expense of the entire cooling apparatus.
The pressure at the compressor inlet may be maintained constant by various means, e.g. by providing a connection between the compressor inlet and outlet which includes a valve arranged to pass gas to the inlet when the inlet pressure falls below a predetermined value. This result, however, in the compressor always running at maximum speed but in the preferred embodiment in which the speed of the compressor is varied in dependence on the compressor inlet pressure the compressor throughput is matched to that of the Joule
Thomson cooler and energy consumption is minimised.
Whilst the cooling apparatus constitutes a closed system it will be appreciated that a relief valve may be provided on the inlet and/or outlet side of the compressor so as to ensure that the inlet andl or outlet pressures do not exceed or become less than the predetermined values since when the compressor is started up the control system may be unable to maintain these pressures at the normal desired operating values.
Further features and details of the present invention will be apparent from the following description of a specific embodiment of cooling apparatus which is given by way of example with reference to the accompanying schematic diagram.
The apparatus includes a compressor 2 whose high pressure outlet 4 is connected by a line 5 to the inlet 6 of a Joule-Thomson cooler 8, the outlet 10 of which is connected by a line 11 to the low pressure inlet 12 of the compressor. The compressor is of any suitable electrically powered type and is controlled by a controller 14. The cooler 8 is not illustrated in detail but includes a first pathway communicating with the inlet 6 and a Joule-Thomson expansion nozzle and constituted by a finned tube wound around a tubular former accommodated within a Dewar flask and a second pathway constituted by the space between the Dewar flask and the finned tube and communicating with the outlet 10 and through which, in use, the refrigerant gas flows and cools the incoming gas.The cooler produces liquified gas and is arranged to cool a thermal load which in this case is secured to the inner wall of the Dewar flask. The cooler is of the self regulating type, that is to say it incorporates a throttling valve arranged to reduce the flow of gas through it in dependence on the volume of the refrigerant present in the Dewar flask or on the amount of refrigerant droplets entrained in the gas flowing through the expansion nozzle and may thus be the type disclosed in British Patent Specification No. 2085139A.The low pressure line 11 incudes a pressure-sensitive switch 16 which is connected to the controller 14 and whose contacts open and close at 0.8 and 1 bar respectively and a relief valve 18 which is arranged to open at 1.1 bar
The high pressure line 5 includes a pressure switch 20 whose contacts open and close at 210 and 190 bar respectively and which is connected to the controller 14 and a relief valve 22 which is arranged to discharge gas into the lower pressure line 11 if the pressure in the high pressure line should exceed 250 bars. All the pressures referred to above are absolute pressures.The compressor and the associated controls and valves referred to above are accommodated in a sealed metal enclosure (not shown) except for the inward and outward relief valve 18, the pressure in the enclosure is not permitted to rise above 1.1 bar or to fall below 0.8 bar by one or more valves which operate to exhaust air into, or admit air from, the atmosphere. The apparatus is designed to operate effectively as a closed system and the valve 18 will only operate under extreme conditions. If the refrigerant is air the valve 18 may permit air to vent in or out of the system but if argon or nitrogen is used the valve 18 should only be able to to vent outwardly.
The high pressure line also includes a non-return valve 24, a gas cleaner 26 of exchangeable cartridge type which removes any water vapour or traces of oil from the compressed gas and a solenoid operated valve 28. The high and low-pressure lines are connected to the cooler via a gimbal coupling 30.
In use, the compressor supplies pressurised gas to the cooler and after expansion the gas then returns to the compressor. The speed of the compressor is controlled by the pressure switch 16 so as to maintain the pressure in the line 11 between 0.8 and 1 bar. Thus when the pressure in the line 11 reached 1 bar the contacts of the switch 16 are closed and the compressor progressively speeds up until the inlet pressure reaches 0.8 bar when the switch contacts open and the compressor speed is progressively reduced. When the apparatus is in steady state operation it will always contain the same mass of refrigerant e.g. air, nitrogen or argon, since it is a closed system. The pressure on the low pressure side is controlled which may result in substantial pressure variations on the high pressure side.Thus at an ambient temperature of 70"C the pressure in the line 5 may be 200 bar whilst at -40 C this pressure may drop to 100 bar.
The increase in the Joule-Thomson coefficient with rising pressure substantially compensates for the decrease in this coefficient with rising temperature.
The cooling efficiency of the cooler remains substantially constant despite changes in the ambient temperature. The relief valves 18 and 22 do not normally open and are only provided to cater for unusual or transient conditions which may occur, especially when starting up the compressor. The pressure switch 20 is arranged to slow the compressor down if the pressure in the line 5 exceeds 210 bar but again this is not operative in steady state conditions.
The control of the pressure on the inlet side of the compressor by varying the speed of the compressor is preferably sufficiently accurate to control the pressure on the outlet side of the cooler and thus the temperature of the liquefied refrigerant to an acceptable value. If this is not practical a pressure maintaining valve may be incorporated in the line between the cooler outlet and the compressor inlet so as, for example, to raise the pressure at the cooler outlet thereby increasing the liquid refrigerant temperature.
Claims (8)
1. Cryogenic cooling apparatus including a compressor whose outlet is connected to the inlet of a Joule-Thomson cooler, the outlet of which is connected to the inlet of the compressor and means arranged to maintain the pressure at the inlet to the compressor substantially within a predetermined range.
2. A compressor as claimed in claim 1 including a pressure sensor arranged to sense the pressure at the inlet to the compressor and to vary the speed of the compressor in dependence on the magnitude of the said pressure.
3. Apparatus as claimed in claim 2, in which the compressor includes a controller connected to the pressure sensor and arranged to increase the speed of the compressor when the said pressure exceeds a first value and to decrease the speed of the compressor when the said pressure is less than a second value which is lower than the first value.
4. Apparatus as claimed in claim 2 or claim 3 in which the compressor and the sensor are arranged so that, in steady state use the pressure at the inlet to the compressor remains between 0.5 and 2 bar.
5. Apparatus as claimed in any one of the preceding claims including a relief valve arranged to discharge refrigerant gas from the outlet side of the compressor to the inlet side when the pressure at the outlet side exceeds a predetermined value.
6. Apparatus as claimed in any one of the preceding claims in which the inlet to the cooler communicates with a first pathway which communicates with a Joule-Thomson expansion nozzle which communicates with a second pathway which is in heat exchange relationship with the first pathway and communicates with the outlet from the cooler.
7. Apparatus as claimed in any one of the preceding claims in which the cooler is of self-regulating type.
8. Cryogenic cooling apparatus substantially as specifically herein described with reference to the accompanying drawing.
Priority Applications (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8432059A GB2168799B (en) | 1984-12-19 | 1984-12-19 | Cryogenic cooling apparatus |
| DE19853544853 DE3544853A1 (en) | 1984-12-19 | 1985-12-18 | DEEP TEMPERATURE COOLING DEVICE |
| FR8518756A FR2580384A1 (en) | 1984-12-19 | 1985-12-18 | CRYOGENIC COOLING APPARATUS |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8432059A GB2168799B (en) | 1984-12-19 | 1984-12-19 | Cryogenic cooling apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2168799A true GB2168799A (en) | 1986-06-25 |
| GB2168799B GB2168799B (en) | 1989-05-17 |
Family
ID=10571431
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8432059A Expired GB2168799B (en) | 1984-12-19 | 1984-12-19 | Cryogenic cooling apparatus |
Country Status (3)
| Country | Link |
|---|---|
| DE (1) | DE3544853A1 (en) |
| FR (1) | FR2580384A1 (en) |
| GB (1) | GB2168799B (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0239375A2 (en) * | 1986-03-24 | 1987-09-30 | British Aerospace Public Limited Company | De-contaminated fluid supply apparatus and cryogenic cooling systems using such apparatus |
| FR2708093A1 (en) * | 1993-07-23 | 1995-01-27 | Air Liquide | Very low temperature refrigeration system. |
| WO1996029551A1 (en) * | 1995-03-23 | 1996-09-26 | Ultra Electronics Limited | Cooler |
Family Cites Families (14)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR552206A (en) * | 1921-05-30 | 1923-04-26 | Escher Wyss & Cie Const Mec | Refrigeration plant with centrifugal compressor |
| DE733778C (en) * | 1938-08-16 | 1943-04-02 | Elektr App Fr Sauter A G Fab | Fully automatic cooling system |
| US3095710A (en) * | 1960-05-18 | 1963-07-02 | Carrier Corp | Anti-surge control for fluid compressor |
| FR1396043A (en) * | 1963-05-06 | 1965-04-16 | Hughes Aircraft Co | Closed cycle cooling system |
| FR1439668A (en) * | 1965-07-09 | 1966-05-20 | Hughes Aircraft Co | Closed circuit cryostat |
| FR1490188A (en) * | 1965-08-23 | 1967-07-28 | Union Carbide Corp | Helium refrigerator |
| US3353370A (en) * | 1966-04-12 | 1967-11-21 | Garrett Corp | Movable, closed-loop cryogenic system |
| US3360952A (en) * | 1966-06-28 | 1968-01-02 | Trane Co | Capacity controlled refrigeration system |
| US3415077A (en) * | 1967-01-31 | 1968-12-10 | 500 Inc | Method and apparatus for continuously supplying refrigeration below 4.2deg k. |
| US3850004A (en) * | 1973-06-27 | 1974-11-26 | Carpenter Technology Corp | Cryogenic helium refrigeration system |
| GB1477666A (en) * | 1974-05-03 | 1977-06-22 | Hymatic Eng Co Ltd | Cooling apparatus |
| US4002039A (en) * | 1975-08-28 | 1977-01-11 | The Bendix Corporation | Self-regulating cryostat |
| DE2738728A1 (en) * | 1977-08-27 | 1979-03-08 | Peter J Dipl Ing Schelauske | Electric motor driven compressor for refrigerator - has regulator for motor speed ensuring constant refrigerant flow rate |
| GB2085139A (en) * | 1980-10-10 | 1982-04-21 | Hymatic Engineering The Co Ltd | Cryogenic cooling apparatus |
-
1984
- 1984-12-19 GB GB8432059A patent/GB2168799B/en not_active Expired
-
1985
- 1985-12-18 FR FR8518756A patent/FR2580384A1/en active Pending
- 1985-12-18 DE DE19853544853 patent/DE3544853A1/en not_active Withdrawn
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0239375A2 (en) * | 1986-03-24 | 1987-09-30 | British Aerospace Public Limited Company | De-contaminated fluid supply apparatus and cryogenic cooling systems using such apparatus |
| EP0239375A3 (en) * | 1986-03-24 | 1988-11-17 | British Aerospace Public Limited Company | De-contaminated fluid supply apparatus and cryogenic cooling systems using such apparatus |
| FR2708093A1 (en) * | 1993-07-23 | 1995-01-27 | Air Liquide | Very low temperature refrigeration system. |
| US5499505A (en) * | 1993-07-23 | 1996-03-19 | L'air Liquide Societe Anonyme Pour L'etude Et L'exploitation Des Procedes Georges Claude | Helium refrigerator with compressor drive control |
| WO1996029551A1 (en) * | 1995-03-23 | 1996-09-26 | Ultra Electronics Limited | Cooler |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2580384A1 (en) | 1986-10-17 |
| GB2168799B (en) | 1989-05-17 |
| DE3544853A1 (en) | 1986-06-19 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19931219 |