Helium reliquefier for low vibration applications

Abstract

A reliquefier for low vibration applications having an inlet for receiving an amount of helium gas from an item of scientific equipment, a cryocooler having a first stage heat exchanger for cooling the amount of helium gas to between 40 and 60 K and a second stage heat exchanger having a series of precooling fins for cooling the amount of helium gas, and a condensing heat exchanger coupled to the second stage heat exchanger for liquifying the amount of helium. An outlet has a flexible tube extending from the condensing heat exchanger and a rigid tube coupled to the flexible tube that can return liquified helium back to the scientific equipment. The flexible tube is formed by an inner hose that is annularly corrugated and an outer hose that that is annularly corrugated and coaxial with the inner hose to provide for vibration dampening.

Description

TITLEHELIUM RELIQUEFIER FOR LOW VIBRATION APPLICATIONS BACKGROUND1. FIELD

[0001] The present disclosure relates to helium reliquefiers and, more specifically, to a design that can be used for low vibration applications.2. DESCRIPTION OF THE RELATED ART

[0002] Reliquifiers are used in connection with various scientific and analytical equipment to recover fluids used for cooling for superconducting components, such as helium. For example, a nuclear magnetic resonance NMR spectrometer is an analytical chemistry instrument used to characterize a wide variety of materials. The NMR spectrometer consists of a superconducting solenoid magnet producing magnetic fields up to 14 T. Superconductors are materials that have no electrical resistance when cooled below the material’s transition temperature. The magnets in NMR spectrometers are cooled with a bath of liquid helium to approximately 4.2 K. Typically the heat generated in an NMR spectrometer causes the liquid helium to boil off and the vapor is either released to atmosphere or captured and recompressed with ancillary equipment. Periodically users need to refill the NMR spectrometer with liquid helium, so the magnet remains cold. NMR spectrometers are passively cooled with liquid helium rather than actively cooled because the vibration from typical cryocooling solutions affects the accuracy of the measurements obtained with the spectrometer. Accordingly, there is a need in the art for a helium reliquefication approach does not provide vibrations that can affect the accuracy of the scientific equipment.BRIEF SUMMARY

[0003] The present invention provides a simple and low-cost reliquefier to recycle the liquid helium boiled off from vibration sensitive equipment, such as an NMR cryostat, to extend the time between liquid helium fills indefinitely and eliminate the need for users to purchase liquid helium. The present invention is capable of providing for continuous reliquefication with no impact on the measurements obtained with the equipment, such as the NMR spectrometer.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0004] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0005] FIG. 1 is a cross-section of a reliquefier according to the present invention.

[0006] FIG. 2 is a side view of a reliquefier according to the present invention.

[0007] FIG. 3 is a partial cross-section of a reliquifier coupled to vibration sensitive equipment according to the present invention.

[0008] FIG. 4 is a series of graphs of acceleration testing of an exemplary reliquefier in three axes using a Wilcoxen 731 A seismic accelerometer.

[0009] FIG. 5 is a series of graphs of vibration improvement using a reliquefier according to the present invention.DETAILED DESCRIPTION

[0010] Referring to the figures, wherein like numerals refer to like parts throughout, there is seen in FIG. 1, a helium reliquefier 100 for use with vibration sensitive equipment 15, such as an NMR spectrometer and associated cryostat. Reliquefier 100 may be used to provide a closed cycle unit that convers a wet cryostat into a dry cryostat. Helium liquefaction rates of 2-25 L / day with recondensing rates of 0.2 - 1.3 W are possible with reliquefier 100 without interference with the operation of vibration sensitive equipment 15.

[0011] Reliquefier 100 comprises a two-stage pulse tube cryocooler with remote rotary valve 11. The expander of cryocooler is enclosed in a cryostat of reliquefier 100 that includes an outer vacuum vessel 1, an inner helium dewar 3, and a radiation shield 7. Pulse tube cryocooler additionally includes heat exchangers for liquefying helium gas provided to reliquefier 100. A first stage heat exchanger 4 cools the helium gas to between 40 and 60 K. Precooling fins 5 are coupled to the 2ndstage regenerator to cool the helium gas further before liquefying on a condensing heat exchanger 6 coupled to the end of the 2ndstage regenerator.

[0012] Referring to FIG. 2, the flow of helium in the pulse tube cryocooler is controlled by a remote rotary valve 11, which is connected to the pulse tube cryocooler by a flexible stainless-steel hose 12 of at least 36 inches in length. Flexible stainless-steel hose 12 helps to isolate reliquefier 100 from the vibration of rotary valve 11, which is the only moving part of reliquefier 100. Pulse tube cryocooler uses remote expansion tanks 14 to reduce the overall height of reliquefier 100.

[0013] As seen in FIG. 1, liquid helium is transferred from reliquefier 100 to the equipment 15, such as an NMR spectrometer having a cryostat liquid helium bath, by a flexible stainless steel transfer tube 8 / 9 and a rigid tube 10, which may be connected to the equipment using the helium, such as by inserting rigid tube 10 into the fill port of the equipment, e.g., the NRM cryostat. Flexible transfer tube 8 / 9 isolates the equipment, such as the NMR spectrometer, from the vibration of the pulse tube cryocooler. Flexible transfer tube8 / 9 consists of two 304 stainless steel corrugated hoses that are coaxial. The outer hose 8 provides the housing for the vacuum insulation required to reduce ambient heat loads to the liquid helium and the inner hose 9 contains the liquid helium. Both hoses 8, 9 are annularly corrugated and compressed to at least 11 corrugations per inch to provide high flexibility. The length of the flexible hose is 6 inches in length to minimize thermal losses and improve vibration isolation.

[0014] Referring to FIG. 3, any helium vapor that is boiled off from equipment 15 travels through a flexible stainless steel vapor return line 16 and back into the inlet port 13 reliquefier 100 for reliquification as described above.

[0015] Referring to FIG. 4, the measurement of acceleration in three axes with a Wilcoxen 731 A seismic accelerometer demonstrates that an exemplary reliquefier 100 would not produce an amount of vibration that would interfere with the operation of equipment 15.

[0016] Referring to FIG. 5, reliquifier 100 demonstrated vibration improvements relative to conventional designs that allow reliquifier 100 to be used with vibration sensitive equipment 15, such as an NMR spectrometers.

[0017] An exemplary reliquifier 100 installed in a 600 MHz NMR spectrometer was operated for 2 months without loss of helium and did not provide any detectable vibrations in a sample spectra of a variety of liquid samples.

Claims

CLAIMSWhat is claimed is:

1. A reliquefier, comprising: an inlet for receiving an amount of helium gas; a cryocooler having a first stage heat exchanger for cooling the amount of helium gas to between 40 and 60 K and a second stage heat exchanger having a series of precooling fins for further cooling the amount of helium gas; a heat exchanger coupled to the second stage heat exchanger for receiving the amount of helium gas and condensing the amount of helium gas to provide an amount of liquified helium; an outlet having a flexible tube extending from the heat exchanger; and a rigid tube coupled to the flexible tube.

2. The reliquefier of claim 1, wherein the flexible tube comprises an inner hose that is annularly corrugated and an outer hose that that is annularly corrugated and coaxial with the inner hose.

3. The reliquefier of claim 2, wherein the inner hose is coupled to the condensing heat exchanger to receive the amount of liquified helium.

4. The reliquefier of claim 3, wherein the outer hose is separated from the inner hose by vacuum.

5. The reliquefier of claim 4, wherein the rigid tube is coupled to a liquid helium bath of a piece of equipment.

6. The reliquefier of claim 5, wherein the piece of equipment is a nuclear magnetic resonance cryostat.

7. The reliquefier of claim 4, further comprising a vessel surrounding the cryocooler and heat exchanger.

8. The reliquefier of claim 7, further comprising a dewar enclosing the cryocooler.

9. The reliquefier of claim 8, further comprising a radiation shield positioned in the vessel between the vessel and the heat exchanger.

10. The reliquefier of claim 9, further comprising a rotary valve positioned remotely from the vessel and connected to the inlet by a hose.

11. The reliquefier of claim 10, further comprising an expansion tank positioned externally of the vessel.

12. A method of providing helium reliquification without interfering with a piece of equipment, comprising the steps of: providing a reliquefier having an inlet for receiving an amount of helium gas, a cryocooler having a first stage heat exchanger for cooling the amount of helium gas to between 40 and 60 K and a second stage heat exchanger having a series of precooling fins for further cooling the amount of helium gas, a heat exchanger coupled to the second stage heat exchanger for receiving the amount of helium gas and condensing the amount of helium gas to provide an amount of liquified helium, and an outlet having a flexible tube extending from the condensing heat exchanger; coupling a liquid helium back of the piece of equipment to the flexible tube with a rigid tube.

13. The method of claim 12, further comprising the step of operating the reliquefier to provide a liquefaction rates of 2 to 25 liters per day with recondensing rates of 0.2 - 1.3 W.

14. The method of claim 13, wherein the piece of equipment comprises a nuclear resonance magnetic spectrometer.

15. The method of claim 4, wherein, operation of the reliquefier does not produce any detectable vibrations that would interfere with the accuracy of the resonance magnetic spectrometer.

Images