US3714942A

US3714942A - Cryogenic gas processing system

Info

Publication number: US3714942A
Authority: US
Inventors: H Fischel; K Cowans
Original assignee: SUB MARINE SYST Inc
Current assignee: SUB MARINE SYST Inc
Priority date: 1969-02-03
Filing date: 1969-02-03
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06

Abstract

EFFICIENT USE OF THE REFRIGERATION CAPACITY OF A CRYOGENIC SUPPLY, WHILE ALSO MAINTAINING TEMPERATURE CONTROL OF A PROCESS CONTROL CRYOGEN DURING PASSAGE OF A GAS MIXTURE IN COMMUNICATION WITH THE PROCESS CONTROL CRYOGEN, IS ACHIEVED BY EMPLOYMENT OF A BYPASS HEAT EXCHANGE BETWEEN THE CRYOGEN SUPPLY AND A PORTION OF THE GAS MIXTURE, WHICH IS ALSO PASSED THROUGH A PRINCIPAL COUNTERFLOW HEAT EXCHANGER. ISOTHREMAL HEAT EXCHANGERS USING THE CRYOGENIC SUPPLY AND THE PROCESSED GAS MIXTURES MAY ALSO BE DISPOSED ALONG THE GAS FLOW PATH TO RESTRICT UNWANTED HEAT DISSIPATION AND TO ASSURE TEMPERATURE UNIFORMITY, SO AS TO OBTAIN EFFICIENT AND FULL RANGE COOLING OF THE GAS MIXTURE. COMPACT AND EFFICIENT HEAT EXCHANGE UNITS ARE DISCLOSED THAT MAY BE DISPOSED AT VARIOUS REGIONS ALONG THE GAS FLOW PATH FOR THESE PURPOSES.

Description

Feb. 6, 1973 H. FISCHEL ETAL 3,714,942

CRYOGENIC GAS PROCESSING SYSTEM Filed Feb. 5, 1969 4 Sheets-Sheet 1 ISOTHERMAL HEAT EXCHANGE SYSTEM I l8 E i PRINCIPAL l 224' couTTTERTLoTT F P24 1 HEAT l l EXOHANGER l I BYPASS i L COUPLTEEARTFLOW I J ExcHAucER CONTROL cmrocsn PROCESSED T GAS 20 1 PTTT OE SSEE |'L5?F Mflflflfl 91W CONTROL FIG T k INVENTORS I00 KENNETH w. COWANS F IG.- 5 B $1333? 5%? FM M1 A TTORNEYS Feb. 6, 1973 H. FTscT-TaL ETAL 3,714,942 CRYOGENIC GAS PROCESSING SYSTEM I F11 d F b. :5, 1969 AMBIENT 4 s E e e PRESSURE heats Sheet 2 BREATHER HEUUM PREggmfiED T" coRTRoL MECHANISM I SUPPLY I t l l {""l' BOIL-OFF I l GAS OZFILL EMITTER I l T 47 5 48 as 85 .el

OXYGEN TEMPERATURE THIRD ISOTHERMAL HEAT EXCHANGER 90 RT 4| 87 I LIQUID OXYGEIfl as To GOZOOLLECTION 1?. 66 e SECOND TsoTRERRAL 73 FIRST ISOTHERMAL RERT EXCHANGER HEAT EXCHANGE? uoum NITROGEN Q 2 INVENTORS KENNETH W. COWANS ANTHONY DICHIRO BY HALBERT FISCHEL Mm M ATTOR EYS Feb. 6, 1973 Filed Feb. 5, 1969 H. FISCHEL ET AL 3,714,942

CRYOGENIC GAS PROCESSING SYSTEM 4 Sheets-Sheet 3 FIG.3

1 5 SECOND ISOTHERWL HEAT sxcumcen FIRST ISOTHE HEAT EXGHANGER INVENTORS KENNETH W. COWANS ANTHONY DICHIRO BY HALBERT FISCHEL A TTORNEYS 4 Sheets-Sheet INVENTORS KENNETH w. co wANs ANTHONY DICHIRO BY HALBERT FISCHEL PM l ATTORNEYS FlG.-7

PROCESSED GAS Feb. 6, 1973 Filed Feb. :5, 1969 United States Patent 3,714,942 CRYUGENIC GAS PROCESSING SYSTEM Halbert Fischel, Van Nuys, Anthony Dichiro, Sun Valley, and Kenneth W. Cowans, Los Angeles, Caiifi, assignors to Sub-Marine Systems, Incorporated Filed Feb. 3, 1969, Ser. No. 795,838 Int. Cl. A26b 7/02 U.S. Cl. 128142 9 Ciaims ABSTRACT OF THE DISCLOSURE Efficient use of the refrigeration capacity of a cryogenic supply, while also maintaining temperature control of a process control cryogen during passage of a gas mixture in communication with the process control cryogen, is achieved by employment of a bypass heat exchange between the cryogen supply and a portion of the gas mixture, which is also passed through a principal counterflow heat exchanger. Isothermal heat exchangers using the cryogenic supply and the processed gas mixtures may also be disposed along the gas flow path to restrict unwanted heat dissipation and to assure temperature uniformity, so as to obtain efiicient and full range cooling of the gas mixture. Compact and efiicient heat exchange units are disclosed that may be disposed at various regions along the gas flow path for these purposes.

BACKGROUND OF THE INVENTION This invention relates to cryogenic gas processing systems, and more particularly to gas mixture processors which shift the temperature of the gas mixtures between substantially varying limits.

Increasing use of cryogens, such as liquid nitrogen and liquid oxygen, in industrial and scientific applications has led to increasingly stringent requirements as to efiiciency and performance. In the course of improvement of cryogenic systems it has become increasingly important to make the best possible use of the refrigeration capacity of the cryogen. Cooling of an incoming gas by a cryogen in an efi'icient manner, with a unit which is at the same time compact and relatively inexpensive, can be a difficult problem where the functional, structural or operative demands impose flow rate, space, or other limitations.

An example of one modern cryogenic system upon which extreme demands are imposed is to be found in a previously filed patent application entitled, Life Support System and Method, Ser. No. 623,616, filed Mar. 16, 1967, and owned by the assignees hereof. In the patent application referred to there is disclosed a compact and efiicient system and method for the automatic regulation of the partial pressure of a gas within a gas mixture, such as oxygen within a breathable gas mixture. This is a closed circuit system utilizing a liquid oxygen supply to adjust the partial pressure of the oxygen and the breathable mixture so as to provide an appropriate mixture irrespective of physiological usage and extremely wide variations in pressure. Although the principle is useful in a number of ways, the example of a life support system for hyperbaric environments is particularly significant, both in terms of extent of prospective use and in terms of the criticality of the problems encountered. The present system may likewise be utilized in a variety of applications, but the problems which it overcomes are best typified by the life support type of system and it is described mainly in that context.

Ina small, self-contained underwater breathing apparatus system using a cryogenic supply, it is at once evident that the gases to be inspired must be raised to a 3,734,942 Patented Feb. 6, 1973 breathable, i.e. near-ambient level, whereas the expired gases must be lowered to the near-cryogenic region. These opposite shifts in temperature of the gas mixture to be processed and the processed gas mixture can obviously be effected at least to a certain extent by a heat exchanger. Space, size and operative limitations, however, all tend to limit the extent to which the incoming gas mixture end of the processor can be cooled by the outflowing gas mixture. Even with an extremely high efficiency heat exchanger, various particular factors can act to prevent the full range lowering of the temperature of the incoming gas mixture. Consequently, to the extent that additional cooling may have to be provided by the processor cryogen itself, there is ineificient use of such cryogen. In addition, some source of refrigeration capacity must compensate for losses arising from the operation of the heat exchanger itself.

In such a system, it is particularly found that nonuniformities in heat distribution, arising in part from the freedom of movement required for a life support system, can cause substantial losses. Elements immersed in a cryogen at one time during operation of the system in one attitude may thereafter shift to a substantially higher temperature in a different attitude when they are out of contact with the cryogen. Such elements thereafter absorb some refrigeration capacity when again contacted by the cryogen. It is therefore highly desirable to assure efficient and substantial heat interchange between cryogens and gas mixtures, with compact units which provide the necessary relationships without, however, requiring complex structures or substantial volumes of space.

SUMMARY OF THE INVENTION The objects and purposes of the present invention are realized by cryogenic gas processing systems utilizing novel heat exchange systems and elements for coaction between cryogens and gas mixtures. One aspect of the present invention relates to the employment of bypass heat exchange flows in conjunction with principal heat exchange flows, for super-cooling of a portion of the flow of the gas mixture sufficient to achieve the desired final temperature while relaxing operative demands on the principal heat exchanger. A separate refrigeration means, which may be a part of the system used for other purposes, is employed to cool the bypass flow.

Another aspect of the present invention is the provision, in a cryogenic gas processing system, of a system for effecting efficient interchange between a gas mixture to be processed, and cryogens or gases at lower temperatures. In a specific example of a closed circuit life support system in accordance with the invention, boil-off gases from a temperature control cryogen are utilized to cool a very small proportion of the expired gas mixture, the remainder of which is fed into a principal heat exchanger. In addition, the expired gases subsequent to heat exchange are passed in serial fashion through at least two heat exchangers, which may be cooled by various refrigeration sources, including the processed gases themselves, or by the temperature control cryogen or its vapors. In a specific example, utilized in conjunction with the closed circuit life support system, a temperature control cryogen is maintained within an elongated chamber and a cryogenic oxygen vessel is centrally disposed within the chamber. A pair of isothermal heat exchangers is disposed on either side of the oxygen vessel within the chamber, such that independently of the attitude of the system at least one of the isothermal heat exchangers is in contact with the temperature control cryogen at all times. A conduit system passes the incoming gas mixture serially through the two isothermal heat exchangers prior to entry into the interchange volume of the oxygen vessel. This system assures substantial temperature uniformity within the entire temperature control chamber.

Other features of the invention provide material improvements in the efficiency which can be obtained in interchange of heat between gas mixtures and cryogens, as well as full thermodynamic equilibrium between a selected constituent of the gas mixture and the processor cryogen. In a specific example of an isothermal heat exchanger, an extended surface area member having at least a partially hollow interior and wicking properties with respect to the associated cryogen is disposed in contact with an interior member having high heat conductivity, within which a gas conduit is disposed. The cryogen wets the entire wicking member, and provides a high capacity refrigeration source through the interior member to contacting apertured members, such as screen elements, disposed in the gas path. To assure thermodynamic equilibrium in a life support system between the breathable mixture containing oxygen and a liquid oxygen in the oxygen vessel, independently of system attitude, the inlet and outlet conduits may be centrally disposed within the oxygen vessel and coaxially disposed relative to each other. A cylindrical wicking member within the oxygen vessel is always in contact with the oxygen, independently of the attitude of the system. A conduit system from the inlet conduit passes into the central region of the oxygen vessel within a confined path along an apertured member, such as a fine mesh screen, disposed in contact with and wetted by wicking member. This arrangement insures intimate contact over a large area between the incoming gas mixture and the liquid oxygen. The processed gases then pass through a central aperture system which is always at least partially open irrespective of the attitude of the system.

In another system in accordance with the invention, a bypass isothermal heat exchange relationship is employed in conjunction with a principal heat exchanger. In this system, however, the principal heat exchanger is divided into two sections, and the bypass unit diverts a small proportion of the inflowing gases through the temperature control cryogen past only one of the heat exchanger sections.

BRIEF DESCRIP'IlION OF THE DRAWINGS A better understanding of the invention may be had by reference to the following description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a block diagram and schematic representation of a cryogenic gas processing system in accordance with the invention;

FIG. 2 is a combined block diagram and perspective view, somewhat simplified and partially broken away, of a more specific form of a system in accordance with the invention;

FIG. 3 is a side sectional view of the system of FIG. 2, showing further details thereof;

FIG. 4 is an end sectional view of a portion of a bypass heat exchanger employed in the arrangement of FIGS. 2 and 3;

FIG. 5 is a perspective view, partially broken away, of an isothermal heat exchanger employed in the arrangement of FIGS. 2 and 3;

FIG. 6 is a perspective view, partially broken away, of an arrangement of an oxygen vessel and interior system employed in the system of FIGS. 2 and 3, showing further details thereof; and

FIG. 7 is a combined block diagram and schematic representation of another form of cryogenic gas processing system in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION In a generalized example of one system in accordance with the invention, referring now to FIG. 1, a temperature control cryogen 10 is maintained within a first vessel 1g which encompasses an interior second vessel 14 within which a process control cryogen 16 is stored. A substantially confined volume is defined by the interior vessel 14, and the process control cryogen 16 occupies only part of this volume. Thus in accordance with the systems and methods disclosed in the previously filed patent application, Ser. No. 623,616, the partial pressure of a selected gas in a gas mixture to be processed is adjusted to a selected level by passing the gas mixture into the confined volume, in communication with the process control cryogen 16, establising thermodynamic equilibrium between a selected gas constituent and the cryogen 16, and extracting the equilibrated gas from the confined volume.

One significant advantage of this system as applied to underwater life support usages is that the vital component, oxygen, in a breathable mixture is maintained in a desired partial pressure range irrespective of the much greater partial pressures of inert gases which make up the breathable mixture at substantial underwater depths. This regulation system is not only precise and sensitive, but highly stable because the gas whose partial pressure is to be controlled, such as oxygen, as regulated in accordance with the temperature of the process control cryogen 16, which in turn is stabilized and controlled by the temperature of the temperature control cryogen 10. As will be evident from the considerations given below, however, practical compact and inexpensive systems cannot use complex heat stabilization schemes or arbitrarily large amounts of cryogen without becoming economically un realistic. In underwater life support systems, for example, only a given quantity of cryogen can be manipulated, and this must be utilized to its fullest potential, or the work time of a system user may be drastically shortened.

In the system of FIG. 1, a boil-off line 18 extending into the interior volume of the vessel 12 is responsive to the pressure on the temperature control cryogen 10. The confined boil-off gas may be varied in pressure to change its temperature and therefore the temperature of the cryogen 10 itself. A cryogen boil-oil control 20 coupled to the line 18 is settable to adjust the gas pressure. Also as described in the previously filed application, it is necessary for some applications, such as life support systems in particular, to utilize a heat exchanger to shift the temperature of the gas mixture being fed into the processor from the ambient or near ambient range to the near cryogenic range, and to shoft the temperature of the gas subsequent to processing oppositely within this range. A principal counterflow heat exchanger 22 is utilized for this purpose, preferably of a type such as is disclosed probably in the previously filed application, because of its high efliciency, compact size and low pressure gradient. It should be recognized, however, that efliciencies well in excess of are necessary, and that in fact efliciencies in excess of 99% are highly desirable, because the constant wastage of refrigeration capacity which otherwise results can again severely shorten the length of time a user can Work with a given initial oxygen supply in the system.

In accordance with the invention, substantial operative advantages in a cryogenic gas processing system are achieved by the utilization of a bypass heat exchanger 24 in conjunction with the principal counterflow heat exchanger 22. The bypass counterflow heat exchanger 24 receives a small fraction, typically from /z% to 5% and in the present example only approximately 2%, of the inflowing gases to be processed. The bypassed gases are cooled, either in isothermal or counter-current or other flow relationship, by a suitable refrigeration source, here the boil-off gases from the temperature control cryogen 10. Because the bypass flow is very small, adequate cooling is achieved to bring the bypass gas flow dOWn to near the temperature of the cryogen. The boil-off gases are here maintained static in the bypass exchanger 24, but an isothermal exchange or counterflow exchange using a C11" culating system may be used to provide the desired cooling.

The operative results, whichever of these alternatives is used, impose only a slight drain on the refrigeration capacity of the temperature control cryogen 10, while supercooling the bypass flow relative to the main flow. The principal counterflow heat exchanger 22 no longer imposes the same operative limitation on the system because although there is a full flow of outgoing gas, there is less incoming gas, This imbalance in favor of the cold gas tends to minimize the temperature differential between the counterflowing gases and to best utilize the capabilities of the heat exchanger. It also tends to insure that the final temperature of the gas to be processed is adequately lowered to the desired temperature range prior to entry into the cryogenic system.

Another feature in accordance with the invention which is advantageously utilized in conjunction with the bypass heat exchanger 24, but may be employed separately, com prises an isothermal heat exchange system 26, which utilizes the refrigeration capacity of the temperature control cryogen such as to further lower the temperature of the incoming gases, and also to stabilize the temperatures of the various component parts of this system. A detailed example of an isothermal heat exchange system utilizing a series of separate isothermal heat exchangers disposed along the gas flow path is described below in conjunction with the system of FIGS. 2 and 3.

A specific cryogenic processor in accordance with the invention, referring now to FIGS. 2 and 3, comprises a self-contained underwater breathing apparatus disposed principally in a pair of pressure vessels comprising first and second double-walled insulated

cylindrical tanks

39, 31. The system also includes a breather mechanism 33, a pressurized helium supply 35, a helium control 37 and a boil-off gas emitter 39. These units are shown in block diagram form in FIG. 2. only, in order to simplify the drawings, and will be only generally described. The breather mechanism 33, typically a mouthpiece and breather bag system, provides the expired gas mixture as inflow gases to the processor, and passes the outflow gases after processing to the user. Helium from the supply 35 is injected into the system by the control 37 in response to the ambient pressure, so as to equalize pressure with the environment. Boil-oft gases from the temperature control cryogen, to be described, are injected into the environment by the boil-off gas emitter 39. As discussed in the previously filed application, Ser. No. 613,616, this arrangement together with the gas processing system provides a closed circuit breathing apparatus of high capacity, small size and great reliability.

A substantially rectangular principal heat exchanger 41 of the counterflow type occupies most of the interior volume of the first tank 30 and includes, adjacent the opposite ends, diflerent side header rings 43, 45 disposed coaxially with the longitudinal central axis of the heat exchanger 41 and about the periphery of the exchanger. Inflowing gas mixtures pass through

inlet tubes

47, 48 into the first header 43, which is the upper header as viewed in FIGS. 2 and 3, and pass toward the lower end of the exchanger 41. Terms such as upper and lower will be used for convenience of reference as applied to the positions shown in FIGS. 2 and 3, even though it will be understood the system operates in any attitude. The inflowing gas mixture enters the exchanger 41 from the sides, but passes directly out the lower end. During this flow, CO is frozen out of the gases, and it passes freely into the lower end of the first tank '30. The outflowing or processed gases from the processor enter the second side header 45 through a 90 angle conduit 50, pass in counterflow relationship to the inflowing gases, and out the upper end of the heat exchanger 41 through a central outlet tube 51 coaxial with the longitudinal axis of the exchanger 41.

A bypass heat exchanger 53 parallels the principal heat exchanger 41, and is coupled to receive a small fraction, e.g. between about /2% and about 5%, of the flowing gases from the upper side header 43. At the second or lower end of the first tank 34 the inflowing bypass gas component combines with the main flow from the principal exchanger 41. The bypass exchanger 53, seen in section in FIG. 4, comprises a number of parallel tubes 55 containing boil-oft gases, and an internally finned conduit 57 containing the bypass inflow gases. The tubes 55 are closed at their upper ends in this example, so that the bypass exchanger functions isothermally.

A support tube 58 is welded to join the two

tanks

30, 31 and contains an internal system of three coaxial tubes which condut the various gases between the various units in the two

tanks

30, 31. Boil-01f gases from liquid nitrogen 68 within the second tank 31 are conducted from centrally disposed open end of a tube 62 within the tank 31, into the outer coaxial passageway defined between an outer sleeve 64 and an intermediate sleeve 66, then into the small parallel tubes 55 through a header conduit 68. Processed gases are passed within the central coaxial tube 70, which is an extension of the 90 angle coupling 50 to the bottom side header 45. The intermediate passageway, defined between the central tube 70 and the intermediate sleeve 66, contains the inflowing gases.

As best seen in FIG. 3, therefore, processed or outflowing gases go through the center of this coaxial system between the

tanks

30, 31 and the nitrogen boil-off gases go through the outer passageway, while the inflowing gases pass intermediate these two flows. Consequently, after the inflow gases pass through the

heat exchangers

41, 53, they are surrounded on both sides by colder gases, and further cooled toward the cryogenic range. This system forms part of a first isothermal heat exchanger 72, the remainder of which comprises a fine mesh screen 73 about the interior tube 70 in the region at which the gases to be processed flow out of the

heat exchangers

41, 53. The lower end of the interior volume of the first tank 30 may be sealed ofl at the lower header 45, or a conduit system may be arranged to confine the gases further in flowing toward the processor.

The second tank 31 comprises the principal portion of the processor, including the temperature control cryogen, in this instance the liquid nitrogen 60. The liquid nitrogen 60 shifts in the tank 31 in accordance with any arbitrary attitude adopted by the user of the system, and is arranged to have a certain volumetric relationship to the total interior volume of the second tank 31, being in excess of some predetermined figure, such as about 10%, of the volume. A second isothermal heat exchanger 75 adjacent the inlet-outlet system is in the region of the lower hemispherical end of the second tank 31, and a third isothermal heat exchanger 77 is spaced apart from the second isothermal heat exchanger 75, and adjacent the opposite or upper hemispherical end of the second tank 31. A process control cryogen vessel, here an oxygen vessel 79 contains at least a predetermined minimum volume of liquid oxygen 81 disposed between the second and third

isothermal heat exchangers

75, 77 and interconnected to both by a centrally disposed coaxial conduit system. The oxygen vessel, and the interior conduit system are shown in greater detail in FIG. 6, whereas further detail as to the internal arrangement of the third isothermal heat exchanger 77 is shown in FIG. 5.

As may be seen in FIGS. 2 and 3, however, an interior cylindrical wicking member 83 within the oxygen vessel 79 occupies a sulficient part of the interior volume of the oxygen vessel 79 such that a portion of the wicking member 8.3 is immersed in liquid oxygen 81 at all attitudes of the second tank 31. The boil-off control device comprises an adjustable bellows 85 coupled to a boil-off line 87 having an outlet in a selected region of the second tank 31. As described in application Ser. No. 623,616 above, a number of boil-ofl? lines 87 may be utilized, each having an outlet in a different region of the interior volume of the second tank 31, so that at least one is always open to the boil-off gases. Only two of such lines 87 are shown in FIG. 2. Liquid oxygen for filling the oxygen vessel 79 is provided through an inlet valve 89 coupled by a conduit 90 (FIG. 2 only) into the interior of the oxygen vessel 79. The setting of the bellows 85 is regulated mechanically by an oxygen temperature sensor 91 including a sensing element centrally disposed within the oxygen vessel 79. A closed tube gas system exerting a variable pressure, such as is described in the previously filed patent application, may be advantageously utilized for providing this sensing and control function.

The second isothermal heat exchanger 75 and the third isothermal heat exchanger 77 each have extended surface areas formed by wick members 93', 95, respectively. These

wick members

93, 95 may be of any suitable material that is readily formed or machined and has a wicking property when in contact with the temperature control nitrogen 60. Sintered brass is a suitable material for this purpose, because it has a porosity and pore size capable of rapid propagation of the cryogen. The extended exterior and interior surface areas of the wicking members, together with the rapid propagation of the cryogen from one surface to the other, provides a heat pipe action with respect to a heat source at one of the surface areas. Vaporizing cryogen at one of these surfaces absorbs large amounts of heat, due both to the heat of vaporization and because the vaporized liquid is immediately supplanted by cryogen.

The interior configurations of the

heat exchangers

75, 77 will best be understood by reference to FIG. 5, in conjunction with the sectional view of FIG. 3. Inasmuch as the

heat exchangers

75, 77 substantially similar, except for shape, only one need be described in detail. The wicking member 95 of the third isothermal heat exchanger 77 is in the general form of a hollow body of revolution disposed coaxial with a central axis which is at or close to the central axis of the second tank 31. The principal cylindrical portion of the wicking member 95 coaxial with the central axis includes an integral radially outwardly extending flange in an intermediate region. If the liquid nitrogen 60 in the vessel is adjacent the upper end of the tank 31, as seen in FIGS. 2 and 3, therefore, either the upper end or the radially extending flange of the wicking member 95 is wetted by the liquid nitrogen 60. If the attitude of the second tank 31 is slanted or in the position shown, of course, the wetting affects only the second isothermal heat exchanger 75, at least one of these

exchangers

75, 77 is therefore always in contact with the liquid nitrogen 60 and due to the wicking action provides a volumetric dispersion of the cryogen. An interior hollow cylindrical element 97 of high thermal conductivity, such as copper, is in contact with the interior surface of the wicking member 95, and also surrounds and is in contact with an exterior tube 99 forming part of the coaxial conduit 100' for the infiowing and outflowing gases. .In the region of the third heat exchanger 77, this coaxial conduit 100 has a closed end 102 which confines the infiowing gases to a reentrant path between the outer passageway defined between the outer tube 99 and an interior tube 104. Adjacent the copper cylinder 97, the outer flow path is interrupted by a system of screens 106 abutting both the exterior tube 99 and the interior tube 104, and comprising separate disc-shaped copper screens of fine mesh which permit flow of the gas mixture without substantial pressure drop but which have good thermal contact through the outer wall 99 with the copper cylinder 97, and therefore with the cryogen 60 through the wicking member 95.

By virtue of this arrangement, the refrigeration capacity which is obtained is the equivalent of a massive finned copper element of many times greater size. The interface between the wicking member 95 and the copper cylinder 97 comprises a large area for cryogen boil-off, in thermal exchange relation with the flowing gases. Because of the heat pipe action the heat is rapidly and efficiently absorbcd in evaporative cooling. In addition, whatever the attitude of the second tank 31, substantial further cooling of the incoming gases is effected, to bring the temperature of the inflow gases being fed into the oxygen vessel 79 close to the temperature of the liquid oxygen 81. Consequently, the refrigeration capacity of the liquid oxygen 81 is not dissipated in cooling the inflow gases.

The configuration of the second isothermal heat exchanger 75 is substantially similar, except that the exterior flange portions are discontinuous, or include apertured portions, in order to receive the internal conduit system.

The internal conduit system within the oxygen Ve l 79, and the functioning of the wicking member 83 and associated components, will be better understood by reference to FIG. 6, in conjunction with FIGS. 2 and 3. The liquid oxygen 81 of course flows to the lower portion of the vessel 79, whatever the attitude of the associated system. The oxygen 81 occupies less than half but more than some minimum amount, here approximately 5%, of the total available interior volume of the vessel 79. The cylindrical wicking element 83 is coaxial with the central axis of the vessel 79, and has a diameter and length such that some surface to the wicking member is always in contact with the liquid, irrespective of the disposition of the oxygen. As previously discussed, the wicking member 83 may be of sintered brass or other sintered or porous materials suitable for liquid oxygen may be used. The nterior surface of the wicking member, facing the centrally disposed coaxial conduit system is covered and n abutting, thermal exchange contact with a fine mesh copper screen 108, corrugated so that the corrugation ridges lie parallel to the central axis of the wicking member 83 to provide longitudinal passageways. The screen 108 is coextensive with the wicking member 83 except for a central region along its length at which radially disposed pipes 110, 111, only two of which are shown, communicate between the outer passageway in the coaxial conduit 100, and the space between the cylindrical screen 108 and an interior sleeve 113. Thus infiowing gas, which is returned from the third isothermal heat exchanger 77 through the outer passageway in the coaxial conduit 10 enters the radial pipes 110, 111 and then passes along the screen 108 between the wicking member 83 and the inner sleeve 113. In passing along this length, the gases are formed into a thin cylindrical sheet which flows along the length of the wire screen 108 within the passageways defined by the corrugations to whichever end of the structure is open, dependent upon the attitude of the system. The finely apertured screen 108 is wetted by the oxygen and provides an extremely high liquid oxygen surface area, so that the thin cylindrical sheet of infiowing gases thus is exposed in all regions to intimate interchange relation with the liquid oxygen 81. Consequently, complete thermodynamic equilibrium between the liquid phase and the vapor phase of the oxygen is assured, and the desired processing takes place in this region. The processed gas passes out either or both ends of the space between the outer wicking member 83 and the interior sleeve 113, and is diverted into the interior of the hollow inner sleeve 113, to communicate with apertures 115 in the outer tube 99, these apertures being closed off from the passageway for the incoming gases by a radial barrier 117 in the coaxial conduit 100. Thus at this point the processed gases fiow outwardly from the system back toward the second isothermal heat exchanger 75. The disposition of the array of apertures 115 close to the approximate center of the interior of the oxygen vessel 79 assures that some apertures will always be open to the outflowing gas mixture.

To recapitulate the flow of the gas mixture, in both the infiowing and outflowing directions, therefore, reference should be made to FIGS. 2 and 3. The infiowing gas, provided from the breather mechanism 33 through the

inlet conduits

47, 48 enters the side header 43 of the principal heat exchanger 41, and also a small amount, approximately 2% in the practical example currently being referred to, is diverted through the bypass heat exchanger '53. T gases pass longitudinally along the

heat exchangers

41, 53, being emitted, along with CO particles, at the open lower end of the heat exchangers, and diverted across the screen 73 into the only available opening, comprising the passageway between the intermediate coaxial sleeve 66 and the central coaxial tube 70. The gases then pass through the second isothermal heat exchanger through a 90 turn (best seen in FIG. 3) and then within the interior tube 104 in the coaxial conduit 100. The inflowing gases pass entirely through the center of the oxygen vessel 79 up to the third isothermal heat exchanger 77, where they are returned along the outer passageways defined between the central tube 104 and the outer tube 99, into the central region of the oxygen vessel 79. Within this vessel 79 the gas is processed by being exposed to a large surface area of liquid oxygen 81 maintained at a selected temperature, and then returned along the outer passageway of the coaxial system 100 back toward the second isothermal heat exchanger 75. Adjacent that heat exchanger 75, the now processed gas is diverted from the outer passageway through a U-connection 120 into the central tube 70 between the second tank 31 and the first tank 30, and back into the lower header 45 for passage in counterflowing fashion along the principal heat exchanger 41 only and back through the central outlet conduit 51 to the breather mechanism 33.

It will therefore be evident that the refrigeration capacity of the liquid nitrogen 60, and the refrigeration capacity also of the boil-off gases from this cryogenic source, are utilized with great efficiency, Any tendency of the oxygen vessel 79 to be non-uniformly heated if maintained in one attitude for a substantial length of time is effectively counteracted not only by the internal wicking system, but also by the flow arrangement, which assures that either the second or third isothermal heat exchangers will adequately cool the inflowing gas prior to passage of this gas in intimate contact with the liquid oxygen surface. The coaxial arrangement of the passageway system, including the interior of the liquid oxygen vessel 79 not only provides a readily fabricated structure making highly efiicient usage of the interior space of the tank 31, but assures achievement of symmetry between the operative parts of the system.

In addition, the refrigeration capacity of the temperature control cryogen is further utilized by employing the boil-off gases first to elfect an initial additional cooling of the inflowing gases after the heat exchanger, and then to substantially supercool the bypass gases in the incoming flow prior to their recombination with the principal mass of inflowing gases.

A different arrangement of a system in accordance with the invention is shown in FIG. 7, this arrangement being preferred for applications in which there is a relatively low loading imposed on the refrigeration capability, and in which the heat exchanger has a high efiiciency. In this arrangement, the process control cryogen 16 and the temperature control cryogen 10, together with the associated

vessels

12, 14 are as previously designated. The heat exchanger, however, is divided into a first section 124 and a second section 126, with the inflowing gases after passing through the first section being supplied to a carbon dioxide trap 128 before passage through the second section 126. The outflowing gases from the processor pass serially through the second section 126 and then through the first section 124. A separate bypass of a minor amount of the incoming gas flow is diverted, however, to pass in heat exchange relation through the temperature control cryogen and then is recombined with the outgoing gas flow between the first and second

heat exchanger sections

124, 126.

The bypass gas flow is preferably passed in isothermal heat relation with temperature control cryogen, although it need not necessarily be passed in exchange relation 10 with the liquid itself. The term temperature control cryogen as used herein, is intended to refer to the boil-oil gases as well as the liquid constituent of the cryogen.

This bypass arrangement, in conjunction with the two section heat exchanger, provides balanced flow in the first heat exchange section 124, but imbalanced flow in the second section. Thus the second section 126 has a greater flow of outflowing cold gas so as to assure full lowering of the temperature of the inflowing gas to the processor. Although equal flows are present in the counterflowing masses in the first section, the bypass component is substantially supercooled, so as to increase the temperature differential and tend to secure a greater degree of cooling in the first section 124. This partial usage of the refrigeration capacity of the cryogen enables smaller and more economical heat exchangers to be utilized under the stated conditions, and in other applications.

Although there have been described above and illustrated in the drawings various forms of improved cryogenic gas processing systems, and units therefore, it will be appreciated that the invention is not limited thereto but encompasses all forms and variations falling within the scope of the appended claims.

What is claimed is: 1. A system for life support comprising: breather mechanism means for use by an individual; liquid oxygen means, including means for maintaining the liquid oxygen in a selected temperature range;

conduit means coupling said breather mechanism means to said liquid oxygen means to pass inflowing and outflowing gases therebetween;

heat exchanger means disposed along said conduit means for passing inflowing and outflowing gases in counterflow relationship; and

bypass means coupled to said conduit means to bypass at least a portion of said heat exchanger means with a minor fraction of said inflowing gas to imbalance the flows in said heat exchanger means, said bypass means including refrigerating means for cooling said minor fraction of said inflowing gas.

2. The invention as set forth in claim 1 above, wherein said means for maintaining the liquid oxygen in a selected temperature range comprises temperature control cryogen means, and wherein said bypass means is coupled to pass inflowing gases in heat exchange relation with at least a portion of said temperature control cryogen means.

3. The invention as set forth in claim 2 above, wherein said bypass means is coupled to pass approximately /2% to approximately 5% of the inflowing gases around the inflowing side of said heat exchanger means, and wherein said bypass means is coupled to place the inflowing gases in heat exchange relation with boil-01f gases from said temperature control cryogen means.

4. The invention as set forth in claim 2 above, wherein said heat exchanger means comprises at least two serially disposed sections, wherein said bypass means is coupled to pass approximately /2% to approximately 5% of the inflowing gases from between two of the sections on the inflowing side to between two of the sections on the outflowing side of said heat exchanger means, and wherein said bypass means is coupled to place the inflowing gases in heat exchange relation with said temperature control cryogen means.

5. A system for processing gas flows for a utilization system utilizing processed gas and expelling exhaust gas for processing comprising:

a vessel containing a cryogen and the vapor of said cryogen;

conduit means coupling said utilization system and said vessel to process said gas flows by passing exhaust gases from said utilization system into contact with said cryogen vapor and passing said processed gas from said vessel to said utilization system;

heat exchanger means disposed along said conduit means for passing inflowing and outflowing gases in counterflow heat exchange relationship; and

bypass means coupled to said conduit means to bypass at least a portion of said heat exchanger means with a minor fraction of said inflowing gas to imbalance the flows in said heat exchanger means, said bypass means including refrigerating means for cooling said minor fraction of said inflowing gas. 6. In a process system in which a gas is processed by being passed into control communication with a confined volume containing a process control liquid-vapor system in substantial thermodynamic equilibrium maintained within a selected cryogenic temperature range, the improvement comprising:

temperature control means including a hollow storage vessel and a temperature control liquid-vapor system contained therein, said vessel at least partially encompassing the volume containing the process control liquid-vapor system and the temperature control liquid-vapor system being in heat exchange relationship with the process control liquid-vapor system;

principal counterflow heat exchanger means receiving gas to be processed and processed gas, and passing these in heat exchange relationship, said principal heat exchanger means conducting a substantial majority of the total flow of gas to be processed; and

bypass heat exchanger means coupled to receive vapor from said temperature control liquid-vapor system, and a substantial minority of the total flow of gas to be processed, and passing these in heat exchange relationship.

'7. The invention as set forth in claim 6 above, including in addition isothermal heat exchanger means providing heat exchange between the processed gas and said process control liquid-vapor system.

*8. A system for processing a gas mixture by passing said mixture into and out of mixing relationship with a liquid-vapor system at cryogenic temperature comprising:

storage means including a liquid-vapor system in substantial thermodynamic equilibrium; at flow path system coupled with said storage means to provide an inflow path to said storage means for passing said inflow gases into mixing relationship with said cryogen vapor and to provide an outflow path for gas [flow after passing in mixing contact with said cryogen vapor; principal heat exchanger means coupled to pass a major portion of the gas mixture inflow to said storage means and the gas mixture outflow from said storage means in counterflow relationship; and refrigerating means receiving the remaining minor portion of the gas mixture inflow and coupled to bypass at least a part of said principal heat exchanger means. 9. The invention as set forth in claim 8 above, wherein said storage means further includes a temperature control liquid-vapor system in heat exchange relationship with said first-mentioned liquid-vapor system, said refrigerating means bypasses the entire principal heat exchanger means, and said refrigerating means passes the received portion of the gas mixture inflow in heat exchange relationship with vapor from said temperature control liquid-vapor system.

References Cited UNITED STATES PATENTS 3,306,061 2/1967 Scott et al 62-45 X 3,350,229 10/1967 Justi 62-52 X 3,304,729 2/ 1967 Chandler et al 62-52 X 3,417,920 12/1968 Tyson 165-35 X FOREIGN PATENTS 816,874 7/1959 Great Britain 128-203 ALBERT W. DAVIS, JR., Primary Examiner US. Cl. X.R.