Title:
CRYOGENIC HEAT TRANSFER DEVICE
United States Patent 3736936
Abstract:
Heat transfer devices especially suitable for cryosurgery are disclosed each including an elongated tubular housing of low thermal conductivity having an open end and a closed end. A conical probe member of high thermal conductivity is mounted at and extends from the closed end of the housing. A capillary wick lining the inner lateral surface of the housing is adapted to convey a volatile working fluid such as liquid nitrogen at a temperature of -196°C from the vicinity of the open end of the housing to the vicinity of the closed end. A working fluid reservoir is disposed about the open end of the housing in fluid communication with the capillary wick. An annular evacuated chamber is provided about the outer surface of the reservoir and a substantial portion of the outer lateral surface of the housing to afford thermal insulation.
US Patent References:
Cryogenic applicator with probe means
Pytryga - June 1965 - 3190081
CRYOSURGICAL PROBE
Nestrock - January 1969 - 3421508
SURGICAL INSTRUMENT
Thomas, Jr. - March 1969 - 3434477
CRYOEXTRACTOR
Gans - July 1969 - 3455304
LIVESTOCK BRANDING APPARATUS
Ziegler - December 1969 - 3485060
Cryogenic applicator with probe means
Pytryga - June 1965 - 3190081
CRYOSURGICAL PROBE
Nestrock - January 1969 - 3421508
SURGICAL INSTRUMENT
Thomas, Jr. - March 1969 - 3434477
CRYOEXTRACTOR
Gans - July 1969 - 3455304
LIVESTOCK BRANDING APPARATUS
Ziegler - December 1969 - 3485060
Inventors:
Basiulis, Algerd (Redondo Beach, CA)
Reed Jr., Elmer E. (Downey, CA)
Reed Jr., Elmer E. (Downey, CA)
Application Number:
05/207431
Publication Date:
06/05/1973
Filing Date:
12/13/1971
View Patent Images:
Export Citation:
Assignee:
Hughes Aircraft Co. (Culver City, CA)
Primary Class:
Other Classes:
607/105, 606/116, 62/293
International Classes:
A61B18/02; F25B19/00; A61B18/00; A01K11/00; F25D3/00; A61B17/36
Field of Search:
128/303.1,41X,400 119/1 62/293
US Patent References:
Primary Examiner:
Medbery, Aldrich F.
Claims:
What is claimed is
1. A heat transfer device comprising:
2. A heat transfer device according to claim 1 and further including means for providing a vapor exhaust path from said reservoir.
3. A heat transfer device according to claim 2 wherein said means defining said reservoir includes a removable cap member having a vapor exhaust port therein.
4. A heat transfer device according to claim 1 wherein said means defining said reservoir includes first and second detachable members, and means for forming a hermetic seal between said first and second members when in attached relationship.
5. A heat transfer device according to claim 1 wherein said thermally insulating means includes a shell member disposed about and spaced from said housing and a portion of said reservoir means and hermetically bonded thereto, the space between said shell member and said housing and said reservoir portion being evacuated.
6. A heat transfer device for performing cryosurgery by freezing comprising:
7. A heat transfer device according to claim 6 wherein said means defining said reservoir includes a removable cap member having a vapor exhaust port therein.
8. A heat transfer device according to claim 6 wherein said housing is bent in the region where it enters said working fluid reservoir.
9. A heat transfer device according to claim 6 and further including an essentially U-shaped vent tube having one end extending into said housing via said open end, and an essentially L-shaped exhaust tube in vapor communication with the other end of said vent tube and extending externally of said means defining said reservoir.
10. A heat transfer device comprising:
11. A heat transfer device for performing cryosurgery by freezing comprising:
12. A heat transfer device comprising:
13. The heat transfer device of claim 12 wherein said capillary means and said cryogen gas conduit means are housed in the same housing.
1. A heat transfer device comprising:
2. A heat transfer device according to claim 1 and further including means for providing a vapor exhaust path from said reservoir.
3. A heat transfer device according to claim 2 wherein said means defining said reservoir includes a removable cap member having a vapor exhaust port therein.
4. A heat transfer device according to claim 1 wherein said means defining said reservoir includes first and second detachable members, and means for forming a hermetic seal between said first and second members when in attached relationship.
5. A heat transfer device according to claim 1 wherein said thermally insulating means includes a shell member disposed about and spaced from said housing and a portion of said reservoir means and hermetically bonded thereto, the space between said shell member and said housing and said reservoir portion being evacuated.
6. A heat transfer device for performing cryosurgery by freezing comprising:
7. A heat transfer device according to claim 6 wherein said means defining said reservoir includes a removable cap member having a vapor exhaust port therein.
8. A heat transfer device according to claim 6 wherein said housing is bent in the region where it enters said working fluid reservoir.
9. A heat transfer device according to claim 6 and further including an essentially U-shaped vent tube having one end extending into said housing via said open end, and an essentially L-shaped exhaust tube in vapor communication with the other end of said vent tube and extending externally of said means defining said reservoir.
10. A heat transfer device comprising:
11. A heat transfer device for performing cryosurgery by freezing comprising:
12. A heat transfer device comprising:
13. The heat transfer device of claim 12 wherein said capillary means and said cryogen gas conduit means are housed in the same housing.
Description:
FIELD OF THE INVENTION
This invention relates generally to heat transfer devices, and more particularly relates to a wholly self-contained, handheld cryogenic surgery tool which is readily portable, easily and quickly activated and convenient to use.
DESCRIPTION OF THE PRIOR ART
Certain surgical operations, such as a hemorroidectomy, may be performed quickly and painlessly by freezing the cells of the affected tissue. As subfreezing temperatures are reached and ice formation occurs in the cell, cellular organization is irreversibly altered. As the frozen tissue thaws, water is removed from the interior of the cell, resulting in cellular dehydration and destruction. Cryosurgical techniques are also being used in the treatment of chronic cervicitis, endometrial carcinoma, Parkinsonism, cataracts, and other diseases.
The usual procedure in cryosurgery is to lower the temperature of the diseased tissue to at least about -20°C. There are a variety of techniques for achieving such low tissue temperatures. One method is to dip an applicator such as a cotton swab or copper disk into liquid nitrogen (which is at -196°C) and then apply it to the diseased tissue. However, the use of such an applicator usually requires repeated applications, and great care must be taken to insure that only the diseased tissue is destroyed and not the surrounding healthy tissue.
Apparatus presently employed for performing cryosurgery consists of a control console with a liquid nitrogen supply and a cryoprobe. The console houses a Dewar container, having a capacity of 5 liters, and associated control and monitoring circuits. A heating system for thawing the cryoprobe is also included in the console. An input hose conveys liquid nitrogen from the Dewar container to the cryoprobe, while an output hose returns the liquid nitrogen to the console where it is exhausted into the atmosphere. In operation, liquid nitrogen (at -196° C) is placed in the Dewar container, and the container is sealed. Pressure within the container is increased, forcing the nitrogen through the input hose to the cryoprobe. The cryoprobe tip is cooled to about -180°C by the flow of the liquid nitrogen past the cryoprobe. The liquid nitrogen is then returned to the supply console via the output hose to be exhausted to the atmosphere as a vapor.
Although the aforedescribed apparatus has been used successfully in performing cryosurgery, about one minute of operation time is required before stabilization at the desired low temperature is achieved, largely because of the inefficiency of cooling by liquid flow. Moreover, since the cryoprobe is connected to the console unit by bulky hoses, two hands are required to hold the cryoprobe apparatus during the surgery. Thus, the apparatus is rather cumbersome to use, and the surgeon must be assisted in all but the simplest of operations. In addition, the entire apparatus (including the control and supply console) is relatively bulky and weights about 100 pounds, and a relatively large supply of liquid nitrogen is required for the apparatus to operate properly. Thus, a constraint is imposed on use of the apparatus by the availability of manpower to move both the apparatus itself and an adequate supply of liquid nitrogen to the site where the operation is to be performed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simple, reliable and convenient heat transfer device especially suitable for operation at cryogenic temperatures.
It is a further object of the present invention to provide a heat transfer device for performing cryosurgery which reaches the desired operating temperature very quickly and maintains that temperature readily.
It is a still further object of the invention to provide a small, handheld cryosurgery tool which is completely self-contained and readily portable.
In accordance with the foregoing objects, a heat transfer device according to the invention includes an elongated housing of low thermal conductivity having an open end and a closed end. A probe member of high thermal conductivity is mounted at and extends outwardly from the closed end of the housing. A capillary wick is longitudinally disposed within the housing for conveying a volatile working fluid from the vicinity of the open end of the housing to the vicinity of the closed end. A working fluid reservoir is provided about the open end of the housing in fluid communication with the capillary wick. Thermal insulation is provided about the outer surface of the reservoir and a substantial portion of the outer lateral surface of the housing.
The foregoing and other objects and features of the present invention will become readily apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a longitudinal sectional view illustrating a heat transfer device according to one embodiment of the present invention;
FIG. 2 is a perspective view illustrating a heat transfer device according to another embodiment of the invention; and
FIG. 3 is a longitudinal sectional view of a portion of the device of FIG. 2 as taken along line 3--3 of FIG. 2.
Referring more specifically to FIG. 1, a heat transfer device according to the invention may be seen to include a thin-walled elongated tubular housing 10 having a closed end 11 and an open opposite end 12 which may be of reduced diameter as shown. The housing is preferably of a material of low thermal conductivity such as stainless steel, for example. The vicinity of the closed end 11 of the housing 10 functions as an evaporation region where a working fluid contained within the housing is vaporized by applied heat. A tapered probe 14, shown as having a generally conical configuration, is mounted within extension 10a of the housing 10 with its base contacting the housing end wall 11 alternatively, separate end wall member 11 may be eliminated with the base of probe 14 constituting an end wall for the housing 10. The probe 14, which should be of a material of high thermal conductivity, absorbs heat from a source, such as living tissue for example, and transfers heat by conduction to the housing wall 11. The probe may be held in place by frictional force with the inner lateral surface of housing extension 10a or, alternatively, by threads provided on extension 10a and probe 14. It is pointed out that while a particular probe shape has been illustrated, the shape of probe 14 is not critical and may vary depending upon the particular application of the heat transfer device.
A capillary wick 15 lines the inner lateral surface of the housing 10. The wick 15 may be made of any material through which fluid can travel by capillary forces, examples of suitable wick materials being felt cloth, stainless steel screen, and sintered metal fibers. It is pointed out that the capillary wick 15 need not line the entire inner lateral surface of housing 10, and other wick arrangements such as a plurality of longitudinally extending wick strips circumferentially spaced along the inner surface of housing 10 may be employed in the alternative.
A working fluid reservoir 16 is provided for the housing 10 in the vicinity of its open end 12. The reservoir 16 is defined by a tubular member 17 coaxially mounted about housing 10 at its open end region and an annular member 19 extending inwardly from the lower edge of member 17 to the outer surface of housing 10. The annular member 19 is welded or otherwise attached to the member 17 and to the housing 10 so as to form a fluid tight seal therewith. The reservoir members 17 and 19 are preferably of a material of low thermal conductivity such as stainless steel, for example. In order to provide fluid communication between the reservoir 16 and the capillary wick 15, a plurality of circumferentially spaced apertures 18 may be provided in housing 10 just above where it is sealed to annular reservoir member 19.
In order to provide thermal insulation for the device, a tubular metal shell 20 is coaxially disposed about the housing 10 and the reservoir members 19 and 17 in a manner providing an annular space between the shell 20 and the members 10, 17 and 19, the end regions of the shell 20 being in hermetically bonded relationship with the respective end regions of the housing 10 and the reservoir member 17. The annular space between the shell 20 and the housing 10 and reservoir members 17 and 19 is evacuated to provide the desired thermal insulation. A coating of fiberglass or plastic may be applied over the outer surface of the shell 20 to provide additional thermal insulation, if desired.
The open upper end of reservoir 16, which affords a fluid inlet to the reservoir 16, may be covered by a cap 21 during operation of the device. The cap 21 consists of a flat circular member 22 having a central exhaust port 23 axially aligned with the opening in end 12 of housing 10 and a lip 24 projecting downwardly from the circumferential edge of member 22. Thermal insulation for the cap 21 may be afforded by an evacuated chamber defined by members 22, 24, and a metal shell 25 disposed about and spaced from the members 22 and 24 and in a hermetically bonded relationship therewith.
The cap 21 may be attached to the reservoir 16 by mating threads 26 on the inner surface of an annular extension 27 of the shell 25 and on the outer surface of the shell 20 adjacent its upper end. A fluid tight seal may be provided between the cap 21 and the reservoir 16 by means of an O ring 28 disposed in an annular groove-defining member 29 mounted between the shell 20 and the reservoir member 17 at the upper ends thereof, and an annular flange 30 projecting from the cap 21 into the groove of member 29 and adapted to compress O ring 28.
In operation of the heat transfer device of FIG. 1, a suitable low temperature working fluid 40 at a temperature below its boiling temperature is poured into the reservoir 16. Examples of particular working fluids which may be employed are liquid nitrogen at -196° C, oxygen at -183° C, or freon at -81° C.
The working liquid 40 in the reservoir 16 flows into the housing 10 through apertures 18, wetting the capillary wick 15. The liquid 40 moves into the wick 15 and is conveyed by capillary action along the wick 15 toward the end of the housing 10 adjacent the probe 14 as long as wick 15 is not saturated. However, once the wick 15 becomes saturated, additional liquid is precluded from entering the housing 10 via apertures 18.
Upon reaching the evaporator wall 11, the liquid 40 becomes vaporized because the temperature of evaporator wall 11 is initially much higher than the boiling temperature of the liquid 40. It is well known that in the process of vaporization a liquid will absorb heat from its surroundings and thereby lower the temperature of the surroundings. Thus, as the liquid 40 reaching evaporator wall 11 continues to be vaporized, the temperature of evaporator wall 11 (and hence probe 14) is lowered to the boiling temperature of the liquid 40.
When the probe 14 is placed in contact with a heat source, such as living tissue for example, heat is transferred from the heat source to the probe 14 and conveyed by conduction to the evaporator 11, causing a slight rise in the temperature of evaporator 11. This in turn causes more liquid 40 to be vaporized which again lowers the temperature of evaporator 11 and probe 14. Thus, the probe 14 is maintained essentially at the boiling temperature of the working fluid 40.
Since the vaporizing fluid causes a pressure increase in the region of the housing 10 adjacent the evaporator 11, the vapor travels along the housing to the vicinity of the open end 12. There some of the vapor condenses into liquid as it contacts the colder temperature of the capillary wick 15. The remaining vapor passes through the opening at end 12 and is exhausted to the atmosphere through port 23.
A heat transfer device according to another embodiment of the present invention is illustrated in FIGS. 2 and 3. Components in the embodiment of FIGS. 2 and 3 which are similar to respective components in the embodiment of FIG. 1 are designated by the same reference numerals as their corresponding components in FIG. 1 except for the addition of a prefix numeral "1."
The embodiment of FIGS. 2 and 3 differs from the embodiment of FIG. 1 in that housing 110 is bent by about 45° in the region 150 where housing 110 enters reservoir 116. Also, apertures 118 providing fluid communication between the reservoir 116 and the housing 110 are located closer to the open end 112 of the housing 110. The reservoir 116, including tubular member 117 and end member 119, as well as thermally insulating outer shell member 125, is detachable from the remainder of the device in order to facilitate filling the reservoir 116 with working fluid. Mating threads 126 are provided on the outer surface of shell 125 near its end region and on the inner surface of enlarged tubular extension 152 of a funnel-like transition member 154 hermetically bonded to the shell 120 surrounding the portion of housing 110 outside of reservoir 116. An essentially U-shaped vent tube 160, mounted within the reservoir 116 by means not shown, has one end extending into the housing 110 to the vicinity of bend 150 and the other end extending to a region 162 externally of the housing 110 in the vicinity of the transition member 154. The vent tube 160 conveys vaporized working fluid through the contained liquid 140 in the reservoir 116 to the region 162 from where it is vented to the atmosphere externally of the reservoir via an essentially L-shaped exhaust tube 164.
It should be apparent from the foregoing that the present invention provides a self-contained, simple, and readily portable heat transfer device which is especially suitable for performing cryosurgery. Moreover, the device reaches the desired low operating temperature very quickly and maintains that temperature readily. In fact, heat transfer devices according to FIG. 1 and FIGS. 2-3 have been constructed which weigh slightly over two pounds and reach an operating temperature of -196° C within 30 seconds after their respective reservoirs 16 and 116 have been filled with liquid nitrogen at a temperature of -196° C.
Although the present invention has been shown and described with reference to particular embodiments, nevertheless, various changes and modifications obvious to one skilled in the art to which the invention pertains are deemed to lie within the purview of the invention.
This invention relates generally to heat transfer devices, and more particularly relates to a wholly self-contained, handheld cryogenic surgery tool which is readily portable, easily and quickly activated and convenient to use.
DESCRIPTION OF THE PRIOR ART
Certain surgical operations, such as a hemorroidectomy, may be performed quickly and painlessly by freezing the cells of the affected tissue. As subfreezing temperatures are reached and ice formation occurs in the cell, cellular organization is irreversibly altered. As the frozen tissue thaws, water is removed from the interior of the cell, resulting in cellular dehydration and destruction. Cryosurgical techniques are also being used in the treatment of chronic cervicitis, endometrial carcinoma, Parkinsonism, cataracts, and other diseases.
The usual procedure in cryosurgery is to lower the temperature of the diseased tissue to at least about -20°C. There are a variety of techniques for achieving such low tissue temperatures. One method is to dip an applicator such as a cotton swab or copper disk into liquid nitrogen (which is at -196°C) and then apply it to the diseased tissue. However, the use of such an applicator usually requires repeated applications, and great care must be taken to insure that only the diseased tissue is destroyed and not the surrounding healthy tissue.
Apparatus presently employed for performing cryosurgery consists of a control console with a liquid nitrogen supply and a cryoprobe. The console houses a Dewar container, having a capacity of 5 liters, and associated control and monitoring circuits. A heating system for thawing the cryoprobe is also included in the console. An input hose conveys liquid nitrogen from the Dewar container to the cryoprobe, while an output hose returns the liquid nitrogen to the console where it is exhausted into the atmosphere. In operation, liquid nitrogen (at -196° C) is placed in the Dewar container, and the container is sealed. Pressure within the container is increased, forcing the nitrogen through the input hose to the cryoprobe. The cryoprobe tip is cooled to about -180°C by the flow of the liquid nitrogen past the cryoprobe. The liquid nitrogen is then returned to the supply console via the output hose to be exhausted to the atmosphere as a vapor.
Although the aforedescribed apparatus has been used successfully in performing cryosurgery, about one minute of operation time is required before stabilization at the desired low temperature is achieved, largely because of the inefficiency of cooling by liquid flow. Moreover, since the cryoprobe is connected to the console unit by bulky hoses, two hands are required to hold the cryoprobe apparatus during the surgery. Thus, the apparatus is rather cumbersome to use, and the surgeon must be assisted in all but the simplest of operations. In addition, the entire apparatus (including the control and supply console) is relatively bulky and weights about 100 pounds, and a relatively large supply of liquid nitrogen is required for the apparatus to operate properly. Thus, a constraint is imposed on use of the apparatus by the availability of manpower to move both the apparatus itself and an adequate supply of liquid nitrogen to the site where the operation is to be performed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a simple, reliable and convenient heat transfer device especially suitable for operation at cryogenic temperatures.
It is a further object of the present invention to provide a heat transfer device for performing cryosurgery which reaches the desired operating temperature very quickly and maintains that temperature readily.
It is a still further object of the invention to provide a small, handheld cryosurgery tool which is completely self-contained and readily portable.
In accordance with the foregoing objects, a heat transfer device according to the invention includes an elongated housing of low thermal conductivity having an open end and a closed end. A probe member of high thermal conductivity is mounted at and extends outwardly from the closed end of the housing. A capillary wick is longitudinally disposed within the housing for conveying a volatile working fluid from the vicinity of the open end of the housing to the vicinity of the closed end. A working fluid reservoir is provided about the open end of the housing in fluid communication with the capillary wick. Thermal insulation is provided about the outer surface of the reservoir and a substantial portion of the outer lateral surface of the housing.
The foregoing and other objects and features of the present invention will become readily apparent from the following detailed description of preferred embodiments of the invention when considered in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 is a longitudinal sectional view illustrating a heat transfer device according to one embodiment of the present invention;
FIG. 2 is a perspective view illustrating a heat transfer device according to another embodiment of the invention; and
FIG. 3 is a longitudinal sectional view of a portion of the device of FIG. 2 as taken along line 3--3 of FIG. 2.
Referring more specifically to FIG. 1, a heat transfer device according to the invention may be seen to include a thin-walled elongated tubular housing 10 having a closed end 11 and an open opposite end 12 which may be of reduced diameter as shown. The housing is preferably of a material of low thermal conductivity such as stainless steel, for example. The vicinity of the closed end 11 of the housing 10 functions as an evaporation region where a working fluid contained within the housing is vaporized by applied heat. A tapered probe 14, shown as having a generally conical configuration, is mounted within extension 10a of the housing 10 with its base contacting the housing end wall 11 alternatively, separate end wall member 11 may be eliminated with the base of probe 14 constituting an end wall for the housing 10. The probe 14, which should be of a material of high thermal conductivity, absorbs heat from a source, such as living tissue for example, and transfers heat by conduction to the housing wall 11. The probe may be held in place by frictional force with the inner lateral surface of housing extension 10a or, alternatively, by threads provided on extension 10a and probe 14. It is pointed out that while a particular probe shape has been illustrated, the shape of probe 14 is not critical and may vary depending upon the particular application of the heat transfer device.
A capillary wick 15 lines the inner lateral surface of the housing 10. The wick 15 may be made of any material through which fluid can travel by capillary forces, examples of suitable wick materials being felt cloth, stainless steel screen, and sintered metal fibers. It is pointed out that the capillary wick 15 need not line the entire inner lateral surface of housing 10, and other wick arrangements such as a plurality of longitudinally extending wick strips circumferentially spaced along the inner surface of housing 10 may be employed in the alternative.
A working fluid reservoir 16 is provided for the housing 10 in the vicinity of its open end 12. The reservoir 16 is defined by a tubular member 17 coaxially mounted about housing 10 at its open end region and an annular member 19 extending inwardly from the lower edge of member 17 to the outer surface of housing 10. The annular member 19 is welded or otherwise attached to the member 17 and to the housing 10 so as to form a fluid tight seal therewith. The reservoir members 17 and 19 are preferably of a material of low thermal conductivity such as stainless steel, for example. In order to provide fluid communication between the reservoir 16 and the capillary wick 15, a plurality of circumferentially spaced apertures 18 may be provided in housing 10 just above where it is sealed to annular reservoir member 19.
In order to provide thermal insulation for the device, a tubular metal shell 20 is coaxially disposed about the housing 10 and the reservoir members 19 and 17 in a manner providing an annular space between the shell 20 and the members 10, 17 and 19, the end regions of the shell 20 being in hermetically bonded relationship with the respective end regions of the housing 10 and the reservoir member 17. The annular space between the shell 20 and the housing 10 and reservoir members 17 and 19 is evacuated to provide the desired thermal insulation. A coating of fiberglass or plastic may be applied over the outer surface of the shell 20 to provide additional thermal insulation, if desired.
The open upper end of reservoir 16, which affords a fluid inlet to the reservoir 16, may be covered by a cap 21 during operation of the device. The cap 21 consists of a flat circular member 22 having a central exhaust port 23 axially aligned with the opening in end 12 of housing 10 and a lip 24 projecting downwardly from the circumferential edge of member 22. Thermal insulation for the cap 21 may be afforded by an evacuated chamber defined by members 22, 24, and a metal shell 25 disposed about and spaced from the members 22 and 24 and in a hermetically bonded relationship therewith.
The cap 21 may be attached to the reservoir 16 by mating threads 26 on the inner surface of an annular extension 27 of the shell 25 and on the outer surface of the shell 20 adjacent its upper end. A fluid tight seal may be provided between the cap 21 and the reservoir 16 by means of an O ring 28 disposed in an annular groove-defining member 29 mounted between the shell 20 and the reservoir member 17 at the upper ends thereof, and an annular flange 30 projecting from the cap 21 into the groove of member 29 and adapted to compress O ring 28.
In operation of the heat transfer device of FIG. 1, a suitable low temperature working fluid 40 at a temperature below its boiling temperature is poured into the reservoir 16. Examples of particular working fluids which may be employed are liquid nitrogen at -196° C, oxygen at -183° C, or freon at -81° C.
The working liquid 40 in the reservoir 16 flows into the housing 10 through apertures 18, wetting the capillary wick 15. The liquid 40 moves into the wick 15 and is conveyed by capillary action along the wick 15 toward the end of the housing 10 adjacent the probe 14 as long as wick 15 is not saturated. However, once the wick 15 becomes saturated, additional liquid is precluded from entering the housing 10 via apertures 18.
Upon reaching the evaporator wall 11, the liquid 40 becomes vaporized because the temperature of evaporator wall 11 is initially much higher than the boiling temperature of the liquid 40. It is well known that in the process of vaporization a liquid will absorb heat from its surroundings and thereby lower the temperature of the surroundings. Thus, as the liquid 40 reaching evaporator wall 11 continues to be vaporized, the temperature of evaporator wall 11 (and hence probe 14) is lowered to the boiling temperature of the liquid 40.
When the probe 14 is placed in contact with a heat source, such as living tissue for example, heat is transferred from the heat source to the probe 14 and conveyed by conduction to the evaporator 11, causing a slight rise in the temperature of evaporator 11. This in turn causes more liquid 40 to be vaporized which again lowers the temperature of evaporator 11 and probe 14. Thus, the probe 14 is maintained essentially at the boiling temperature of the working fluid 40.
Since the vaporizing fluid causes a pressure increase in the region of the housing 10 adjacent the evaporator 11, the vapor travels along the housing to the vicinity of the open end 12. There some of the vapor condenses into liquid as it contacts the colder temperature of the capillary wick 15. The remaining vapor passes through the opening at end 12 and is exhausted to the atmosphere through port 23.
A heat transfer device according to another embodiment of the present invention is illustrated in FIGS. 2 and 3. Components in the embodiment of FIGS. 2 and 3 which are similar to respective components in the embodiment of FIG. 1 are designated by the same reference numerals as their corresponding components in FIG. 1 except for the addition of a prefix numeral "1."
The embodiment of FIGS. 2 and 3 differs from the embodiment of FIG. 1 in that housing 110 is bent by about 45° in the region 150 where housing 110 enters reservoir 116. Also, apertures 118 providing fluid communication between the reservoir 116 and the housing 110 are located closer to the open end 112 of the housing 110. The reservoir 116, including tubular member 117 and end member 119, as well as thermally insulating outer shell member 125, is detachable from the remainder of the device in order to facilitate filling the reservoir 116 with working fluid. Mating threads 126 are provided on the outer surface of shell 125 near its end region and on the inner surface of enlarged tubular extension 152 of a funnel-like transition member 154 hermetically bonded to the shell 120 surrounding the portion of housing 110 outside of reservoir 116. An essentially U-shaped vent tube 160, mounted within the reservoir 116 by means not shown, has one end extending into the housing 110 to the vicinity of bend 150 and the other end extending to a region 162 externally of the housing 110 in the vicinity of the transition member 154. The vent tube 160 conveys vaporized working fluid through the contained liquid 140 in the reservoir 116 to the region 162 from where it is vented to the atmosphere externally of the reservoir via an essentially L-shaped exhaust tube 164.
It should be apparent from the foregoing that the present invention provides a self-contained, simple, and readily portable heat transfer device which is especially suitable for performing cryosurgery. Moreover, the device reaches the desired low operating temperature very quickly and maintains that temperature readily. In fact, heat transfer devices according to FIG. 1 and FIGS. 2-3 have been constructed which weigh slightly over two pounds and reach an operating temperature of -196° C within 30 seconds after their respective reservoirs 16 and 116 have been filled with liquid nitrogen at a temperature of -196° C.
Although the present invention has been shown and described with reference to particular embodiments, nevertheless, various changes and modifications obvious to one skilled in the art to which the invention pertains are deemed to lie within the purview of the invention.