GB2431982A - Cryostat Heat Influx Reduction - Google Patents

Cryostat Heat Influx Reduction Download PDF

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Publication number
GB2431982A
GB2431982A GB0522608A GB0522608A GB2431982A GB 2431982 A GB2431982 A GB 2431982A GB 0522608 A GB0522608 A GB 0522608A GB 0522608 A GB0522608 A GB 0522608A GB 2431982 A GB2431982 A GB 2431982A
Authority
GB
United Kingdom
Prior art keywords
turret
cryostat
cryogen
entrant
baffle
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
Application number
GB0522608A
Other versions
GB2431982B (en
GB0522608D0 (en
Inventor
Norbert Huber
Huaiyu Pan
Patrick William Retz
Stephen Paul Trowell
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Siemens AG
Siemens Magnet Technology Ltd
Original Assignee
Siemens AG
Siemens Magnet Technology Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Siemens AG, Siemens Magnet Technology Ltd filed Critical Siemens AG
Priority to GB0522608A priority Critical patent/GB2431982B/en
Publication of GB0522608D0 publication Critical patent/GB0522608D0/en
Priority to CNA2006101433424A priority patent/CN1971773A/en
Publication of GB2431982A publication Critical patent/GB2431982A/en
Application granted granted Critical
Publication of GB2431982B publication Critical patent/GB2431982B/en
Expired - Fee Related legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F17C13/005—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure
    • F17C13/006—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure for Dewar vessels or cryostats
    • F17C13/007—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure for Dewar vessels or cryostats used for superconducting phenomena
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C3/00—Vessels not under pressure
    • F17C3/02—Vessels not under pressure with provision for thermal insulation
    • F17C3/08—Vessels not under pressure with provision for thermal insulation by vacuum spaces, e.g. Dewar flask
    • F17C3/085—Cryostats
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C13/00—Details of vessels or of the filling or discharging of vessels
    • F17C13/005—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure
    • F17C13/006—Details of vessels or of the filling or discharging of vessels for medium-size and small storage vessels not under pressure for Dewar vessels or cryostats
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2205/00—Vessel construction, in particular mounting arrangements, attachments or identifications means
    • F17C2205/03—Fluid connections, filters, valves, closure means or other attachments
    • F17C2205/0302—Fittings, valves, filters, or components in connection with the gas storage device
    • F17C2205/0352—Pipes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/01—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the phase
    • F17C2223/0146—Two-phase
    • F17C2223/0153—Liquefied gas, e.g. LPG, GPL
    • F17C2223/0161—Liquefied gas, e.g. LPG, GPL cryogenic, e.g. LNG, GNL, PLNG
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2223/00—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel
    • F17C2223/03—Handled fluid before transfer, i.e. state of fluid when stored in the vessel or before transfer from the vessel characterised by the pressure level
    • F17C2223/033—Small pressure, e.g. for liquefied gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0337—Heat exchange with the fluid by cooling
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2227/00—Transfer of fluids, i.e. method or means for transferring the fluid; Heat exchange with the fluid
    • F17C2227/03—Heat exchange with the fluid
    • F17C2227/0367—Localisation of heat exchange
    • F17C2227/0369—Localisation of heat exchange in or on a vessel
    • F17C2227/0372—Localisation of heat exchange in or on a vessel in the gas
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2265/00—Effects achieved by gas storage or gas handling
    • F17C2265/03—Treating the boil-off
    • F17C2265/032—Treating the boil-off by recovery
    • F17C2265/033—Treating the boil-off by recovery with cooling
    • F17C2265/034—Treating the boil-off by recovery with cooling with condensing the gas phase
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F17—STORING OR DISTRIBUTING GASES OR LIQUIDS
    • F17C—VESSELS FOR CONTAINING OR STORING COMPRESSED, LIQUEFIED OR SOLIDIFIED GASES; FIXED-CAPACITY GAS-HOLDERS; FILLING VESSELS WITH, OR DISCHARGING FROM VESSELS, COMPRESSED, LIQUEFIED, OR SOLIDIFIED GASES
    • F17C2270/00—Applications
    • F17C2270/05—Applications for industrial use
    • F17C2270/0527—Superconductors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/20—Arrangements or instruments for measuring magnetic variables involving magnetic resonance
    • G01R33/28—Details of apparatus provided for in groups G01R33/44 - G01R33/64
    • G01R33/38—Systems for generation, homogenisation or stabilisation of the main or gradient magnetic field
    • G01R33/3804—Additional hardware for cooling or heating of the magnet assembly, for housing a cooled or heated part of the magnet assembly or for temperature control of the magnet assembly
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F6/00—Superconducting magnets; Superconducting coils
    • H01F6/04—Cooling

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Containers, Films, And Cooling For Superconductive Devices (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)

Abstract

A cryostat has a liquid cryogen 22 and a gaseous atmosphere 18 composed of gas boiled off from the liquid cryogen. The cryostat vessel (10 fig 1) has a non-vertical re-entrant turret 12, the lower end of which has a horizontal surface 32 at the boundary between the lower end 17 of the re-entrant turret and the gaseous atmosphere within the cryostat. The horizontal surface may be provided by an associated baffle 30, at the lower end of the turret, and the baffle may be composed of a material having a lower thermal and electrical conductivity than the remainder of the turret. The cryostat may be within a magnetic resonance imaging (MRI) system or nuclear magnetic resonance (NMR) imaging system, and the cryogen may be liquid helium. The design of the cryogen turret, and in particular the horizontal surface, is used to reduce circulating convective currents (14 fig 1), termed 'backflow'.

Description

<p>REDUCTION OF HEAT INFLUX THROUGH ACCESS TURRET</p>
<p>The present invention relates to Cryostats, particularly cryostats containing a liquid cryogen and a gaseous atmosphere composed of gas boiled off from the liquid cryogen, which comprise a non-vertical, re-entrant turret.</p>
<p>Such cryostats are employed to retain superconducting magnet coils at superconducting temperatures by full or partial immersion in a cryogen fluid. Commonly, the cryogen fluid is liquid helium, which boils at a temperature of about 4 K, and holds immersed magnet coils at that temperature. Such superconducting magnet coils are typically employed to generate very strong magnetic fields in magnetic resonance imaging (MRI) or nuclear magnetic resonance (NMR) imaging.</p>
<p>It is required to minimise the heat influx from the turret into the cryostat.</p>
<p>Heat influx will cause liquid cryogen to boil. This boiled off cryogen must either be recondensed by active refrigeration, or vented and periodically replenished. Both of these options are costly, and much effort is expended in developing arrangements to reduce heat influx into the cryogen vessel.</p>
<p>The present invention addresses the reduction of heat influx into a cryogen vessel.</p>
<p>The magnet coils are energised by passing current through the turret components. This produces significant heat in the turret that temporarily increases the heat flux into the cryogen vessel. The warm gas generated in this way can contribute to the risk of a magnet quenching during energisation.</p>
<p>This invention minimises the heat transported into the cryogen vessel from the turret during energisation, thereby reducing the risk of magnet quench.</p>
<p>Fig. 1 schematically illustrates a conventional cryostat. A cryogen vessel is usually retained within an outer vacuum chamber, with thermal shields, and possibly also solid insulation, placed in a vacuum space between the cryogen vessel and the outer vacuum container. The outer vacuum container, shields and solid insulation are well known in themselves, and are not illustrated in Fig. 1.</p>
<p>A turret 12 is conventionally provided, to allow access to the cryogen vessel for cryogen filling and venting, for current injection to magnet coils (not illustrated) housed within the cryogen vessel, and potentially other purposes. The turret 12 is essentially a continuous tubular element extending from the exterior of the cryostat to the cryogen vessel. It is one of the most significant paths of heat transfer into the cryogen vessel.</p>
<p>Various techniques are typically employed to reduce the heat influx through the turret, such as by active refrigeration of the turret, and the use of materials of low thermal conductivity in the construction of the turret.</p>
<p>Additionally, it is known to increase the length of the access tube beyond that strictly necessary, in order to further benefit from a low thermal conductivity of the material of the turret. In order to avoid excessive height gain of the cryostat as a whole, such turrets may be arranged as re-entrant turrets -that is, the lower end of the turret projects into the cryogen vessel rather than terminating at the surface of the cryogen vessel. In order to further reduce the overall height of the cryostat, the turret may be inclined at an angle to the vertical. The turret 12 shown in Fig. 1 is such a non-vertical, re-entrant turret.</p>
<p>There are two situations of heat influx which may be considered. These are static and dynamic heat influx. The static heat influx is the situation with the system in normal operation. The dynamic heat influx is the situation which arises during energisation (ramping) of the magnet coils. In the dynamic situation, electrical current is conducted through the material of the turret, causing heating of the turret and production of warm, boiled off gas. The present invention is particularly useful in the case of dynamic heat influx.</p>
<p>During magnet ramping, the turret is the most important source of heat into the cryogen vessel. For a fixed current lead turret, the turret surfaces become relatively hot, such as of the order of 150 K, since the material of the turret serves as a conductor of electrical current. This heat is known to be transported to superconducting magnet coils housed in the cryostat by conduction in electrical current leads and convection of cryogen gas in the turret, through radiation from the turret surfaces, and through convection within the gas in the cryogen vessel. This is particularly problematic for superconducting magnet coils which are only partially immersed in liquid cryogen.</p>
<p>The present inventors have identified an additional mode of heat transport from the turret into the cryogen vessel, which is illustrated in Fig. 1. The cryogen vessel 10 of Fig. I includes a typical, right cylindrical turret 12.</p>
<p>The turret is non-vertical and re-entrant. The angle between the plane of the lower end 17 of the re-entrant turret and the horizontal is labelled 0.</p>
<p>Convective currents 14, 16 circulate at the base of the turret 12, transporting cryogen gas into contact with the warm surface of turret 12, then directly into the gaseous atmosphere 18 of the cryogen vessel 10. This effect is named backflow, and is caused by thermal density changes of the gas causing free convection, it is greatest for large angles 0. Such backfiow convection occurs even when the pressure P2 within the cryogen vessel is greater than the pressure P1 outside it. For all non-vertical fixed-current lead turrets 12 with positive pressure in the cryogen vessel, backflow 14 from the turret base opposes the main gas flow 20 caused by boiling of the liquid cryogen 22 and injects hot gas into the cryogen vessel.</p>
<p>It may not be possible to manufacture a fixed-current lead high-current turret, such as those designed to carry electrical currents in excess of 700A without inducing excessive cryogen gas, or magnet coil, temperatures without consideration of the effect of backflow heating. The present invention addresses the issue of backilow 14, and proposes a modification to the cryostat to reduce the incidence and effect of backflow 14.</p>
<p>The present invention accordingly provides a cryostat containing a liquid cryogen and a gaseous atmosphere composed of gas boiled off from the liquid cryogen, the cryos tat comprising a non-vertical, re-entrant turret. A lower end of the re-entrant turret is configured to create a substantially horizontal surface at the boundary between the lower end of the re-entrant turret and the gaseous atmosphere within the cryostat. The substantially horizontal surface may be provided by provision of a suitable baffle at the lower end of the re-entrant turret.</p>
<p>The above, and further, objects, characteristics and advantages of the present invention will be described with reference to certain embodiments, given by way of examples only, together with the accompanying drawings wherein: Fig. 1 illustrates a conventional cryogen vessel comprising a non-vertical re-entrant turret; and Fig. 2 illustrates a cryogen vessel comprising a non-vertical re-entrant turret adapted according to the present invention.</p>
<p>Fig. 2 shows an example of backflow minimised according to an embodiment of the present invention. According to the present invention, the lower end of the re-entrant turret is configured so as to create a substantially horizontal surface 32 at the boundary between the turret 12 and the gaseous atmosphere 18 of the cryogen vessel 10, to minimise 0. In the illustrated embodiment, this is achieved by providing a baffle 30 at the lower end 17 of the turret 12. The baffle 30 is configured so as to create a substantially horizontal surface 32 at the boundary between the turret 12 and the gaseous atmosphere 18 of the cryogen vessel 10, to minimise 0.</p>
<p>Use of such a turret, optionally employing a baffle, enables turrets 12 to enter the cryogen vessel 10 at angles other than the vertical, to suit overall cryostat design. This is potentially useful for top-mounted turrets, which are not necessarily vertical, and is particularly useful for cryostats which utilise a side-mounted turret.</p>
<p>The backilow effect has been predicted by computational fluid dynamics modelling of the current ramping conditions for a conventional cryostat arrangement for holding a superconducting magnet. The backflow effect 14, 16 has been shown to account for elevated temperatures in the cryogen gas 18 at the top of the vessel 10, with predictions in close agreement with gas temperature measurements made on conventional cryostat arrangements. The present invention has been shown to reduce backfiow to a sufficient extent to avoid high temperatures within the cryogen vessel.</p>
<p>The present invention provides at least some of the following advantages: * Backflow is minimised by a substantially horizontal surface 32 at the lower end 17 of the turret 12, thereby reducing heat influx into the cryogen gas atmosphere.</p>
<p>* The risk of quench during energisation is reduced for magnets housed in cryostats with turrets which are not mounted vertically.</p>
<p>Future designs that require high current in association with a non-vertical turret must include consideration of backflow and will benefit from the use of the present invention, so that the gas temperature may remain sufficiently low during current ramp to minimise quench risk and enable magnet operation.</p>
<p>In principle, the present invention may be applied to all cryostats incorporating a non-vertical service neck, not only for those used for cooling magnet coils for MRI or NMR imaging applications, by providing a horizontal boundary surface 32 between the turret 12 and the cryogen vessel inner volume 18. The present invention may particularly be used with a liquid helium cryogen providing cooling at a temperature of about 4K, but may be used with other fluid cryogens.</p>
<p>Where a baffle is used, the material of the baffle is preferably of lower electrical and thermal conductivity than the material of the remainder of the re-entrant turret. This is to avoid heating of the baffle due to the passage of electric current through it, and to reduce the conduction of heat down the baffle towards the magnet, thereby avoiding increasing the risk of magnet quench.</p>
<p>The present invention accordingly provides an advantageous configuration of the lower end of the service turret which minimises quench risks associated with warm cryogen gas by reducing backflow from the turret into the cryogen vessel..</p>

Claims (1)

  1. <p>CLAIM S</p>
    <p>1. A cryostat containing a liquid cryogen and a gaseous atmosphere composed of gas boiled off from the liquid cryogen, the cryostat comprising a non-vertical, re-entrant turret, characterised in that a lower end of the re-entrant turret is configured as a substantially horizontal surface at the boundary between the lower end of the reentrant turret and the gaseous atmosphere within the cryostat.</p>
    <p>2. A cryostat according to claim I wherein the lower end of the re-entrant turret comprises a baffle configured to create the substantially horizontal surface, at the boundary between a lower end of the baffle and the gaseous atmosphere within the cryostat.</p>
    <p>3. A cryostat according to claim 1 or claim 2, wherein the baffle is composed of a material having a lower thermal and electrical conductivity than the remainder of the re-entrant turret.</p>
    <p>4. A cryostat according to any of claims 1-3, wherein the liquid cryogen is liquid helium.</p>
    <p>5. A cryostat substantially as described and/or as illustrated in Fig. 2 of the accompanying drawing.</p>
    <p>6. A magnetic resonance imaging (MRI) or nuclear magnetic resonance (NMR) imaging system comprising a cryostat according to any preceding claim.</p>
GB0522608A 2005-11-05 2005-11-05 Reduction of heat influx through access turret Expired - Fee Related GB2431982B (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB0522608A GB2431982B (en) 2005-11-05 2005-11-05 Reduction of heat influx through access turret
CNA2006101433424A CN1971773A (en) 2005-11-05 2006-11-06 Cryostat heat influx reduction

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB0522608A GB2431982B (en) 2005-11-05 2005-11-05 Reduction of heat influx through access turret

Publications (3)

Publication Number Publication Date
GB0522608D0 GB0522608D0 (en) 2005-12-14
GB2431982A true GB2431982A (en) 2007-05-09
GB2431982B GB2431982B (en) 2008-06-18

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GB0522608A Expired - Fee Related GB2431982B (en) 2005-11-05 2005-11-05 Reduction of heat influx through access turret

Country Status (2)

Country Link
CN (1) CN1971773A (en)
GB (1) GB2431982B (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4221834A (en) * 1975-11-17 1980-09-09 Develco, Inc. Superconductive magnetic shield and method of making same
JPS61104681A (en) * 1984-10-29 1986-05-22 Hitachi Ltd Cryostat
US4625520A (en) * 1984-09-05 1986-12-02 Hitachi, Ltd. Superconducting device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4221834A (en) * 1975-11-17 1980-09-09 Develco, Inc. Superconductive magnetic shield and method of making same
US4625520A (en) * 1984-09-05 1986-12-02 Hitachi, Ltd. Superconducting device
JPS61104681A (en) * 1984-10-29 1986-05-22 Hitachi Ltd Cryostat

Also Published As

Publication number Publication date
CN1971773A (en) 2007-05-30
GB2431982B (en) 2008-06-18
GB0522608D0 (en) 2005-12-14

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Effective date: 20091105