U.S. patent application number 12/924808 was filed with the patent office on 2011-04-28 for method of heating and heating apparatus.
Invention is credited to Keith D. Patch, Simon G. Stone, Linda A. Tempelman, Craig Thompson.
Application Number | 20110097678 12/924808 |
Document ID | / |
Family ID | 43898731 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110097678 |
Kind Code |
A1 |
Patch; Keith D. ; et
al. |
April 28, 2011 |
Method of heating and heating apparatus
Abstract
Method of heating and heating apparatus. According to one
embodiment, the heating apparatus is designed for warming infusion
fluids and includes a pair of catalytic heaters positioned around a
cartridge containing the infusion fluid. Each catalytic heater
includes a pair of frames jointly defining a cavity. One of the
frames per heater is positioned proximate to the cartridge and
includes an input port for receiving a liquid solution of methanol.
The other frame per heater is positioned distal to the cartridge
and includes an input port for receiving oxygen gas and an output
port for exhaust gases. A first fluid diffusion medium is
positioned within the methanol frame, and a second fluid diffusion
medium is positioned within the oxygen frame. Sandwiched between
the two diffusion media are a pervaporation membrane facing the
first diffusion medium and a porous metal catalyst facing the
second diffusion medium. Methanol in liquid form is supplied to the
pervaporation membrane, which then transports the methanol in vapor
form to the catalyst, where combustion occurs. Heat from the
combustion reaction is then conducted through the heater to the
cartridge containing the infusion fluid.
Inventors: |
Patch; Keith D.; (Lexington,
MA) ; Tempelman; Linda A.; (Lincoln, MA) ;
Stone; Simon G.; (Arlington, MA) ; Thompson;
Craig; (Sudbury, MA) |
Family ID: |
43898731 |
Appl. No.: |
12/924808 |
Filed: |
October 5, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61278273 |
Oct 5, 2009 |
|
|
|
Current U.S.
Class: |
432/1 ;
432/94 |
Current CPC
Class: |
A61M 5/44 20130101; A61M
2205/364 20130101; A61F 7/12 20130101; A61F 2007/126 20130101; F23D
91/04 20150701; F23C 13/08 20130101 |
Class at
Publication: |
432/1 ;
432/94 |
International
Class: |
F24C 15/00 20060101
F24C015/00 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The U.S. Government has a paid-up license in this invention
and the right in limited circumstances to require the patent owner
to license others on reasonable terms as provided for by the terms
of SBIR Phase I Contract Nos. 1R43GM083360-01A1 awarded by
NIH/NIGMS.
Claims
1. A method of heating a material to be warmed, said method
comprising the steps of: (a) providing a porous metal catalyst
suitable for catalyzing the combustion of a gaseous fuel in the
presence of oxygen; (b) supplying the porous metal catalyst with
the gaseous fuel and with oxygen, whereby the gaseous fuel is
combusted and heat is generated; and (c) transferring the heat
generated to the material to be warmed.
2. The method as claimed in claim 1 wherein the porous metal
catalyst comprises an unsupported porous metal.
3. The method as claimed in claim 1 wherein the porous metal
catalyst comprises a porous metal deposited on an oxygen-inert
support particulate sinter or metal.
4. The method as claimed in claim 1 wherein the porous metal
catalyst comprises a noble metal.
5. The method as claimed in claim 5 wherein the noble metal
comprises a platinum group member.
6. The method as claimed in claim 1 wherein the porous metal
catalyst comprises a non-noble metal.
7. The method as claimed in claim 6 wherein the non-noble metal
comprises a transition metal member.
8. The method as claimed in claim 1 wherein said supplying step
comprises providing a pervaporation membrane, said pervaporation
membrane having an input face and an output face, the output face
being in proximity to the porous metal catalyst, and supplying the
input face of said pervaporation membrane with a fluid fuel,
whereby the pervaporation membrane transports the fluid fuel from
said input face to said output face in vapor form so that the fluid
fuel exits said pervaporation membrane at said output face as the
gaseous fuel.
9. The method as claimed in claim 8 wherein said pervaporation
membrane has a pore size ranging from 0 to 400 nm.
10. The method as claimed in claim 9 wherein said pervaporation
membrane has a pore size ranging from 100 to 300 nm.
11. The method as claimed in claim 8 wherein said pervaporation
membrane comprises a solid ion-conductive polymer electrolyte
membrane.
12. The method as claimed in claim 8 wherein said pervaporation
membrane comprises a fluorocarbon-based polymer.
13. The method as claimed in claim 8 wherein said pervaporation
membrane comprises a hydrocarbon-based polymer.
14. The method as claimed in claim 8 wherein the fluid fuel is
supplied to the pervaporation membrane in liquid form.
15. The method as claimed in claim 8 wherein the fluid fuel is
supplied to the pervaporation membrane in gaseous form.
16. The method as claimed in claim 1 wherein the gaseous fuel
comprises a hydrocarbon.
17. The method as claimed in claim 1 wherein the gaseous fuel
comprises an alcohol.
18. The method as claimed in claim 17 wherein the gaseous fuel
comprises methanol.
19. The method as claimed in claim 1 wherein the oxygen supplied to
the porous metal catalyst is supplied as ambient air.
20. The method as claimed in claim 1 wherein the oxygen supplied to
the porous metal catalyst is supplied as a high purity oxygen
gas.
21. The method as claimed in claim 1 wherein said transferring step
comprises using a heat exchanger to transfer heat to the material
to be warmed.
22. The method as claimed in claim 1 wherein said transferring step
comprises using a heat pipe to transfer heat to the material to be
warmed.
23. The method as claimed in claim 1 wherein the material to be
warmed comprises at least one gas.
24. The method as claimed in claim 23 wherein the at least one gas
comprises at least one gas selected from the group consisting of
air, nitrogen, oxygen, an anesthetic gas, an analgesic gas, and an
inert gas.
25. The method as claimed in claim 1 wherein the material to be
warmed comprises at least one liquid.
26. The method as claimed in claim 25 wherein the at least one
liquid is selected from the group consisting of water, glycols, and
oils.
27. The method as claimed in claim 25 wherein the at least one
liquid comprises an infusion fluid.
28. The method as claimed in claim 27 wherein the infusion fluid is
selected at least one fluid selected from the group consisting of
crystalloid, saline, whole blood, plasma, packed red cells,
platelets, and artificial blood.
29. The method as claimed in claim 1 wherein the material to be
warmed is selected from the group consisting of a warming mattress,
a warming pad, a warming blanket, a warming clothing, and a thermal
management device.
30. The method as claimed in claim 1 wherein the material to be
warmed is selected from the group consisting of a solid, a gel, and
a semi-solid.
31. An apparatus for heating a material, said apparatus comprising:
(a) a porous metal catalyst suitable for catalyzing combustion of a
gaseous fuel in the presence of oxygen; (b) a pervaporation
membrane, the pervaporation membrane having an input face and an
output face, the output face being in sufficient proximity to the
porous metal catalyst to supply the porous metal catalyst with fuel
in vapor form; (c) means for supplying the input face of the
pervaporation membrane with a fluid fuel, whereby the fluid fuel
travels from the input face of the pervaporation membrane to the
output face of the pervaporation membrane and is emitted from the
output face of the pervaporation membrane in vapor form; (d) means
for supplying the porous metal catalyst with oxygen; and (e) means
for transferring heat generated by combustion of the gaseous fuel
to a material to be warmed.
32. The apparatus as claimed in claim 31 wherein the porous metal
catalyst comprises an unsupported porous metal.
33. The apparatus as claimed in claim 31 wherein the porous metal
catalyst comprises a porous metal deposited on an oxygen-inert
support particulate sinter or metal.
34. The apparatus as claimed in claim 31 wherein the porous metal
catalyst comprises a noble metal.
35. The apparatus as claimed in claim 34 wherein the noble metal
comprises a platinum group member.
36. The apparatus as claimed in claim 31 wherein the porous metal
catalyst comprises a non-noble metal.
37. The apparatus as claimed in claim 36 wherein the non-noble
metal comprises a transition metal member.
38. The apparatus as claimed in claim 31 wherein said pervaporation
membrane has a pore size ranging from 0 to 400 nm.
39. The apparatus as claimed in claim 38 wherein said pervaporation
membrane has a pore size ranging from 100 to 300 nm.
40. The apparatus as claimed in claim 31 wherein said pervaporation
membrane comprises a solid ion-conductive polymer electrolyte
membrane.
41. The apparatus as claimed in claim 31 wherein said pervaporation
membrane comprises a fluorocarbon-based polymer.
42. The apparatus as claimed in claim 31 wherein said pervaporation
membrane comprises a hydrocarbon-based polymer.
43. An apparatus for heating a material, said apparatus comprising:
(a) a catalytic heater, said catalytic heater comprising: i. a
housing, the housing defining a cavity and having a fuel input port
for receiving a fuel, an oxygen input port for receiving oxygen
gas, and an exhaust outlet port for discharging exhaust gases, ii.
a first fluid diffusion medium disposed in said cavity and in fluid
communication with said fuel input port, iii. a second fluid
diffusion medium disposed in said cavity and in fluid communication
with said oxygen input port and said exhaust outlet port, iv. a
porous metal catalyst suitable for catalyzing combustion of a
gaseous fuel in the presence of oxygen, said porous metal catalyst
being disposed between said first and second fluid diffusion media
and in contact with said second fluid diffusion medium, v. a
pervaporation membrane for supplying the porous metal catalyst with
fuel in vapor form, the pervaporation membrane having an input face
and an output face, the input face being in contact with the first
fluid diffusion medium, the output face being in contact with the
porous metal catalyst; (b) means for supplying the catalytic heater
with a fuel; and (c) means for supplying the catalytic heater with
oxygen gas.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims the benefit under 35 U.S.C.
119(e) of U.S. Provisional Patent Application No. 61/278,273, filed
Oct. 5, 2009, the disclosure of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0003] The present invention relates generally to methods of
heating and heating apparatuses and relates more particularly to
methods of heating and heating apparatuses suitable for warming
intravenous fluids or the like.
[0004] Excessive hemorrhaging, hypothermia and shock are among the
emergency conditions that often demand timely infusion of fluids,
such as whole blood, crystalloid or packed red cells.
Unfortunately, the infusion of large volumes of such fluids, which
are often below body-temperature, contributes to hypothermia in
these trauma patients. The on-site treatment of trauma victims with
warmed intravenous fluids (infusate) during the critical first hour
after the onset of a medical emergency (the so-called "Golden
Hour") requires effective portable heating equipment. However,
to-date, such equipment is not yet available. Consequently, medical
emergencies in remote areas or during disasters, such as hurricanes
or terrorist attacks, often result in the "Golden Hour" passing
without appropriate trauma treatment of these victims.
[0005] An early research effort to develop a portable infusion
heater was that of Belmont Instrument Corporation. In 1992, Belmont
Instrument Corporation demonstrated an inductive magnetic
heating-based prototype. Two efforts to develop a portable infusion
warmer were awarded in 2006 to CUBE Technology and Catalytic
Devices International under U.S. Army SBIR Topic A06-157,
"Liquid-Fueled Catalytic Heater for Infusion Fluids." However, none
of these three efforts got beyond the Phase I, proof of concept
level of effort.
[0006] The use of flameless heater packs by military personnel in
the field to warm infusion fluids has been evaluated (see Modesto,
"Avoiding hypothermia in trauma: use of the flameless heater pack,
meal ready to eat, as a field-expedient means of warming
crystalloid fluid," Mil. Med., 165:903-4 (2000)). These heater
packs are similar to those used to heat meals-ready-to-eat (MRE)
rations. Such flameless packs can only provide a limited quantity
of heat at an uncontrolled temperature and are not reusable. This
approach was found to be worthwhile only in cases where there is no
access to proper medical heating equipment.
[0007] Existing infusion warmers generally have insufficient
battery capacity to power the electrical resistance heating
mechanisms. A recent study by Dubick evaluated the suitability of
four commercially-available fluid heating devices for use in
military forward surgical and combat areas (see Dubick, "Evaluation
of commercially available fluid-warming devices for use in forward
surgical and combat areas," Mil. Med., 170(1):76-82 (2005)). These
forward surgical and combat areas are quite similar to the numerous
remote, rural locations that exist across the United States and to
the conditions that would exist in the event of a natural or
terrorist disaster. The study included two floor model warmers and
two portable units. The Level 1 Model 1000 (Smiths Medical, Dublin,
Ohio) and FMS 2000 (Belmont Instruments, Billerica, Mass.) were
evaluated for hospital use and were found to be suitable for
Department of Defense (DoD) forward surgical units. Of the two
portable units tested, the THERMAL ANGEL heater (Estill Medical
Technologies, Dallas, Tex.) was found to be better suited for use
in the most-forward echelons of care because it is lightweight and
battery-powered. The RANGER heater (Arizant Healthcare, Eden
Prairie, Minn.) was a more efficient fluid warmer than the THERMAL
ANGEL heater, but it required external electrical power. The
THERMAL ANGEL heater, the most portable of the four units tested,
and the only unit not requiring external power, uses electrical
resistance heaters powered by a 3.0 kg battery pack. This device
was designed for heating 1-3 units of blood (450 mL/unit) from
20.degree. to 38.degree. C. In the aforementioned Dubick study, the
ability of the THERMAL ANGEL unit to warm refrigerated fluids to
body temperature was very limited. This was particularly true with
the crystalloid volume expander Lactated Ringer's solution, which
could not be warmed to a minimum infusion temperature of 32.degree.
C. at a flow rate of 150 mL/min.
[0008] The rechargeable battery used by the THERMAL ANGEL heater is
a 12-V battery that stores 7.2 Amph (Estill Medical Technologies,
TA-BCE Battery Product Information), resulting in a stored energy
content of 86.4 Whr. Dividing by the battery mass gives a specific
energy of 28.8 Wh/kg. Estill Medical Technologies specifies that
the battery charge will last through the heating of approximately
one to three units of blood from 20.degree. to 38.degree. C. The
ability to heat only one to three units of blood before battery
recharge or replacement severely limits the field use of the
product, particularly in disaster situations where large numbers of
patients must be treated.
[0009] Difficulties in battery supply logistics and charge cycle
management have led to the examination of alternative power
sources, including fuel cells and solar panels (see Defense Update,
"Portable electrical power: battery supplies and logistics lessons
learned in Operation Iraqi Freedom 2003," Defense Update:
International Online Defense Magazine, 2004(1),
http://www.defense-update.com/features/du-1-04/batteries-lessons-iraq.htm
(Jun. 13, 2006)). Fuel cells have generally not come into use in
civilian applications, due to their present high initial costs. A
solar panel alternative is generally impractical for civilian
pre-hospital emergency medicine applications, due to the large
solar panel area required and the probability of insufficient solar
irradiance to power the device.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a novel
heating method.
[0011] It is another object of the present invention to provide a
novel heating method that overcomes at least some of the
shortcomings discussed above in connection with existing heating
methods.
[0012] Therefore, according to one aspect of the invention, there
is provided a method of heating a material to be warmed, said
method comprising the steps of (a) providing a porous metal
catalyst suitable for catalyzing the combustion of a gaseous fuel
in the presence of oxygen; (b) supplying the porous metal catalyst
with the gaseous fuel and with oxygen, whereby the gaseous fuel is
combusted and heat is generated; and (c) transferring the heat
generated to the material to be warmed.
[0013] It is still another object of the present invention to
provide a novel heating apparatus.
[0014] Therefore, according to another aspect of the invention,
there is provided an apparatus for heating a material, said
apparatus comprising (a) a porous metal catalyst suitable for
catalyzing combustion of a gaseous fuel in the presence of oxygen;
(b) a pervaporation membrane, the pervaporation membrane having an
input face and an output face, the output face being in sufficient
proximity to the porous metal catalyst to supply the porous metal
catalyst with fuel in vapor form; (c) means for supplying the input
face of the pervaporation membrane with a fluid fuel, whereby the
fluid fuel travels from the input face of the pervaporation
membrane to the output face of the pervaporation membrane and is
emitted from the output face of the pervaporation membrane in vapor
form; (d) means for supplying the porous metal catalyst with
oxygen; and (e) means for transferring heat generated by combustion
of the gaseous fuel to a material to be warmed.
[0015] According to still another aspect of the invention, there is
provided an apparatus for heating a material, said apparatus
comprising: (a) a catalytic heater, said catalytic heater
comprising (i) a housing, the housing defining a cavity and having
a fuel input port for receiving a fuel, an oxygen input port for
receiving oxygen gas, and an exhaust outlet port for discharging
exhaust gases, (ii) a first fluid diffusion medium disposed in said
cavity and in fluid communication with said fuel input port, (iii)
a second fluid diffusion medium disposed in said cavity and in
fluid communication with said oxygen input port and said exhaust
outlet port, (iv) a porous metal catalyst suitable for catalyzing
combustion of a gaseous fuel in the presence of oxygen, said porous
metal catalyst being disposed between said first and second fluid
diffusion media and in contact with said second fluid diffusion
medium, (v) a pervaporation membrane for supplying the porous metal
catalyst with fuel in vapor form, the pervaporation membrane having
an input face and an output face, the input face being in contact
with the first fluid diffusion medium, the output face being in
contact with the porous metal catalyst; (b) means for supplying the
catalytic heater with a fuel; and (c) means for supplying the
catalytic heater with oxygen gas.
[0016] Additional objects, as well as aspects, features and
advantages, of the present invention will be set forth in part in
the description which follows, and in part will be obvious from the
description or may be learned by practice of the invention. In the
description, reference is made to the accompanying drawings which
form a part thereof and in which is shown by way of illustration
various embodiments for practicing the invention. The embodiments
will be described in sufficient detail to enable those skilled in
the art to practice the invention, and it is to be understood that
other embodiments may be utilized and that structural changes may
be made without departing from the scope of the invention. The
following detailed description is, therefore, not to be taken in a
limiting sense, and the scope of the present invention is best
defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are hereby incorporated
into and constitute a part of this specification, illustrate
various embodiments of the invention and, together with the
description, serve to explain the principles of the invention. In
the drawings wherein like reference numerals represent like
parts:
[0018] FIG. 1 is a simplified schematic diagram of a first
embodiment of a heating apparatus constructed according to the
teachings of the present invention, certain components of the
apparatus being shown in cross-section; and
[0019] FIG. 2 is a simplified schematic diagram of a second
embodiment of a heating apparatus constructed according to the
teachings of the present invention, certain components of the
apparatus being shown in cross-section, said heating apparatus
being used as an experimental set-up for the examples discussed
below.
DETAILED DESCRIPTION OF THE INVENTION
[0020] A major innovation of this invention is the development of a
reusable, portable heater/warmer for infusion fluids that uses a
non-flammable liquid fuel to provide heating capacity in a portable
device for the full range of trauma treatment. The infusion warmer
could also be non-portable. A preferred non-flammable liquid fuel
comprises an alcohol mixed with water, and in particular a 15-24%
methanol solution. Alternately, a hydrocarbon, alcohol, or other
flammable or non-flammable liquid or gaseous fuels could be
employed including mixtures and, especially, mixtures with water.
Gaseous fuels could include hydrocarbons, hydrogen, or a mixture of
fuel gases. An objective of this invention is to provide a
liquid-fueled catalytic heater that can warm a large number of
units of infusate at a flow rate of up to 500 mL/min using one fuel
cartridge. Another objective is to warm 20 units of infusate using
one cartridge of methanol (or other hydrocarbon) fuel (possibly in
aqueous solution). This will allow either treating 20 patients with
1 unit each or treating one patient with 20 units of infusate. 20
units of blood are sufficient to cover all but the most extreme
single cases and are sufficient to meet the infusion needs for 92%
of trauma patients (see Novikov et al., "Fluid and Blood Therapy in
Trauma," Trauma Anesthesia, Cambridge University Press, New York,
N.Y., pp. 101-20 (2008)). By changing the fuel cartridge,
additional patients can be treated by the system (or more than 20
units of fluid can be given to a single patient).
[0021] A specific technical innovation in this invention is the use
of a pervaporation membrane to supply methanol fuel vapor at a
controlled rate to a catalytic oxidation chamber, wherein the
methanol vapor reacts with oxygen from air to produce heat which is
transferred to flowing infusate. In addition to ambient air,
oxygen-containing gas (10-90%) or high purity oxygen gas (90-100%)
could also be employed. The catalyst used in the catalytic
oxidation chamber can comprise an unsupported porous metal or a
porous metal deposited on an oxygen-inert support particulate
sinter or metal. The porous metal catalyst can comprise a noble
metal, such as a platinum group member, or a non-noble metal, such
as a transition metal member. A preferred embodiment of this
invention includes integration of the fuel supply, catalytic
oxidation cell and heat transfer device, as well as selection of
operating parameters to provide safe, efficient, controlled heating
of infusion liquids. In addition to the heat transfer device being
a heat exchanger, a heat pipe could be used. The infusion fluid
being warmed could include one or more of crystalloid, saline,
whole blood, plasma, packed red cells, platelets, artificial blood,
or other biological liquids. Other non-biological liquids could be
heated; gases and solid materials, including gels or semi-solids,
could also be heated.
[0022] A "dry heat" version of this invention was demonstrated,
where heat is catalytically produced by the methanol-fueled device,
and passes through first a metal (aluminum) and then a plastic (an
AZIRANT RANGER heat transfer cassette) surface to reach the
infusion fluid. A major advantage of this dry heat method is that
there is no chance of contaminating the infusion fluid with the
liquid fuel. A disadvantage of this method is the potential for
cooling of the heated infusion fluid after it leaves the heater and
as it passes down an intravenous (IV) line to the patient's
catheter.
[0023] A water-heated version could also be produced using this
technology, where the heat that is catalytically produced by the
methanol-fueled device is released to a sterile water supply. Such
a sterile water supply would then pass through a direct contact
heat exchanger to heat the infusion liquid. A major advantage of
this water-heated version is that a long, tube-in-tube direct
contact heat exchanger can be used, delivering the heated infusate
to close proximity of the patient's catheter. A major disadvantage
is the potential for contamination of the heated infusate should
there be a defect (e.g. a water-to-infusate leak) in the long,
tube-in-tube direct contact heat exchanger.
[0024] Rather than heating a liquid, heat from the reaction chamber
could be transferred to a gas or gas mixture including one or more
of the following: air, nitrogen, oxygen, anesthetic, analgesic
and/or inert gases.
[0025] A preferred embodiment of this technology involves a
portable infusion heater that can initially be used in the field,
at the site of a medical problem. Subsequently, the methanol-fueled
device would travel with the patient during transport (by ambulance
or Med-Flight) to a hospital, then during the patient's assessment
in an emergency department. Warm transfusions could be maintained
as the patient is transported to a diagnostics area and could
continue during that diagnostic assessment to find the source(s) of
any bleeding. Warm infusion fluids can continue to be supplied
during the patient's transport to an operating room and during an
operation. During an extended, complicated operation, transitioning
to a conventional, 120 VAC utility-powered fluid heater would be
possible. This continuum of infusion represents a great improvement
over conventional, electrically-powered heaters, where infusion of
warmed fluids is often interrupted, e.g. during transport to the
operating room.
[0026] In order to ensure compliance with applicable health and
safety requirements, a small catalytic converter could be added to
treat the effluent exhaust. Such a converter could significantly
reduce aerobic methanol vapor concentrations. Testing of this
catalytic converter technology was successfully conducted and
showed essentially complete removal of methanol in the effluent
exhaust. The catalytic converter may or may not need electric heat
in order to provide acceptable methanol destruction efficiency.
Although platinum was used, various catalysts, including non-noble
metal catalysts (e.g. nickel), are available to provide suitable
reactivity.
[0027] A hybrid heating arrangement could also be possible,
involving a combination of electric heat and methanol-sourced heat.
The electric heat (as a supplement or boost) could be provided by
either batteries (in a portable application) or from a utility's
120 VAC wall connection (for a stationary application). A capacitor
could be included for shaping peak power demand of the device.
[0028] Either the warm exhaust gas leaving the heater and/or the
warm liquid fuel leaving the heater could be passed either directly
or indirectly to another process, including a heat transfer device.
Heat from the heater and/or this heat transfer device could be used
in a patient heating process or in other thermal management
devices.
[0029] Heat from the catalytic reaction chamber could also be
transferred to a solid, gel, or semi-solid, for use warming a
patient or other possible use.
[0030] In addition to heating infusate fluids, a methanol-fueled
device as herein described could produce heat for many existing,
medical devices that are cord-powered off of 120 VAC power,
including: bed heating pads, bed heating mattresses,
adhesive-backed heating pads for attachment to patients, heated
blankets that are positioned on top of patients, warming clothing,
etc. Heat from a methanol-fueled device can warm, either directly
or indirectly, either water or air for such purposes. Warmed
liquids or gases from the device can be used to inflate the patient
warming system. Other methanol-heated medical devices would also be
possible, including other form factors and configurations.
[0031] Referring now to FIG. 1, there is shown a simplified
schematic view of a first embodiment of a heater apparatus
constructed according to the teachings of the present invention,
said heater apparatus being represented generally by reference
numeral 11.
[0032] Apparatus 11 comprises a pair of catalytic heaters 13-1 and
13-2. Heaters 13-1 and 13-2 are essentially identical to one
another, except that heater 13-2 is a mirror image of heater 13-1.
Therefore, it is to be understood that, apart from its mirror-image
orientation, the discussion below of heater 13-1 is applicable to
heater 13-2. Heater 13-1 comprises a pair of frames 15-1 and 15-2.
Each of frames 15-1 and 15-2 is preferably made of a
heat-conductive material, such as aluminum or a like metal. Frames
15-1 and 15-2 are joinable to one another (by means not shown). The
interior of frame 15-1 defines a flow field 16-1, and the interior
of frame 15-2 defines a flow field 16-2, with frames 15-1 and 15-2
jointly defining a cavity in fluid communication with flow fields
16-1 and 16-2. Frame 15-1 further includes an inlet port 17 and an
outlet port 19, both of which are in fluid communication with flow
field 16-1, and frame 15-2 further includes an inlet port 21 and an
outlet port 23, both of which are in fluid communication with flow
field 16-2.
[0033] Heater 13-1 further comprises a pair of fluid diffusion
media 25-1 and 25-2. Media 25-1 and 25-2 may be identical to one
another and may be fluid diffusion media of the type used, for
example, in electrochemical cells. Media 25-1 is positioned within
frame 15-1 against flow field 16-1, and media 25-2 is positioned
within frame 15-2 against flow field 16-2.
[0034] Heater 13-1 further comprises a pervaporation membrane 27
and a porous metal catalyst 29 sandwiched between media 25-1 and
25-2, with pervaporation membrane 27 having opposing faces in
intimate contact with catalyst 29 and media 25-2, respectively, and
with porous metal catalyst 29 having opposing faces in intimate
contact with pervaporation membrane 27 and media 25-1,
respectively. Pervaporation membrane 27 may be a permselective
membrane or a microporous membrane.
[0035] Apparatus 11 further comprises an infusion fluid receptacle
31, which may be used to hold a quantity of fluid to be warmed by
heaters 13-1 and 13-2. Receptacle 31 may be, for example, a plastic
bag having a serpentine shape, with one side of receptacle 31 in
intimate contact with heater 13-1 and the opposing side of
receptacle 13 in intimate contact with heater 13-2. Receptacle 31
may receive fluid to be warmed from a fluid source 33 conducted
through a length of tubing 34. A temperature sensor 35 connected to
a controller 37 (by means not shown) may be used to monitor the
temperature of fluid prior to its being warmed. After being warmed
in receptacle 31, the fluid may be conducted to a patient (not
shown) through a length of tubing 39. A temperature sensor 41
connected to controller 37 (by means not shown) may be used to
monitor the temperature of fluid that has been warmed in receptacle
31.
[0036] Apparatus 11 further comprises a fuel cartridge 51, which
may contain a quantity of a methanol solution or the like.
Cartridge 51 is fluidly connected to a fluid pump 53 through a
length of tubing 55. Pump 53 is electrically connected to
controller 37 and is fluidly connected to inlet ports 21 of heaters
13-1 and 13-2 through a length of tubing 57. A temperature sensor
59 connected to controller 37 (by means not shown) may be used to
monitor the temperature of fluid that is being pumped to inlet
ports 21.
[0037] Apparatus 11 further comprises a fan 61 for blowing ambient
air into inlet ports 17 through a length of tubing 63. Fan 61 may
be connected to controller 37 (by means not shown). A temperature
sensor 65 connected to controller 37 (by means not shown) may be
used to monitor the temperature of air that is being supplied to
inlet ports 17.
[0038] Apparatus 11 further comprises a length of tubing 71
connected to outlet ports 19 for removing the exhaust and other
fluids from heaters 13-1 and 13-2. A temperature sensor 73
connected to controller 37 (by means not shown) may be used to
monitor the temperature of the exhaust fluids.
[0039] Apparatus 11 has small auxiliary power requirements for pump
53, fan 61 and controller 37. These power requirements are
minimized so that they can be supplied by a long-lasting, small
battery (not shown).
[0040] In use, methanol solution is pumped from cartridge 51 into
flow fields 16-2, and ambient air is blown into flow fields 16-1.
The methanol solution diffuses through media 25-2 and is then
conducted in vapor phase to porous catalyst 29, where it then
reacts with oxygen to generate carbon dioxide and heat. The
generated heat is transferred through frames 15-1 and 15-2 to
receptacle 31 and, in turn, to the fluid contained within
receptacle 31. After being warmed, this fluid is then administered
to the patient. The carbon dioxide and other excess fluids
remaining in flow field 16-1 are discharged through outlets 19. As
can be appreciated, by monitoring the temperatures of the various
fluids, controller 37 may be used to adjust the rate at which
fluids are pumped into heaters 13-1 and 13-2.
[0041] The following examples are illustrative only and do not in
any way limit the present invention:
Example 1
[0042] The steady-state equipment arrangement shown in FIG. 2 was
used for laboratory testing of the prototype hardware. The 120 VAC
methanol heater was provided to reduce the required time to startup
the test stand and in case insufficient heat was supplied by the
apparatus of this invention. The methanol sensor loop and pure
methanol feed pump subsystem were provided to maintain a constant
methanol concentration (6 M) in the circulating liquid. The small
(1 liter) methanol solution recirculation tank was provided to
reduce the volume of circulating methanol, and thus speed the
transient responsiveness of the prototype. The large (5 liter)
methanol feed tank was designed to provide fresh solution to make
up for methanol solution consumption in the recirculation loop. A
compressed air tank and mass flow controller were used in the
permselective membrane, methanol-fueled heater apparatus; it is
also possible that a prototype would use a variable speed fan or
blower for controlling the air supply. To allow facile
documentation of heating performance of the laboratory apparatus,
an infusion fluid recirculation loop was used, including both a
city water heat exchanger for initial cooling, and an
electrically-powered mechanical chiller to return the recirculated
infusate to the desired temperature (e.g. 5.degree. C.). Type K
thermocouples were used to monitor inlet and discharge
temperatures; a carbon dioxide sensor measured the air-side exhaust
effluent. Flow meters were also provided on the recirculated
infusate loop and the recirculated methanol solution loop.
[0043] The prototype included two 203 sq. cm methanol-fueled cells
that transferred heat from the methanol stream to the infusate
(water) stream. The two cells made a sandwich with an Arizant
Ranger Model 24365 High Flow I.V. Blood/Fluid Warming Set (the
disposable heat exchanger in FIG. 2). Each cell was assembled with
the following materials: [0044] Membrane: General Electric PVDF
(Polyvinylidene Fluoride) Transfer Membrane, Part No. 1214429,
Model No. PV2HY00010, 220 nm pore size. Other membranes have been
and could be used. For example, a permselective membrane could be
used that possessed a pore size ranging from 0 to 800 mm, or
preferably a pore size of 100 to 300 mm. The permselective membrane
could be comprised of a solid ion-conductive polymer electrolyte
membrane, a fluorocarbon-based polymer, a hydrocarbon-based
polymer, or other material. [0045] Air-side support: Wetproofed
Toray H-060 with platinum catalyst, similar to state-of-the-art
direct methanol fuel cell (DMFC) supports. Although platinum was
used, various catalysts are available to provide suitable
reactivity. Although Toray H-060 was used, other support materials
could be selected, providing they were stable under the conditions
in the catalytic oxidizing chamber. [0046] Methanol-side support:
Toray H-060, untreated. Although Toray H-060 was used, other
support materials could be selected, providing they were stable
under the conditions in the fuel-side chamber. Results from
operating the prototype with the electric heat turned off included
the following: [0047] 100 cc/min. infusate recirculation rate,
5.degree. C. inlet temperature, 52.degree. C. outlet temperature
(in excess of the desired outlet temperature of 40.degree. C.)
[0048] 8,000 scc/min inlet air flow rate, 24.6.degree. C. inlet
temperature, 50.7.degree. C. outlet (exhaust) temperature,
exhausting 10.4% V/V carbon dioxide, or an equivalent of 770 mA/sq.
cm carbon dioxide production [0049] 285 cc/min 6 M methanol
recirculation rate, 46.4.degree. C. inlet temperature, 51.2.degree.
C. outlet temperature
[0050] This operating point demonstrates a heat production rate
(temperature rise) of 47.degree. C., which is in excess of the
desired 35.degree. C. temperature rise, without use of any electric
heat.
Example 2
[0051] Additional tests reached the design goal of a temperature
rise of 35.degree. C.+/-1.degree. C. with infusion recirculation
rates of 100 and 500 cc/min using crystalloid (normal saline)
solution rather than water. Due to the limited size of the
prototype, caused by the fixed size of the commercially-obtained
disposable heat exchanger that the system was designed around, the
500 cc/min test required a limited amount of supplemental
electrical heating to reach the desired temperature rise. (The 100
cc/min test was conducted with the electric heat disabled.) Based
on related direct methanol fuel cell experience, it is possible to
produce a suitable system design and to adjust the air and methanol
solution circulation rates to produce the desired temperature rise
of 35.degree. C. at an infusate flow rate of 500 cc/min without the
use of supplemental electrical heat.
[0052] The embodiments of the present invention described above are
intended to be merely exemplary and those skilled in the art shall
be able to make numerous variations and modifications to it without
departing from the spirit of the present invention. All such
variations and modifications are intended to be within the scope of
the present invention as defined in the appended claims.
* * * * *
References