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Патент USA US3037369

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June 5, 1962
J. B. sTARNEs ETAL
3,037,360
PRODUCTION OF‘ COLD REFRIGERANT GAS
Filed May 17. 1960
4 Sheets-Sheet 1
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INVENTORS
JESSE B. STARNES
PAUL E. LOVEDAY
RICHARD R. CARNEY
A 7'TORNEV
June 5, 1962
J. B. STARNES ET AL
.
3,037,360
PRODUCTION‘ OF cow REFRIGERANT GAS
Filed May 17, 1960
4 Sheets-Sheet 5
INVENTORS
JESSE B. STARNES
PAUL E. LOVEDAY
RICHARD R. CARNEY
‘WWW
A TTORN Y
June 5, 1962
3,037,360
J. B. STARNES ET AL
PRODUCTION OF cow REFRIGERANT GAS
Filed May 17, 1960
4 Sheets-Sheet 4
lNVENTORS
JESSE B. STARNES
PAUL E. LOVEDAY
RICHARD R. CARNEY
B
A T TORNE )2
.
Unite States
latent
3,037,360
Patented June 5, 19162
1
2
3,037,360
air is provided ‘at ambient temperature and at a desired
flow rate, the gas containing at least one condensable im
purity such as carbon dioxide as an atmospheric contami
nant. A source of low-boiling lique?ed gas refrigerant,
PRODUCTION OF COLD REFRIGERANT GAS
Jesse B. Starnes, Snyder, Paul E. Loveday, Tonawanda,
and Richard R. Carney, Kenmore, N.Y., assignors to
Union Carbide Corporation, a corporation of New
York
Filed May 17, 1960, Ser. No. 29,628
10 Claims. (Cl. 62-97)
e.g. nitrogen, is also provided and the compressed gas is
cooled and at least partially cleansed by indirect heat ex
change with the liquid refrigerant. The heat exchange is
continued for su?icient duration to completely vaporize the
liquid refrigerant, and the cooled, cleaned gas is mixed
‘This invention relates to a method of and apparatus 10 with the vaporized refrigerant so as to form the cold
refrigerant gas at desired volume and temperature.
for producing a cold refrigerant gas, and more speci?cally
In a preferred embodiment, the compressed gas stream
to a system ‘for producing a cold gaseous refrigerant in
is supplied at a ?rst higher pressure, reduced to a second
selectable quantities and of selectable temperature.
lower pressure, and thereafter throttled sufficiently to ob
Cold refrigerant gases are widely used for treating ma
terials. For example, the physical strength of welded 15 tain critical ?ow before cooling with the liquid refrigerant.
The expression “critical ?ow” as used herein refers to the
honeycomb panels such as the type disclosed in U.S. Pat
gas flow quantity existing when the absolute pressure ratio
ent No. 2,849,591 to Fullerton et al. is greatly bene?ted
in the throttling step reaches a certain maximum value,
by low temperature treatment after welding. Also, cold
which on further increase in such ratio does not further
refrigerant gases may 'for example be employed in chilling
metal parts prior to shrink ?tting, freezing and refrigerat 20 decrease the mass ?ow rate.
It will be noted that one of the important features of a
ing perishable products such as foods or biologicals, ad
preferred embodiment of this invention is the employment
in low temperature grinding operations.
of liquid nitrogen as the refrigerant, and recovery of its
The prior art has proposed numerous systems for sup
latent and sensible refrigeration by indirect heat exchange
plying cold refrigerant gases. For example, a high pres
sure refrigeration circuit employing a closed fluid stream 25 with the compressed air. One could vaporize liquid nitro
gen by atmospheric heat and then superheat the resultant
such as Freon could be employed, but the required equip
nitrogen gas also by external heat to the desired tempera
ment has been found to be prohibitively expensive.
ture for the refrigerant gas. However, this procedure
Another proposal has been to introduce an air stream
would be extremely inef?cient because over one-half of
into a liquid refrigerant scrubber, but such an arrange
ment only provides a gas mixture at one temperature 30 the available refrigeration in the liquid nitrogen is dis
level. Industrial needs dictate that a practical cold refrige
rant gas generation system be capable of producing gas at
selectable :?ow rates and selectable temperatures. For this
reason, the scrubbing arrangement would also require
auxiliary means for varying the gas temperature, and
such means entail additional complicated equipment and
expense.
carded to the atmosphere.
Any system which utilizes
external heat to vaporize a low temperature lique?ed gas
and warm the resultant vapor to the desired temperature
for refrigerant purposes can deliver a volume of refriger
ant gas only equivalent to the volume of lique?ed gas con
sumed. ‘In the present method, the latent heat of the
liquid nitrogen is employed to cool and clean a large
volume of another gas, air, which is then employed to
A principal object of this invention is to provide an im
augment the total volume of delivered refrigerant gas.
proved system for producing cold refrigerant gas in se
40 Assume, for example, that a consumer requires 1,000 cu.
lectable quantities and at selectable temperatures.
ft. N.T.P. per hr. of refrigerant gas at ——100° F. A simple
Another object is to provide an improved cold refrig<
erant ‘gas generation system which is simpler and more
liquid nitrogen vaporizing and superheating system using,
atmospheric heat would require 1,000 cu. ft. N.T.P. per
e?icient than the heretofore proposed systems.
hr. of liquid nitrogen for this purpose. In marked con
These and other objects and advantages of this inven
tion will be apparent from the following description and 45 trast, the present invention requires only 250 cu. ft. N.T.P.
er hr. liquid nitrogen, the remainder of the gas volume
accompanying drawings in which:
FIGURE 1 is a schematic ?ow diagram of a system
for producing a cold refrigerant gas according to the
being provided as low cost raw air.
In the present invention, liquid nitrogen is uniquely
suited as the source of refrigeration in view of its inertness,
50 cleanliness, and low boiling point of —320° F. at atmos
FIGURE 2 is an enlarged front elevational view of a
present invention;
x."
hydraulically expanded assembly which is rolled to form
the internal passageways of the heat exchanger in ‘FIG
URE 1;
pheric pressure. ‘Other refrigerants do not possess all of
these characteristics. For example, solid carbon dioxide
has been considered and discarded since its sublimation
temperature is about —109° R, which imposes a severe
FIG. 3 is an enlarged partial isometric view of the 55
limitation on this compound as a refrigerant at the —lO0°
FIGURE 2 assembly;
'F. level. The driving force for heat transfer (AT) would
‘FIGURE 4 is an elevation-a1 view taken partly in cross
be very small at the end of the refrigeration step, and the
section, of a heat exchanger suitable for employment in
sensible refrigeration available in the refrigerant gas at
the FIGURE 1 system;
I
FIGURE 5 is an end view of the heat exchanger taken 60 this temperature level is also very small.
Although nitrogen is the preferred low-boiling lique?ed
along the line 5-.~5 of FIGURE 4;
FIGURE 6 is an end View of a heat exchanger similar
, to that shown in rFIGURES 4 and 5, but modi?ed to afford
countercurrent instead of concurrent flow;
gas refrigerant, air is the preferred compressed gas, and
the invention will be speci?cally described in terms of
these components, it is to be understood that other ?uids
may be used in the invention. For example, nitrogen,
FIGURE 7 is a front elevational view of an alternate 65
helium, neon or argon would be suitable for use as the
heat exchanger suitable for use in the FIGURE 1 system;
and
.
FIGURE 8 is a front elevational view of another alter
nate heat exchanger.
compressed gas component, and any lique?ed gas having
a boiling point below about 120° K. may be employed
as the lique?ed gas refrigerant, for example, argon, helium
According to this invention, a method is provided for 70 or neon. If the particular intended use for the cold re
frigerant gas necessitates an inert ?uid, a combination of
producing a cold refrigerant gas at desired, selectable
nitrogen liquid and compressed nitrogen gas may be ad- a
volume and temperature vwherein compressed gas such as
3,037,360
3
FIGURE 1, liquid nitrogen is stored in thermally insulated
A
A valve 38, preferably of the extended stem type, is
provided at the discharge end of the nitrogen passageway
25, the latter ?uid having been vaporized and superheated
container 10. This container may, for example, be of
the type disclosed in US. Patent No. 2,725,722 to P. M.
in such passageway. The nitrogen flow rate is held sub
stantially constant by the uniform pressure within the
Ahlstrand et al., or in US. Serial No. 599,733 ?led July
24, 1956 in the name of P. E. Loveday et al., now Patent
No. 2,951,348. Container 10 is provided with suitable
liquid nitrogen supply container 10 and by a ?xed setting
of valve 38. On discharge of cold nitrogen gas from valve
vantageously employed in the practice of this invention.
Referring now more speci?cally to the drawings and
38 into the surrounding space, mixing occurs between
safety devices to prevent excessive pressure buildup there
the cold nitrogen gas and the partially cooled and cleaned
in, as for example, bursting disk 11 and gas relief valve 12. 10 air, thereby producing the desired cold refrigerant gas.
Also, a source of compressed nitrogen gas may he provided
The latter is then discharged from heat exchanger assem
and introduced to the container 10 through conduit 13
bly 17 for use as desired through conduit 39 extending
having regulator valve 14 therein. The compressed nitro
through the casing wall. The temperature of the cold
refrigerant gas may be visually observed by reading
gen gas serves to generate su?icient pressure in container
10 to force the liquid out through withdrawal conduit 15
and control valve 16 therein.
If container 10 is to be portable and thus service sev
eral stationary heat exchangers, or is to be removed for
recharging with liquid nitrogen, it may be connected to
heat exchanger assembly 17 by charging conduit 18. The
latter is connected at opposite ends to withdrawal con~
duit 15 and delivery conduit 19 by couplings 20, and con
tains safety valve 21 to prevent excessive pressure buildup
when the nitrogen ?ow path is dead-ended in heat ex
changer 17. The liquid nitrogen ?ow is controlled by
means of valve 22 in delivery conduit 19, the latter also
containing pressure gage 23 and safety valve 24. Liq
uid nitrogen delivery conduit 19‘ passes through the outer
walls of heat exchanger 17 and terminates in passageway
25.
Compressed air containing normal atmospheric im
purities is introduced through conduit 26, cleaned of
solid particles in ?lter 27, and reduced in pressure to an
intermediate value such as 60 p.s.i.g. in regulator 28.
Pressure gage 29 provides a visual indication of the pres
sure downstream of regulator 28, and the air stream is
further throttled to valve 30 su?iciently to obtain critical
?ow across such valve. The pressure downstream of valve
30 may be on the order of 22 p.s.i.g., and due to the
critical ?ow feature, further reduction of pressure would
not produce an increase in the mass ?ow rate. The low
pressure air, preferably at about 22 p.s.i.g., is then passed
through ?ow-indicating rotameter 31 to heat exchanger
assembly 17, the temperature and pressure of such gas
being visually indicated by thermometer 32 and gage 33,
respectively. By maintaining a constant intermediate pres
sure after valve 28, and maintaining critical ?ow across
valve 30, the air ?ow rate is made independent of pres
sure ?uctuations which may occur within the heat ex
changer assembly 17 or the air supply piping.
Heat exchanger assembly 17 comprises a casing 34
which is thermally insulated by a layer of low-conductive
gage 40.
As previously discussed, the nitrogen and air ?ow rates
are preferably maintained constant, so that the discharge
temperature indicated by gage 40 will not vary signi?
cantly despite possible pressure ?uctuations. One of the
important advantages of the invention is that extreme
?exibility in cold refrigerant gas ?ow rates and tempera
tures is achieved in a simple and reliable manner.
For
example, if a relatively colder refrigerant gas is desired
this may be achieved by further opening the nitrogen
discharge valve.
On the other hand, if a warmer re
frigerant gas is needed, valve 38 would be closed an
appropriate amount. If a relatively larger quantity of
refrigerant gas is to be provided at the same tempera
ture, either or both regulator ‘28 and valve 30 are opened
to increase the .air ?ow and valve 38 is further opened
to increase the nitrogen ?ow a corresponding amount.
Since the circulating air Will always be cooled below
the dew point of water and often below the dew point
of carbon dioxide, these atmospheric contaminants will
be continuously deposited on the various surfaces inside
casing 34. Continuous operation of the heat exchanger
assembly 17 Without shut down would eventually result
in excessive pressure drop on the air side due to de
posited water ice and solid carbon dioxide. However,
duplicate assemblies may be provided and operated alter
nately with the off-stream assembly being thawed and
prepared for reuse. If desired, only the colder portion
of the heat exchanger assembly need be duplicated for
alternate operation; the remaining major portion of the
exchanger freezes out a minor part of the impurities and
is capable of extended operation without thawing. To
this end, drain conduits 41 are provided for removal of
water from the casing.
As shown in detail in FIGURES 2 and 3, the pre
ferred nitrogen conduit comprises a pair of elongated
conductive sheets 50 and 51, preferably of aluminum
or other heat conductive metal, disposed in spaced con
material 35 such as polyurethane foam, so as to reduce
tact to form a cellular structure having therebetween a
the heat in leak and loss of refrigeration to the atmos
labyrinth of internal passages 52, 53, 54, 55 and 56 for
nitrogen ?ow. These passages may be formed by plac
ing ?at sheet 5-5 upon ?at sheet 51, and bonding together
in suitable manner the marginal edges and registering
areas 57, illustrated herein the form of rectangular and
square buttons, and hydraulically expanding the areas
adjacent thereto to form walls 50 and 51 of the internal
passageways. This expansion can be accomplished by
providing inlet and outlet connections opening into
the unbonded areas between the sheets 59 and 51, and
phere. Although the heat exchanger may be any type
affording intimate thermal contact between the nitrogen
refrigerant and the cooling air, a pair of coiled and elon
gated thermally conductive plates disposed in spaced con
tact to form a cellular structure, have been found par
ticularly suitable. These plates are illustrated schemati
cally in FIGURE 1 as forming nitrogen passageway 25,
and will be described later in detail. The vaporizing nitro
gen in passageway 25 and the cooling air ?ow cocurrently
in thermal association from one end to the other end
of heat exchange assembly 17 in the space bounded by
casing 34 and longitudinal baffle 36, whereupon the flows
through which hydraulic ?uid is introduced for expanding
such areas to provide passages. The internal passages
' formed thereby may be of varying shape and dimension
through the length of conduit 25 to suit the character of
the ?uid ?owing in the passages at each point therein.
The passages adjacent the liquid inlet are preferably of
of baf?e 36 and second longitudinal ba?le 37 for further
heat exchange. Finally, the flow directions of the two 70 the type shown in FiGURE 3 which permit low and
approximately equal flow resistance in either vertical or
heat exchanging ?uids are again reversed for end-to-end
horizontal directions. Such pattern is conducive to good
passage through the space bounded by the opposite side
distribution of the liquid across the width of the vaporizer
of second longitudinal ba?le 37 and casing 34. Safety
so that the operating load is uniform.
valve 37a is provided to relieve any abnormal pressure
Above the liquid distributing section containing pas
buildup Within casing 34.
75 sages 52, the passages are preferably formed as long,
are reversed and the two streams pass in the opposite
direction through the space boundedby the opposite side
I).
3,037,360
5
6
and collect in such compartment. Second S-shaped drain
vertical channels 53 comprising the vaporizing section.
conduit 84 connects with the inner container 72, and
drains water condensing in the next 360° of the air ?ow
path. Additional drain conduits may be provided if
Such passages are advantageous in promoting a priming
action wherein the ?uid with increasing vapor content
accelerates upward through the channels and by its turbu
lence brings the ?uid in good heat exchange relation
desired.
Although the air and nitrogen streams have been illus
trated and described as being heat exchanged cocurrently,
countercurrent flow is also practicable. The latter offers
with the conduit walls.
As the nitrogen ?uid emerges from the upper ends
of vaporizing channels 53, any remaining unvaporized
certain advantages since the air would be cooled to a
liquid will either be disengaged from the vapor in pas
sages 54 above, or will be reduced to tiny vapor-borne 10 much lower temperature by the nitrogen and would there
fore be considerably cleaner with respect to carbon diox
droplets or mist. The passages 54 forming the separa
ide. Also, liquid water may be ?rst condensed and
tor section are somewhat similar to passages 52, provid
drained oif so that the life of the frost zone is longer.
ing low flow resistance in vertical and horizontal direc
Simultaneously, the nitrogen is warmed to a substan
tions favorable to disengagement of remaining liquid.
Passages 54 also provide much extended wall surfaces 15 tially higher temperature by countercurrent heat exchange,
and subsequent mixing would provide the same degree
on which any disengaged liquid is held and vaporized.
of operating ?exibility as with cocurrent heat exchange.
A vapor superheating section above the separator sec
One advantage of cocurrent exchange is that the dis
tion contains long vertical passages 55 similar to vaporiz
charge temperatures of the mixed streams are somewhat
ing channels 53. If desired, passages 55 may be inter
easier to control and maintain at desired levels.
rupted by one or more horizontal passages 58 for assur
FIGURE 6 illustrates how the heat exchanger of
ing good distribution of the fluid among the superheating
FIGURES 4-5 may be arranged for countercurrent rather
channels.
Above the superheating section, a gas collecting sec
than cocurrent heat exchange. That is, the positions of
tion is formed of passages 56 similar to passages 52.
the nitrogen inlet and outlet connections are interchanged
The warmed gas leaving passages 55 ?ows upwardly 25 so that liquid nitrogen is introduced to the innermost
and horizontally to the withdrawal connection 59, and
spiral through conduit 85 and discharged as gaseous
the horizontal ?ow must be accompanied by very low
nitrogen from the outermost spiral through connection 86
pressure difference across the width of the heat exchanger
for mixing with cooled air to form the cold refriger
so as not to upset the flow distribution.
It will be noted that the vaporizer section (passages 30
ant gas.
FIGURE 7 shows an alternative heat exchanger as
53) and superheating section (passages 55) of FIGURE
sembly 90 which could be substituted for the assembly 17
of FIGURE 1. That is, the assembly within the dotted
jority of the heat transfer into the gas material and
lines of FIGURE 1 may be replaced with assembly 90.
comprise the major portion of the heat exchanger length.
Referring now more speci?cally to the latter, casing 90a
FIGURES 4 and 5 show an assembly preferred as 35 contains two nitrogen passageways 91 piped in parallel,
the heat exchanger 17 of FIGURE 1, although other
which may be of the partially bonded, hydraulically ex
types of heat transfer surface could be employed, for ex
panded type illustrated in FIGURES 2 and 3. Low pres
ample, externally ?nned tubes or smooth tubes, metal
sure air is introduced downwardly through opening 92
bonded to sheets of metal. However, the FIGURES
in the top of the casing 90a, and ?ows in countercurrent
2—5 construction is preferred from the standpoints of 40 indirect heat exchange with vaporizing liquid nitrogen
convenience, compactness, portability and low cost. The
rising through either of passageways 91, the latter hav
FIGURE 2 and 3 sheet assembly is preferably coiled into
ing been introduced through conduit 19 at the base of
a spiral 70 around a center pipe core 71, and the spiral
the assembly. The warmed vaporized nitrogen is with
2 are fore-shortened.
These sections provide the ma
assembly is positioned inside an inner pressure container
consisting of cylindrical side walls 72 and welded end
closures 73.
Outer cylindrical casing 74 with end clo
drawn from the top ‘of conduits 91 into a manifold 93, and
45 directed through conduit 94 having ?ow control valve
95 therein. Meanwhile the cold, cleaned air leaves the
bottom of casing 90a through conduit 96, and is joined
by the vaporized nitrogen from conduit 94 for mixing
sures '75 form a space 76 for insulation around the inner
container.
Liquid nitrogen is introduced through conduit 77 into
the internal passageways 25 .at the outer edge of the
spiral heat exchanger. After ?owing through the ex
changer to the inside edge of the spiral, the resulting
cold nitrogen gas leaves the passageways 25 through
outlet connection 78 joining discharge valve 38. This
valve is positioned in side the center pipe core 71 and it
and formation of the cold refrigerant gas.
50
It will be
appreciated that the desired quantities and proportion of
air and nitrogen may obtained by the same procedure as
previously described in conjunction with FIGURE 1.
Furthermore, although illustrated in FIGURE 7 in the
vertical position, this is not essential and the horizontal
55 or up-ended positions are suitable and would assist drain
discharges cold nitrogen gas into such core.
age of water from the exchanger.
Two radial partitions 79 are positioned across the
FIGURE 8 illustrates still another alternate heat ex
insulation space 76 and are longitudinally sealed to the
changer assembly 97 similar in appearance to that of
inner wall of the outer casing 74 and the outer wall of
FIGURE 7, except that the vaporized nitrogen stream is
the inner container 72 so as to form an inlet compart
60 not withdrawn from the heat exchanger for external mix
ment 80 for the warm air entering through conduit 19.
ing. Instead, it is released directly from the upper ends
This compartment is devoid of insulation and the air is
of passageways 91 into the entering air stream and returns
distributed uniformly along the length of the exchanger
downwardly on the shell side of the casing 98 in heat
by means of holes 81 drilled in the container wall 72
exchange with vaporizing nitrogen inside the passageways
within the air inlet compartment 80. The inlet air ?ows 65 91. The performance of the FIGURE 8 heat exchanger
spirally around the nitrogen passageway heat transfer sur
differs slightly from that of FIGURE 7 in that the clean
fames 25 toward the center of the exchanger and enters
nitrogen dilutes the carbon dioxide and water content of
the center pipe core 71 through opening 81a, cut in its
the entering air and therefore tends to reduce the amount
wall. Here, the‘air mixes with the vaporized nitrogen
of impurity deposition on the heat transfer surfaces.
released into the same space through valve 38, and the 70 This will prolong the operating life of the heat ex
resulting cold refrigerant gas exits from the exchanger
through conduit 82.
changer between thawout periods, but is also increases
the amount of carbon dioxide present in the resultant cold
refrigerant gas. Furthermore, liquid nitrogen control
First drain conduit 83 terminating in inlet air com
valve 99 is required in the nitrogen inlet conduit 19 rather
partment 80 is provided for removing water which would
otherwise condense in the ?rst 180° of the air ?ow path 75 than the discharge conduit from the heat exchanger.
spar/pee
7
8
Although the preferred embodiments have been de
scribed in detail, it is contemplated that modi?cations
air with the flow adjusted, colder vaporized nitrogen so as
of the method and the apparatus may be made and that
some features may be employed without others, all within
the spirit and scope of the invention as set forth herein.
What is claimed is:
l. A method for producing a cold refrigerant gas at de
temperature.
sired, selectable volume and temperature which comprises
the steps of supplying compressed air at ambient temper
to form said cold refrigerant gas at desired volume and
7. Apparatus for producing a cold refrigerant gas at
desired, selectable volume and temperature including
means for supplying compressed air at ambient tempera
ture and at adjustable ?ow rates; means for supplying
liquid nitrogen refrigerant; means for passing said com
pressed air and said liquid nitrogen in sufficient indirect
ature and at a desired ?ow rate, such air containing at 10 heat exchange so as to cool the air and simultaneously
completely vaporize the liquid nitrogen; and means for
least carbon dioxide as an atmospheric contaminant; sup
plying liquid nitrogen refrigerant; cooling and at least
partially cleaning said compressed air by indirect heat
exchange with said liquid nitrogen; continuing such heat
exchange for suf?cient duration to completely vaporize
said liquid nitrogen; mixing the cooled and cleaned air
with the vaporized nitrogen so as to form said cold
refrigerant gas at desired volume and temperature.
2. A method according to claim 1 wherein the com
pressed air stream is supplied at a ?rst higher pressure,
reduced to a second lower pressure, and thereafter throt
tled su?‘iciently to obtain critical ?ow before cooling with
said liquid nitrogen.
3. A method according to claim 1 wherein the ?ow of
mixing the cooled air with the vaporized nitrogen so as to
form said cold refrigerant gas.
8. Apparatus according to claim 7 in which means are
rovided for reducing the pressure of the compressed air,
means for throttling the reduced pressure air sufficiently
to obtain critical ?ow across such means, and means for
passing the throttled air to the indirect heat exchange
means.
9. Apparatus according to claim 7 in which means are
provided for adjusting the dew of vaporized nitrogen be
fore passage to said means for mixing with the cooled
air.
10. Apparatus for producing a cold refrigerant gas at
vaporized nitrogen mixing with the cooled air is adjust
desired selectable volume and temperature including
able.
4. A method according to claim 1 wherein the indi
rect heat exchange between the compressed air and vapor
means for supplying compressed air at a ?rst pressure,
ambient temperature and at adjustable ?ow rates; means
izing nitrogen is cocurrent.
5. A method according to claim 1 wherein the indi
rect heat exchange between the compressed air and vapor
izing nitrogen is countercurrent.
for supplying liquid nitrogen refrigerant; means for re
ducing the pressure of said compressed air to a second
lower pressure; means for sufficiently throttling the re
duced pressure air to obtain critical ?ow across such
means; means for passing the throttled air and said liquid
nitrogen in sufficient indirect heat exchange so as to cool
6. A method for producing a cold refrigerant gas at
desired, selectable volume and temperature which com
prises the steps of supplying compressed air at a ?rst
pressure, ambient temperature and a selectable ?ow rate,
such air containing at least carbon dioxide as an atmos
nitrogen; means for adjusting the ?ow of such vaporized
nitrogen to a desired quantity; and means for mixing the
pheric contaminant; supplying liquid nitrogen refrigerant;
so as to form said cold refrigerant gas.
the air and simultaneously completely vaporize the liquid
?ow adjusted and vaporized nitrogen with the cooled air
reducing the pressure of said compressed air to a sec
ond lower pressure, and thereafter sufficiently throttling
such lower pressure air to obtain critical ?ow; cooling
and at least partially cleaning the throttled air by indi
rect heat exchange with said liquid nitrogen; ‘continuing
such heat exchange for su?icient duration to completely
vaporize said liquid nitrogen; adjusting the ?ow of the
vaporized nitrogen, and mixing the cooled and cleaned
References Cited in the ?le of this patent
UNITED STATES PATENTS
2,685,181
2,922,286
2,926,501
Schlitt ________________ __ Aug. 3, 1954
Rae _________________ __ Jan. 26, 1960
2,951,346
Collins et a1 ___________ __ Sept. 6, 1960
Morrison ____________ __ Mar. 1, 1960
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