U.S. patent application number 11/998484 was filed with the patent office on 2008-07-24 for oxygen humidifier.
Invention is credited to John H. Burban, Robert O. Crowder, Carl M. Geisz, Michael Spearman.
Application Number | 20080173175 11/998484 |
Document ID | / |
Family ID | 39358770 |
Filed Date | 2008-07-24 |
United States Patent
Application |
20080173175 |
Kind Code |
A1 |
Spearman; Michael ; et
al. |
July 24, 2008 |
Oxygen humidifier
Abstract
An apparatus and method for separating breathable oxygen gas
from a source of gas and then humidifying the oxygen gas while
preventing over humidification of the oxygen gas, the apparatus
comprising a gas pathway located on a first side of a water
transfer member, an oxygen gas pathway located on a second side of
the water transfer member and a separator for separating the
breathable oxygen gas from a gas located on the first side of the
water transfer member and directing the breathable oxygen gas past
the second side of the water transfer member while maintaining the
pressure of the gas substantially equal to the pressure of the
breathable oxygen gas to thereby humidify the breathable oxygen gas
while preventing a moisture condensation in the breathable oxygen
gas.
Inventors: |
Spearman; Michael; (The
Woodlands, TX) ; Burban; John H.; (Lake Elmo, MN)
; Crowder; Robert O.; (Lino Lakes, MN) ; Geisz;
Carl M.; (St. Paul, MN) |
Correspondence
Address: |
Carl L. Johnson;Jacobson and Johnson
Suite 285, One West Water Street
St. Paul
MN
55107-2080
US
|
Family ID: |
39358770 |
Appl. No.: |
11/998484 |
Filed: |
November 30, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11593827 |
Nov 7, 2006 |
7384297 |
|
|
11998484 |
|
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Current U.S.
Class: |
95/117 ;
96/108 |
Current CPC
Class: |
H02G 15/113 20130101;
H02G 3/081 20130101; H02G 15/007 20130101 |
Class at
Publication: |
95/117 ;
96/108 |
International
Class: |
B01D 53/14 20060101
B01D053/14; B01D 53/18 20060101 B01D053/18 |
Claims
1-21. (canceled)
22. An apparatus for separating breathable oxygen from a source of
gas comprising: a compressor for providing a source of compressed
gas; an adsorption bed for separating a breathable oxygen gas from
a compressed gas of said compressor; a de-pressurizing flow
controller for expanding the breathable oxygen gas separated by the
adsorption bed; and a water transfer member having a gas pathway on
a first side of said water transfer member for receiving a gas
therethrough and an oxygen-enriched gas pathway on a second side of
said water transfer member for receiving the breathable oxygen gas
therethrough wherein the pressure of the gas directed through the
gas pathway of said water transfer member is substantially equal to
the pressure of the breathable oxygen gas directed through the gas
oxygen-enriched gas pathway of said water transfer member to
humidify the breathable oxygen gas while preventing moisture
condensation in the breathable oxygen gas.
23. The apparatus of claim 22 including a muffler for abating the
noise created by an oxygen-depleted gas as the oxygen-depleting gas
exits the system.
24. The apparatus of claim 22 wherein the water transfer member is
located within an enclosed structure of the apparatus for
separating breathable oxygen from a source of gas.
25. The apparatus of claim 22 including a fan for directing gas
through said gas pathway of said water transfer member and wherein
said de-pressurizing flow controller is located upstream of said
oxygen-enriched gas pathway of said water transfer member to help
maintain the pressure of the gas in said gas pathway of said water
transfer member substantially equal to the pressure of the
breathable oxygen gas in said oxygen-enriched gas pathway of said
water transfer member.
26. The apparatus of claim 22 wherein the water transfer member
comprises a membrane device having a selective membrane with a
greater selectivity for water over both nitrogen and oxygen.
27. The apparatus of claim 26 wherein the membrane device comprises
a hollow fiber membrane device, a flat sheet membrane device, or a
spiral wound membrane device.
28. The apparatus of claim 26 wherein said selective membrane has a
selectivity for water over both nitrogen and oxygen of at least
10.
29. The apparatus of claim 26 wherein said selective membrane has a
selectivity for water over both nitrogen and oxygen of at least
100.
30. The apparatus of claim 22 wherein said compressor is located
downstream of said gas pathway of said water transfer member and
said de-pressurizing flow controller is located upstream of said
oxygen-enriched gas pathway of said water transfer member to help
maintain the pressure of the gas in said gas pathway of said water
transfer member substantially equal to the pressure of the
breathable oxygen gas in said oxygen-enriched gas pathway of said
water transfer member.
31. The apparatus of claim 22 wherein said compressor is located
upstream of said gas pathway of said water transfer member and said
de-pressurizing flow controller is located downstream of said
oxygen-enriched gas pathway of said water transfer member to help
maintain the pressure of the gas in said gas pathway of said water
transfer member substantially equal to the pressure of the
breathable oxygen gas in said oxygen-enriched gas pathway of said
water transfer member.
32. The apparatus of claim 22 wherein said de-pressurizing flow
controller comprises a pressure regulator and a control valve.
33. The apparatus of claim 22 wherein said de-pressurizing flow
controller comprises a control valve.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of pending
U.S. patent application Ser. No. 11/593,827; filed on Oct. 5, 2004;
titled OXYGEN HUMIDIFIER and claims priority to U.S. Provisional
Application Ser. No. 60/509,115, which was filed on Oct. 6, 2003;
titled OXYGEN CONCENTRATOR MEMBRANE HUMIDIFIER.
FIELD OF THE INVENTION
[0002] The present invention relates to humidification of a
breathable oxygen and more specifically, to humidifying of
breathable oxygen such as an oxygen-enriched gas while minimizing
the possibility of condensation and bacterial growth.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0003] None
REFERENCE TO A MICROFICHE APPENDIX
[0004] None
BACKGROUND OF THE INVENTION
[0005] Oxygen concentrators to produce breathable oxygen for a
person requiring an oxygen-enriched atmosphere generally operate in
the following manner. A compressor supplies compressed ambient air
to a bed of molecular sieves. The molecular sieves adsorb nitrogen
gas from the compressed ambient air to provide a gas with a high
oxygen content. The oxygen-enriched gas then exits the bed of
molecular sieves and passes through a regulator and a patient
adjustable needle valve, which controls the gas flow rate. The
oxygen-enriched gas can then be supplied to a patient who can
breath the oxygen-enriched gas. In general, most oxygen
concentrators contain two beds of molecular sieves. While one bed
of molecular sieves is in operation to produce the oxygen-enriched
gas, the second bed of molecular sieves is being purged of the
adsorbed nitrogen in order to regenerate the bed of molecular
sieves. The two beds of molecular sieves allow the oxygen
concentrator to supply a continuous flow of an oxygen-enriched gas
to the patient. Oxygen concentrators manufactured by Invacare.RTM.,
Respironics.RTM., and Sunrise.RTM. use two beds of molecular sieves
for the creation of a continuous supply of an oxygen-enriched gas
from a source of ambient air.
[0006] One of the problems that arises in the use of the molecular
sieves is that the molecular sieves not only adsorb nitrogen, but
also water vapor. Thus the oxygen-enriched gas being delivered to
the patient can be extremely dry, typically with a dew point of
-40.degree. F. or lower (a relative humidity of less than 0.5%).
The dry gas can cause dehydration of the nasal passages and
respiratory system, which can lead to patient discomfort and
irritation.
[0007] There are existing humidifiers for humidifying
oxygen-enriched gas flowing to the patient. These humidifiers
generally have a source of liquid water positioned to allow the
oxygen-enriched gas to bubble through the liquid water, thus
humidifying the oxygen-enriched gas. While these humidifiers work
for humidifying the oxygen flow, they do have several major
drawbacks. First, unless the water is re-supplied, eventually the
water completely evaporates, ending all humidification. Second,
standing water offers a site for bacterial growth. This is
especially true since the water for the bubbler is usually located
on the exterior of the oxygen concentrator, and thus is open to
environmental contamination.
[0008] In addition, bacteria growing in standing water can become
aerosolized during the bubbling process and be carried along with
the oxygen-enriched gas, potentially reaching to the patient.
Third, manufacturers of oxygen concentrators often go to great
lengths to minimize the noise output of their oxygen concentrators.
Providing for a source of liquid water for humidifying
oxygen-enriched gas located outside a cabinet of the oxygen
concentrators and thus outside of the oxygen concentrators' noise
abatement measures can contribute significantly to the noise
generated by the oxygen concentrator through the noisy bubbling
action.
[0009] The use of membrane devices to humidify oxygen-enriched gas
is also known in the art. These membrane devices work by using
selective membranes to transfer moisture from one gas to another
gas without significant transfer of other components. This transfer
of moisture from one gas to another gas is accomplished by using a
membrane having a greater selectivity for water over the other
components such as both oxygen and nitrogen. The selectivity of a
membrane for water compared to oxygen and nitrogen is defined by
the ratio of the water permeability to the permeability of either
the oxygen or nitrogen. It is noted that the aforementioned
selective membranes have a selectivity for water over oxygen or
nitrogen of greater than 1, more preferably greater than 10, and
most preferably greater than 100.
[0010] In use, the above-mentioned membrane device is in contact
with both a high-pressure compressed stream of gas exiting the
compressor and a lower-pressure oxygen-enriched stream of gas
exiting a regulator and needle valve. Moisture passes from the
high-pressure compressed stream of gas through the selective
membrane to the lower-pressure oxygen-enriched stream of gas.
[0011] The use of membrane devices for gas humidification have
advantages over oxygen concentrators that humidify their gases with
bubblers. Firstly, the operator never needs to fill or refill the
membrane devices with water as moisture for humidification is
obtained from ambient air. Secondly, oxygen concentrators that
humidify through the use of membrane devices are quieter than
oxygen concentrators that humidify with bubblers as the membrane
devices do not contribute to the sound produced by the oxygen
concentrators.
[0012] Membrane devices such as the ones disclosed in the articles
of Yonago Acta Medica, 1999; 42: 185-188 and Internal Medicine,
Vol. 36, No. 12 (Dec. 1997) do have one major problem in that
membrane devices introduce the possibility of over humidifying the
oxygen-enriched gas. This over humidification introduces the
possibility of condensation and thus bacterial growth. More
specifically, since membrane devices used in oxygen concentrators
are usually installed down stream of the compressor, the partial
pressure of the water vapor is frequently above the vapor pressure
of water at room temperature. It is noted that since the stream of
gas coming out of the compressor is usually at a temperature that
is greater than the ambient temperature there is not necessarily
condensation inside the membrane device. However, the
lower-pressure stream of oxygen-enriched gas that enters the
membrane device from the regulator and needle valve can become
humidified to a partial pressure that is likely above the room
temperature vapor pressure. This means that as the oxygen-enriched
gas cools enroot to the patient, condensation can occur. This not
only means that the patient can periodically receive liquid water,
but also that there exists a risk of bacterial growth.
[0013] There are two current methods for dealing with the issue of
over humidification by the membrane devices. Firstly, the membrane
devices can be used in an environment where the ambient humidity
never exceeds an amount that would cause the oxygen-enriched gas to
become over humidified. However, since many of these devices are
used in patient's home under a variety of environmental conditions,
the ambient humidity is difficult to control. Secondly, a shunt can
be installed so that a portion of the oxygen-enriched gas bypasses
the membrane device, remaining at an extremely low humidity. When
the streams of oxygen-enriched gas are later remixed, an optimal
humidity can be achieved. This system however, requires adjustment
by the user to match ambient conditions as well as requiring
additional valves and tubing.
SUMMARY OF THE INVENTION
[0014] An apparatus and method for humidifying an oxygen-enriched
gas while preventing over humidification of the oxygen-enriched
gas. The apparatus comprising a gas pathway on a first side of a
water transfer member such as a membrane device having a selective
membrane with a greater selectivity for water over both nitrogen
and oxygen, an oxygen-enriched gas pathway located on a second side
of the water transfer member and a separator for separating a
breathable oxygen from a gas located in the first side of the water
transfer member and directing the breathable oxygen past the second
side of the water transfer member while maintaining the pressure of
the gas in the first side of the water transfer member
substantially equal to the pressure of the breathable
oxygen-enriched gas in the second side of the water transfer member
to thereby humidify the breathable oxygen while preventing moisture
condensation in the breathable oxygen.
[0015] In one embodiment of the present invention the membrane
device is installed in the oxygen concentrator such that the
membrane device engages a stream of ambient air prior to the
compression of the ambient air by a compressor while an
oxygen-enriched gas engages the membrane device after the
oxygen-enriched gas has engaged a regulator and needle valve. In an
alternative embodiment of the present invention, the membrane
device is installed in an oxygen concentrator such that the
membrane device engages the stream of ambient air after compression
of the ambient air by the compressor while the oxygen-enriched gas
engages the membrane device prior to the engagement of the
oxygen-enriched gas with the gas regulator.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a diagrammatic view of a prior art oxygen
concentrator using a bubbler for humidification of the
oxygen-enriched gas;
[0017] FIG. 2 is a diagrammatic view of a prior art oxygen
concentrator using a membrane device for humidification of the
oxygen-enriched gas;
[0018] FIG. 3 is a cross sectional view of a hollow fiber membrane
device that could be used in an oxygen concentrator for
humidification;
[0019] FIG. 3A is a cross sectional view showing the transfer of
moisture from a first stream of gas to a second gas located in the
membrane device;
[0020] FIG. 4 shows an embodiment of the oxygen concentrator of the
present invention;
[0021] FIG. 5 shows an alternative embodiment of the oxygen
concentrator of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0022] Referring to FIG. 1, FIG. 1 shows a typical oxygen
concentrator 10 which uses a bubbler 33 for humidification. In the
oxygen concentrator 10 of FIG. 1, ambient air is drawn into an
inlet 12 of an inlet filter 11. The inlet filter 11 functions to
remove a portion of the particulates and bacteria from the ambient
air. Inlet filter 11 includes an outlet 13 that is in fluid
communication with an inlet 15 of a compressor 14 for increasing
the pressure of the ambient air. An outlet 16 of the compressor 14
is in fluid communication with an inlet 18 of an adsorption bed 17,
adsorption bed 17 comprising of molecular sieves for enriching the
gas with oxygen by removing nitrogen therefrom.
[0023] In regards to adsorption bed 17, adsorption bed 17 actually
is comprised of more than one (1) bed of sieves, as described
earlier, and includes a switching valve and associated controls.
For simplicity, we describe adsorption bed 17 as a single unit.
[0024] The adsorption bed 17 includes an outlet 19 and an outlet
20. A portion of the gas that flows through the adsorption bed 17
that is enriched in oxygen and depleted of moisture discharges
through outlet 19 at a pressure close to the pressure of the
entering air at inlet 18. Another portion of the gas enriched in
nitrogen and moisture discharges through outlet 20 during the
regeneration stage. As shown in FIG. 1, outlet 20 is in fluid
communication with a muffler 94, which quiets the oxygen-depleted
air as it exits the system.
[0025] A buffer tank 21 having an inlet 22 in fluid communication
with the outlet 19 of the adsorption bed 17 and an outlet 23 in
fluid communication with an inlet 25 of a pressure regulator 24
function to smooth out fluctuations in pressure and flow of the
oxygen-enriched gas from the adsorption bed 17.
[0026] The pressure regulator 24 having outlet 26 in fluid
communication with an inlet 28 of flow control valve 27 maintains a
constant pressure of oxygen-enriched gas flowing to the flow
control valve 27 while the flow control valve 27 maintains a
constant flow rate. The combination of the pressure regulator 24
and the flow control valve 27 provides a constant flow of
oxygen-enriched gas to the patient.
[0027] Oxygen concentrator 10 also includes an outlet filter 30
having an inlet 31 and an outlet 32, inlet 31 being in fluid
communication with the outlet 29 of the valve 27. Outlet filter 30
functions as a final safety device by preventing unwanted materials
from reaching the patient while simultaneously preventing foreign
materials and bacteria from entering into the oxygen concentrator
10 when it is not in use.
[0028] Oxygen concentrator 10 further includes a bubbler 33
generally located external of oxygen concentrator 10 for
humidification of the oxygen-enriched gas. In the aforementioned
arrangement, any humidification of the oxygen-enriched gas takes
place outside the oxygen concentrator 10 at the bubbler 33. Bubbler
33 includes an inlet 34 and an outlet 35 with the inlet 34 being in
fluid communication with the outlet 32 of the outlet filter 30.
[0029] Referring to FIG. 2, FIG. 2 is another embodiment of a prior
art oxygen concentrator 36 that uses a membrane device 63 to
humidify the oxygen-enriched gas.
[0030] As shown in FIG. 2, ambient air is drawn into an inlet 38 of
an inlet filter 37. In regards to inlet filter 37, inlet filter 37
functions to allow ambient air into oxygen concentrator 36 while
simultaneously blocking particulates and bacteria from entering
into oxygen concentrator 36. Inlet filter 37 includes an outlet 39
in fluid communication with an inlet 41 of a compressor 40.
[0031] Referring to FIG. 2, the membrane device 63 of oxygen
concentrator 36 comprises a membrane (shown for example in FIG. 3A)
having a greater selectivity for water over both oxygen and
nitrogen. Membrane device 63 includes a first pathway 43 and a
second pathway 60, the two pathways separated by a selective
membrane. The first pathway 43 includes an inlet 44 and an outlet
45 and the second fluid pathway 60 includes an inlet 61 and an
outlet 62. Fluid pathway 43 is shown in FIG. 2 designated by a
dotted line and fluid pathway 60 is shown designated by a dashed
line wherein an outlet 42 of compressor 40 is in fluid
communication with the inlet 44 of the membrane device 63 and an
inlet of 47 of an adsorption bed 46 is in fluid communication with
the outlet 45 of the first pathway 43.
[0032] The adsorption bed 46 includes an outlet 48 and an outlet
49. A portion of the gas flowing through the adsorption bed 46 is
enriched in oxygen and depleted of moisture is discharged through
outlet 48 at a pressure close to the pressure of the entering air
at inlet 47. Another portion of the gas enriched in nitrogen and
moisture discharges through outlet 49 during the regeneration
stage. Outlet 49 is shown in FIG. 2 fluid communication with a
muffler 50, muffler 50 providing sound abatement by quieting the
oxygen-depleted air as it exits the system.
[0033] A buffer tank 51 having an inlet 52 in fluid communication
with the outlet 48 of the adsorption bed 46 and an outlet 53 in
fluid communication with an inlet 55 of the pressure regulator 54
smoothes out fluctuations in pressure and flow of oxygen-enriched
gas from the adsorption bed.
[0034] Referring to FIG. 2, pressure regulator 54 having an outlet
56 in fluid communication with an inlet 58 of a flow control valve
57 maintains a constant pressure of oxygen-enriched gas flow to a
flow control valve 57. The flow control valve 57 having an outlet
59 in fluid communication with the inlet 61 of the membrane device
63 maintains a constant flow rate of oxygen-enriched gas. The
combination of the pressure regulator 54 and the flow control valve
57 provides a constant flow of oxygen-enriched gas to the
patient.
[0035] In regards to membrane device 63, while the selective
membrane in membrane device 63 permits water vapor to pass from
fluid pathway 43 to fluid pathway 60, other gases such as oxygen
and nitrogen are hindered from passing therethrough. Since the
oxygen-enriched gas entering membrane device 63 at inlet 61 is
extremely dry, there exists a driving force for water vapor to pass
across the selective membrane from the high-pressure compressed air
in pathway 43 to the lower pressure dry oxygen-enriched gas located
in pathway 60. Thus the humidity of the oxygen-enriched gas is
higher when the oxygen-enriched gas exits the membrane device 63 at
outlet 62 than when the oxygen-enriched gas enters membrane device
63 at inlet 61. It is noted that while the membrane selectivity is
high, the oxygen level is changed only by dilution with water
vapor.
[0036] It is noted that those skilled in the art will realize that
the diffusion of water vapor across the selective membrane is
driven by a difference in chemical potential of water in the two
gases. Those skilled in the art will also realize the chemical
potential difference can be substituted with a concentration
difference or partial pressure difference in this case by a change
in the mass transfer coefficient which relates driving force with
flux across the membrane. This means that once the partial pressure
of water in the lower pressure oxygen-enriched gas in the membrane
device 63 approaches the partial pressure of the stream of higher
pressure air in pathway 43, the driving force for water transfer
drops to zero, and thus the water flux drops to zero. This mean
that the partial pressure of water in the oxygen-enriched gas
exiting the membrane device 63 at outlet 62 can not be higher than
the partial pressure of water in the stream of air entering
membrane device 63 at inlet 44.
[0037] To draw a parallel to a heat exchanger, the stream being
heated can never leave the heat exchanger hotter than the heating
stream enters the heat exchanger. If the membrane device 63 is
functioning well, the partial pressure of water in the
oxygen-enriched stream leaving at outlet 62 will be close to the
partial pressure of water in the air stream entering at inlet 44.
This is especially true since the airflow from first inlet 44 to
the first outlet 45 of membrane device 63 is usually significantly
greater than the oxygen-enriched gas flowing from the second inlet
61 to the outlet 62 of pathway 60.
[0038] Since the partial pressure of water in the stream of air
entering membrane device 63 at inlet 44 is increased from the
ambient partial pressure of water by the compression ratio, it can
be significantly higher than the vapor pressure of water at ambient
temperature. Since the temperature of the air entering at inlet 44
is also increased from ambient temperature by compression, and this
heat is transferred to the oxygen-enriched gas in the membrane
device 63 by the movement of the heated moisture, there will most
likely not be condensation anywhere in membrane device 63. However,
if the oxygen-enriched air stream exiting membrane device 63 were
allowed to cool to ambient temperature to enable a patient to
breath the oxygen-enriched air, harmful condensation can occur.
[0039] In order to alleviate the condensation problem the prior art
oxygen concentrator of FIG. 2, includes a bypass valve 64, the
bypass valve 64 having an inlet 65 and an outlet 66, the outlet 66
is in fluid communication with the outlet 62 of membrane device 63
and an inlet 68 of the outlet filter 67, which does any final
filtration and system protection before the oxygen-enriched gas is
delivered to the patient via an outlet 69 of outlet filter 67.
Bypass valve 64 is adjusted such that a portion of the
oxygen-enriched gas bypasses the membrane device 63 and thus
remains extremely dry. If bypass valve 64 is adjusted correctly,
the oxygen-enriched gas from the second outlet 62 of membrane
device 63 and from the outlet 66 of bypass valve inlet 64 combine
and produce a mixed partial pressure of water that is below the
vapor pressure of water at ambient temperature, thereby preventing
condensation down stream as the oxygen-enriched gas cools to
ambient temperature. However, if bypass valve 64 is adjusted
incorrectly than either too much or too little oxygen-enriched gas
will bypass the membrane device 63 thus resulting in either
condensation in the oxygen-enriched gas downstream or insufficient
humidification of the oxygen-enriched gas. Since the adjustment of
bypass valve 64 must match current ambient conditions, bypass valve
64 is required to be adjusted by the patient as environmental
conditions such as ambient temperature, ambient humidity, and total
oxygen-enriched gas flow changes.
[0040] Referring to FIG. 3, FIG. 3 shows an embodiment of a
membrane device 70 used in the oxygen concentrator of the present
invention that eliminated the need to mix the flows as shown in
FIG. 2. Although the membrane device 70 shown in FIG. 3 comprises a
hollow fiber membrane device, a flat sheet membrane or a spiral
wound membrane device could also be used to accomplish the same
task. Membrane device 70 includes a first air inlet 71, a first air
outlet 72, a second gas inlet 73 and a second gas outlet 74.
[0041] In a hollow fiber membrane device 70 as shown in FIG. 3, the
membrane comprises the shape of a plurality of tubes with each of
the tubes being called a hollow fiber and is represented by
reference numeral 75. The materials of the plurality of hollow
fiber 75 are chosen such that water vapor can permeate across the
hollow fiber 75 more easily than either oxygen or nitrogen. As
shown in FIG. 3, each of the plurality of hollow fiber 75 comprises
a hollow fiber inlet 76 and a hollow fiber outlet 77 that are in
fluid communication with each other down the interior of the hollow
fiber 75. The hollow fibers 75 are placed into a shell 78 to make
up the module. The bundle of hollow fibers 75 are sealed by a
potting compound 79 at both ends so that the interiors of the
hollow fibers 75 are not in fluid communication with the exterior
of the hollow fibers 75.
[0042] As further shown in FIG. 3, the second inlet 74 of the
membrane device 70 is in fluid communication with an inlet plenum
80. The inlet plenum 80 is also in fluid communication with the
inlet 76 of the hollow fibers 75. The second outlet 73 of the
membrane device 70 is in fluid communication with an outlet plenum
81. The outlet plenum 81 is also in fluid communication with the
outlet 77 of the hollow fibers 75. The first inlet 71 of the
membrane device 70 is in fluid communication with the first outlet
72 of the membrane device 70 along the exterior of the hollow
fibers 75.
[0043] Although the hollow fiber module is shown in FIG. 3
operating with the air located on the inside of the hollow fibers
75 and the oxygen-enriched gas located on the outside of the hollow
fibers 75 flowing counter-currently, the present module would also
work using cross or co-current flow, or with the air on the outside
of the hollow fibers 75 and the oxygen-enriched gas on the inside
of the hollow fibers 75.
[0044] Referring to FIG. 3A, FIG. 3A is a cross-sectional view
showing the operation of a membrane device 81. In the operation of
membrane device 81 a stream of ambient air represented by reference
number 83, is directed from an inlet filter 82 into a first inlet
84 of the membrane device 81. Once in membrane device 81 the stream
of ambient air 83 is directed through a first pathway 85 of
membrane device 81. Once ambient air 83 reaches the end of membrane
device 81, the ambient air 83 is then directed out of membrane
device 81 through a first outlet 86 of membrane device 81 for
separation to an oxygen-enriched stream.
[0045] As previously noted, the process of oxygenating the stream
of air 83 results in a depletion of moisture from the air 83, which
can cause patient discomfort when the dry oxygenated air stream is
fed to a patient. In order to solve the aforementioned problem, the
now oxygen-enriched but dry air 92, shown as dotted lines, is
redirected back into membrane device 81 by way of a second inlet 87
through a second pathway 88 of the membrane device 81 for
humidification.
[0046] As shown in FIG. 3A, a selective membrane 90 located within
membrane device 81 separates the first pathway 85 from the second
pathway 88. Selective membrane 90 functioning to allow a portion of
moisture such as in the form of water vapor 91 from the stream of
air 83 located within the first pathway 85 to pass therethrough
while simultaneously hindering other gases such as oxygen and
nitrogen from passing therethrough. The diffusion of water vapor 91
across selective membrane 90 is driven by a difference in chemical
potential of water in the two gases. That is, since the
oxygen-enriched gas 92 entering at second inlet 87 is extremely
dry, there is a driving force for water vapor 91 to pass from the
stream of air 83 in the first pathway 85 across the selective
membrane 90 to the oxygen-enriched air 92 located in the second
pathway 88.
[0047] FIG. 4 shows an embodiment of the oxygen concentrator 92 of
the present invention. Oxygen concentrator 92 uses a membrane
device 63 similar to the membrane device shown in FIG. 2, but with
the first inlet 44 of the membrane device 63 in fluid communication
with the outlet 39 of the inlet filter 37 and the first outlet 45
of the membrane device 63 in fluid communication with the inlet 41
of the compressor 40. Thus the same stream of air is passed through
the membrane device 63 from the first inlet 44 to the first outlet
45 as shown in FIG. 2, but the stream of air is now at
approximately ambient pressure and thus at nominally the same
pressure as the oxygen-enriched gas passing from the second inlet
61 to the second outlet 62 of the membrane device 63. This means
that the partial pressure of water in the oxygen-enriched gas
exiting at the second outlet 62 of the membrane device 63 should be
no greater than the partial pressure of water in the air entering
the membrane device 63 at the first inlet 44 of the membrane device
63 and thus no greater than the ambient partial pressure of water.
As a result, as the oxygen-enriched gas cools on the way to the
patient, condensation is inhibited or eliminated. Thus there is no
need of a bypass valve as in FIG. 2.
[0048] It is sometimes thought by those experienced in the art that
a total pressure gradient across the membrane is required to
produce flux across the membrane, suggesting that the module would
need to be installed as in FIG. 2. However, since flux across the
membrane is caused by a partial pressure gradient of a compound in
the respective streams, and the oxygen-enriched gas enters the
membrane device 63 at the second inlet extremely dry, there is
still a partial pressure gradient of water to drive the membrane
flux even though the total pressure on the two sides of the
membrane is nominally equal.
[0049] If membrane device 63 is designed with sufficient membrane
area and sufficient membrane permeability for the water vapor, then
the partial pressure of water in the oxygen-enriched gas exiting
membrane device 63 at the second outlet 62 will be close to the
partial pressure of water in the ambient air that the patient is
breathing. Thus oxygen-enriched gas will be delivered to the
patient with humidity similar to the ambient air without having to
make any adjustments for ambient conditions. It is noted that as
ambient conditions change, the system will automatically adjust
accordingly.
[0050] In further regards to the embodiment of FIG. 4, similar to
the embodiment of FIG. 2, an added benefit of the embodiment of
FIG. 4 is sound abatement which is partially provided by a muffler
50, muffler 50 quieting the oxygen-depleted air as the
oxygen-depleted air exits the system. In addition, since the
membrane device 63 is connected between the air inlet 37 and the
compressor 40, the module dampens some of the sound coming back
from the compressor before it exits at the inlet filter 37. This
acts to reduce the overall noise of the oxygen concentrator unit
92.
[0051] Referring to FIG. 5, FIG. 5 shows an alternative embodiment
93 of the oxygen concentrator of the present invention. Similar to
the oxygen concentrator of FIG. 2 and 4, the oxygen concentrator of
FIG. 5 employs the membrane device 63 for humidification of
oxygen-enriched gas. However, unlike the oxygen concentrator of
FIGS. 2 and 4, the second inlet 61 of the membrane device 63 is in
fluid communication with the outlet 53 of the buffer tank 51, and
the second outlet 62 of the membrane device 63 is shown in fluid
communication with the inlet 55 of the pressure regulator 54
resulting in the oxygen-enriched gas in membrane device 63 being at
a pressure higher than ambient.
[0052] However, the pressure of the oxygen-enriched gas in membrane
device 63 is lower than the pressure of the air in the first
pathway 43 of membrane device 63 by only the pressure drop through
the oxygen concentrator adsorption bed 46 and the buffer tank 51,
which since the oxygen-enriched gas flow is usually on the order of
5 liters per minute or less, is not a great difference.
[0053] As previously noted, the partial pressure of water in the
oxygen-enriched gas exiting the membrane device 63 at the second
outlet 62 is not higher than the partial pressure of water in the
air entering the membrane device 63 at the first inlet 44. The
partial pressure of water in the air at the first inlet 44 of the
membrane device 63 is also higher than the ambient partial pressure
of water by the compression ratio, that is the compressed air
pressure divided by the ambient pressure in absolute terms, and may
be higher than the vapor pressure of water at ambient temperature,
but due to compression is at an elevated temperature and most
likely contains no condensate. However, since the vapor pressure of
water in the oxygen-enriched gas at the second outlet 62 of the
membrane device 63 will be decreased by a similar pressure ratio
upon expansion in regulator 54 and valve 57, the partial pressure
of water in the oxygen-enriched gas delivered to the patient will
be no greater than the ambient partial pressure of water. Thus the
system of FIG. 5 also prevents the possibility of condensation in
the oxygen-enriched stream.
[0054] As noted above, the present invention also includes a method
of providing a source of breathable humidified oxygen gas
comprising the steps of (1) directing a gas containing oxygen past
a first side of a water permeable membrane device 63; (2)
separating the oxygen gas from the gas; and (3) directing the
oxygen gas past a second side of the water permeable membrane
device 63 while maintaining the pressure of the gas on the first
side of the water permeable membrane device 63 substantially equal
to the pressure of the oxygen gas on the second side of the water
permeable membrane device 63 to thereby humidify the oxygen gas to
a humidity level substantially equal to or less than a humidity
level of the gas on the first side of the water permeable membrane
device 63. The aforementioned method can also include the steps of
(4) directing a gas containing oxygen past a first side of a water
permeable membrane device 63 having a selective membrane 90 with a
greater selectivity for water over both nitrogen and oxygen wherein
the water permeable membrane device 63 has a selective membrane 90
having a selectivity for water over both nitrogen and oxygen of at
least 1, more preferably 10, and most preferably a selectivity for
water over both nitrogen and oxygen of at least 100.
[0055] The present invention further includes a method of providing
a source of breathable humidified oxygen comprising the steps of
(1) directing a gas having a first level of humidification past a
first side of a water transfer member; (2) directing a breathable
amount of oxygen gas having a second level of humidification, with
the second level of humidification less than the first level of
humidification of the gas, past a second side of the water transfer
member while maintaining the pressure of the gas on the first side
of the water transfer member substantially equal to the pressure of
the oxygen gas on the second side of the water transfer member to
thereby humidify the oxygen to a humidity level substantially equal
to or less than a humidity level of the gas through water transfer
through the water transfer member.
[0056] The above method can also include the steps of (3) directing
a gas having a first level of humidification past a first side of a
membrane device 63 having a selective membrane 90 with a greater
selectivity for water over both nitrogen and oxygen; (4)
compressing the gas before the gas is directed past the first side
of the water transfer member; (5) compressing the gas after the gas
has been directed past the first side of the water transfer member;
(6) directing the breathable amount of oxygen through a buffer tank
to smooth out fluctuations in pressure and flow of the breathable
amount of oxygen; (7) using a fan to direct a gas having a first
level of humidification past a first side of a water transfer
member; (8) directing an oxygen-depleted gas through a muffler to
reduce the noise of the oxygen-depleted gas as the oxygen-depleted
gas exits the system.
* * * * *