Apparatus and method for rapidly freezing small objects

Abstract

A compact desktop gas liquefaction system having a gas generator, a cooling unit having a Stirling, pulse-tube or Stirling-pulse-tube cooler, and an insulated container to receive the liquefied gas. The system may be used to produce liquid nitrogen, oxygen, argon, natural gas, or air. The insulated container can be quickly disengaged from the gas liquefaction system, thereby minimizing the risk associated with handling liquefied gases. This compact liquefier allows for on-demand and on-site cryogen generation. The system provides a condenser surrounded by an evacuated space for greater efficiency of operation in a limited space.

Description

FIELD OF THE INVENTION

This invention relates generally to the field of gas liquefaction systems.

BACKGROUND OF THE INVENTION

Cryogenics (technology that uses very low temperatures) is already popular in applications such as high-end medical equipment, scientific research, food processing and semiconductor industries. Liquid gas, such as liquid nitrogen (“LN₂”), has enormous potential for a broader application of this technology in various new marketplaces and industries.

LN₂ is used in many commercial and medical applications, including: medical and veterinary treatment, research and laboratory applications; education; machinery shops; and, obviously, refrigeration. One limitation in applying cryogenic technology more broadly is the limitations of the current supply system of LN₂, which is generally available from industrial gas suppliers only for customers who purchase large amounts and live in urban areas. This is because the supply of LN₂ suffers from a host of difficulties. LN₂ is produced at an industrial site and can be delivered to a purchaser, generally within two days of placing an order (provided a sufficiently large quantity is ordered, e.g. 100 litres). Once the LN₂ has been delivered, it must be stored. The longer it is stored, (and the further the delivery site is from the industrial site) the more LN₂ is lost through boil off. Storage of large amounts of LN₂ presents a hazard and may require transfer to smaller containers for handling.

These problems point to the need for a means of liquid gas supply that is readily available on site, and doesn't suffer from the drawbacks associated with transfer and storage of large quantities of liquid gas.

SUMMARY OF THE INVENTION

A small-scale gas liquefaction system is provided that can be used in, for example, medical office, restaurant and bar, and machine shop settings. The liquefaction system requires little or no special set up and can be simply plugged into a standard (single-phase 115 VAC) wall outlet. Depending on the specific embodiment, it will produce 1-20 liters of liquefied gas per day. It provides an economical option for users of relatively small quantities of, for example, LN₂ to obtain liquefied gas.

The invention comprises a gas generator, a cooling unit having a stirling, pulse-tube or stirling-pulse-tube cooler, and an insulated container below said cooling unit to receive the liquefied gas. The liquefied gas falls from the cooling unit directly into an insulated container or dewar, which is connected to the cooling unit with a gas-tight seal. The insulated container can be quickly and easily disengaged from the cooling unit, thereby eliminating the need to transfer the liquefied gas to portable containers. The risks associated with handling the liquefied gases are thereby minimized.

The aforesaid components are sized and configured to allow the liquefaction system to be located on a desk or counter top. Although in the preferred embodiment the invention is used to produce LN₂ from air, alternate embodiments may be used to produce liquid oxygen, natural gas, argon, or air.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself both as to organization and method of operation, as well as additional objects and advantages thereof will become readily apparent from the following detailed description when read in connection with the accompanying drawings. Every drawing does not show every element of the invention, because in some drawings it is necessary to omit selected elements or features in order to clearly show the elements discussed in the drawing. The drawings are not necessarily to scale.

FIG. 1 shows the major components of the invention;

FIG. 2 is a side view of the cooling unit with the insulated container;

FIG. 3 is a cut-away view of the cooling unit elements and the insulated container.

FIG. 4 is a diagram of an embodiment of the invention employing a liftable platform;

FIG. 5 is an elevation view of the left side of the embodiment of FIG. 4, also showing a vacuum means attached to the condenser;

FIG. 6 is a partial view of the cooling unit and the top of the insulated container unit showing the coupling thereof;

FIG. 7 is elevation view of the embodiment of FIG. 4 in which the lift platform has been lowered to remove the insulated container from its connection to the cooling unit;

FIG. 8 is an elevation view of the invention showing an extraction line for withdrawing liquid gas from the container and also showing a liquid level control mechanism.

DETAILED DESCRIPTION WITH REFERENCE TO THE FIGURES

Referring to FIG. 1, a first embodiment of a gas liquefier 10 according to the present invention is shown. The gas liquefier 10 has a gas generator 20, a cooling unit 30, preferably having a stirling, pulse-tube or stirling-pulse-tube cooler, and an insulated container 40.

The invention is not limited to the type of gas liquefied, but in the examples provided for disclosure purposes the gas generator 20 is a nitrogen gas generator that separates nitrogen gas from the air. Suitable gas generators are available from Compressed Gas Technologies Inc. (Windsor, ON, Canada) and System Instruments Co., Ltd. (Tokyo, Japan). In the various alternate embodiments the gas generator will generally have to filter the air to remove dust, etc., and include means for removing water vapor from the gas before it is cooled. In alternate embodiments the gas generator 20 may provide, by way of example, oxygen gas, natural gas, or air to the cooling unit 30 for liquefaction. Commercially available gas generators currently come with physical dimensions as small as 27.5 cm wide, 40 cm deep and 55 cm high.

In the cooling unit 30 the gas from the gas generator 20 is cooled by the stirling, pulse-tube or stirling-pulse-tube cooler to a temperature below the liquefaction temperature for that gas. Suitable coolers are available from Sunpower, Inc. (Ohio) and Smach Co., Ltd. (Osaka, Japan). The liquified gas falls from the cooling unit into the interior of an insulated container 40 (e.g. a dewar). It is not necessary that the gas be pressurized (relative to the ambient pressure). However, to avoid contamination by reverse flow of air, the pressure inside the insulated container 40 is maintained slightly higher than atmospheric pressure.

FIG. 2 and FIG. 3 show side and cut-away views of the cooling unit 30 and insulated container 40. The cooling unit 30 is made up of a stirling, pulse-tube or stirling-pulse-tube cooler 32 housed in an air cooling shroud 38. Fan 44 forces air through the cooling shroud 38 to dissipate heat generated at the hot end of the Stirling, pulse-tube, or Stirling-pulse-tube cooler 32. The cold end of the Stirling, pulse-tube, or Stirling-pulse-tube cooler 32 is connected to a condenser 36 which is housed in a vacuum enclosure 34. Liquefied gas flows down the conduit 42 from the condenser 36 into the interior 55 of insulated container 40.

Gas may be fed to the cooling unit 30 and insulated container 40 from the gas generator 20 in a number of ways. In the embodiment of FIGS. 1, 2, and 3, gas from the gas generator 20 enters the top of the insulated container 40 at a connection point in the neck 52. From the insulated container 40 the gas flows up the conduit 42 to the condenser 36 and then the liquefied gas drops back down the conduit 42 to the insulated container. In this sense the conduit 42 is a two-way conduit. This embodiment requires a gas tight connection between the insulated container 40 and the cooling unit 30.

Referring to FIG. 1, in the preferred embodiment the invention is powered by electricity and can be simply plugged into a conventional electrical outlet, and is sufficiently compact to sit conveniently on a desktop. By way of example, the preferred gas generator is of the type that fits within an envelope of 30 cm in width by 45 cm in depth by 60 cm in height, or approximately 81 liters. The cooling unit and the container described herein, when combined, fit within an envelope that has a volume of approximately 21 liters. Thus, the combined volume of the gas generator, cooling unit, and container is approximately 102 liters (78 cm×9 cm×30 cm), which is sufficiently small to fit upon a lab counter or desktop.

Referring to FIG. 2, and FIG. 3, vacuum enclosure 34 insulates and isolates the cold end of the stirling, pulse-tube or stirling-pulse-tube cooler 32 and the condenser 36 from the atmosphere. There are two ways to remove liquefied gas from the insulated container. In the preferred embodiments, the insulated container 40 may be detached from the system 10 to drain the liquefied gas. Alternatively, the insulated container 40 could be essentially a holding tank, from which liquefied gas could be drained via a drain port (e.g. like a water tap on a sink). In either case, the gas liquefaction system 10 is isolated from the atmosphere except for the connection to the gas supply or gas generator 20.

In one preferred embodiment, the insulated container 40 has a gas tight sealing mechanism such that when it is disconnected from the cooling unit 30, the liquefied contents are completely isolated from the environment. In such embodiments, the insulated container 40 has a pressure release mechanism. The interior of the insulated container 40 also opens to the air once disconnected from the cooling unit 30.

Referring to FIG. 4, an alternative preferred embodiment of the gas liquefaction system has the insulated container 40 supported by a platform 29 that can be raised and lowered by one or more pivotal arms 28 controlled by a lever 57. This permits the container to be raised into position to be filled and lowered into position for accessing the container or removing it from the apparatus. The platform 29 slides over four guide posts 33 one on each of the four corners. (Only two guide posts are visible, the front left post having been removed from the drawing for clarity). These guide posts also support a second platform 31 on which is mounted the cooling unit 30. The gas generator 20 is shown. Two access ports 22 and 24 can also be used to obtain access to the interior 55 of the container 40.

Referring to FIG. 5, the gas supply line from the gas generator (not shown) can be coupled either to the interior 55 of the insulated container 40 by means of gas inlet 21, or to the cooling unit 30, and preferably directly to condenser 37, by means of gas inlet 39. An evacuation outlet 43 permits evacuation of chamber 35 surrounding the condenser by means of a vacuum pump 66. An air shroud 47 surrounds and insulates the cooler 49. A fan 51 cools the hot end of the cooler. Cooling fins 45 also provide for heat dissipation from the hot end of the cooler 49.

Referring to FIG. 6, the top of the insulated container couples to an orifice 62 in the bottom of the cooling unit by means of elongated tube 61 surrounding the conduit 42. O-rings 23A seal the elongated tube to the cooling unit orifice. O-rings 23B seal the upper portion of the container to the lower portion of the cooling unit.

As noted previously, the gas supply line can couple the gas generator either to gas inlet 39 leading to the condenser 37 or to gas inlet 21 leading to the interior of the insulated container 40. If the gas in introduced into the interior of the container, it flow upwards into the cooling unit 30 by means of conduit 42. The liquefied gas then flows back through conduit 42 and into the interior of the container. If the gas is introduced directly to the condenser by inlet 39, the liquefied gas then flows through conduit 42 into the interior of the container.

Referring to FIG. 7, the insulated container 40 has been lowered by rotating pivoting arm 57 from the vertical position shown in FIG. 5 to a horizontal position so that the container has been lowered sufficiently to be pulled away from the conduit 42 in order to access the liquefied gas in the container.

The embodiment shown in FIG. 8 is similar to the embodiment of FIG. 5. Insulated container 40 has a foam insulated extraction line 25, a valve or solenoid 60 controlling flow of liquid gas through the extraction line, and an insulated vacuum jacketed portion 25C of the extraction line. This embodiment permits extraction of liquid gas from the container without moving the container. Extraction line 25 has a portion 25A external to container 40 and a portion 25B internal to the container. Extraction of the liquid gas from the container is accomplished, for instance, by opening the valve and connecting a suction or vacuum source to the opening of the extraction line 25A.

A the preferred embodiment the gas liquefaction system includes means for monitoring the liquid level in the insulated container 40 to avoid over-filling such that, when the liquid reaches a predetermined level, the cooling unit 30 and/or gas supply 20 are turned off or disconnected from the insulated container 40. FIG. 8 shows such a mechanism. A liquid level controller such as a Teragon LC10 LN₂ level controller is employed as shown. Level sensors 64A and 64B are placed in the container 40. The sensors are connected to controller logic circuit device 63, which, in turn, is connected to a valve or solenoid 65 that controls flow of gas into the cooling unit through gas inlet 39. Additionally or alternatively the controller logic device can control the power source of the gas generator. When the fluid gas falls below sensor 64B, the gas generator is activated and the valve 65 is opened. When the liquid gas level reaches sensor 64A, the gas generator is shut off and the valve 65 is closed.

The gas liquefaction system disclosed herein has many useful applications. It can be used in a medical setting where, for example, small amount of LN₂ is often used to treat a number of medical conditions (also known as cryotherapy). This type of treatment is used for conditions, such as:

tumors or cancer, especially those of the skin, cervix, eye, brain, prostate, and liver cancer;

certain early changes in the skin that might signal possible cancer;

actinic keratosis, a skin condition caused by sun exposure, can be treated with cryotherapy;

cervical dysplasia, or abnormal precancerous cells in a woman's cervix that can lead to cancer of the cervix;

warts, including genital warts from human papilloma virus;

other common skin lesions, such as skin tags, hemangiomas, or seborrheic keratoses;

bleeding during standard surgery;

The gas liquefaction system can also be used to quickly freeze, for example, cocktail and beer glasses. It can also be used in mechanical settings or machine shops, where metal parts can be quickly cooled in order make them fit together.

Accordingly, while this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention as herein disclosed.

Claims

1. A gas liquefaction system for producing liquefied gas from a gas, said gas liquefaction system comprising: a) a gas generator (20) for generating the gas;b) a cooling unit (30) for liquefying the gas, said cooling unit comprising: i) a cooler (49);ii) a condenser (37) wherein gas generated by said gas generator is cooled in said condenser sufficiently to liquefy the gas;iii) a vacuum means (66); and,iv) an evacuation chamber (35) surrounding said condenser, said evacuation chamber being in communication with said vacuum means, wherein said vacuum means is operative for evacuating said evacuation chamber whereby a vacuum is produced around said condenser;c) a gas inlet (21, 39) in fluid communication with said gas generator and with one of said interior of said container and said cooling unit;d) a container (40) for receiving and holding the liquefied gas, said container having an interior (55); and,e) a conduit (42) connecting said cooling unit to said interior of said container.

2. The gas liquefaction system of claim 1, wherein said gas inlet conducts the gas from said gas generator to said interior of said container, whereby said conduit conducts the gas from said interior of said container to said cooling unit and said conduit also conducts the liquefied gas back into said interior of said container.

3. The gas liquefaction system of claim 1, wherein said gas inlet conducts gas from said gas generator to said cooling unit, whereby the gas generated by said gas generator flows through said gas inlet an into said cooling unit and the liquefied gas flows through said conduit and into said interior of said container.

4. The gas liquefaction system of claim 3, wherein said gas inlet is in direct communication with said condenser.

5. The gas liquefaction system of claim 1, wherein said cooling unit is one of a Stirling, a pulse-tube, or a Stirling-pulse-tube cooler.

6. The gas liquefaction system of claim 1, configured to be sufficiently small to be positioned on a desktop.

7. The liquefaction system of claim 1, wherein said cooling unit and said gas generator combined fit within a total volume of no more than approximately 102 liters.

8. The gas liquefaction system of claim 1, wherein said container is coupled to said cooling unit.

9. The gas liquefaction system of claim 8, wherein the coupling of said container to said cooling unit is accomplished by means of an elongated tube (61) surrounding said conduit and coupled to an orifice (62) in said cooling unit.

10. The gas liquefaction system of claim 9 wherein said elongated tube is sealed to the orifice of said cooling unit by at least one O-ring (23A).

11. The gas liquefaction system of claim 8, wherein said container can be disconnected from and reconnected to said cooling unit by lowering and raising, respectively, said container relative to said cooling unit.

12. The gas liquefaction system of claim 1 further comprising: a) a platform (29) for supporting said container;b) a raising and lowering means (28, 29, 33, 57) for raising and lowering said platform whereby raising said platform by said raising and lowering means positions said container to be filled, and lowering said platform by said raising and lowering means positions said container to be accessed or removed.

13. The gas liquefaction system of claim 1, further comprising: a) a platform (29) for supporting said container;b) at least one pivotal arm (28) connected to said platform wherein said platform is raised and lowered by pivoting said pivotal arm; and,c) a lever (57) connected to said pivotal arm for pivoting said pivotal arm in order to raise and lower said platform,whereby raising said platform positions said container to be filled, and lowering said platform positions said container to be accessed or removed.

14. The gas liquefaction system of claim 1, wherein said container is a handheld container.

15. The gas liquefaction system of claim 1, wherein said gas generator is operative to generate nitrogen gas from air.

16. The gas liquefaction system of claim 1, further comprising an extraction line (25) in communication with said interior of said container, wherein the liquid gas is extracted from said container through said extraction line without moving said container.

17. The gas liquefaction system of claim 16 wherein said extraction line has at least one insulated portion (25C).