U.S. patent application number 11/200738 was filed with the patent office on 2005-12-29 for method and apparatus for vaporizing fuel for a reformer fuel cell system.
Invention is credited to Benz, Uwe, Motzet, Bruno, Reinke, Michael J., Tischler, Alois, Voss, Mark, Wattelet, Jonathan, Weisser, Marc.
Application Number | 20050287409 11/200738 |
Document ID | / |
Family ID | 21693324 |
Filed Date | 2005-12-29 |
United States Patent
Application |
20050287409 |
Kind Code |
A1 |
Reinke, Michael J. ; et
al. |
December 29, 2005 |
Method and apparatus for vaporizing fuel for a reformer fuel cell
system
Abstract
Rapid response to a fuel cell system of the type including a
reformer (32) in response to a change in load is achieved in a
system that includes a fuel tank (24), a water tank (20) and a
source (42) of a fluid at an elevated temperature. A heat exchanger
(28) is provided for vaporizing fuel and water and delivering the
resulting vapor to the system reformer (32) and includes an inlet
(64) and an outlet (66) for the fluid. It includes a plurality of
fluid flow paths (100), (102), (104) extending between the inlet
(64) and outlet (66) as well as a fuel inlet (56) and a fuel outlet
(58) spaced therefrom. The fuel inlet (56) and outlet (58) are
connected by a plurality of fuel flow paths (52) that are in heat
exchange relation with the fluid flow paths (100), (102), (104) and
the fuel water inlet (56) is located adjacent the upstream ends of
the fluid flow paths (100), (102), (104).
Inventors: |
Reinke, Michael J.;
(Franklin, WI) ; Wattelet, Jonathan; (Gurnee,
IL) ; Voss, Mark; (Franksville, WI) ; Benz,
Uwe; (Uhldingen-Muhlhof, DE) ; Motzet, Bruno;
(Weilheim/Teck, DE) ; Tischler, Alois; (Dorfen,
DE) ; Weisser, Marc; (Owen/Teck, DE) |
Correspondence
Address: |
WOOD, PHILLIPS, KATZ, CLARK & MORTIMER
500 W. MADISON STREET
SUITE 3800
CHICAGO
IL
60661
US
|
Family ID: |
21693324 |
Appl. No.: |
11/200738 |
Filed: |
August 10, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11200738 |
Aug 10, 2005 |
|
|
|
10000860 |
Oct 24, 2001 |
|
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6936364 |
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Current U.S.
Class: |
429/413 ;
429/424; 429/434; 429/506; 429/514 |
Current CPC
Class: |
F28D 9/0068 20130101;
F28F 2250/102 20130101; F28D 2021/0064 20130101; F28F 3/027
20130101; H01M 8/0668 20130101; F28D 2021/0043 20130101; H01M
8/04074 20130101; Y02E 60/50 20130101; H01M 8/04164 20130101; H01M
8/0618 20130101 |
Class at
Publication: |
429/026 ;
429/020; 429/034; 429/017 |
International
Class: |
H01M 008/04; H01M
008/06 |
Claims
We claim:
1. A fuel cell system including. a fuel reservoir for storing a
liquid fuel for a fuel cell; a fuel cell for consuming a fuel and
generating electricity therefrom; a fuel reformer for receiving
fuel in a vaporized state and connected to the fuel cell for
providing a fuel thereto for consumption therein; and a fuel
vaporizer interposed between the fuel reservoir and the fuel
reformer for receiving liquid fuel from the fuel reservoir and
vaporizing the liquid fuel to the vaporized state for delivery to
the fuel reformer, and including a heat exchanger having a hot
fluid inlet, a hot fluid outlet and a core interconnecting said
inlet and said outlet, said core having alternating hot fluid
passages extending between said hot fluid inlet and said hot fluid
outlet and in heat exchange relation with liquid/vaporized fuel
passages, said hot fluid passages each being defined by two,
elongated spaced, generally parallel bars, a fin or fins between
said bars and extending the length thereof and two separator plates
bonded to and sandwiching said bars and said fin(s), said heat
exchanger further including a liquid fuel inlet and a vaporized
fuel outlet, each said liquid/vaporized fuel passage extending
between said liquid fuel inlet and said vaporized fuel outlet and
including an undulating spacer nested between generally parallel
bar sections and separator plates bonded to and sandwiching said
spacer to define a plurality of flow ports of relatively small
hydraulic diameter.
2. The fuel cell system of claim 1 wherein most, but not all, of
the separator plates are located within said core and each of said
most separator sheets is common to adjacent ones of said hot fluid
passages and said liquid/vaporized fuel passages.
3. The fuel cell system of claim 2 wherein said bars, said bar
sections, said fins, said separator plates and said undulating
spacers are bonded together by braze metal.
4. The fuel cell system of claim 1 wherein said core is a stack of
said bars, said bar sections, said fins, said separator plates and
said undulating spacers arranged to define said alternating hot
fluid passages in heat exchange relation with liquid/vaporized fuel
passages.
5. The fuel cell system of claim 1 wherein said undulating spacer
is in plural sections and said bar sections are oriented with
respect to said undulating spacer sections to define multipass
liquid/vaporized flow passages, at least one pass of said multipass
liquid/vaporized flow passages being in countercurrent relation to
said hot fluid passage.
6. The fuel cell system of claim 5 wherein at least one another
pass of said multipass liquid/vaporized flow passages is in
concurrent relation to said hot fluid passages.
7. The fuel cell system of claim 6 wherein said at least one pass
is connected to said vaporized fuel outlet and said at least one
another pass of said multipass liquid/vaporized fuel flow passages
is connected to said liquid fuel inlet.
8. The fuel cell system of claim 7 wherein the cross-sectional area
of said at least one pass is greater than the cross-sectional area
of said at least one another pass.
9. The fuel cell system of claim 7 wherein said at least one pass
has an increasing cross-sectional area as said vaporized fuel
outlet is approached.
10. The fuel cell system of claim 9 wherein said increasing
cross-sectional area is provided by a step-wise increase.
11. The fuel cell system of claim 9 wherein said increasing
cross-sectional area is provided by a continuous increase.
12. The fuel cell system of claim 7 wherein said at least one
another pass has an increasing cross-section in the direction of
flow away from liquid fuel inlet.
13. The fuel cell system of claim 12 wherein said increasing
cross-sectional area is provided by a step-wise increase.
14. The fuel cell system of claim 12 wherein said increasing
cross-sectional area is provided by a continuous increase.
15. The fuel cell system of claim 7 wherein said at least one path
and said at least one another pass are separate by an elongated
divider having one end closer to said liquid fuel inlet than said
vaporized fuel outlet and an opposite approximately midway between
said liquid fuel inlet and said vaporized fuel outlet.
16. The fuel cell system of claim 15 wherein said divider is
straight.
17. The fuel cell system of claim 15 wherein said divider is
stepped.
18. The fuel cell system of claim 1 wherein said undulating spacer
includes a plurality of spacer sections separated by gaps.
19. A method of vaporizing liquid fuel and water prior to its
introduction into a reformer in a fuel cell system, comprising the
steps of: a) causing a stream of hot fluid to traverse a flow path
such that the fluid is at maximum temperature at the beginning of
the flow path and at a lower temperature at a location downstream
of said beginning; b) vaporizing the liquid water and fuel by
bringing liquid water and liquid fuel into heat exchange relation
with said stream at said beginning and flowing the water and fuel
concurrently with said stream and in heat exchange relation
therewith to said location; and c) subsequently flowing the
vaporized water and fuel in heat exchange relation and
countercurrent with said stream back to said beginning and out of
contact with the flow of water and fuel occurring during the
performance of step b) to superheat the vaporized water and fuel;
steps a), b) and c) being performed in a continuous operation.
20. The method of claim 19 wherein step c) is followed by the step
of directing the vaporized and superheated water and fuel to a
reformer in a fuel cell system.
21. The method of claim 19 wherein said fuel is methanol.
22. A fuel cell system including: a fuel reservoir for storing a
liquid fuel for a fuel cell; a fuel cell for consuming a fuel and
generating electricity therefrom; a fuel reformer for receiving
fuel in a vaporized state and connected to the fuel cell for
providing a fuel thereto for consumption therein; and a fuel
vaporizer interposed between the fuel reservoir and the fuel
reformer for receiving liquid fuel from the fuel reservoir and
vaporizing the liquid fuel to the vaporized state for delivery to
the fuel reformer, and including a heat exchanger having a hot
fluid inlet, a hot fluid outlet and a core interconnecting said
inlet and said outlet, said core having alternating hot fluid
passages extending between said hot fluid inlet and said hot fluid
outlet and in heat exchange relation with liquid/vaporized fuel
passages, a fin or fins in said hot fluid passages, said heat
exchanger further including a liquid fuel inlet and a vaporized
fuel outlet, each said liquid/vaporized fuel passage extending
between said liquid fuel inlet and said vaporized fuel outlet and
including an undulating spacer to define a plurality of flow ports
of relatively small hydraulic diameter, said spacer being formed of
a plurality of spacer sections, each separated by a gap.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of Ser. No. 10/000,860,
filed Oct. 24, 2001 and entitled "Method and Apparatus for
Vaporizing Fuel for a Reformer Fuel Cell System".
FIELD OF THE INVENTION
[0002] This invention relates to fuel cell systems of the type
including a reformer that creates a hydrogen rich gas for use in
the fuel cell from a liquid fuel whose composition includes
hydrogen. More specifically, the invention relates to the
vaporization of the fuel prior to its admission to the
reformer.
BACKGROUND OF THE INVENTION
[0003] Recent years have seen a marked increase in interest in fuel
cell for the generation of electric power. One area where interest
is high is in the design of propulsion systems for vehicles. As is
well known, a typical fuel cell combines hydrogen and oxygen to
generate electricity which may then be used to power an electric
motor which can be used to provide propulsion for a vehicle.
[0004] While such systems have held promise for many years, most
have been out of reach from the practical standpoint in that they
require the vehicle to carry hydrogen as the fuel. The provision of
oxygen for the fuel cell reaction is not a problem in that it is
readily available from ambient air. In any event, early proposals
required that hydrogen be carried in liquid form or in gaseous form
at extremely high pressures. In either case, the vessels for
carrying the hydrogen were large, heavy and cumbersome in
comparison to fuel tanks for vehicles powered by internal
combustion engines.
[0005] Moreover, there was and is no infrastructure in place to
provide for the fueling of vehicles with liquid hydrogen or
hydrogen under high pressure to allow widespread use of fuel cells
in vehicles. And if that were not enough, where liquid hydrogen is
considered as the fuel, considerable expense in terms of equipment
necessary to assure vaporization of liquid hydrogen so that it can
be used by the fuel cell is a further drawback. Consequently, fuel
cell systems to date have been non-competitive with conventional
internal combustion engine propulsion systems.
[0006] More recently, in order to solve the above difficulties,
there have been a variety of proposals of fuel cell systems
employing a so-called reformer. Reformers are chemical processors
which take an incoming stream of a hydrocarbon containing or
hydrocarbon based material and react it with water to provide an
effluent that is rich in hydrogen gas. This gas, after being
further treated to rid it of fuel cell poisoning constituents, most
notably carbon monoxide, is then provided to the anode side of a
fuel cell. Ambient air is provided to the cathode side of the fuel
cell. The oxygen in the air and the hydrogen in the anode gas are
reacted to provide water and generate electricity that may be used
to power a load such as an electric motor.
[0007] The reformer must receive the fuel and water in vapor form.
Consequently, if the disadvantage of high pressure vessels
associated with some pure hydrogen fuel cells is to be avoided,
some means of carrying the fuel in a liquid form in a tank
comparable to gasoline or diesel fuel tanks must be provided along
with the means for vaporizing the water and the fuel prior to its
admission to the reformer. While for many non-vehicular
applications, the matter of vaporizing the water and the fuel may
be handled relatively simply, the problem is much more difficult
where the production of electricity by the fuel cell is expected to
respond rapidly to a change in electrical load. In the vehicular
context, this means that the fuel cell must respond rapidly to
changes commanded by the driver of the vehicle through changes in
the position of the fuel cell equivalent of a conventional gas
pedal.
[0008] It has been determined that the rapidity of response of the
fuel cell to a commanded change depends on the mass of water and
fuel in the vaporizer that feeds vaporized water and fuel to the
reformer. The greater the mass of fuel and water in the vaporizer,
the longer the response time. Consequently, it has been determined
that to be effective in fuel cell systems powering loads which
require rapid response to a change in conditions that the mass of
fuel and water in the vaporizer be held to an absolute minimum. To
meet this requirement, it is highly desirable that the fuel and
water side of the vaporizer have as small a volume as possible.
[0009] In vehicular applications, it is also highly desirable that
the overall vaporizer be as small in size as possible in terms of
volume and in weight. Bulk and weight are highly disadvantageous in
that weight reduces the overall fuel efficiency of the vehicle and
bulk reduces the load carrying capacity of the vehicle to the point
that it is impractical to provide a vehicle that can compete with
conventionally powered vehicles in use today. It is also desirable
to achieve a very short system start-up time.
[0010] The present invention is directed to overcoming one or more
of the above problems.
SUMMARY OF THE INVENTION
[0011] It is the principal object of the invention to provide a new
and improved fuel cell system of the reformer type and more
particularly, an improved fuel vaporizer for use in a reformer fuel
system. It is also an object of the invention to provide a new and
improved method for vaporizing fuel for use in a fuel system of the
type including a reformer.
[0012] According to one facet of the invention, there is provided a
method of vaporizing liquid fuel and water prior to its
introduction into a reformer in a fuel cell system. The method
includes the steps of a) causing a stream of hot fluid to traverse
a flow path such that the fluid is at maximum temperature at the
beginning of the flow path and at a lower temperature at a location
downstream of the beginning of the flow path, b) vaporizing the
liquid water and fuel by bringing liquid water and liquid fuel into
heat exchange relation with the stream of hot fluid at the
beginning of that stream and flowing the water and fuel
concurrently with the stream and in heat exchange relation
therewith to the downstream location; and c) subsequently flowing
the vaporized water and fuel in heat exchange relation and
countercurrent with the stream of hot fluid back to the beginning
and out of contact with flow of water and fuel occurring during the
performance of step b) to superheat the vaporized water and fuel.
Steps a), b) and c) are performed in a continuous operation.
[0013] According to a preferred embodiment, step c) is followed by
the step of directing the vaporized and superheated water and fuel
to a reformer in a fuel cell system.
[0014] In a highly preferred embodiment, the fuel is methanol.
[0015] According to another facet of the invention, there is
provided a fuel cell system that includes a fuel reservoir for
storing a liquid fuel for a fuel cell, a fuel cell for consuming
fuel and generating electricity therefrom, and a fuel reformer
connected to the fuel cell for providing the fuel thereto for
consumption therein. The fuel reformer receives fuel in a vaporized
state. A fuel vaporizer is interposed between the fuel reservoir
and the fuel reformer for receiving liquid fuel from the fuel
reservoir and vaporizing the liquid fuel to the vapor state for
delivery to the fuel reformer. The fuel vaporizer includes a heat
exchanger having a hot fluid inlet, a hot fluid outlet and a core
interconnecting the inlet and the outlet. The core has alternating
hot fluid passages and extending between the hot fluid inlet and
the hot fluid outlet in heat exchange relation with
liquid/vaporized fuel passages. The hot fluid passages each are
defined by two, elongated spaced, generally parallel bars, a fin or
fins between the bars extending the lengths thereof and two
separate sheets bonded to and sandwiching the bars and the fin(s).
The heat exchanger further includes a liquid fuel inlet and a
vaporized fuel outlet. Each of the liquid/vaporized fuel passages
extend between the liquid fuel inlet and the vaporized fuel outlet
and include an undulating spacer nested between generally parallel
bar sections and separator sheets bonded to and sandwiching the
spacer to define a plurality of flow ports of relatively small
hydraulic diameter.
[0016] In one embodiment of the invention, most, but not all, of
the separator sheets are located within the core and each of such
separator sheets is common to adjacent ones of the hot fluid
passages and the liquid/vaporized fuel passages.
[0017] In a preferred embodiment, the fin or fins may be of the
lanced and offset variety.
[0018] In one embodiment, the bars, the bar sections, the lanced
and offset fins, the separator sheets and the undulating spacers
are bonded together by braze metal.
[0019] A preferred embodiment contemplates that the core be a stack
of bars, bar sections, lanced and offset fins, separator sheets and
undulating spacers arranged to define the alternating hot fluid
passages in heat exchange relation with the liquid/ vaporized fuel
passages.
[0020] A preferred embodiment also contemplates that the undulating
spacer be in plural sections and that the bar sections are oriented
with respect to the undulating spacer sections to define multi-pass
liquid/vaporized flow passages, at least one pass of the multi-pass
liquid/vaporized fuel passages being in countercurrent relation to
the hot fluid passages.
[0021] In one embodiment, at least one other pass of the multi-pass
liquid/vaporized fuel flow passages is in concurrent relation to
the hot fluid passages.
[0022] Preferably, the one pass is connected to the vaporized fuel
outlet and the other pass of the multi-pass liquid/vaporized fuel
flow passages is connected to the liquid fuel inlet.
[0023] In a highly preferred embodiment, the cross-sectional area
of the one pass connected to the outlet is greater than the
cross-sectional area of the pass connected to the inlet.
[0024] Preferably, the hot fluid inlet and the hot fluid outlet are
each pyramid shaped and have an open base connected to the
core.
[0025] The invention also contemplates a fuel vaporizing system for
use in a fuel cell propulsion system which includes a source of
liquid fuel, a source of water, and a source of fluid at an
elevated temperature. Also included is a heat exchanger for
vaporizing fuel and water and delivering the resulting vapor to a
reformer. The heat exchanger has an inlet for the fluid and an
outlet for the fluid spaced therefrom. The inlet is connected to
the fluid source. A plurality of fluid flow paths extend between
the fluid inlet and the fluid outlet and have upstream ends at the
fluid inlet and downstream ends at the fluid outlet. A fuel/water
inlet and a fuel/water outlet which is spaced from the fuel/water
inlet are connected by a plurality of fuel/water flow paths that
are in heat exchange relation with the fluid flow paths. The
fuel/water inlet is connected to the fuel and water sources and
located adjacent the upstream ends of the fluid flow paths.
[0026] Preferably, the fuel/water flow paths are multiple pass flow
paths with an upstream most one of the fuel/water flow paths
flowing concurrent with the fluid flow paths and a downstream most
one of the fuel/water flow paths flowing countercurrent to the
fluid flow paths.
[0027] In a highly preferred embodiment, the heat exchanger is a
plate heat exchanger including a stack of separate sheets defining
a configuration of fluid flow paths and fuel/water flow paths in
alternating relation, and turbulators are disposed in the fluid
flow paths.
[0028] One embodiment of the invention contemplates that the
fuel/water flow paths are flattened and have a major dimension and
a minor dimension with the minor dimension being 1.0 mm or less.
Preferably, the minor dimension is about 0.5 mm.
[0029] Other objects and advantages will become apparent from the
following specification taken in connection with the accompanying
drawings.
DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic illustrating a typical fuel cell
system of the type employing a reformer with which the fuel
vaporizer of the present invention may be employed;
[0031] FIG. 2 is a perspective view of a fuel vaporizer made
according to the invention;
[0032] FIG. 3 is a plan view of the structure of fuel side passages
employed in the vaporizer;
[0033] FIG. 4 is an enlarged, sectional view taken approximately
along the line 4-4 in FIG. 3;
[0034] FIG. 5 is a view similar to FIG. 3 but of the hot gas side
of the vaporizer;
[0035] FIG. 6 is an enlarged, fragmentary, sectional view taken
approximately along the line 6-6 in FIG. 5;
[0036] FIG. 7 is a perspective view of a typical lanced and offset
fin construction that may be employed in the hot gas side of the
vaporizer;
[0037] FIG. 8 is an exploded view of part of a core of a vaporizer
made according to the invention;
[0038] FIG. 9 is a plan view of an alternate embodiment of the
structure of the fuel side passages; and
[0039] FIG. 10 is a plan view of still another alternate embodiment
of the structure of the fuel side passages.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] An exemplary embodiment of the invention will be described
herein in the environment of intended use in a vehicle and one
which utilizes methanol as a hydrogen containing liquid that is
combined with water to produce a hydrogen rich gas for use in the
fuel cell. Methanol is a preferred fuel because it is easy to
reform into the anode gas. However, it is to be understood that the
invention may be employed with efficacy in non-vehicular
applications, particularly where rapid response to a load change is
required. The vaporizer may also be employed with efficacy in other
reformer type fuel cell systems that employ a liquid fuel other
than methanol as, for example, ethanol, gasoline, diesel fuel, etc.
Consequently, the invention should not be regarded as limited to
vehicular systems or methanol type systems except insofar as
expressly so stated in the appended claims.
[0041] Turning now to FIG. 1, one type of fuel cell system
embodying a reformer with which the invention may be used is
illustrated in FIG. 1. This system is specifically intended to be
employed in a vehicle but may be used to advantage in other
environments.
[0042] The system includes a fuel cell 10 with provision for an
anode gas inlet stream on a line 12. The anode gas typically will
be hydrogen, carbon dioxide, and water vapor.
[0043] The fuel cell also includes an inlet line 14 leading to the
cathode side of the fuel cell and through which an oxygen rich
stream is received. In the usual case, the stream will be air.
[0044] The fuel cell also includes a cooling loop, generally
designated 16 as is well known.
[0045] The cathode exhaust is discharged on a line 18 which
eventually leads to a water tank or reservoir 20. That is to say,
water, the product of the chemical reaction within the fuel cell
10, is provided to the water tank 20 for later reuse in the
reforming process.
[0046] In addition to the water tank 20, the system includes a fuel
tank 24 which, in the system shown, contains methanol. Pumps 26
that are electrically driven by battery power during start-up or by
the electricity produced by the fuel cell 10 during operation,
meter water and methanol in a desired ratio to separate inlets or a
common inlet of a fuel vaporizer 28 made according to the
invention. The water/methanol mixture is vaporized and discharged
on a line 30 to the inlet of a reformer and catalytic burner 32.
The reformer and catalytic burner 32 in turn discharges reformate
(hydrogen, water, carbon monoxide and carbon dioxide) on a line 34
to a gas purification reactor 36 where the carbon monoxide content
of the gas is reduced to the point where it will not poison fuel
cell 10. The gas purification reactor 36 discharges to the inlet
line 12 to the anode of the fuel cell 10.
[0047] The system also includes an exhaust line 38 on which exhaust
gas is discharged. The exhaust gas is expanded through a
compressor/expander 44 and discharged as exhaust. A recirculation
line 46 for hot gas may also be provided.
[0048] Electric power generated by the fuel cell 10 is employed,
during operation, to drive pumps, motors, etc. within the system as
well as to provide electric power for the load to be driven by the
system. For start up, battery power may be used. In the case of a
vehicular propulsion system, the load will typically be a motor
coupled to the vehicle traction system.
[0049] Turning now to FIG. 2, a preferred form of a fuel vaporizer
28 made according to the invention is illustrated. The same
includes a core 50 made up of a series of plates, bars, spacers and
fins to be described in greater detail hereinafter. These
components define a fuel/water flow path through the vaporizer
which is shown schematically by an arrow 52. A liquid fuel inlet to
the flow path 52 is provided by a header 54 and a relatively small
diameter tube 56 connected thereto. A similar header (not shown)
supports a large diameter tube 58 which serves as a vaporized fuel
outlet. The difference in size of the tubes 56 and 58 is due to the
fact that the fuel and water mix enters the tube 56 as a liquid and
thus is at a relatively greater density than the fuel exiting
through the outlet tube 58 which is in vapor form. Consequently, to
avoid a large pressure drop, because of the greater volumetric flow
rate at the outlet tube 58, the outlet tube 58 has a larger
cross-sectional area.
[0050] The core 50 has opposed ends 60 and 62. The end 60 is an
inlet end and includes an inlet header 64. The end 62 is an outlet
end and includes an outlet header 66. The header 64 is connected to
receive hot gas from the reformer and catalytic burner 32 (FIG. 1)
and deliver it through hot gas fluid flow passages that are in heat
exchange relation with the flow path 50 which is in the form of a
plurality of passages as well. As will be seen, the core 50 is a
stack of the previously mentioned components that define
alternating fuel/water flow paths and hot gas flow paths. It is to
be noted that the inlet and outlet headers 64, 66 for the hot gas
are preferably pyramid shaped having a round opening 68 at their
apexes and an opposite, open base (not shown) which is in fluid
communication with hot gas fluid flow paths (not shown) within the
core 50.
[0051] Turning to FIG. 3, a typical fuel side subassembly
constituting a methanol/water flow path defining structure is
illustrated. The same includes a T-shaped bar 70 having a top end
72 of the T and an upright 74. The bar 74 extends between two side
bars 76 and 78 which are parallel and extend substantially the
length of the core 50 (FIG. 2) except for a relatively small break
or gap 80 between the bar 78 and the top 72 of the T which aligns
with the inlet manifold 54 and a relatively larger break or gap 82
at the end of the bar 76 adjacent the top 72 of the T 70 which
aligns with the methanol/water outlet manifold (not shown) which is
connected to the outlet tube 58.
[0052] At the end of the bars 76 and 78 remote from the top 72 of
the T 70, a cross bar 84 is located to seal off such end.
[0053] Nestled between the bars 70, 76, 78 and 84 is an undulating
spacer, generally designated 86 which is made up of a plurality of
spacer sections 88 having the configurations illustrated in FIG. 3.
In several instances such as shown at 90, gaps are located between
adjacent ones of the spacer sections 88 and small tabs 92 may be
provided on the bar 74 as well as the bars 76 and 78 to maintain
the gaps 90.
[0054] FIG. 4 is a section taken approximately along the line 4-4
in FIG. 3 illustrating the undulating spacer 86. The spacer 86
extends between the bars 76 and 78 (as well as the bar 74) which is
not shown in FIG. 4 and is sandwiched in that location by separator
plates 94 which are not illustrated in FIG. 3. The spacer 86 is
bonded as by brazing to the separator plates 94. The spacer 86 acts
as an internal fin and may be louvered, lanced and offset, a
herringbone or any other configuration that allows bonding to the
separator plates 94.
[0055] In the usual case, corrosion resistant materials such as
stainless steel or Inconel are utilized to resist the corrosive
effects of the fuel water mixture introduced through the gap 80
from the header 54. As a consequence, a plurality of flow ports or
passages 96 are formed between adjacent convolutions of the spacers
86 and provide for fuel flow in the direction illustrated by arrows
98 in FIG. 3.
[0056] It will be noted that the bar 74 is not centered on the top
72 of the T 70, but rather, is located to intersect the same at a
spot approximately 10% to 50% of the distance from the gap 80 to
the gap 82. This provides a minimum of flow resistance to the
fuel/water mixture as it vaporizes and increases in volume as a
result.
[0057] To minimize the mass of fuel located in the fuel passages
52, of which FIGS. 3 and 4 show a single one, the height of the
insert is 1.0 mm or less and preferably, about 0.5 mm. This
provides a small hydraulic diameter for the ports 96 which
typically will be on the order of 0.49 mm. However, where a
decrease in response time can be tolerated, the hydraulic diameter
may be increased. The lower limit on hydraulic diameter will depend
on the required mass flow rate for a given system, the tolerable
pressure drop, the total free flow area provided for fuel flow and
other like factors.
[0058] The gaps 90, in the direction of flow are between 1 and 3 mm
and the distance between adjacent ones of the gaps 90 is between 20
and 30 mm. The gaps 90 provide for redistribution of flow and aid
in reducing undesirable pulsation in flow. The outside dimensions
of the assembly for one embodiment of the invention are illustrated
in FIG. 3.
[0059] It should be recognized that while the fuel side subassembly
has been described as a fabricated structure made up of separators,
bars and undulating spacers, the invention does contemplate the use
of extruded structures could be employed to provide each pass
previously described if the desired relatively small hydraulic
diameter for a given system can be obtained.
[0060] Turning now to FIG. 5, a typical subassembly defining the
hot gas flow passage is illustrated. The same includes spaced,
parallel bars 100, 102 between which is nested a lanced and offset
fin, generally designated 104, which serves as a turbulator for the
fuel gas. FIG. 6 fragmentarily illustrates the lanced and offset
fin 104 between two separator plates 94 (which are identical to the
separator plates 94 in FIG. 4) and may be common with those
illustrated in FIG. 4 in most instances as will be described. The
fin 104 is sandwiched between the separator plates 94 and brazed
thereto. The height of the lanced and offset fin is 3.4 mm in the
illustrated embodiment. While lanced and offset fins are known in
the art, FIG. 7 illustrates a perspective view of such a fin. In
the preferred embodiment, the fin, as mentioned previously, is 3.4
mm high with a fin density of 9 fins per centimeter. Overall
dimensions of the hot gas side subassembly which defines the fluid
flow passages are illustrated in FIG. 5 and are identical to those
shown in FIG. 4.
[0061] FIG. 8 is an exploded view of a part of a stack of
alternating ones of the subassemblies shown in FIG. 3 and FIG. 5
making up the core 50.
[0062] To facilitate assembly, braze foil strips 106 are also
provided and located to sandwich a separator plate 94 in each
instance except for the top and bottom separator plates 94 in the
stack defining the core 50 (FIG. 2). The braze foil sheets 106 will
not be apparent in the final assembly as such although the residue
of braze metal therefrom will be present. If desired, other means
of locating braze metal at desired locations may be used, as for
example, powder coating, the use of braze clad sheets and the
like.
[0063] From top to bottom, a separator plate 94 will be provided
followed by a braze foil sheet 106. This in turn will be followed
by an assembly of the bars 70, 74, 76, 78 with the undulating
insert 86 nested between the same as mentioned previously. That
structure is then followed by a braze foil sheet 106, a separator
plate 94, a further braze foil sheet 106, and then the bars 100,
102 with the fin 104 nestled between the same. That structure, in
turn, will be followed by a braze foil sheet 106, a separator plate
94 and another braze foil sheet 106 which in turn is followed by
another of the assemblies of the bars 70, 74, 76, 78 with the
undulating spacer 86 nested therebetween. That in turn will be
followed by a braze foil sheet 106, a separator plate 94, another
braze foil sheet 106, and the bars 100 and 102 with the fin 104
nestled between the same. This construction is repeated until the
desired height of the stack is virtually complete at which time the
last set of bars and spacer 86 for fin 104 is in place which in
turn will then be followed by another braze foil sheet 106 and a
bottom separator plate 94.
[0064] To facilitate assembly, a fixturing tab 110 extends across
the gap 82 between the top 72 of the T 70 and the adjacent end of
the bar 76. A similar fixturing tab 112 extends across the gap 80
between the bar 76 and the top of the T 72. In a like fashion,
fixturing tabs 114 extend between the bars 100 and 102 at the inlet
end of the fluid flow passage subassembly while a similar fixturing
tab 116 extends between the opposite ends of the bars 100, 102. The
fixturing tabs 110, 112, 114, 116 are removed, as by a machining or
cutting operation after the entire core 50 has been brazed
together.
[0065] In addition to the dimensions given previously, typical
dimensions for the separator plates 94 and the braze foil sheets
106 (or cladding or coating if used instead of the sheets) are as
follows. Their outer dimensions are generally the same as the
sub-assemblies which are shown in FIGS. 3 and 5. Typically, the
braze foil sheets 106 will have a thickness in the range of about
0.01-0.05 mm, preferably 0.02 mm, while the separator plates 94
will have a thickness of 0.2 mm. Pressure resistance is provided by
the fact that the crests of both the undulating spacer 86 and the
lanced and offset fin 104 are brazed to the separator plates
94.
[0066] With the fixturing tabs removed, the headers 54, 64 and 66
as well as the water/methanol outlet header (not shown) are welded
to the core 50 at the locations mentioned previously.
[0067] In the usual case, a water and methanol mixture will be
introduced through the inlet tube 56, that is, through a single
inlet. However, it is to be understood that multiple inlets may be
used if desired. It should also be understood that it is possible
to utilize the vaporizer of the present invention to vaporize only
the hydrogen containing fuel and not the water which may be
vaporized in a separate vaporizer with the outlet streams then
combined prior to their admission to the reformer 32.
[0068] Alternative embodiments of the fuel side structure are
illustrated in FIGS. 9 and 10. In the interest of brevity, where
components similar or identical to those previously described have
been used, they will not be redescribed and the same reference
numerals will be employed.
[0069] In basic terms, the embodiments shown in FIGS. 9 and 10 are
intended to make further provision for the fact that the incoming
fuel, a mixture of water and methanol partly in vapor form and
partly in liquid form, will have a higher density than the outgoing
fuel, which will all be in vapor form. In order to minimize flow
resistance, the embodiments in FIGS. 9 and 10 have an ever
expanding cross-sectional area as one moves from fuel inlet 80 to
the fuel outlet 82. In the embodiment illustrated in FIG. 9, the
upright 74 of the T-shaped bar 70 joins with the top 72 of the
T-shaped bar 74 at a location that is about 10% of the distance
from the inlet 80 to the outlet 82 along the top 72 of the T-shaped
bar 74. This junction is shown at 150 in FIG. 9.
[0070] The opposite end of the upright 74 is designated 152 and
terminates at a location that is approximately mid-way between the
bars 76 and 78 (as measured along the top 72 of the T-shaped bar
74) and spaced from the bar 84 by a distance approximately as in
the embodiment of FIG. 3. As a consequence, it will be appreciated
that the cross-sectional area of the flow path for a flow direction
in the arrows 98 will continually increase from the inlet 80 to the
outlet 82 so that as the fuel mixture density reduces as a result
of vaporization of the liquid phase and heating of the vapor phase
decreases its density (increases its volume), the same readily
flows through the expanding flow path without measurably increasing
flow resistance.
[0071] The embodiment of FIG. 10 is generally similar but in this
case, the upright 74 is divided into a series of connected steps
shown at 154, 156, 158 and 160. Thus, in the embodiment of FIG. 10,
the increase in cross-sectional area continues from the inlet 80 to
the outlet 82 but in a stepwise fashion as opposed to the
continuously occurring increase that occurs in the embodiment of
FIG. 9.
[0072] In some cases, it may be desirable to form the various bars
as flanges or ribs in the separator plates which abut one another
or another separator plate and which are bonded thereto; and
references herein to "bars" are intended to encompass such
structures.
[0073] Nonetheless, it will be recognized that in both embodiments,
the increasing cross-sectional area of the fuel flow path to
accommodate the decreasing density of the fuel mixture to eliminate
high flow resistance is present.
[0074] The foregoing results in a construction wherein the
fuel/water stream is introduced adjacent the hot gas inlet so as to
immediately be subjected to heat exchange with the hot gas when the
latter is at its highest temperature. The same then flows
downstream in concurrent relation to the hot gas until a point
generally adjacent the hot gas outlet 66 where the fuel/water
reverses direction to flow countercurrent to the hot gas flow and
finally to the fuel outlet. That is to say, the presence of the T
70 in the fuel passage subassembly provides a multi-pass flow path
for the fuel with the upstream most pass entering at the point of
highest temperature of the hot gas and the downstream most pass of
the fuel flowing countercurrently to also be discharged at the
point where the hot gas is at its highest temperature. This is
thought to provide a highly beneficial effect in that because the
flow pass arrangement results in the highest temperature
differential between the fuel and the hot gas at the point of
entrance of the fuel as a liquid, it is more rapidly vaporized than
if a different flow regime were to be employed. Consequently, the
density of the fuel stream is immediately lowered considerably by
rapid vaporization of the fuel which in turn means that the mass of
fuel contained within the vaporizer 28 at any given instant is
minimized. This provides for a much more rapid response of the fuel
cell to a change in command as, for example, when an operator of a
vehicle utilizing the system for propulsion steps on the equivalent
of a gas pedal in a conventional internal combustion engine
propulsion system.
[0075] It will also be appreciated that the extremely small height
and hydraulic diameter of the ports 96 defining the fuel flow
passages results in a minimum volume for fuel, thereby minimizing
the mass of fuel that is in the vaporizer 28, whether in gaseous or
liquid form. Again, the response is maximized.
[0076] Importantly, the use of a lanced and offset fin such as the
fin 104 in the fluid flow passages for the hot gas provides
excellent turbulation within those passages thereby maximizing heat
transfer and in turn permitting the volume of the fuel side of the
vaporizer to be minimized for the same purpose.
[0077] It should be noted that the invention is not limited to the
use of tail gas as a heat source. Any gas at an elevated
temperature and having sufficient heat capacity to perform the
required vaporization may be utilized. In fact, in some instances,
particularly during the start-up of the system, methanol from the
tank 24 may be utilized to produce the hot gas needed to vaporize
the fuel.
* * * * *