WO1998028161A1

WO1998028161A1 - Membrane and system for the treatment of air streams in vehicle cabins

Info

Publication number: WO1998028161A1
Application number: PCT/US1997/022964
Authority: WO
Inventors: Harold T. Couch; Alan D. Williams
Original assignee: United Technologies Corporation
Priority date: 1996-12-20
Filing date: 1997-12-17
Publication date: 1998-07-02

Abstract

An air treatment system for conditioning cabin air of a vehicle or enclosure is disclosed. The system comprises an air duct for directing air having a first flow direction to the cabin; a circulating air treatment substance; a membrane positioned in the air duct for treating the air with the circulating air treatment substance prior to the air entering the cabin. The membrane is positioned substantially transverse to the first flow direction. A supply for supplying an air treatment substance to the membrane and circulating the air treatment substance in the membrane for use in treating the air, is also provided. A screen (10) is also disclosed for use in treating air, having a flow path, with an air treatment substance, prior to expulsion of the air from an air duct into a cabin. The screen (10) comprises a membrane (11) including a plurality of hollow fiber membrane elements (12). The membrane (11) is adapted for placement in the duct transverse to the flow path of the air. The screen further comprises channels for circulating the air treatment substance through the membrane for treatment of the air.

Description

Membrane and System for the Treatment of Air Streams in Vehicle Cabins

Technical Field This invention is directed to a system for treating air designated for public enclosures or in a vehicle cabin, particularly an aircraft or submarine, and more particularly, to a membrane and an associated system for use in an air duct of an air conditioning system of such a vehicle for treating, and most particularly, humidifying air prior to its expulsion into the vehicle cabin.

Background Art

Humidification and other forms of air treatment in closed systems, such as aircraft cabins and submarine cabins, is desirable for creating a comfortable atmosphere for passengers therein. Currently, control, if any, over inadvertent introduction of water borne bacteria, viruses, and miscellaneous salts during humidification and other treatment of air in such cabins is incomplete and imprecise. Since different concentrations of humidity are desired in different cabin areas due to occupancy, altitude, weather, and air flow requirements, such imprecision inhibits effective elimination of discomfort. In addition to humidification, it is also desirable to remove contaminants from air prior to expulsion into such cabins. It may also be desirable to dehumidify air and remove CO₂ from air prior to its expulsion into cabins.

With particular regard to humidification, current aircraft flight decks can receive up to 10 to 20 times the amount of fresh air per person in comparison to passenger compartments. This is at least partially due to the need to maintain alertness. This amount of air expelled into the flight decks has the effect of overdrying the flight deck and dehydrating the crew, thereby requiring humidification. Current humidification systems do not pathogens into the system, such as in the case of the spread of the Legionaries sickness where a viral type pathogen which is originally water borne can thrive in any water accumulation occurring in the air ducts. Also, existing humidification systems raise great concerns with regard to microbes originating from the humidifying system and spreading to the humidified air. Humidifying devices for humidifying air supplied to an enclosure or the like are known. The most notable of these prior art devices are misting devices that mechanically sling fine water droplets into a dry air stream with the idea that, if the droplets are small enough, they will quickly evaporate and thus humidify the air.

The prior art humidifying devices have been found to be troublesome in several areas. The troublesome aspects of these devices can create adverse health and comfort conditions for persons exposed to the humidified air produced. In particular, bacteria can grow within these humidifying devices and can be readily dispelled with the humid fresh air. In addition, the potable water used in these devices usually contains minerals which eventually clog or foul equipment and these minerals are also dispelled with the air and leave deposits on exposed articles, such as electronic equipment. Similar problems exist regarding other air treatments, such as for dehumidification and CO2 removal. Accordingly, humidification devices and other air treatment devices that correct these known deficiencies of the prior art devices have been sought.

For example, misting devices which use simple evaporation leave all of the impurities originally present in the water stream, in the humidified air stream. Devices which use the technique of steam injection are better, leaving most of the minerals behind and killing most of the bacteria. However, these devices are energy extravagant and if there are enclosures used wherein steam can condense and liquids accumulate, before reuse of the liquid, bacteria can multiply. There exists a need, therefore, for an air treatment system which is light weight, prevents substantial accumulation of air treatment substances in air ducts, and which also provides for the desired amount of humidification, dehumidification, decontamination, or carbon dioxide removal, prior to expulsion of the air into occupied cabins.

Disclosure of the Invention The primary object of this invention is to provide an improved humidification system for use in air ducts associated with the air circulation systems of vehicles, particularly aircraft and submarines.

Another object of this invention is to provide a screen membrane capable of insertion into an air duct of an existing air circulation system of a vehicle, particularly an aircraft, which membrane functions to accomplish at least one of the ends: humidify air; dehumidify air; decontaminate air; and/or remove carbon dioxide from air.

And still another object of this invention is to provide a system using at least one, and preferably multiple screens having membranes adapted for insertion in air ducts of air circulation systems of vehicles or buildings or other public enclosures, which system functions to accomplish at least one of the ends: humidify air; dehumidify air; decontaminate air; and/or remove carbon dioxide from air, which air is designated to be circulated through the vehicle, particularly an aircraft. The objects and advantages of the present invention are achieved by the air treatment system disclosed herein for conditioning air in a vehicle or other closed environment. The system comprises means for directing air having a first flow direction to the cabin; a circulating air treatment substance; a membrane means for treating the air with air treatment substance prior to the air entering the cabin. The membrane means is positioned substantially transverse to the first air flow direction. Means for supplying an air treatment substance to the membrane means and for circulating the air treatment substance in the membrane means for use in treating the air is also provided. The objects and advantages are further achieved by the screen of the present invention for use in treating air, having a flow path, with an air treatment substance, prior to expulsion of the air from an air duct into a cabin. The screen comprises a membrane including a plurality of hollow fiber membrane elements. The membrane is adapted for placement in the duct transverse to the flow path of the air. The screen further comprises means for circulating the air treatment substance through the membrane for treatment of the air.

Brief Description of the Drawings FIG. 1 is an elevational view of a screen comprising hollow fiber membrane elements in accordance with the principles of the present invention used for treating air to be circulated through air ducts of passenger occupied vehicles, particularly an aircraft;

FIG. 1 A is an enlarged view of encircled area 1 A of FIG. 1 , showing the arrangement and relative size of the hollow fiber membrane elements comprising the screen assembly of FIG. 1 , in accordance with the principles of the present invention;

FIG. 1 B. is an enlarged cross-sectional view of the hollow fiber membrane elements taken along line 1 B-1 B of FIG. 1A; FIG. 1 C is an enlarged view of encircled area 1 C of FIG. 1 , showing the membrane elements extending into peripheral transport channels used for air treatment substance circulation;

FIG. 2 is a cross-sectional enlarged, partially cut-away view of another embodiment of a membrane, in accordance with the principles of the present invention;

FIG. 2A is an enlarged view of area 2A of FIG. 2, indicating an alternative embodiment of the membrane elements;

FIG. 3 is a cross-sectional view, similar to FIG. 2, of an alternative embodiment of the screen shown in FIG. 1 , including membrane support means; and FIG. 4 is a schematic perspective view of an air treatment system, in accordance with the principles of the present invention, which includes an air duct, a plurality of screens having membrane, an air treatment substance source, and the air treatment substance.

Modes for Carrying Out the Invention

Referring now to the drawings in detail, there is shown in FIG. 1 , an elevational view of a screen in accordance with the principles of the present invention, designated generally as 10. Screen 10 is adapted to be placed in an air duct of an air circulation system of an aircraft, submarine or other transportation vehicle, having passenger and/or crew compartments for treating unconditioned air. Screen 10 generally includes a membrane 11 , having a plurality of hollow fiber membrane elements or fibers 12 arranged as a single panel, treatment substance inlet 14, effluent stream output 16, treatment substance circulation channels 18, and support flange 19. In a preferred embodiment, air treatment substance 13 is water and screen 10 humidifies air designated for expulsion into a passenger or crew cabin of a vehicle such as an aircraft or submarine. However, it should be understood that the present invention is not limited to such use. That is, the air treatment substance 13 may be in other forms for performing other functions such as, a liquid desiccant for dehumidifying air or a carbon dioxide absorbent for removing carbon dioxide from the air. Accordingly, for the purpose of dehumidifying the air, a hydroscopic reagent may be used in place of water. For the purpose of removing CO₂ from the air, a CO₂ absorbing reagent such as sodium hydroxide (NAOH) or diethylene amine (DEA) can be used.

For the purpose of the following detailed discussion, water is the designated air treatment substance, it being understood that the same description substantially applies, unless otherwise noted, equally to the use and application of other air treatment substances. Support-flange 19, having outer peripheral edges 30, frames membrane 11 and functions as a peripheral support therefor. Support-flange 19 preferably includes connected inlet legs 21 on two sides of the frame and outlet legs 22 on the other two sides of the frame, which legs include channels 18 for introducing air treatment substance 13 to air flowing through the membrane. Typically the air treatment substance will not be totally depleted into the air stream, and accordingly, will circulate through legs 21 to legs 22, or visa versa. Outlet legs 22 are therefore provided on the opposite side of the frame for recovering any of the air treatment substance 13 not passed into the air stream from legs 21. In the case of humidification, the excess flow 17, will contain all the impurities or pathogens originally present in the total water flow but are prevented from entering into the air stream by the action of the membrane. With a caustic or other dehumidifying or carbon dioxide absorbing air treatment substance, excess flow 17 will also include substances removed from the air stream. Channels 18 extend through legs 21 and 22 for circulation through the membrane of the air treatment substance . As shown in FIG. 1 , in order for the air treatment substance 13 to pass from inlet legs 21 to the outlet legs 22, the substance must pass through the full length of a hollow fiber membrane elements 12, regardless of the flow direction of the air treatment substance, i.e. from left to right or from top to bottom, or visa versa. This feature is consistent with an important design characteristic of screen 10, that the flow resistance between the inlet and outlet distribution channels 18 of legs 21 and 22, respectively, be small in comparison to the flow resistance within an individual hollow fiber membrane element 12, which characteristic ensures that the total inlet substance flow will be approximately equally proportioned among all of the hollow fiber membrane elements. The shape of flange 19, as shown, is selected to fit a similarly shaped air duct, as shown in FIG. 4. Support-flange 19, therefore, has an outer shape which mates with the inner shape of the air duct. Accordingly, circular flanges or other shaped flanges are contemplated for use with similarly shaped ducts. Flange 19 is preferably formed from a substantially rigid material, such as plastic, so as to provide the necessary support. Membrane 11 is secured in flange 19 by means known in the art, such as, by being pressed between separable halves of the peripheral flange or by being molded in place. Channels 18 are molded or otherwise formed throughout flange 19, preferably through the entire length of all of its legs 21 , allowing for fluid communication and circulation between the various legs for allowing use and distribution of previously unused air treatment substance. The design and chemical composition of membrane 11 is selected based on the specific function of the membrane and also on the contaminants that may be present in the air treatment substance, such as water. Two preferable membrane designs are disclosed. For humidification, the membrane is preferably hydrophilic in design while for CO₂ or other caustic removal, the membrane is hydrophobic in design, as described in detail below. Each of the membrane designs discussed below exhibits long-term resistance to membrane fouling by divalent ions. Each of the designs discussed below is a hollow fiber membrane, as shown in FIG. 1A, including a plurality of hollow fiber membrane elements 12, 12', preferably having a distance "b" therebetween and a thickness "t". In a typical application, the lattice spacing or fiber separation distance "b", as shown in FIG. 1 A, is five times (5x) the diameter of the hollow fiber membrane elements. Accordingly, and for example, for a membrane 11 having hollow fiber membrane elements each with approximately a .04 in. outside diameter, in one preferred embodiment, spacing "b" would be approximately .20 in.

The first preferred type of hollow fiber membrane is a high permeation rate membrane which includes a plurality of hollow fiber membrane elements 12 preferably arranged in a crossing, interwoven or lattice pattern, as shown in FIG. 1A. Each hollow fiber membrane element 12 is porous, wherein each pore preferably has a size of approximately 0.02 microns or less to suppress bacterial penetration. This type of membrane is generally referred to as a nanofiltration membrane or a loose, reverse osmosis membrane. Preferably, membrane 11 is chlorine, oxidation, and ozone resistant. The preferred material for forming membrane 11 and achieving these properties is a porous plastic material, such as polyvinylidine diflouride (PVDF) or a polysulfone. The material preferably includes an additive or surface treatment imparting hydrophillic ligands such as the hydroxy (-OH) sulphonic, sulfonate (-SO₃H or SO₃ M, where M is any univalent ion such as sodium or potassium) or amine (-Ni H₂) groups, rendering the membrane hydrophilic. Other plastic materials, additives, or surface treatments which are known to be hydrophilic may also be used.

The elements 12 of membrane 11 , as shown in FIG. 1A, and in cross section in FIG. 1 B, are preferably hollow, highly absorbent, and extend open-end first into channels 18, as shown in FIG. 1 C. In this manner, as water runs through channels 18, it flows into the elements 12 through the open ends 23 thereof. A water tight seal is provided between the elements 12 and channels 18 in the area of the elements entering flange 19. Such a seal enables pressure control within the internal volume of membrane 11 of screen 10 relative to the unconditioned air 15, so as to allow the membrane to operate at a subambient (lower than ambient) pressure. The pressure differential allows for water evaporation into the unconditioned air stream and the prevention of air contamination by microbe transference. That is, maintenance of a subambient pressure within the internal volume of the hollow fiber membrane elements prevents "weeping", and thereby prevents the introduction of any water borne solids into the air stream being humidified. The water 13 is then transferred into the walls of the elements due to the hydrophilic nature of the same, as illustrated by the arrows in the cross-sectional view of FIG. 1 B. The pressure within channels 18 and elements 12 and at the seals between the channels and fibers in screen 10, is maintained via system 110, discussed below, at a pressure lower than the air pressure of the on flowing air. Accordingly, water droplets do not form on the surface of elements 12. Water remains within the material of the elements and is subject only to evaporation by the oncoming air flow. As air flows toward and against membrane 1 1 , water is transferred into the passing air. Accordingly, the pressure differential which exists between the channels and elements of membrane 1 1 of screen 10 and the outside air prevents injection of viruses and minerals into the air stream being humidified and provides a second line of defenses against bacterial contamination. That is, bacteria and viruses do not have vapor pressure. Since the pressure inside screen 10 is less than the air pressure, the microbes are not caused to move into the air, thereby preventing contamination. Similarly, potentially air polluting air treatment reagents, such as those used for CO₂ removal from air, as discussed above, are maintained within the internal volume of the membrane via this pressure differential.

Preferably, water through this type of design has a flux rate through membrane 1 1 of approximately 100 liters/hour/square meter (approximately 20 lbs/ft²-hr) of membrane surface area, or greater. In order to control the level of humidification, multiple membranes can be used for a system. Accordingly, as it is desired to increase and decrease humidification, banks of adjacent membranes 1 1 can be activated and deactivated, respectively. This can be accomplished by known means for directing the air treatment substance to and away from the adjacent membranes and its associated components, through flanges 19. For example, a single screen 10 with a membrane 1 1 can humidify from zero to 20% humidity. Two screens 10 in combination can humidify to approximately 36% humidity. For such results, the expected vaporization rate would be approximately 40 lbs./ft² -hr.

Alternatively, and for applications where potentially air polluting reagents are used for treating the air, such as in C0₂ removal, a hydrophobic material may be used for at least partially forming the elements 12 of membrane 11. Preferred hydrophobic materials include polypropylene, polyethylene, polyvinylidene, or polysulphone, or any higher order substituted variants of these resin bases. In this manner, the elements would not be absorbent of the air treatment reagent, such as sodium hydroxide, thereby avoiding contamination of the air therewith. However, for such applications, the elements include a larger pore size for allowing exposure of the oncoming air to the reagent, for treatment. The pressure differential between the internal volume of the membrane 11 and ambient air, as discussed in greater detail below, is such that the reagent is not transferred to the air but simply functions to treat it. For example, for a .02 micron pore using a hydrophobic membrane material, 300-400 psi would be required to force the reagent or caustic through the membrane wall. As the pressure in actual use is much lower than this, such weeping is avoided. Accordingly, the other embodiment of the membrane elements used to form membrane 11 , designated as elements 12", are shown in FIG. 2A. The membrane elements 12' are formed from, as above, a porous plastic material like PVDF or a polysulphone appropriately treated to achieve hydrophillic surface characteristics, but with a thin coating of a hydrophilic material 25 on the inside surface 27 of the elements 12'; as opposed to a surface treatment or the use of additives or copolymers affecting the bulk or whole of the plastic. Air treatment results, as per the discussion above, due to a water-vapor pressure differential developed on inside surface 27, relative to the outside water vapor pressure. However, since the elements are not entirely hydrophillic, the air treatment substance or reagent does not penetrate entirely through the elements 12', thereby avoiding air contamination. However, the reagent is exposed to the air via the porous nature of the elements and therefore, the air is treated. For this type of membrane and the desired evaporation rate, the desirable water flux rate is 10 liters/hr/m² (approximately 2 lbs/ft^2' hr) across the air side boundary layer, and if required, much higher. Supplemental structural reinforcement of membrane 11 thereof may be achieved by way of a plurality of wires 28 extending from and/or secured between flange 19, similar to the securement elements 12, 12' of membrane 11 , as shown in FIG. 3. Such an arrangement is preferred if the application is such that high velocity air flow or other factors require additional membrane support. Accordingly, in such an arrangement, in place of an element at a given number of elements 12, 12', a support wire is provided. For example, at the position of every fifth or sixth membrane element, a steel wire might be used instead of another fiber membrane element. Elements extending in either direction or at different number intervals can be replaced to achieve the desired level of support.

In each of the embodiments discussed above, the pressure drop across a single membrane is sufficiently low, approximately .05 to .40 inches of water. As shown in system 110 of FIG. 4, multiple screens 10, 10' can be used in existing air ducts for increasing air humidification or other treatment, without causing an excessive pressure drop.

Referring now to FIG. 4, an air treatment system, and most preferably, an air humidification system is shown and designated generally as 110. System 110 includes an air duct 112 for directing air in a desired direction and to the screens 10, which are designed in accordance with the detailed description set forth above, a water or treatment substance pump 114 for supplying the water or other air treatment substance to and circulating the water or other air treatment substance through the membranes, and fluid line or lines 116 connecting pump 114 to membranes 11 for fluid transfer thereto.

As shown in FIG. 4, membranes 11 are positioned in duct 112 such that they are transverse to the direction of the airflow through the duct. Each screen 10 is secured on its peripheral edges 30 to the inner wall 118 of duct 112, in a manner to create an airtight seal between the peripheral edges of the screens and the inner walls of the duct. As shown in FIG. 4, multiple screens are used as needed so as to increase the level of humidification and/or contaminant removal desired for a particular application. Typically, contaminant removal will require more screens than humidification. Accordingly two to three screens may be used for humidification while five screens may be desired for scavenging CO₂, odors, etc.

For system 110, pump 114 is connected via line 116 to inlet 14 of screen 10. Pump 114 pumps the water 13 from a potable water source 124 through line 116 to inlets 14 of screens 10. The water is forced through channels 18 (shown in FIGS. 1-3) and into the open ends 23 (shown in FIG. 1 C) of the protruding, hollow, and porous fibers 12. In this embodiment, pump 114 pumps water into the membrane 11 from which water is transferred via evaporation to the air running through the duct transverse to the membranes. The hydrophilic material in elements 12 forming membranes 11 , or the coating 25 on the inside surface 27 of elements 12' optionally used for forming membrane 11 , enhance the removal of contaminants from the air as the air moves through membrane 11 for humidification or other treatment.

In operation of system 110, flange 19 of screens 10 are secured to the inner wall 118 of duct 112 in a manner for achieving a water resistant bond between the flange and the inner wall. Air is forced through duct 112 and potable water is pumped from source 124 via pump 114 through line 116 into inlet channels 18 of leg 21 and fibers 12 of membranes 11. The water enters the inlet channels of the screen and is circulated through and absorbed in fibers 12, 12' of the membranes 11. Unused water exits inlet channels 18 of legs 21 and enters outlet channels 18 of legs 22 where the water is further pushed through elements 12, 12'. With the water in fibers or elements 12, 12' the water is transferred to the air via evaporation for humidification thereof. In the case of membrane 11 ', enhanced removal of contaminants is achieved via the thin coating of concentrated hydrophilic material. Any number of membranes can be used in duct 112 so as to provide the desired level of humidification, dehumidification, decontamination, or CO₂ removal, as required by the particular area of the cabin to which the air is being expelled. Due to the open nature of the construction, pressure drop is substantially reduced thereby accommodating the use of the desired number of membranes.

The primary advantage of this invention is that an improved humidification system is provided for use in air ducts associated with the air circulation systems of vehicles or other enclosures, particularly aircraft and submarines. Another advantage of this invention is that an air humidification system is provided which also functions to remove contaminants from humidified air prior to the expulsion of the humidified air into passenger and/or crew occupied areas of a vehicle, particularly an aircraft. Still another advantage of this invention is that a system is provided for dehumidifying air circulated through the air circulation system of a vehicle, particularly an aircraft. And still another advantage of this invention is that a system is provided for removing contaminants from humidified air prior to expulsion of the air into occupied areas of aircraft, submarines, and other vehicles. Another advantage of this invention is that a screen is provided having a membrane for insertion into an air duct of an air circulation system of a vehicle, particularly aircraft, which membrane functions to at least one of humidify air, dehumidify air, decontaminate air, and remove carbon dioxide from air. And still another advantage of this invention is that a system is provided using at least one, and preferably multiple screens having membranes adapted for insertion in air ducts of air circulation systems of vehicles, which system functions to at least one of humidify air, dehumidify air, decontaminate air, and remove carbon dioxide from air to be circulated through the vehicle, particularly an aircraft.

Although the invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made without departing from the spirit and scope of the invention.

Claims

1. An air treatment system for conditioning cabin air of a vehicle, comprising: means for directing air having a first flow direction to said cabin; a circulating air treatment substance; a membrane means for treating said air with said circulating air treatment substance prior to said air entering said cabin, wherein said membrane means is positioned substantially transverse to said first flow direction in said means for directing; and means for supplying said air treatment substance to said membrane means and for circulating said air treatment substance in said membrane means for use in treating said air.

2. The system according to claim system according to claim 1 , wherein said membrane means comprises at least one panel of hollow fiber membrane elements.

3 The system according to claim 2, wherein said membrane means comprises a plurality of panels of hollow fiber membrane elements.

4. The system according to claim 3, wherein said hollow fiber membrane elements are arranged in a lattice pattern.

5. The system according to claim 4, wherein each of said plurality of hollow fiber membrane elements is porous and highly absorbent of said air treatment substance

6. The system according to claim 2, wherein said membrane means comprises a nanofiltration membrane.

7. The system according to claim 6, wherein said air treatment substance is water.

8. The system according to claim 2, wherein said membrane means is at least one of chlorine, oxidation and ozone resistant.

9. The system according to claim 1 , wherein said membrane means comprises at least one panel of a plurality of porous hollow fiber membrane elements, wherein each of said elements has a coating of hydrophilic material an inner surface thereof, wherein said air treatment substance flows through said elements against said coating for transference into said elements.

10. The system according to claim 9, wherein said hollow fiber membrane elements are formed from a hydrophobic material and said air treatment substance comprises a reagent for at least one of dehumidyfying said air and removing CO₂ from said air.

11. The system according to claim 1 , wherein said membrane means includes means for circulating said air treatment substance therethrough.

12. The system according to claim 11 , wherein said means for circulating comprises channels surrounding said membrane means for transporting said air treatment substance and for equalizing flow of said air treatment substance distributed to said membrane means.

13. The system according to claim 12, wherein said membrane means comprises a plurality of crossing hollow fiber membrane elements, wherein each of said plurality of crossing hollow fiber membrane elements is porous to said air treatment substance, and wherein each of said hollow fiber membrane element includes at least one open end extending into said transport channels for receiving said air treatment substance.

14. The system according to claim 13, wherein each of said plurality of hollow fiber membrane elements is highly absorbent of said air treatment substance.

15. The system according to claim 13, wherein said air treatment substance is water for humidifying said air and each of said membrane elements is hydrophilic.

16. The system according to claim 12, further including a peripheral support flange to which said membrane means is attached, wherein said channels are formed in said peripheral support flange.

17. The system according to claim 16, further including supplemental means for supporting said membrane means.

18. The system according to claim 17, wherein said peripheral support flange includes a plurality of connected legs, said supplemental means comprises a plurality of support wires extending between and secured to said plurality of connected legs for supporting said elements.

19. The system according to claim 1 , wherein said air treatment substance comprises water, and wherein said membrane means for treating is for humidifying said air via said water.

20. The system according to claim 10, wherein said air treatment substance comprises one of a hydroscopic and a carbon dioxide absorbing reagent, and wherein said membrane means is for one of dehumidifying said air and removing carbon dioxide from said air.

21. The system according to claim 20, wherein said reagent is selected from the group consisting of sodium hydroxide and diethylene amine and said hydrophobic material is selected from the group consisting of polypropylene, polyethylene, polyvinylidene, and polysulphone.

22. The system according to claim 1 , wherein said membrane means has an internal volume and includes one of means for facilitating evaporation of said air treatment substance into said air and means for substantially blocking the transfer of contaminants to said air from said air treatment substance.

23. The system according to claim 22, wherein said membrane means has an external water vapor pressure, and wherein said means for substantially blocking and said means for facilitating comprises means for creating a pressure differential between said internal volume and said external water vapor pressure, said pressure differential for preventing said contaminants from transferring to said air during treatment.

24. The system according to claim 23, wherein pressure in said internal volume is less than pressure of said air.

25. A screen for use in treating air having a flow path with an air treatment substance prior to expulsion of said air from an air duct into a cabin, comprising: a membrane including a plurality of hollow fiber membrane elements, said membrane adapted for placement in said duct transverse to the flow path of said air; and means for circulating said air treatment substance through said membrane for treatment of said air.

26. The screen according to claim 25, wherein said air treatment substance is water for use by said membrane for humidifying said air, wherein each of plurality of hollow fiber membrane elements is hydrophilic.

27. The screen according to claim 26, wherein said membrane comprises a high permeation rate reverse osmosis membrane having pores of a size in the nanofiltration range.

28. The screen according to claim 26, wherein said membrane is one of chlorine, ozone, and oxidation resistant.

29. The screen according to claim 25, wherein said membrane includes a peripheral support flange and said means for circulating comprise channels formed in said peripheral support flange for receiving and circulating said air treatment substance.

30. The screen according to claim 29, wherein said channels are further for expelling effluents

31. The screen according to claim 30, wherein said channels include an inlet for receiving said air treatment substance and an outlet for expelling said effluents.

32. The screen according to claim 29, wherein said plurality of hollow fiber membrane elements are arranged in a crossing pattern, wherein each of said hollow fiber membrane elements includes at least one open end extending into said channels for receiving said air treatment substance.

33. The screen according to claim 25, wherein each of said plurality of hollow fiber membrane elements is comprised of a material which is highly absorbent of said air treatment substance.

34. The screen according to claim 33, wherein said material comprises a hydrophilic porous plastic.

35. The screen according to claim 34, wherein said hydrophilic, porous plastic is selected from the group consisting of polyvinylidine fluoride (PVDF) and polysulphone, wherein said polysulphone includes an additive rendering it hydrophilic.

36. The screen according to claim 33, wherein said hollow fiber membrane elements include an internal surface and volume adapted to receive said air treatment substance and are formed from a hydrophobic material, said elements having a coating of hydrophilic material on said internal surface.