CA1093332A - Self-pressurizing cryogenic apparatus and method - Google Patents

Abstract

ABSTRACT

Apparatus and method for dispensing a jet of cryogenic coolant selectively in single gaseous phase and in dual gaseous and finely divided liquid phase from a self-pressurizing source of heat saturated liquid coolant. The coolant is stored under constant pressure and in a heat-saturated condition and, when needed, is partially expanded into an expansion chamber equipped with a coolant jetting orifice and a venting orifice regulatable to control coolant flow from the jetting orifice in single or dual phase. The liquid coolant is conveniently stored in a hand-held dewar flask equipped with a pressure relief valve and utilizing a relatively long, small bore passage as the coolant jetting orifice.

Description

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1 This invention relak~s to cryog~nic apparatus, and more particularly to simply constructed, hand held means for dispensing a jet of cryogenic coolant onto an area to be necroti~ed from a self-pressurizing source of heat saturated liquid coolant having a boiling point ~elow -lOO~C~
B~CKGROUWD OF T~ E~$sc~
Equipment for dispensing a cryogenic lique~ied gas onto a surace or object to be sharply cooled has been proposed hereto-fore. These are designed to utilizel liquefied gas such as helium, nitrogen, oxygen, air, carbon dioxide9 etcO stored in a suitable container. The liquid coolant is supplied thQrefrom to a dis-pensing port or nozzle in various ways including applying heat electrically ox otherwise to the coolant to vaporize the liquid.
Other designers pressurize the storage container to produce coolant flow ~y introducing air u~der pressure into the skorage container while other designers provide the storage container with a normally open vent which is closed to initiate coolant flow whereby the vapor pressure which develops within the con-tainer produces a 10w o coolant to the dispensing nozzle. The pressure build-up is slow and uncertain and vari2~ widely depend-ing on the volume o the vapor spaca and the qua~tity of liquid coolant in the storaga chamber~ tha rate of heat leakage into the container and other ~actors.
~ ne ca~egory o~ prior ~ryogenic de~ices dispenses a jet of coolant vapor direct~y onto the area to be coolad whexea~ those o~ another category con~ine the straam of coolant vapor to a 10w passage typically provided with a return bend sector formed of excell~nt heat conductive material and venting to tha atmosphere at a remote point.. The heat conduc~ing member can be placed close to or in contact with the surface to be cool~d without risking direct contact o~ the gas coolant with that surface.

It has been recogniz~d that it would be advantageous to deliver coolant in liquid phase onto or in close proximity to the

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area to be sharply cooled in order to utill~e the latent heat oE
vaporization of the coolant as it changes to the gas phase. However, this presents numerous serious problems which have not been resolved prior to this invention. Foremost among these problems i8 control of the liquid coolant delivered and the amount of cooling provided.
It is manifestly not feasible to deliver even a minute stream of liquid coolant onto living tissue. Not only is the coollng capacity of liquld coolant very great but, upon enterlng the a~mosphere, becomes rapidly superheated with resultant vigorous boiling and uncontrolled dispersal.
Attempts have been made to create a spray of liquefied coolant particles of which can be dispensed directly onto the area to be necrotized. However, the equipment heretofore provided for this purpose is subject to many shortcomings and disadvantages including instability and erratic coolant flow, inability to form a stable, small diameter ~et, fluctuating spurts of the coolant jet, time delay and waste involved in establishing a coolant ~et, continuing change in the rate of flow, the highly inefficient use of a given charge of liquid coolant, and the need for recharging a hand-held reservoir several times a day.
SUMMARY OF THE INVENTION
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The present invention provides a cryogenic apparatus for . - producing subfreezing temperatures comprising an eY~pansion chamber having an inlet and an outlet and adapted to be connected to a source of pressurized liquid cryogen maintained substantially at a predeter-mined pressureJ bleed passage means in communication with the interior of the expansion chamber and the atmosphere, communication to the atmoæphere being~controlled by a valve which when closed provides a ~low of gaseous phase cryogen from said outIet and when open provides .

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a dual phase flow of finely divided l:Lquid cryogen mixed with the gaseous phase cryogen from said outlet.
In a preferred embodlment, the lnvention provldes cryogenic apparatus for selectively spraylng cryogen in single gas phase or dual phase gas and liquld which comprises:
a source of pressuriæed liquid cryogen;

an expanslon chamber connected to said source through a flow control valve;
a restricted spray nozzle having a diameter measured ln mils connected to said expanslon chamber through which cryogen is discharged to atmosphere by the pressure in said expanslon chamber; and means to reduce the pressure in said expansion chamber to cause the discharge cryogen to change from single phase gas discharge to dual phase gas and liquid particle comprising:
a bleed passage connected to said extension chamber sized to convey gaseous cryogen under pressure from said chamber in amounts sufficient to reduce slightly the pressure in said chamber; and manually operable valve means to open and close said bleed passage.

To avoid the numerous shortcomings and disadvantages of prior cryogenic equipment, there is provided by this invention a self-pressuriæing, self-stabilizing source of heat saturated liquid coolant. This coolant may be stored either in a stationary large capacity reservoir or a readily portable hand-held dewar flask.
~; Such a flask having a capacity of approximately one pint of liquid is found adequate for seven to eight hours of normal usa~e without recharging yet is so small and light welght to be grasped in the hand and readily manoeuvred to meet operating requirements. The liquid .
coolant is automatically maintained at a predetermined uniform pressure by a pressure relief valve and, in consequence, the liquid is in continuous :
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1 r~adiness for dispensiny in a stable heat saturated condition.
When open, a coolant ~low control valve permits the coolant to flow into an expansion cha~ber e~uipped with a relatival~ long small bore outlet noz~le or orifice and a normally open venting orifice cooperating with the outlet or coolan~ jetting ori~ice to limit the pressure differential across the flow cont~ol valv~
to a ~raction of the pressure in the supply chamber. Thi.s pres-sure differantial greatly limits the ~lashing of coolant into vapor. Additionally, and by properly proportioning th~ sizes of 1~ the outlet and venting orifices and the.regulatio~ of the latter, the invention apparatus is instantly self-stabilizing and operable to dispense either a needle-like jet of coolant in a dual phasa o~ fins liquid particles and gas~ or a jet o~ gaseous phase cnolant depanding upon whether gaseous coolant is vented ~rom tha venting ori~ice. The incr~ased velocity imparted to the jet owing to the 1ashing of some superheated li~uid into gas aids vary substantially in increasing the "chill-factor" and thereby the effectivenass and ef~icienc~ of the device. For example, when using liquid nitrogan as the coolant, the temperature of this coolant in gas phase whan dispensed ~rom the nozzle of this invention is somawhat about 32F whereas the temperature of the issuing jet o~ dual phasa coolant containi~g suparheated liquid coolant is at least -300F. Further lowering o the temperature known as the "chill-~actor'l results as the rapidly ~lowing jet of particles o~ liquiLd coolant ~lash into tha gaseous phase.
I~ the ventillg passage is open a portion of the coolant which is flashed into gas is bled rom the expansion chamber and the resulting small drop of pressure in the expansion chamber con-verts tha jet discharge substantially instantly from single to ~ dual phase constituen~y without need for adjusting the 1OW con-trol valve~ ~ikewise, the jet discharge is converted instantly back to single phase by closing the venting orifice~ Partial closing o~ the vsnting orifice merely varies tha relative pro-`:

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portions o~ gas and liquid in the jet.
The stability oE the device is enhanced by insulating the liquid f]ow tube extending between the coolant supply and the expansion chamber. This avoids re-liquefication of a portion of the coolant vapor in the upper portion of the dewar during a dlspensing cycle where a dispensing operation occurs before a new charge of coolant has become fully heat saturated.
The present self-pressurizing, self-stabilizing cryogenic device is selectively operable to dispense a jet of single-phase or dual phase coolant having a boiling point below -100 C.
The present devlce is quickly convertible between single phase gaseous constituency and dual phase constituency.
The present device may be a self-contained hand-held cryogenic device which is instantly sel-stabilizing to dispense a ~et of finely divided li~uid coolant.
The present cryogenic device allows for selectively dispensing a stabilized ~et of coolant in either single gaseous phase at a temperature above freezing or in a dual phase at a temperature at least as low as -300 F.
The present self-pressuri7ed cryosurgery device is instantly self-stabilizing and effective to dispense a continuous non-varying coolant ~et or a readily varied ~et of either single or dual phase coolant.
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The present self-pressurized, self-stabilizing cryogenic device includes means for varying the phase consistency of a jet of .
dispensed coolant by controlling a venting orifice or bleed passage in communication with the space at the entrance end of the ~et dispensing orifice.

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The present invention is more readily understood upon reading the following specification and claims and upon considering in connection therewlth the attached drawing to which they relate.
Referring now to the drawing in which a preferred embodiment of the invention is illustrated:
Figure 1 is an elevational view partly in cross-section of one illustrative embodiment of the invention;
Figure 2 is a fragmentary cross-sectional view on an enlarged scale taken through the upper portion of Fig~re l;
Figure 3 is a fragmentary view partly in cross-section of the control valve for the venting orifice, and Figure 4 is a graphical representation oE the pressure conditions existing in the expansion chamber for various positions of the throttle valve, the uppermost horizontal line representing the constant coolant reservoir pressure, the middle curve representing the pressure when the venting valve is closed, and the lower curve representing the pressure conditlon when the venting valve is open.
Referring initially more particularly to Figure 1, there is shown an exemplary embodiment of the invention cryogenic device, ~ ~ 20 designated generally 10, when utilizing a dewar flask 11 as a source ;~ of heat saturated liquid coolant or cryogen 12. A suitably widely used coolant comprises liquefied nitrogen although it will be understood that any oE a considerable number of other liquefied gases having a boiling point of -100C or lower, are suitable and may be used in .
practicing the principles of this invention. ,Dewar 11 is of generally conventional construction including a stainless steel inner container 13 sealed at its charging inlet 14 to a stainless ste~l outer evacuated container 15. The tubular neck 16 of the outer container is provided with threads 17 mateable with the threads of a heat insulating linlng 18~ of the dewar cover or cap 19.

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, ~33~2 The dispensing and control components of the cryogenic device will be best understood by reference to Figures 2 and 3. These components include a maln body fitting 20 having a threaded tubular shank projecting downwardly from its lower side and extending through an opening in to the top of the dewar cap 19. A threaded bushing 22 is screwed to the lower end of shank 21 and serves to hold the latter firmly assembled to cap 19 along with a thick~walled elastomeric stopper 24 normally closing the dewar charging inlet 25.
As is best shown in Figure 1, stopper 24 has a shoulder seatlng against the outer rim edge of this inlet. Clamped between the lower end of main body 20 and the top of cap 19 is a curvilinear guard 27 effective to safeguard the.user's fingers from contact with the very cold components of the device when in use. Guard 27 may be made of poor heat conductive material, such as stainless steel and includes an upturned tang 28 (Figures 1, 3) extending along one sidewall of main body 20.
. Supported on the side of main body 20 is a precision valve - 30 having a rotary control knob 31 for controlling the position of a throttle or needle valve 32 normally closed against a seat 33. This val.ve controls the flow of liquid coolant into a tubular expansion housing 35 projecting laterally from the top of main body 20. The lower end of passage 34 is in communication with a tube 36 which is sllver-soldered to main body 20 and to a tube 38 extending into ~:~ close proximity to the bottom of the coolant container 13. Tube 38 is thin-wallecl b~ass or stainless steel to present as small a conductive : ~ :
: ~ heat path as i9 practical into the liquid coolant. This junction between tubes 36 and 38 may be silver-soldered and is located below the threaded tubular extension 21 to simplify replacement and repair of ~ ~ tube 38 should the latter become damaged when cap 19 ls disassembled : : 30 for charging or otherwise. Each of the tubes 36 and 38 is preferably :

333~2 covered with heat insulating material 39,40 to aid ln stabiling the operaLion of the apparatus by preventing the flow of liquid .~, . ~ .

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1 coolant through these tubas to cool and condense portions of the coola~t vapor present above the liquid leval. This could inter-fere with maintaining a uniform pressure head on the liquid while valve 32 is open and could cause unstable condltions in the jet of coolant before the coolant becomes fully heat saturated.
The dewar is automatically maintained at a predetermined superatm~spheric pressure by the vapor pressure o the coolant supply as by a pressure relief valve 43 mounted in the side of main body 20 in communication through passage 44 with the interior of the tubular extension or shank 210 The valve proper 45 of the relief valve is normally held seated against the vutlet end of passage 34 by a calibrated spring, not shown, but housed within the valve body. ~n ex~ension 46 pro~ruding ~rom ~his valve is readily manipulatable by the operator's finger to unseat the valva and release the prassura in the dewar whenevsr this is desirable, as before removing cap 19 to renew the supply of coolant 120 Penmanently asse~bled to the outer end of expansion chamber 35 is a Luer fitting 50 o~ well kn~wn construction providing a readily disconnactable coupling ~or ~he shank ~ittin~ 51 o~ a non-pointed or blunt-enaea hypoder~ic ~eedle~52 providing an elongated small bore nozzle ox outlet orifioe f~r chamber 35~ It will be understood that oth~r ou~la~ ori~ice constructions ca~ be employed but readily availabl~-hypodermic needle~s having bores ranging .. in siza from 22 to 25 gauge have been found highly satisfactory . and are quickly and ea~ily substituted for one anothe~ to vary , ., the siza of the ~oolant jet aispe~s~d from the expansion chamber.
A 22 gauge needle has a bore diameter of approximately 17 mils as compared to the 11 mil bors of a guage 25 needle. ~eeal9 leng~hs of 1/4~ to 3/4" are ~ound very satis-factory ~r use with outlet orifi~es ranging in size from 11 ~-o 17 mils in diamefer.
The length of the ne6dle ~aries with the siæe of the bleeder : ori~ice~ A longer needle ~ecessitates ble2ding a greater volume .

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1 of gaseous phase coolant from th~ expansion char~er.
A very important fur~her ~eature of the inv~ntîon is the provision of means for venting coolant in gas phase ~xom chamber 35. As herein shown by way of example, this v0nting means is provided by tube 54 extending along the interior of chamber 35 with its right-hand end in communication with a pa~sage 55 formed interiorly of body 20. This passage is shown in dot and dash line and includes a vertical ley and a horizontal leg the latter of which opens to the atmosphere on tha left-hand side o~ the main body 20 (Figure 3). ~ormally, the outlet end of passage 55 is closed by a valve 56 mounted on one end o~ an L-shaped operat-ing lever 57 of poor heat conductive material such as stai~less steel. Lever 57 is supported on pivot pins 58 carried by a bracket 59 secured to the side of body 20, and is spring biased by spring 60 to seat the valve 56 against the outlet end of passage S5.
To avoid tolexance problems in the manuacture of the vent-ing orifice or passage, it is found convenient to provide this passage with a loose packing ox restrictor to limit the flow of coolant gas all~wed to escapa to the atmosphere. A very satis-factory restrictor comprises a mass o brass wool or the like here shown as located at the junction o~ the v~rtical and hori-zontal le~s o~ passage 55~ Arcess to this mass 63 is provided by a closure cover ~4 ~o the end that the density of this rast-rictor may be readily adjusted at the time of manufacture.
Thereafter, closure plug 64 may be suitably secured in place since no ~urther adjustment is raquired so long as the same size pressure ralief valve 43 and the sam0 range o sizes of outlet ori~ice needles 52 are employed.
Referring now to Figure 4, there is shown a graph depicting typical opsrating conditions ~or the cryogenic device herein de~cribed when using liquid nitrogen as the coolant and a prassure relief valve calibrated to maintain a pressure o~ 10 psig~ Ik _9~

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1 will b~ undarstood that thls pr~ssure is merely representative of a pressure found to provide excellent operating characteristics when using outlet passages o~ the range of sizes described above~
This constant pressure condition is, represented by the straight horizontal line 65 in Figure 4. The next lower curve 66 repre~
sents the pressura condition within expansion chamber 35 when a 22 gauge needle 52 is employed a~ the jstting orifice as needle valve 32 is opened from its closed to its open positionr Curve 67 shows the slightly lower pres~ure condition axis ting in the expansion chamb~r with control lever 57 depressed to open val~e 56 normally closing the venting passage or orifice 55.
~ ormally the dewar ~lask is charged with liquid nitrogen and needle valve 32 and venting valve 56 are closed. With the pressure relief valve 43 set or example, to maintain the pres-sure within the flask at 10 psig, the coolant will be heat saturated and have a temperatura of -312 DF. As soon as control knob 31 is opexated to open needle valve 32, liquid coolant will rise through conduit 38 and flow past the needle ~alve whereupon a porti~n of Lt will quickly,become supex-heated as it experiences : 20 a pres~ure drop i~ ~lowing past the needle valve into the rala-- tively,warm expan~ion chamber 35. The résulting vi~len~ ~oiling or flashing o~ the coolant ~ractionates the liquid into a multi-plicity of fine mi~ute particles as other portio~s convert to the .
gaseous phasa, thPreby almost instantly raising the back pressure in thè expansion ~hamber to a ~alue soméwha~ in excess o~ one pound less than l:he internal dewar pressure~ Coolànt in sub-' stantially pure gaseo,us phase then jats at high velocity from .b ~
~ the jetting ori~ice. ~A layer o frost also quickly collects on -the outer surface o tha expansion charriber 35 theraby providing 30 an exc!ellenf heaf; insulating layer for f his chaTr~er which greatly minimizes the quanf ity of coolant going into its gas phase9 The c:ryo~urgery de~rice may now be grasped in the operator's hand and manipulated to direct the jet of gaseouæ coolant onto 33;~:

1 an area to be sharply cooled~
I the operatox wishes to convert the jet to one comprised principally of ~inely divided particles of coolant in liquid phase intermixed with gaseous phase coolant, he simply depresses lever 57 to open vent ~alve 56. Immediately that this takeæ
place the jet converts to a high velociky small diameter jet o~
the dual phase coolant. The conversion occurs su~stantially instantly, smoothly and in a highly stable manner without need ~or making any adjustmants or change in the position o~ th~;
needle valve.
Opening o~ the venting valve is observed to allow a small amount o~ gaseous phase coolant to be bled from the forward end of the expansion chamber and this is accompanied by à sli~h~ drop in the expansion chamber pressure as is clearly evident ~rom a comparison of cur~es 66 a~d 57 in Figure 4. Under the operating conditions depicted, this pressure drop is a small ~raction o 1 psi ~or all positions o~ throttle valva 32 corresponding to hal~
to ~ully open position. It is observed that the volwme o~ coolant issuing ~rom the venting passage 55 is relatively small and completely in gas phaseO So long as the venting valve 56 remains open the device continues to operate in the same uni~orm stable manner irrespective o tha position in which the device is held or the manner in whi~h it is manipulated. The coolant jet may bs directed at will by the operator in either vertical direction or in any intermediata direckion withvu~ change in the character-istic of the je~.
Upon relaase o~ the pressure on the oparating hand~le 57 o~
valve 56, this valve recloses cuttLng off the discharge o~
gaseous coolant ~.rom the venting orifice 55 whereupon the device instantly resumas jatting of gas phase coolant through ths jetting ~ri~icaO ~here i5 no need to make any ad~ustmant of tha naedle valve.

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l If the operator wishes to change the size and flow rate of the jet he simply cl~ses valve 32 and detaches needle 51,52 ~rom the Iuer fitting 50 and substitutes a needle of different size.
When the coolant dispenser i~s not in use, valves 32 and 56 remain closed. Relief valve 43 opens only momentarily at inter-vals as necessary to maintain ths internal pressure of the dewar constant with the result that coo:Lant losses are very small between operating cyclesO For example, it is ound that a dewar having a charge capacity of approximately one pint is adequate for seven to eight hours of normal usage, o~ many times longer than prior cryogenic dispensers of similar storage capacity.
While the particular sel pressurizing cryogenic apparatus and mathod herein sho~ and disclosed in detail is fully capable of attaining the objects and providing the advantages hereinbeore stated, it is to be understood that it is marely illustrative of the presently preferred embodiment of the invention and that no limitations are intended to the detail of construction or design herein sho~ other than a~ defined in the appended claimsO

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Cryogenic apparatus for producing sub-freezing temperatures comprising an expansion chamber having an inlet and a small bore restricted outlet and adapted to be connected by a flow control valve to a source of pressurized liquid cryogen maintained substantially at a predetermined pressure, bleed passage means in communication with the interior of the expansion chamber and the atmosphere, communication to the atmosphere being controlled by a valve which when closed provides a flow of gaseous phase cryogen from said outlet and when open provides a dual phase flow of finely divided liquid cryogen mixed with the gaseous phase cryogen from said outlet.

2. Cryogenic apparatus as claimed in claim 1 wherein the valve for controlling communication to the atmosphere is manually controlled and is independent of said inlet and outlet.

3. Cryogenic apparatus as claimed in claim 1 wherein the expansion chamber is elongated and the inlet and outlet are located adjacent the opposite ends thereof.

4. Cryogenic apparatus as claimed in claim 1 wherein the expansion chamber is mounted on a removable closure for the inlet of a dewar chargeable with liquid cryogen and includes means for supplying pressurized liquid cryogen to the inlet of the expansion chamber.

5. Cryogenic apparatus as claimed in claim 4 wherein the means for supplying pressurized liquid cryogen to said inlet of said expansion chamber is a manually controlled valve.

6. Cryogenic apparatus as claimed in claim 1 wherein the valve for controlling communication to the atmosphere is normally closed whereby the pressure in the expansion chamber is maintained slightly higher than when said valve is open.

7. Cryogenic apparatus for selectively spraying cryogen in single gas phase or dual phase gas and liquid which comprises:
a source of pressurized liquid cryogen;
an expansion chamber connected to said source through a flow control valve;
a restricted spray nozzle having a diameter measured in mils connected to said expansion chamber through which cryogen is discharged to atmosphere by the pressure in said expansion chamber; and means to reduce the pressure in said expansion chamber to cause the discharge cryogen to change from single phase gas discharge to dual phase gas and liquid particle comprising:
a bleed passage connected to said expansion chamber sized to convey gaseous cryogen under pressure from said chamber in amounts sufficient to reduce slightly the pressure in said chamber; and manually operable valve means to open and close said bleed passage.

8. Cryogenic apparatus as claimed in claim 7 wherein valve means are provided to control the flow of gaseous cryogen through said bleed passage.

9. Cryogenic apparatus as claimed in claim 7 wherein said bleed passage is open to interior of said chamber adjacent the inlet to said spray nozzle.

10. Cryogenic apparatus as claimed in claim 7 wherein the bleed passage is effective to reduce the pressure in said chamber by less than 1 psi.

11. Cryogenic apparatus as claimed in claim 7 wherein the expansion chamber is elongated and the inlet and outlet are located adjacent the opposite ends thereof.

12. Cryogenic apparatus as claimed in claim 7 wherein the expansion chamber is mounted on a removable closure for the inlet of a dewar chargeable with liquid cryogen and includes means for supplying pressurized liquid cryogen to the inlet of the expansion chamber.

13. Cryogenic apparatus as claimed in claim 7 wherein pressure relief valve means are provided to control the maximum pressure of said source.