Self-pressurizing cryogenic apparatus and method

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.

This invention relates to cryogenic apparatus and more particularly to 
simply constructed, hand-held means for dispensing a jet of cryogenic 
coolant onto an area to be necrotized from a self-pressurizing source of 
heat saturated liquid coolant having a boiling point below -100.degree. C. 
BACKGROUND OF THE INVENTION 
Equipment for dispensing a cryogenic liquefied gas onto a surface or object 
to be sharply cooled has been proposed heretofore. These are designed to 
utilize liquefied gas such as helium, nitrogen, oxygen, air, carbon 
dioxide, etc., stored in a suitable container. The liquid coolant is 
supplied therefrom to a dispensing port or nozzle in various ways 
including applying heat electrically or otherwise to the coolant to 
vaporize the liquid. Other designers pressurize the storage container to 
produce coolant flow by introducing air under pressure into the storage 
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 container produces a flow of 
coolant to the dispensing nozzle. The pressure build-up is slow and 
uncertain and varies widely depending on the volume of the vapor space and 
the quantity of liquid coolant in the storage chamber, the rate of heat 
leakage into the container and other factors. 
One category of prior cryogenic devices dispenses a jet of coolant vapor 
directly onto the area to be cooled whereas those of another category 
confine the stream of coolant vapor to a flow passage typically provided 
with a return bend sector formed of excellent heat conductive material and 
venting to the atmosphere at a remote point. The heat conducting member 
can be placed close to or in contact with the surface to be cooled without 
risking direct contact of the gas coolant with that surface. 
It has been recognized that it would be advantageous to deliver coolant in 
liquid phase onto or in close proximity to the area to be sharply cooled 
in order to utilize the latent heat or 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 is 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 cooling 
capacity of liquid coolant very great but, upon entering the atmosphere, 
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 jet, fluctuating spurts 
of the coolant jet, time delay and waste involved in establishing a 
coolant jet, 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 
To avoid the numerous shortcomings and disadvantages of prior cryogenic 
equipment, there is provided by this invention a self-pressurizing, 
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 usage without recharging, yet is so small and lightweight 
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 readiness for dispensing in a 
stable heat saturated condition. When open, a coolant flow control valve 
permits the coolant to flow into an expansion chamber equipped with a 
relatively long small bore outlet nozzle or orifice and normally open 
venting orifice cooperating with the outlet or coolant jetting orifice to 
limit the pressure differential across the flow control valve to a 
fraction of the pressure in the supply chamber. This pressure differential 
greatly limits the flashing of coolant into vapor. Additionally, and by 
properly proportioning the sizes of the outlet and venting orifices and 
the regulation of the latter, the invention apparatus is instantly 
self-stabilizing and operable to dispense either a needle-like jet of 
coolant in a dual phase of fine liquid particles and gas, or a jet of 
gaseous phase coolant depending upon whether gaseous coolant is vented 
from the venting orifice. The increased velocity imparted to the jet owing 
to the flashing of some superheated liquid into gas aids very 
substantially in increasing the "chill-factor" and thereby the 
effectiveness and efficiency of the device. For example, when using liquid 
nitrogen as the coolant, the temperature of this coolant in gas phase when 
dispensed from the nozzle of this invention is somewhat about 32.degree. 
F. whereas the temperature of the issuing jet of dual phase coolant 
containing superheated liquid coolant is at least -300.degree. F. Further 
lowering of the temperature known as the "chill-factor" results as the 
rapidly flowing jet of particles of liquid coolant flash into the gaseous 
phase. 
If the venting passage is open a portion of the coolant which is flashed 
into gas is bled from the expansion chamber and the resulting small drop 
of pressure in the expansion chamber converts the jet discharge 
substantially instantly from single to dual phase constituency without 
need for adjusting the flow control valve. Likewise, the jet discharge is 
converted instantly back to single phase by closing the venting orifice. 
Partial closing of the venting orifice merely varies the relative 
proportions of gas and liquid in the jet. 
The stability of the device is enhanced by insulating the liquid flow 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 dispensing cycle where a dispensing 
operation occurs before a new charge of coolant has become fully heat 
saturated. 
Accordingly, it is a primary object of this invention to provide a 
self-pressurizing, self-stabilizing cryogenic device selectively operable 
to dispense a jet of single-phase or dual phase coolant having a boiling 
point below -100.degree. C. 
Another object of the invention is the provision of a unique method and 
apparatus for dispensing a jet of cryogenic coolant from a heat saturated 
uniformly pressurized source thereof and which is quickly convertible 
between single phase gaseous constituency and dual phase constituency. 
Another object of the invention is to provide a self-contained hand-held 
cryogenic device which is instantly self-stabilizing to dispense a jet of 
finely divided liquid coolant. 
Another object of the invention is the provision of a cryogenic device for 
selectively dispensing a stabilized jet 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.degree. F. 
Another object of the invention is the provision of a self-pressurized 
cryosurgery device which is instantly self-stabilizing and effective to 
dispense a continuous non-varying coolant jet or a readily varied jet of 
either single or dual phase coolant. 
Another object of the invention is the provision of a self-pressurized, 
self-stabilizing cryogenic device having 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 jet dispensing orifice. 
These and other more specific objects will appear upon reading the 
following specification and claims and upon considering in connection 
therewith the attached drawing to which they relate.

Referring initially more particularly to FIG. 1, there is shown an 
exemplary embodiment of the invention cryogenic device, 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 of a 
considerable number of other liquefied gases having a boiling point of 
-100.degree. C. 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 steel 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 lining 18 of the dewar 
cover or cap 19. 
The dispensing and control components of the cryogenic device will be best 
understood by reference to FIGS. 2 and 3. These components include a main 
body fitting 20 having a threaded tubular shank projecting downwardly from 
its lower side and extending through an opening in 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 tubular dewar 
charging inlet or opening 25. As is best shown in FIG. 1, stopper 24 has a 
shoulder seating 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 (FIGS. 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 valve 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 silver-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-walled brass or stainless steel to present 
as small a conductive heat path as is practical into the liquid coolant 
and to assure that failure or breakage of the cryogen dispensing tubes 
will occur in tube 38 rather than in the inner end of tube 36. 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 the relatively weak tube 38 should the latter become damaged when cap 
19 is disassembled for charging or otherwise. Each of the tubes 36 and 38 
is preferably covered with heat insulating material 39, 40 to aid in 
stabilizing the operation of the apparatus by preventing the flow of 
liquid coolant through these tubes to cool and condense portions of the 
coolant vapor present above the liquid level. This could interfere with 
maintaining a uniform pressure head on the liquid while valve 32 is open 
and could cause unstable conditions in the jet of coolant before the 
coolant becomes fully heat saturated. 
The dewar is automatically maintained at a predetermined superatmospheric 
pressure by the vapor pressure of 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 21. 
The valve proper 45 of the relief valve is normally held seated against 
the outlet end of passage 34 by a calibrated spring, not shown, but housed 
within the valve body. An extension 46 protruding from this valve is 
readily manipulatable by the operator's finger to unseat the valve and 
release the pressure in the dewar whenever this is desirable, as before 
removing cap 19 to renew the supply of coolant 12. 
Permanently assembled to the outer end of expansion chamber 35 is a Luer 
fitting 50 of well known construction providing a readily disconnectable 
coupling for the shank fitting 51 of a non-pointed or blunt-ended 
hypodermic needle 52 providing an elongated small bore nozzle or outlet 
orifice for chamber 35. It will be understood that other outlet orifice 
constructions can be employed but readily available hypodermic needles 
having bores ranging in size from 22 to 25 guage have been found highly 
satisfactory and are quickly and easily substituted for one another to 
vary the size of the coolant jet dispensed from the expansion chamber. A 
22 guage needle has a bore diameter of approximately 17 mils as compared 
to the 11 mil bore of a guage 25 needle. Needle lengths of 1/4" to 3/4" 
are found very satisfactory for use with outlet orifices ranging in size 
from 11 to 17 mils in diameter. The length of the needle varies with the 
size of the bleeder orifice. A longer needle necessitates bleeding a 
greater volume of gaseous phase coolant from the expansion chamber. 
A very important further feature of the invention is the provision of means 
for venting coolant in gas phase from chamber 35 thereby to vary the 
pressure in chamber 35 relative to the substantially predetermined 
pressure in the dewar flask without adjusting the flow control valve 30. 
As herein shown by way of example, this venting means is provided by tube 
54 extending along the interior of chamber 35 with its right-hand end in 
communication with a passage 55 formed interiorly of body 20. This passage 
is shown in dot and dash lines and includes a vertical leg and a 
horizontal leg the latter of which opens to the atmosphere on the 
left-hand side of the main body 20 (FIG. 3). Normally, the outlet end of 
passage 55 is closed by a valve 56 mounted on one end of an L-shaped 
operating lever 57 of poor heat conductive material such as stainless 
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 55. 
To avoid tolerance problems in the manufacture of the venting orifice or 
passage, it is found convenient to provide this passage with a loose 
packing or restrictor to limit the flow of coolant gas allowed to escape 
to the atmosphere. A very satisfactory restrictor comprises a mass of 
brass wool or the like here shown as located at the junction of the 
vertical and horizontal legs of passage 55. Access to this mass 63 is 
provided by a closure cover 64 to the end that the density of this 
restrictor may be readily adjusted at the time of manufacture. Thereafter, 
closure plug 64 may be suitably secured in place since no further 
adjustment is required so long as the same size pressure relief valve 43 
and the same range of sizes of outlet orifice needles 52 are employed. 
Referring now to FIG. 4, there is shown a graph depicting typical operating 
conditions for the cryogenic device herein described when using liquid 
nitrogen as the coolant and a pressure relief valve calibrated to maintain 
a pressure of 10 psig. It will be understood that this pressure is merely 
representative of a pressure found to provide excellent operating 
characteristics when using outlet passages of the range of sizes described 
above. This constant pressure condition is represented by the straight 
horizontal line 65 in FIG. 4. The next lower curve 66 represents the 
pressure condition within expansion chamber 35 when a 22 guage needle 52 
is employed as the jetting orifice as needle valve 32 is opened from its 
closed to its open position. Curve 67 shows the slightly lower pressure 
condition created in the expansion chamber when the control lever 57 is 
depressed to open valve 56 normally closing the venting passage or orifice 
55. 
Normally the dewar flask is charged with liquid nitrogen and needle valve 
32 and venting valve 56 are closed. With the pressure relief valve 43 set, 
for example, to maintain the pressure within the flask at 10 psig, the 
coolant will be heat saturated and have a temperature of -312.degree. F. 
As soon as control knob 31 is operated to open needle valve 32, liquid 
coolant will rise through conduit 38 and flow past the needle valve 
whereupon a portion of it will quickly become super-heated as it 
experiences a pressure drop in flowing past the needle valve into the 
relatively warm expansion chamber 35. The resulting violent boiling or 
flashing of the coolant fractionates the liquid into a multiplicity of 
fine minute particles as other portions convert to the gaseous phase, 
thereby almost instantly raising the back pressure in the expansion 
chamber to a value somewhat in excess of one pound less than the internal 
dewar pressure. Coolant in substantially pure gaseous phase then jets at 
high velocity from the jetting orifice. A layer of frost also quickly 
collects on the outer surface of the expansion chamber 35 thereby 
providing an excellent heat insulating layer for this chamber which 
greatly minimizes the quantity of coolant going into its gas phase. The 
cryosurgery device may now be grasped in the operator's hand and 
manipulated to direct the jet of gaseous coolant onto an area to be 
sharply cooled. 
If the operator wishes to convert the jet to one comprised of finely 
divided particles of coolant in liquid phase intermixed with gaseous phase 
coolant, he simply depresses lever 57 to open vent valve 56. Immediately 
that this takes place the jet converts to a high velocity small diameter 
jet of dual phase coolant. The conversion occurs substantially instantly, 
smoothly and in a highly stable manner without need for making any 
adjustments or change in the position of the needle valve. 
Opening of the venting valve is observed to allow a small amount of gaseous 
phase coolant to be bled from the forward end of the expansion chamber and 
this is accompanied by a slight drop in the expansion chamber pressure as 
is clearly evident from a comparison of curves 66 and 67 in FIG. 4. Under 
the operating conditions depicted, this pressure drop is a small fraction 
of 1 psi for all positions of throttle valve 32 corresponding to half to 
fully open position. The volume of coolant issuing from the venting 
passage 55 is relatively small and completely in gas phase. So long as the 
venting valve 56 remains open the device continues to operate in the same 
uniform stable manner irrespective of the position in which the device is 
held or the manner in which it is manipulated. The coolant jet may be 
directed at will by the operator in either vertical direction or in any 
intermediate direction between vertical and horizontal without change in 
the characteristics of the jet. 
Upon release of the pressure on the operating handle 57 of valve 56, this 
valve recloses cutting off the discharge of gaseous coolant from the 
venting orifice 55 whereupon the device instantly resumes jetting of gas 
phase coolant through the jetting orifice. There is no need to make any 
adjustment of the needle valve. 
If the operator wishes to change the size and flow rate of the jet he 
simply closes valve 32 and detaches needle 51, 52 from the Luer fitting 50 
and substitutes a needle of different size. 
When the coolant dispenser is not in use, valves 32 and 56 remain closed. 
Relief valve 43 opens only momentarily at intervals as necessary to 
maintain the internal pressure of the dewar constant with the result that 
coolant losses are very small between operating cycles. For example, it is 
found that a dewar having a charge capacity of approximately one pint is 
adequeate for seven to eight hours of normal usage, or many times longer 
than prior cryogenic dispensers of similar storage capacity. 
While the particular self-pressurizing cryogenic apparatus and method 
herein shown and disclosed in detail is fully capable of attaining the 
objects and providing the advantages hereinbefore stated, it is to be 
understood that it is merely illustrative of the presently preferred 
embodiment of the invention and that no limitations are intended to the 
detail of construction or design herein shown other than as defined in the 
appended claims.