CH509555A - Heat exchanger for life support systems - Google Patents

Abstract

The exchanger comprises separate parallel passages along which gases are passed in heat-exchange relationship on opposite sides of a plastic heat exchange membrane which constitutes a common wall for the passages. The membrane which is pref. corrugated, consists of a series of successive peaks and valleys at both its faces extending parallel to the separate passages. The exchanger is used in closed circuit life support systems, e.g. diving equipment, to cool the exhaled gases and to heat the breathable mixture from the O2 reservoir to a suitable breathing temp.

Description

       

  
 



  Process for removing carbon dioxide from a mixture
 gas and apparatus for its implementation
 The present invention relates to a process for removing carbon dioxide from a gas mixture and an apparatus for its implementation. A number of considerations considerably complicate the problems presented by sustaining life in hostile environments, such as those encountered under positive pressure conditions. Regardless of the pressure at which a diver works, he must have the appropriate quantity of oxygen and this quantity, depending on the partial pressure of oxygen, is between approximately 0.2 and 1 bar.

  Consequently, to work at great depths (60-120 meters), divers must breathe a mixture in which oxygen constitutes a very small percentage (for example from 5% to 2% respectively) of the complete mixture. Unless you stay at a given depth or constantly make adjustments, changes in the oxygen percentage should be done automatically since either too much oxygen or too little oxygen can be fatal within a short period of time. time by oxygen poisoning or anoxia, respectively. It is also extremely important to maintain accurate ratios to reduce the risk of any non-fatal damage and to reduce the time required for decompression.



   The term positive pressure is intended herein to refer to a high pressure environment or an environment in which the pressure is greater than that of a normal environment for a human.



  If the pressure is high enough, it is inherently hostile to human life, as is a low pressure environment if its pressure is low enough. Taking the range of normal atmospheric pressure as a reference, the low pressure environment can also be called a negative pressure environment. Even an isobar environment can be hostile to human existence and may require a life support device if one encounters extreme temperatures or excessive pollutants.



   The appropriate breathing mixture for positive pressure environments is not comparable to that for normal atmospheres. Of course, the exhaled carbon dioxide must be removed from the circuit if the gas is to be recirculated. If the system is in a fully closed circuit or in a semi-closed circuit, it is further desirable that there is no substantial change in the respiratory pressure required as the CO2 increases. accumulates, as it does when there is back pressure. The narcotic effects of inert gases under pressure must be suppressed or eliminated. For example, if there is nitrogen in the breathing mixture, it should be limited to a partial pressure which does not exceed approximately 3.5 bar.

  For these and other reasons, breathing mixtures for performing underwater work mainly use helium or any other stabilizing inert gas or a mixture of inert gases and oxygen, in combination.



   Other critical requirements that are placed on life support devices are due to the need to maintain given oxygen and carrier gas reserves as long as possible, and to safety factors which, inherently, are necessary for such devices. Safety factors are, in general, the object of great attention today because modern devices use pressure sensitive mechanical valves whose failure, catastrophic or intermittent, is inadmissible.



   As such devices have been used more widely, factors other than safety factors have also become increasingly important.



  For example, when breathing a mixture with a high helium content, the heat loss from the body is extremely large. Consequently, means must be provided for heating the devices or the underwater stations to maintain reasonable working or living conditions. The heat expenditure is generally unrelated to the other functions performed within a life support apparatus, but if it could be effectively combined with the life support function, the entire installation would not only be more compact and less expensive, but the available energy sources would be used more efficiently.



   Apparatus of this nature must perform a variety of different functions, including purification by removal of gases contaminated with water vapor, toxic hydrocarbons, and carbon dioxide, the use of transmission arrangements. efficient heating, and performing the necessary adjustment operations to regulate temperatures and, where necessary, pressures. The present invention takes all these aspects into account, since although they constitute corollaries of the main problem of controlling the partial pressure of a selected gas in the gas mixture, they form the basis of the main objectives of the devices. maintenance of life and that, moreover, they present a large number of independent uses.

  A large number of these functional requirements are satisfied by apparatus according to the invention in a particularly advantageous and special manner, as indicated separately below.



   Other life support devices may relate to entirely different environments but, nevertheless, must provide a breathable mixture at an appropriate pressure range.



  In space and superatmospheric devices low pressure environments are found and it is often preferable to use pure oxygen at a chosen pressure lower than atmospheric pressure.



  Although pressure regulation is relatively simple, failures can still occur. Perhaps the greatest dangers are produced by the inflammability of a respiratory medium consisting of pure oxygen, and these risks can be considerably reduced by mixing with pure oxygen even a small proportion of an inert gas. In existing devices, the extraction of contaminants from pure oxygen maintained at a given pressure poses relatively simple control problems. When, however,
The oxygen must be diluted in a given proportion with a suitable inert gas, significant additional equipment must be used with current techniques.

  The elements of the gas mixture must be determined in relation to the total pressure prevailing in the apparatus and the necessary corrections must be carried out by appropriate combinations of injections of pure gaseous constituents and withdrawals of the gas mixture.



   The process according to the invention is characterized in that the gas mixture is made to flow along a substantially linear path with a low pressure gradient, heat is extracted from the gas mixture to establish a net temperature gradient s' extending to a temperature level below the precipitation point of carbon dioxide, and the precipitated carbon dioxide is passively collected almost directly after its precipitation.



   The appended drawing represents, by way of example, several embodiments of the apparatus for implementing the method according to the invention.



   Fig. 1 is a schematic view of a first embodiment.



   Fig. 2 is a graph relating to FIG. 1.



   Fig. 3 is a perspective view, with cutaway, of a second embodiment.



   Fig. 4 is a section corresponding to FIG. 3.



   Fig. 5 is a simplified and ideal view of a heat exchanger system for use in the system of FIGS. 3 and 4.



   Fig. 6 is a perspective view partially cut away and considerably enlarged of a detail of a part of the heat exchanger of FIG. 5.



   Fig. 7 is a combined block diagram with partial cut away and in perspective of a temperature control system, intended for use in the system of FIGS. 3 and 4, and
 Fig. 8 is a block diagram showing a different form of life support system according to the invention and suitable for use in negative pressure environments.



   The diagram in fig. 1 shows a complete device in an ideal form as well as a basic variant which fulfills an additional function. It goes without saying, however, that the various aspects of the apparatus can be applied to a large number of different needs, in different ways. Depending on the requirements of the device and the particular environments, however, only certain aspects should be used.

  For a given life support device, the most appropriate combination will depend on factors such as whether the device is intended for single use or multiple use, whether it is to be a fixed or mobile device, whether it is to be used in a positive pressure environment or in a negative pressure environment, and whether the user is to be isolated from or exposed to the environment directly.



   The closed circuit device of FIG. 1 comprises an inlet and outlet device 10, such as a diver's mouthpiece for a movable individual assembly or suitable couplings with a volume containing a breathable gas in a scuba diving apparatus, which volume is part of the closed circuit device. In most positive pressure devices, the gases in the volume are at a pressure of a few bars or more. The gas flow path in the apparatus is determined by a set of one-way valves 12, 13, 14 which circulate the gases in the proper direction in the apparatus.

 

  An expansion bag 16 is shown mounted on the flow path for incoming contaminated gases and for leaving purified gases. As a result, an individual breathes into the expansion bag 16 and draws gases through the apparatus through the expansion bag 16 so that the bag 16 facilitates the work of breathing by compensating for variations in the volume of the lungs. . The bag 16 also serves as a compensating collector for a part of the water vapor in the gases.



   An additional quantity of water vapor which is in the incoming gases is removed in a conventional chamber 18 for removing water, such as for example a desiccant assembly. Compensation for variations in ambient pressure is accomplished by injecting pressurized helium gas through an adjustable pressure regulator 20 of any suitable type commercially available.



  The pressure regulator 20 includes a control device 22 of the control valve, called a purge button, which can be operated by hand to fully open the helium line and momentarily pressurize the apparatus. The incoming gases are sent from the water removal chamber 18 into a closed liquid oxygen chamber 24 having a volume containing gas which is separated from the liquid oxygen 25, but which is in communication with the latter. . The gases are extracted from the volume containing the gas and are returned through the one-way valve 14 to the inlet and outlet mechanism 10.

  The incoming gases, freed of their water vapor, can be freed of carbon dioxide by any conventional means, and their appropriate temperature using any conventional means, such as a cryogenic tank. or a refrigerator. Although a heat exchanger 26 has been shown and the latter has particular advantages, its use is not necessary to bring gases to a suitable state in the region containing the gas of the liquid oxygen tank 24. Likewise , the gases withdrawn from the liquid oxygen tank 24 can be reheated to a temperature allowing them to be breathed using a mechanism suitable for the installation or used separately.



   No gas mixing arrangement or control valves need to be used to inject or proportion the oxygen, and no detection equipment is needed to directly measure the oxygen pressure or the oxygen percentage. use. The temperature of the liquid oxygen in the container 24 is maintained within a selected range, for example between approximately 770 K and 900 K, which determines a predetermined partial pressure of the gaseous oxygen in the volume containing the gas which is in communication. with liquid oxygen. The partial pressure of oxygen depends only on the equilibrium conditions at the separation surface between gaseous oxygen and liquid oxygen. Equilibrium conditions are obtained when the oxygen vapor is at a saturation level, while the gas mixture is in thermodynamic equilibrium with the liquid.



   The oxygen equilibrium at saturation is shown in the phase curves of pressure as a function of temperature for oxygen and nitrogen in fig. 2.



  These equilibrium relationships between multiphase partial pressures and temperatures are not significantly influenced by the partial pressures of other gaseous elements, nor by the absolute pressure level of the mixed gases. As a result, when the temperature of liquid oxygen is kept within selected limits, the partial pressure of oxygen is also regulated, so that the oxygen content of the breathing mixture is directly related to the needs of the oxygen. user, and not in relation to the characteristics of the respiratory gas mixture itself. Indeed, the physiological needs are satisfied by the nascent gas coming from liquid oxygen 25.

  Again, it should be explicitly noted that, although a higher temperature control can be achieved by using a surrounding cryogenic tank 28, in its entirety, the control criterion is provided by maintaining a temperature range. set and selected at the separation surface between gas and liquid, and not by the means by which this range is obtained. For example, a sufficiently large liquid oxygen tank maintained in a heat-insulated environment may have sufficient life for a large number of uses, even when no control device is used to maintain the temperature of the liquid oxygen in it. the chosen range.



   However, the apparatus shown in FIG. 1 has particular advantages and especially when used with personal and mobile equipment. A counter-current type heat exchanger 26 passes the contaminated gases arriving from an inlet side 30 to an outlet side 31 of the heat exchanger in a direction of flow opposite to that of the breathing gas mixture. which passes from its inlet 33 to its outlet 34. As a result, the exhaled gases arriving which move between points 30 and 31 are brought from a temperature close to the temperature level of respiration to a temperature close to the cryogenic level , while the temperature of the aspirated mixture which exits is raised in approximately the same range.



  The drop in temperature of the incoming gases causes carbon dioxide to precipitate which contaminates them and which can consequently be eliminated in a solid CO2 collector, 36, mounted on a bypass duct 38 of the incoming gas duct.



   The cryogenic tank 28 is preferably thermally insulated and it contains liquid nitrogen or any other suitable cryogen or cryogenic mixture whose boiling point is comparable to that of liquid oxygen, provided that its critical temperature is ie the upper limit of the vapor-pressure equilibrium curve of the cryogen is not below the working temperatures of liquid oxygen. The cryogenic tank 28 may also include an enclosure 42 relating to liquid helium, connected by a conduit 44 to the adjustable pressure regulator 20. The storage of liquid helium at low temperature in the container 42, in this way, forms an extremely large volume of gas intended for use in the breathing mixture.

  Other gases, such as neon or argon, can, however, be used to regulate the pressure of the breathing mixture.



   The cryogenic tank 28 is maintained in the desired temperature range chosen for the liquid oxygen. For this purpose, a suction 46 of the gases released by boiling is connected to a conduit passing through a pressure control 50 to an exhaust receiver 52. Although the gases released by boiling can be used to effect heat exchange, the main use of this arrangement is to adjust the temperature of the cryogen by adjusting the back pressure of its vapor, as described in more detail below. The pressure control 50 can be simply a mechanically biased valve, or it can use other devices described below.

  The exhaust receiver 52 can be in any of a variety of forms, and is used to isolate the environment of the pressure setting 50 from nitrogen by providing the necessary energy (in case of necessary) to release gases given off by boiling into the environment. For example, a pump can be used for this purpose.



  Where possible, however, a vacuum reservoir or a separate operating device can be used as a receiver.



   In summary, therefore, the vital functions of a life support apparatus are fulfilled within this apparatus. Not only is the partial pressure of oxygen set, but proper compensation is made for pressure variations in a high pressure environment, which variations are reflected inside the closed circuit apparatus.



  Contaminants are removed and an appropriate breathing mixture is provided on an ongoing basis. This device provides extensive protection against catastrophic failure, as it does not use any sensitive functional element whose operation is critical to the operation of the device. The adjustment of the partial pressure of the oxygen has, in fact, a long-lasting time constant because the temperature of the cryogenic tank and that of the liquid oxygen cannot change suddenly.



  Therefore in the event that the temperature control ceases to act. the user has sufficient time to observe and adjust the conditions of the device.



   This closed-circuit device also allows the temperature relationships to be used in a corresponding way through the various elements of the device. These relationships can, however, be changed considerably. If a sufficiently large cryogenic tank 28 can be used, the heat exchanger 26 may have relatively small dimensions or relatively low efficiency, or it may in fact be omitted altogether. When the heat exchanger 26 is of a highly efficient type, the useful life of a given supply of cryogen is greatly increased and hence the volume of cryogen can be reduced.

  For example, in a practical apparatus, a heat exchanger with an efficiency of about 98% for a uniform countercurrent heat transfer rate of 126 kcal / minute, but of relatively small size is used in conjunction with a tank. compact cryogenic 28 inside which is maintained a container 24 containing liquid oxygen and a container 42 containing helium gas. This device provides an operating time greater than five hours for ambient pressures greater than 35 bars with a fluid storage volume of approximately 14 dom3. Not only is the assembly extremely efficient, it can be compact and light.



   The possibility of using liquid oxygen in this closed circuit apparatus will appear further from the following considerations. The heat capacity of one mole of gaseous helium, considering helium as the inert gas, at constant pressure is approximately 5 calories per degree Kelvin. The average respiration rate for a man is about 0.5 to 1.0 moles per minute at atmospheric pressure when changing from rest to moderate work. As a benchmark for comparison, for an ambient pressure of about 50 bars which corresponds to a depth of 486 meters in seawater, the respiration rate for moderate work increases to 50 moles per minute.

  If the gases exhaled
 that enter the device are at a temperature
 nominal value of 2850 Kelvin, and if the temperature of
 cryogenic setting is 850 K, so a heat exchanger with an efficiency of 97.5% produces a temperature dif ference of about 5O C. over the 2000 K range, roughly over the entire length of the counter-current heat exchanger. Consequently, 5O C of equivalent heat is transmitted by heat exchange of the gases exhaled to the cryogen before entering the container containing the liquid oxygen.

  The corresponding heat dissipation at a pressure of 50 bar is 250 gram-calories per minute per degree Kelvin of temperature difference for a respiratory volume per minute comparable to 1.0 mole of gas under standard conditions of 1.0 bar at 4O C. For 5O C of temperature drop, up to the temperature of the cryogenic fluid, the heat transmitted is 1250 calories per minute. This is approximately the heat of vaporization of 1.0 moles of liquid nitrogen or liquid oxygen at the temperatures used. As a result, the boiling rate of these fluids, used as a cryogen in a liner, is about 1 mole per minute at an ocean depth of 486 meters. This corresponds to a fluid consumption rate of about 2.0 liters per hour of duration.

  The boiling rate is approximately 22.6 dm3 per minute.



   The automatic adjustment of the oxygen content of an incoming gas can, it should be noted, be reversed as to its meaning or its application in a life-sustaining apparatus, or both. In the generalized apparatus shown in FIG. 1, it is not intended to reverse the direction of flow with respect to that shown. As regards the part of the apparatus relating to the adjustment of the partial pressure of oxygen, it is perfectly possible to obtain a reverse and different operation. Fig. 1 further shows an arrangement for achieving reverse operation of a life support apparatus. In particular.



  the part of FIG. 1 which is inside the dotted rectangle 43 which is called the simulator and which includes the additional functional assemblies connected to the heat exchanger 26 and to the cryogenic tank device by the dotted connections, serves as a simulator or device test whose characteristics correspond to those of a human user.



  In this device, the partition surface of any conventional life support system (not shown) is shown on the left border of the dotted rectangle 43. The life support apparatus which undergoes the The test supplies a gas mixture A, the oxygen content of which is set in the test device, and it receives a gas mixture B, the oxygen content of which is insufficient. Hence, the test apparatus may be called a human simulator as well as a simulator or other test device for determining the operation of life-sustaining apparatus under conditions of arbitrary pressures. .

 

   In this variant of the apparatus of FIG. 1, the water which is in the incoming gas mixture can be removed conveniently by a condenser 45 which precedes the final removal of the water by the desiccant 18. The COo collector 36 is bypassed as on. can be seen by the dotted connection inside the heat exchanger 26 because the device in
 trial course must ensure the necessary removal of
   CO. and toxic hydrocarbons. However, water removal is used to avoid clogging the
 heat exchanger piping.



   The inert gas source 42 is not used, this component again being supplied by the apparatus under test. A substantially constant or intermittent flow rate of carbon dioxide gas through the apparatus can be injected into the outgoing gas mixture, from a source 47 via a regulator 48.



  Finally, an amount of water vapor corresponding approximately to the amount that exists in an exhaled mixture is added by passing the exiting gas through an evaporator 51.



   Heretofore, to properly test a life support device has required either human participation or the use of a complex testing device. In either case, a suitable simulation of human use under high pressure or other pressure conditions was not obtained satisfactorily.



   The test device shown in fig. 1 can be disposed in a test environment at any pressure desired for the operation of a life support apparatus, while as desired simulating a human being. The cryogen back pressure setting 50 is set so as to maintain the temperature of the liquid oxygen at a value such that the exiting gas contains less oxygen than a breathable mixture of oxygen. The apparatus undergoing the test must therefore compensate for this lack by returning the gas mixture to the simulator 43. In addition, the water vapor introduced by the evaporator 51 and the COO coming from the source 47 are eliminated during operation, as part of the essay.

  As the life support apparatus purifies the gases exiting from the simulator and adds oxygen, the simulator 43 decreases the oxygen content to impose a continuous demand for oxygen. The temperature of the liquid oxygen is maintained, for pure oxygen below a temperature level for which the partial pressure of the oxygen is less than 0.2 bar, for example. The two devices can be operated periodically according to various ranges of pressures and temperatures and thus realizes an effective simulation of human demand.



   Figs. 3 and 4 show a detailed example of a second apparatus. It is a self-contained device which not only forms a closed circuit life support arrangement for an individual, but also makes heat available as a by-product for use in the device.



   In the arrangement shown in Figs. 3 and 4, a cryogenic device is used comprising a cylindrical storage vessel 60 for a suitable cryogen, here liquid nitrogen. The storage vessel 60 is provided with cryogenic insulation, not shown in detail, such as a double-wall structure having an intermediate spacing maintained in a vacuum. Alternatively, the wall of the storage vessel may be made of a composite comprising cryogenic insulation of the type comprising multiple layers of a heat reflecting material (eg thin foils of aluminum) between which are interwoven mats of heat. glass or other fibrous mats.

  A reservoir 62 of liquid oxygen is disposed within the main storage vessel 60, the reservoir being spherical in shape and only partially filled with liquid oxygen 63, so that a closed volume is maintained. above liquid oxygen 63 to contain gases. A quantity of liquid oxygen of less than half fills the spherical vessel so that the gas outlet 64 which reaches the center of the sphere does not enter the liquid, for any orientation.



  The liquid oxygen can be introduced by an inlet valve connected to the conduit going to the orifice 64. A wick 65 here in the general form of a hollow surface of revolution is placed inside the reservoir 62 d. liquid oxygen, and extends into liquid oxygen 63. Wick 65 may be any woven wire mesh or any fibrous material, such as asbestos, capable of being wetted by the wick. liquid oxygen so as to considerably increase the surface area exposed. The region of the separation surface between the gas and the liquid is increased to ensure a total saturation of the gases arriving in oxygen vapor and the possibility of rapidly reaching a thermodynamic equilibrium at a given temperature, between oxygen at l. gaseous state.



   A helium tank 67 is also disposed inside the storage vessel 60 and an outlet duct 68 extends inside the helium tank 67 to inject the inert gas into the system, as described further. in detail below.



   An advantageous arrangement of a heat exchanger device 72 for the incoming gases and for the outgoing gases consists in arranging the conduits for the gases in relative heat exchange positions inside a second heating vessel. storage 70 mounted here in the vicinity of the storage vessel 60 of the cryogen and parallel thereto. Advantageously using a heat exchanger 72 constituted by membranes forming multiple parallel channels and arranged so as to have a cross section of generally rectangular shape, as described in more detail in FIGS. 5 and 6 below, a heat exchange system of a minimum volume and a high effective heat transmission surface area is provided.

  To facilitate handling of the life-support apparatus by an individual diver, the second storage vessel 70 may be mounted side by side with respect to the cryogen storage vessel 60. The heat exchanger 72, as can be seen, may comprise an elongated main element disposed at one end, separated by an element 73 forming a CO2 trap and a filter, from a relatively shorter element disposed at the other. end. The main heat exchange element can, for reasons of manufacture and assembly, be divided into a group of shorter standard elements connected in series.



  Reference should be made to the detailed views in fig. 5 and 6 as well as to the description which accompanies them in order to better understand the internal arrangement of the elements of the heat exchanger.

 

   Generally, however, the incoming exhaled gases (indicated by solid arrows) enter an end manifold 74 having an inlet port in selected channels of the heat exchanger. After passing through the heat exchanger and cooling to a suitable temperature, these gases are collected in an outlet end manifold 75. The heat exchanger 72 is arranged such that the purified and compensated gases d Suitably there follow countercurrent flow paths (shown by the dashed arrows pointing upward in these figures) opposite to the flow paths of the contaminated gases passing through neighboring but clearly separated channels.

  A side inlet manifold 77 introduces the compensated gases from the tank 62 into particular channels from where they are extracted from the heat exchanger 72 through a side outlet manifold 78. Between the ends of the heat exchanger 72 and following the CO2 filter 73, the compensated gases are sent through a bypass duct 79.



   The CO filter 73 can take any of a number of forms, any of which comprises means for removing solid COO precipitate flakes from the gas stream within the exchanger. 72. In the arrangement shown, the incoming gases are cooled and brought to a temperature level at which carbon dioxide gas begins to precipitate and cease to be dissolved as a solid residue, approximately. three-quarters of the length of the heat exchanger 72, in a convenient system.

  In the filter 73 for the CO2, an outlet 80 extending from the main length of the heat exchanger 72 is disposed some spacing and slightly above an inlet port 82 for the remaining part of the heat exchanger. heat 72. The inlet 82 is covered by a thin wire mesh 83 serving to ensure the separation of the solidified CO from the gas stream sucked into the remainder of the apparatus.



   Significant advantages are obtained from this combination of COO filter 73 and heat exchanger 72.



  As described in more detail below, the heat exchanger 72 has substantially linear channels having no significant transition. This is the fact that a large cross-sectional area is available for gas flow in a given direction during heat transfer results in a pressure gradient which is small and a small variation in speed along the path. length of flow. The high efficiency of the heat exchanger causes CO to precipitate; over a relatively short length, this length being less than 10 cm in the practical system indicated. The almost completely closed chamber formed by the COo filter is completely open for solid COO particles.

  Along this relatively short channel length, the CO particles do not experience any appreciable mechanical or physical force, and a mass of loose particles is collected at the bottom, observing Fig. 3, of the receiving chamber of the CO2 filter 73.



  The gas stream is diverted in a curved path through the wire mesh 83 to the inlet 82.



  The superimposed arrangement of the outlet 80 and the inlet 82 facilitates the segregation of the solid CO flakes, but because this material does not tend to adhere to other elements, such as the wire mesh 83, no appreciable back pressure is introduced into the device.



   To achieve better thermal insulation, the second storage container 70 may be sealed and its interior kept under vacuum or alternatively it may be filled with foam, or with a conventional cryogenic insulating material.



   The gas flow path to the apparatus begins at the mouth 85 of the breathing apparatus and passes through the conduit device including the expansion bag 86 (which is only shown generally) to pass through the inlet of the water removal device, here constituted by a drying chamber 88. On the duct, at the outlet part of the drying chamber 88, is mounted a sensitive regulating valve 90 to the pressure of a high pressure environment. Regulating valve 90 opens into a conduit 92 connected to the outlet conduit 68 which accesses the helium tank 67. A regulator 93 mounted on the helium line can be used to apply a desired pressure drop to the gases from the tank to. high pressure helium 67.

  At will, the helium pipe can pass through a heat exchange position with a warmer body so as to be brought closer to a temperature level allowing breathing. Regulating valve 90 includes a purge button to pressurize the apparatus with helium to purge the lines and provide free flow. A special safety arrangement is thus added to the apparatus by the closed-circuit arrangement combined with the injection of an inert gas at high pressure. If a clogging occurs in the channels of the heat exchanger, or in the event that liquid enters the ducts forming part of the device, these can be reopened almost instantly. to use them by injecting high pressure helium.

  This flushing or flushing of the apparatus does not influence the oxygen remaining in the apparatus when the purge is complete, since the proper proportion of oxygen is restored almost immediately.



   To simplify the figures, the harness of the diver operating the assembly has not been shown, because any back structure or conventional harness can be used. Likewise, the unidirectional control valves have not been shown in FIGS. 3 and 4.



   The incoming gases flow from the outlet end manifold 75 of the heat exchanger 72 into the storage vessel 60. Inside the latter, the gas stream is further cooled by passing it by performing a heat exchange with the cryogen, in coils 95 wound inside the storage vessel 60. The coils 95 provide isothermal heat exchange between the cryogen and the incoming gas stream, and the resulting gas stream cooling. sufficient to ensure that the heat balance within the liquid oxygen reservoir 62 is not significantly interrupted by the incoming gases. In other words, the exhaled gases do not tend to excessively heat the liquid oxygen.

 

   To ensure a continuous flow, the gas pipe which contains the incoming gases is divided into two separate pipes forming the coils 95, each of which curves in the opposite direction and ends inside the liquid oxygen tank 62 through orifices. opposing facing inlet 96, which are disposed above the level of liquid oxygen. In the normal operating position of this device, the attitude of the reservoirs is, in general, that which is shown in FIG. 3, that is, it is somewhat vertical. When the reservoirs are in this position, the inlet ports 96 are above the level of liquid oxygen. Of course, a constant attitude cannot be maintained under all operating conditions.

  Therefore, the use of two orifices 96 ensures that despite tilting in one direction or the other, at least one of the elements 96 remains open to incoming gas streams. In addition, even when the remaining port 96 can be filled momentarily, the liquid oxygen which is therein returns to the main part of the reservoir 62 as soon as the attitude of the apparatus has returned to approximately normal.



   The outlet 64 for the gas which is centrally located inside the wick-shaped element 65 forms a means for withdrawing the compensated gases from the volume containing them which is inside the reservoir. 62 liquid oxygen, regardless of the orientation of the latter. These gases are passed out of the storage vessel 60 into the side inlet manifold 77 of the heat exchanger and returned through the duct system and the side outlet manifold 78 to the mouth 85.



   It has been previously indicated that a number of means, including a large mass of cryogen, can be used to maintain the partial pressure of oxygen within a selected range. The arrangement shown in Figs. 3 and 4 uses the withdrawal of gases given off by boiling cryogen at an appropriate rate, determined directly by the temperature prevailing inside the reservoir 62 of liquid oxygen. The arrangement is described here only in general terms, as further details regarding the heat exchange relationships and the exhaust control are described in detail in connection with Figs. 5 and 7, below.



   A boiling gas line 97 extends directly into the cryogen storage vessel and introduces the gases given off by boiling, via a feed manifold, in interlocking paths and arranged in a spiral at the same time. The interior of the heat exchanger 72. During the filling of the vessel 60, the cryogen can be introduced through the line 97 for the gas. The boiling gases extract heat from the heat exchanger 72 by passing through a manifold system and going to an exhaust control valve 100. No valve arrangement for the liquid is necessary because the valve arrangement for the liquid is required. pressure of the boiling gases in the pipe 97 is arranged so as to block any flow of liquid inside the pipe 97.

  Confluent cryogen boiling risers, 98A, 98B, 98C and 98D, with open ends and extending into the cryogen storage volume are arranged inside the cryogenic storage vessel. a way that prevents liquid from escaping under the action of gravity. The confluent pipes 98A-D are joined by a common manifold 99 to the boiling pipe 97, inside the clyogenic storage vessel. The curved paths followed by the various 98A-D gas risers are designed to form a trap for the liquid, for virtually any orientation of the apparatus although there is always at least one free path for the flow. gases.

  The common riser manifold 99 is disposed inside the vessel containing the cryogen so as to allow the fluid momentarily trapped in the risers, due to rapid movements, to evaporate within the confines of the vessel in order to exert all the pressure. influence of its corresponding cooling capacity. Each of the gas risers 98A-D terminates in a distinct, separate region within the cryogenic tank 60. Each of them follows two paths re-entering, mutually perpendicular, inside the tank 60, the boundaries of each of the paths. re-entrant being spaced a distance greater than half of the corresponding dimension of the reservoir 60.



   The exhaust control valve 100 is a regulator which operates in response to an actuating mechanical force to pass gases through a receiving device 102. An adjustment knob 103 can be adjusted as described in more detail below, to choose an appropriate operating level.



  The desired mechanical control force for controlling the rate of boiling gases passing through receiving device 102 is exerted by a thermal detector tube arrangement 104 described in detail in connection with the description of FIG. 7. It suffices to indicate now that the thermal detector tube 104 extends inside the reservoir 62 of liquid oxygen and that in response to the temperature which prevails inside the latter it produces a mechanical force acting. on the exhaust control valve 100.

  As a result, when the temperature of the gas-liquid separation surface in the liquid oxygen tank 62 rises above a predetermined value, the pressure in the detector tube 104 opens the control valve. exhaust 100 so as to cause the boiling gases of the cryogen to pass into the receiving device 102. The pressure of the cryogen and therefore its temperature are adjusted in a corresponding manner, and the temperature of the liquid oxygen is maintained in the desired range.



   A positive acting receiver 102 is required to extract the boiling gases only when a low pressure receiver is not available.



  In low pressure environments, the environments themselves can constitute a receiver of infinite dimensions. In stationary devices and in other autonomous devices, it is possible to have a receiver of a different type, such as a container containing gas or liquid, the main content of which is gradually used for other applications and which thus in fact forms a low-pressure enclosure of increasing volume as the apparatus operates or whose main elements (solid, liquid or gas) absorb boiling gases or combine chemically with them to form a residue (solid or liquid), at a pressure which is lower than the pressure of the boiling gases at the inlet of the receiver device 102.



   The receiving device 102 of the mechanism, as seen in FIGS. 3 and 4, however, is particularly useful for high pressure devices intended for individual divers. The escaping gases are drawn in by a compressor 105 driven by a battery 106. An outlet port mounted on the compressor 105 simply injects the gases into the environment, although a collecting tank can be used. separated to limit the formation of gas bubbles in the environment. The heat generated within cell 106 and compressor 105 is also usefully used in the apparatus, however, since refrigerant fluid is circulated in a closed circuit path (not shown in detail for example. simplify the figure) through heat transmission conduits 108 arranged in the garment worn by the diver.

  Most receiving devices are exothermic in nature and give off heat when in operation, and this heat, as seen, can be used for the benefit of the user of a device, that is, an individual wearing a garment. , or a group of individuals within an autonomous device.



   The presence of these different subsets, however, is only one example of the many important aspects which are the corollaries of the fundamental aspects of respiratory gas control.



  Apart from direct and safe flow direction settings and a regulator compensating for variations in ambient pressure, it should be noted that a breathable oxygen mixture is supplied without any mechanism performing detection functions, calculation or regulation. The inlet gases are brought to a suitable temperature range at the heat exchanger 72, they are purified by the effect of the expansion bag 86, a desiccant or a condenser and a chamber. freezer 88 and a carbon dioxide filter 73.

  Entering the volume containing the gas inside the liquid oxygen tank 62, the gases are in an environment whose characteristics, depending on the partial pressure of oxygen, are determined only by the relationships of saturation and thermodynamic equilibrium between liquid oxygen and the gas mixture comprising gaseous oxygen which is in communication with it, as described above. When the temperature inside the liquid oxygen reservoir 62 is automatically maintained within a range of from about 0.2 bar to 1 bar, i.e. the range which is necessary for the breathing mixture.



   Because the basic source of oxygen supply is in liquid form, there is a large supply of breathable oxygen, far greater than the amounts that can be handled and used by most breathing apparatus. current autonomous sailors. In addition, the efficiency of the apparatus is extremely high due to the closed circuit arrangement which ensures that it is only necessary to add the replenishment oxygen during operation of the apparatus.



   The large reservoir of cryogen which constitutes the storage vessel 60 represents a stable cryogenic source. Extremely efficient use is made of this stable source, however, by using an efficient countercurrent heat exchanger 72 to limit heat gains by lowering the temperature of the exhaled mixture to the cryogenic level, while raising the temperature of the exhaled mixture. mixed
 set to a level that allows it to be breathed. In addition, the heat exchanger 72 serves to extract the solidified CO during the cooling of the incoming gases, and presents another advantageous aspect of the apparatus.



   The injection of helium to compensate for the pressure differences between the system pressure and the high pressure environment, as well as the use of a tank
 see helium 67 disposed inside the cryogen, have additional advantages. A large volume of helium can be maintained at low temperature.
 ture of cryogen. We have in this way a
 quantity equal to at least several times the normal useful quantity of inert gas. Although helium constitutes a high percentage of the gas mixture at pressures
 high, it is not used physiologically and therefore a much smaller amount is required. In practical devices, the useful work cycle of a diver is lengthened appreciably.

  A five-hour operating period can be easily obtained without using equipment of such large mass or dimensions as to limit the work produced by the diver.



   In addition, the heat generated during the operation of the receiver system 102 is used to form part of the heat supply inevitably needed in underwater environments.



  The presence of significant amounts of helium in a respiratory mixture greatly increases the rate at which heat is lost by an individual.



  Therefore, the use of the heat produced to power the conduits 108 disposed in the diver's garment satisfies an essential need for such environments and increases the overall efficiency of the apparatus.



   The useful range of partial pressures for oxygen, to support human life, has been reported to be approximately 0.2 to
 1.0 bar. When the whole of the breathed medium is brought into thermal vapor pressure equilibrium with the liquid oxygen to obtain the partial pressure of oxygen, it follows that the temperature range for pure liquid oxygen, which corresponds to the safe levels of oxygen quoted according to the data in fig. 2, is about 77o K to 90O K. The same range of temperature control therefore applies to the surrounding cryogen.



  If, on the other hand, the liquid oxygen is diluted with another cryogenic fluid, the vapor pressure of the first is diluted in a corresponding manner, all other elements remaining equal. In particular, the partial pressure of a gas in thermal equilibrium with its liquid phase, whatever the ambient pressure of foreign gases in direct combination with the liquid, is proportional to the product of the partial pressure of the gas concerned (obtained from the pure liquid) and the fractional molar concentration of the substance in question in the liquid state.

  Consequently, for example, while the partial pressure of gaseous oxygen in equilibrium with pure liquid oxygen at 900 K is 0.98 bar, the partial pressure for a molar concentration of 50 o / o of oxygen liquid (diluted, for example with 50 O / o molar liquid nitrogen) at the same temperature of 90O K is reduced by half, to 0.49 bar. As long as the dilution remains fixed, the respective partial pressures of the liquid components are invariable.



   This physical principle can be applied in an advantageous manner to an apparatus adjusted in a cryogenic manner.



  Therefore, the liquid oxygen can be diluted with another cryogenic fluid provided that the vapor pressure of the resulting diluent fluid is allowable for human respiration. The operating temperature of cryogenic fluids is then raised collectively from that which would be used with pure liquid oxygen, in order to achieve the same level of partial pressure of oxygen in the respiratory medium. If we use
 In dilution, account must be taken of the gradual dilution of liquid oxygen as the latter is selectively removed from solution by evaporation. If this extraction were allowed to continue, the level of the partial pressure of oxygen would be altered even if the temperature were kept constant.

  The effects of dilution can be suppressed by using a larger reserve of liquid, so that the rate of oxygen uptake, compared to the length of the period of use, is not sufficient to change the level of oxygen. the partial pressure of oxygen beyond tolerable limits. In addition, adjustments can be made periodically as liquid oxygen is consumed, to raise the operating temperature and compensate for the decrease in the oxygen level. The main advantage of diluting liquid oxygen, if it is only used for shortened periods of time, is the higher operating temperature of the surrounding cryogen which allows the latter a correspondingly higher operating pressure. high.

  If the pressure of the cryogen is higher than that of the ambient environment, the device can be used in a positive pressure environment without the need for an exhaust compressor or any other type of receiving device. , with the exception of the environment itself.



   Figs. 5 and 6 show the general layout and particular details of a high efficiency heat exchanger system which is extremely compact and uses only elements which can be easily manufactured and easily assembled. The heat exchanger is of the countercurrent type and it solves the problem of the manifolds, that is, to direct the gases in separate channels without a complex mass of links.



   As can be seen in particular in FIG. 6, which is a greatly enlarged view of a segment of the heat exchanger in which the relative dimensions are not to scale in order to more clearly represent the elements, the basic elements of the heat exchanger are made up by thin corrugated membranes 110, the corrugations of which extend parallel and in the direction of the length of the membrane. A number of corrugations on the order of 20 per centimeter can be used in the present system, and the dimension between ridge and valley can be about 0.75 mm with a membrane of the thickness of the order of 0 , 05 mm.

  The membrane 110 itself is preferably of a thermosetting plastic material of one of the types which are conveniently used for thermal shaping, such as the material sold under the tradename Lexan. The corrugated configuration can be obtained by shaping the plastic material between dies, after bringing it to a temperature above its plastic flow temperature. The corrugation or repeated deviation of membrane 110 from its midplane to form gas channels need not follow the sinusoidal shape which is generally associated with the term ripple. On the contrary, the membrane 110 can move away from it and present grooves or ridges and valleys, in any periodic or even aperiodic manner.



   With regard to this basic element of the heat exchanger, a hot gas which is to be cooled is passed on one side of the membrane 110, and a cold gas which is to be heated on the other side of the membrane 110. , in the opposite way. The heat is then transmitted through the thickness of the membrane. Although it is known to pass gases flowing in opposite directions on the different sides of a separator arranged between them, for liquid systems and other systems the apparatus described is special at a number of points. view. The channels formed by the grooves are small, and the membrane 110 is a poor conductor of heat, but is very thin. Thermal energy can therefore be easily transmitted between gases in neighboring channels through the thickness of the membrane.

  An advantage is due to the use of the corrugated membrane due to the periodic separation surface between the gases flowing in opposite directions instead of the heat-conducting fins which characterize the earlier models. The efficiency of heat transfer and the importance of heat transfer per unit volume are therefore considerably increased. In fact, the main limitation of heat energy exchange is not due to the weak insulating effects exhibited by the membrane, but to the transmission of heat energy inside the gas itself. At the same time, however, the relatively low thermal conductivity of membrane 110 ensures that heat is not transmitted along its length parallel to the direction of gas flow.

  Unlike previous heat exchange devices, therefore, the hot and cold opposing ends are not interconnected by a highly conductive medium consisting of the heat exchange element itself and acting as it is. a cold source tending to remain at a median temperature over its entire length and, consequently, to reduce the efficiency of the heat exchanger. Due to the insulation characteristics of the heat exchanger material, it is possible to use a large ratio of cross-sectional area to length without significant decrease in efficiency. The pneumatic impedance of the channel system is low, produces only a small pressure difference and makes breathing much easier.



   To separate the gases, and to serve as collectors, the ridges and valleys on opposite sides of the membrane 110 are attached to a thin intermediate layer 112 and a relatively thicker spacer 114, respectively.



   As can be seen in the two figs. 5 and 6, the intermediate layers are arranged between two membranes 110 and extend over the entire length of the heat exchange structure. However, the struts 114 are discontinuous along the heat exchanger, and the struts 114 and the intermediate open volumes are used for various reasons.



   It is convenient, by way of illustration and description, to regard the layered structure as comprising two membranes 110 disposed between two thicker struts 114 as a heat exchanger element. This element is then limited by the thicker spacers 114 and it comprises a pair of neighboring membranes 110 of the same length between which the intermediate thin layer 112 is interposed over the entire length of the heat exchanger. The layers 112 and the spacers 114 may, like the membranes 110, be of a suitable plastic material. Considering the thin layer 112 as being the center of the structure, the neighboring interior channels whose sides are limited by the layer 112 and by the two neighboring membranes 110 form flow paths going from one end of the heat exchanger. heat at its other end.

  What can be called the outer channels, inside the element, are formed by the channels formed between the opposite sides of the membranes 110 and the outer struts 114.



  A first gas or a first gas mixture passing in a first direction along the heat exchanger within the interior channels is, therefore, completely separated from a second gas or second mixture which passes along the exterior channels. . If a leak occurs due to insufficient bonding between the membrane and the intermediate layer 112, there is neither a significant temperature difference between the gases nor a mixture of different gases. The open volumes that lie between the thicker separate struts 114 provide access to all of the outer channels of an element from one side of the heat exchanger.

  These exterior open volumes communicate with the exterior channels disposed at the lower part (observing Fig. 5) of the upper element, and with the upper side of the heat exchanger element immediately below. All of these open volumes communicate with common side manifolds arranged in two or more regions along the heat exchanger. The necessary separation between the gas mixtures is provided by sealing surfaces 120 which close the channels at the ends of the system, and by sealing membranes 121 which close the interior channels in the region of the side manifolds.



   As can be seen in the two figs. 5 and 6, therefore, the gases which are in the inner channels moving in a first direction (from right to left in Figs. 5 and 6) pass from one end manifold 116 to the opposite manifold. 118. The second gas mixture which passes by flowing in the opposite direction is introduced from a side manifold 122 through the heat exchanger and goes to the opposite side manifold 124.



   The extremely simplified and ideal diagram of fig. 5 therefore shows a complete heat exchanger structure 72, consisting of successive layers of basic heat exchange elements until the desired cross-sectional areas have been obtained to flow the two mixtures. gaseous. We realize that by continuing to superimpose layers of additional elements, we do not modify in any way and we do not complicate the arrangement of the collectors, and that several hundred elements can be used. In a practical example, a heat exchanger having approximate exterior dimensions of 15 cm by 15 cm by 60 cm, exhibits the heat transfer capacity necessary for an individual life support apparatus.

  This apparatus operates between the temperature range allowing respiration and, approximately, the cryogenic range, transmitting approximately 126 kcal per minute with an actual efficiency of approximately 980/0 and with a total volume of the heat exchanger of the order of 14 dm3. The gas channels are linear and, as indicated, there is a large cross-sectional area for the gas flow, as well as an extremely large heat transfer area. As a result, there is only a small pressure difference inside the device. This arrangement is further characterized by the fact that standard heat exchange elements can be assembled along a chosen length and cross-sectional areas.

  To achieve higher capacity or efficiency, these elements can be simply connected in series or in parallel using suitable links arranged between the heat exchange collectors.



   The structure of the heat exchanger is also arranged to perform an additional heat transfer function, by extracting heat from the main gases flowing in counter-current, with high efficiency. It is realized that a drop or rise in temperature can be increased simply by introducing an available high or low temperature source and bringing it into intimate contact with the heat transmitting elements, due to the unrestricted interior volumes which exist between elements and collectors. Apart from this obvious method, however, it is desirable in the present example to provide heat extraction from countercurrent gas mixtures without substantially obstructing gas flow and using a surface. significant heat exchange.

  For this purpose, gases at low temperatures are passed from a boiling manifold 125 through a sinuous duct 126 interposed between the facing clearances of the outer channels of the neighboring heat exchanger elements, and between them. side manifolds 122, 124. The gases in the outer channels are kept separated by thin inner layers 127. Tertiary heat exchange is thus carried out using the boiling gases as a cold source, which acts in a manner important on the two gas streams flowing against the current, through the intermediary of this gas which flows in the second direction inside the heat, between the side collectors 122, 124.



   Due to the fact that the cryogenic reservoir which contains the gas-liquid volume separated by a separation surface is not itself interested in the respiratory medium, the partial pressure which exists there, due to the temperature which also prevails, is the total pressure prevailing in the cryogenic vessel. Due to the fundamental isomorphic relationships which exist between the temperature and a partial pressure of any fluid in equilibrium with its vapor in a closed volume, it is possible to regulate the temperature of the cryogenic fluid by mechanically adjusting the back pressure, which prevails in the cryogenic vessel.

  The partial pressure of the oxygen vapor is obscured, in the mechanical sense, by the presence of a respiratory support medium consisting of inert gases, in appropriate proportions, which consequently avoids any direct mechanical adjustment of the pressure. oxygen. The latter is, however, regulated in an indirect manner by its equilibrium with its corresponding liquid, the temperature of which is identical to that of the cryogenic fluid and can be regulated by adjusting that of the latter.

 

   Fig. 7 shows a suitable arrangement of a receiver for the boiling gases and of a control device for keeping the partial pressure of oxygen constant or within a selected range, in the apparatus of FIGS. 3 and 4. Parts of the device may be conventional and, therefore, they have been shown in a synoptic manner. Other parts are shown in Figs. 3 and 4 and, therefore, they have been deleted here.



   The control mechanical force for controlling the rate of escape of the boiling gases to the receiving device 102 is produced by the pressure of a gas within a thermal detector tube 130. The detector tube thermal 130 has a sealed end 131 which is disposed within the liquid oxygen 63 of the reservoir 62, sufficient gas pressure (e.g. nitrogen) initially existing inside the sealed tube to ensure that some of the interior gas is liquefied within the coil-shaped length 131 of the tube which is immersed in the bath of liquid oxygen. The submerged length is suitably shaped like a coil or other shape to stay in contact with liquid oxygen 63 for all orientations.



  The tube extends outside the liquid oxygen reservoir 62 in communication with an exhaust control valve 100. The gas pressure inside the tube is in communication with a diaphragm 134 which bears against a piston. 136 axially slidable and having a radial vent 138 which moves as piston 136 slides. The radial vent 138 opens and closes an exhaust duct 139 of the compressor 105. A spring 140 normally opposes the opening of the radial vent 138, with a force which depends on the setting of an adjustable control knob. 103.



   The thermal detector tube 130 produces a mechanical force which is determined almost completely only by the temperature of the liquid oxygen.



  The sealed end 131 of the tube held inside the liquid oxygen bath ensures that the liquefied nitrogen inside the sealed tube takes the temperature of the liquid oxygen. Therefore, the partial pressure of nitrogen in the closed volume which constitutes the remainder of the tube represents the total pressure of the gas inside the tube and depends directly on the thermodynamic equilibrium between gas and liquid in the region of the separation surface. Relatively small variations in the absolute level of liquid oxygen temperature, however, represent relatively large pressure variations, and the pressure within the tube therefore covers a wide dynamic range, and produces precise and control forces. substantially linear operating the diaphragm 134.

  Since it can be assumed that there is an almost perfect communication of the pressures within the enclosed gas, and because this pressure is controlled by the equilibrium conditions at liquefaction at one end, the force desired can be transmitted through an elongated tube, and the tube can pass through areas of widely varying temperatures, such as the cryogenic tank, and the associated positive pressure environment. Not only is the closed-circuit temperature controller extremely simple and free from any component or functional assembly subject to failure, it also performs the necessary temperature sensing and transduction with amplified mechanical force at great expense. low.



   In fig. 8, there is shown a different form of the closed circuit life support apparatus, this form being particularly applicable to closed life support environments in spatial or superatmospheric conditions. A life support structure 150 may include one or more individual pressurized garments or a closed volume. In either case, the life support structure 150 forms part of a closed circuit apparatus serving to meet physiological oxygen requirements. A reserve of liquid oxygen is maintained in a closed and heat-insulated tank 152 which forms a closed volume inside which the gaseous oxygen is maintained at saturation and in thermodynamic equilibrium with the liquid oxygen.

  The gases are circulated through the structure 150 by an inlet and outlet system comprising an outlet end 153 and an inlet end 154, the inlet end communicating with the closed volume located therein. of the reservoir 152 containing the liquid oxygen.



   This apparatus advantageously uses what can be considered as a cold source of infinite capacity formed by a superatmospheric or spatial external environment and does not require a receiving system or cryogen or other means to regulate the temperature. of the gas mixture. In its place, a pump 156 circulates gas through a scrubber 157 and through the remainder of the apparatus. A detector 158, which may be of the detector tube type or have a different form of temperature sensitive detector, operates an adjustable bypass valve 159 to circulate gases through the apparatus, so as to maintain a selected range. partial pressures of oxygen.

  The circulation path from pump 156 includes a cryogenic refrigerator 161 operating in conjunction with a counter-current heat exchanger 160 and a bypass circuit which both are connected to the liquid oxygen tank 152. For space applications, an additional length of duct and fins having a sufficient surface area of heat exchange surface with the environment are sufficient as a cold source, if they are isolated from any radiant energy, since the environment is present. approximately at a temperature of 40 K and that, therefore, it represents an infinitely large negative heat capacity factor. Alternatively, a conventional mechanically operated cryogenic refrigerator can be used.

  The heat exchanger 160 receives the gases from the closed volume inside the tank 152 to effect heat transmission with the incoming gases.



   When the structure 150 which contains the life support system operates without a significant physiological demand for oxygen, the only variation in temperature of the liquid oxygen in the tank 152 is due to heat loss or to suction. from the environment. When the oxygen in structure 150 is lost through leakage and physiological use, regardless of variations in the rate of circulation flow, however, valve 159 is controlled to bypass oryogenic refrigerator 161 as long as the liquid oxygen temperature is maintained within the selected range.

 

   The contaminated gas scrubber can be conveniently incorporated into cryogenic refrigerator 159 or heat exchanger 160, with the collected water vapor and carbon dioxide being ejected into the environment. The use of a bypass device is only one method that can be used. Variable refrigeration can also be achieved by using variable flow rates or by varying the efficiency of the cryogenic refrigerator, for example by varying the flow length within a set of conduits.



  Alternatively, the current can be divided in a controlled manner between heating and cooling circuits.



   It is common to use a reserve containing 100 oxo of oxygen at a pressure of the order of 0.35 bar. The flammable nature of pure oxygen, however, indicates the need for an inert element for quenching the gas mixture. The inert gas can be supplied by a source 162 via a pressure regulator 164 opening into the structure 150. Therefore, with a partial pressure of oxygen of about 0.35 bar, a total pressure of 0 , 50 bar, (or any other chosen value) can be obtained by injecting the necessary additional gas through the pressure regulator 164. In such an apparatus, the extinguishing gas must be such that it does not liquefy in the gas chamber. partial pressure range used. Nitrogen and helium are satisfactory for the example given.



   It should also be realized that the partial pressure of the inert gas can itself be regulated directly, by adjusting the oxygen pressure using a pressure regulator, to form the inverse of the apparatus shown. in fig. 8.



   The adjustment of the partial pressure of oxygen can moreover be used in an open circuit apparatus, even if such an apparatus is dispensable, for a reserve of respiratory gas mixture. In addition, the increased efficiencies obtained by using heat exchange mechanisms can either be obtained in some other way or do not need to be used in the apparatus.



      CLAIM I
 A method of removing carbon dioxide from a gas mixture, characterized by flowing the gas mixture along a substantially linear path with a low pressure gradient, extracting heat from the gas mixture to establish a gradient of net temperature extending to a temperature level below the point of carbon dioxide precipitation and the precipitated carbon dioxide is passively collected almost directly after its precipitation.



   SUB-CLAIM
 1. Method according to claim I, for removing carbon dioxide from a gas mixture which can be breathed, characterized in that the gas mixture is cooled to a temperature below the precipitation temperature of the carbon dioxide while maintaining a low pressure gradient during cooling, and the precipitated carbon dioxide is collected as a mass of loose particles.



   CLAIM II
 Apparatus for carrying out the process according to claim I, characterized in that it comprises a first source of gas in a range of temperatures below the precipitation temperature of carbon dioxide, a second source of gas containing carbon dioxide and in a range of temperatures above the carbon dioxide precipitation temperature, a heat exchanger connected to the first and to the second gas source by passing these gases to the heat exchange position, the heat exchanger providing a substantially linear flow of gases with low pressure gradients and having sufficient length and area to cool the gases from the second source to a temperature below the precipitation temperature of carbon dioxide,

   and a device collecting carbon dioxide forming a closed volume, open to gases from the second source passing along the exchanger near the region thereof where the carbon dioxide precipitates.



   SUB-CLAIM
 2. Apparatus according to claim II, characterized in that the exchanger is divided into two sections and in that the collection device is disposed between these sections, and comprises an outlet duct and an inlet duct arranged at the inside a closed chamber, the inlet and outlet ducts being arranged so as to cover each other, a cloth further covering the outlet duct.

** ATTENTION ** end of DESC field can contain start of CLMS **.



   


    

Claims (1)

** ATTENTION ** start of field CLMS can contain end of DESC **. It is common to use a reserve containing 100 oxo of oxygen at a pressure of the order of 0.35 bar. The flammable nature of pure oxygen, however, indicates the need for an inert element for quenching the gas mixture. The inert gas can be supplied by a source 162 via a pressure regulator 164 opening into the structure 150. Therefore, with a partial pressure of oxygen of about 0.35 bar, a total pressure of 0 , 50 bar, (or any other chosen value) can be obtained by injecting the necessary additional gas through the pressure regulator 164. In such an apparatus, the extinguishing gas must be such that it does not liquefy in the gas chamber. partial pressure range used. Nitrogen and helium are satisfactory for the example given. It should also be realized that the partial pressure of the inert gas can itself be regulated directly, by adjusting the oxygen pressure using a pressure regulator, to form the inverse of the apparatus shown. in fig. 8. The adjustment of the partial pressure of oxygen can moreover be used in an open circuit apparatus, even if such an apparatus is dispensable, for a reserve of respiratory gas mixture. In addition, the increased efficiencies obtained by using heat exchange mechanisms can either be obtained in some other way or do not need to be used in the apparatus. CLAIM I A method of removing carbon dioxide from a gas mixture, characterized by flowing the gas mixture along a substantially linear path with a low pressure gradient, extracting heat from the gas mixture to establish a gradient of net temperature extending to a temperature level below the point of carbon dioxide precipitation and the precipitated carbon dioxide is passively collected almost directly after its precipitation. SUB-CLAIM 1. Method according to claim I, for removing carbon dioxide from a gas mixture which can be breathed, characterized in that the gas mixture is cooled to a temperature below the precipitation temperature of the carbon dioxide while maintaining a low pressure gradient during cooling, and the precipitated carbon dioxide is collected as a mass of loose particles. CLAIM II Apparatus for carrying out the process according to claim I, characterized in that it comprises a first source of gas in a range of temperatures below the precipitation temperature of carbon dioxide, a second source of gas containing carbon dioxide and in a range of temperatures above the carbon dioxide precipitation temperature, a heat exchanger connected to the first and to the second gas source by passing these gases to the heat exchange position, the heat exchanger providing a substantially linear flow of gases with low pressure gradients and having sufficient length and area to cool the gases from the second source to a temperature below the precipitation temperature of carbon dioxide, and a device collecting carbon dioxide forming a closed volume, open to gases from the second source passing along the exchanger near the region thereof where the carbon dioxide precipitates. SUB-CLAIM 2. Apparatus according to claim II, characterized in that the exchanger is divided into two sections and in that the collection device is disposed between these sections, and comprises an outlet duct and an inlet duct arranged at the inside a closed chamber, the inlet and outlet ducts being arranged so as to cover each other, a cloth further covering the outlet duct.