U.S. patent application number 10/375834 was filed with the patent office on 2004-08-26 for heat exchanger for heating of fuel cell combustion air.
Invention is credited to Richardson, Curtis A..
Application Number | 20040163800 10/375834 |
Document ID | / |
Family ID | 32824728 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040163800 |
Kind Code |
A1 |
Richardson, Curtis A. |
August 26, 2004 |
Heat exchanger for heating of fuel cell combustion air
Abstract
A heat exchanger for a solid-oxide fuel cell assembly. A
plurality of parallel tubes conveys fuel cell stack exhaust gas
from a first manifold means to a second manifold means. The tubes
are highly corrugated to increase the wall area and decrease the
wall thickness. The tubes are disposed in a jacket through which is
passed incoming air to be heated. The tubes may be linear between
two manifolds, or they may be curved such that the first and second
manifold functions are accommodated within a single component.
Inventors: |
Richardson, Curtis A.;
(Voorheesville, NY) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202
PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
32824728 |
Appl. No.: |
10/375834 |
Filed: |
February 25, 2003 |
Current U.S.
Class: |
165/109.1 ;
165/157 |
Current CPC
Class: |
Y02E 60/50 20130101;
F28D 7/1638 20130101; F28D 2021/0043 20130101; F28F 1/08 20130101;
H01M 8/04074 20130101; F28D 7/06 20130101; F28F 13/12 20130101;
H01M 2008/1293 20130101; H01M 8/04007 20130101 |
Class at
Publication: |
165/109.1 ;
165/157 |
International
Class: |
F28F 013/12; F28D
007/10 |
Claims
What is claimed is:
1. A heat exchanger, comprising: a) at least one corrugated tubular
element, having first and second ends, for conveying a first fluid
at a first starting temperature; and b) jacket means surrounding
said at least one tubular element for conveying a second fluid at a
second starting temperature around said at least one tubular
element, whereby heat is transferred between said first fluid and
said second fluid.
2. A heat exchanger in accordance with claim 1 further comprising
first and second connecting means attached to said first and second
ends, respectively, for conducting said first fluid into and out of
said at least one tubular element.
3. A heat exchanger in accordance with claim 1 further comprising
at least one turbulator disposed within said at least one tubular
element for agitating said first fluid therein.
4. A heat exchanger in accordance with claim 1 wherein said at
least one corrugated tubular element has a surface area at least
twice that of a non-corrugated tubular element of equal length and
diameter.
5. A heat exchanger in accordance with claim 1 wherein said first
fluid and said second fluid are both gases.
6. A heat exchanger in accordance with claim 1 wherein said first
fluid is fuel cell exhaust and said second fluid is air.
7. A heat exchanger in accordance with claim 1 wherein said at
least one tubular element is selected from the group consisting of
linear, U-shaped, and M-shaped.
8. A heat exchanger in accordance with claim 2 further comprising a
plurality of said tubular elements arranged for parallel flow of
said first fluid therein between said first and second connecting
means.
9. A heat exchanger in accordance with claim 2 wherein said first
and second connecting means include first and second end
plates.
10. A heat exchanger in accordance with claim 2 wherein said first
and second connecting means are comprised in a single end
plate.
11. A heat exchanger in accordance with claim 8 comprising an array
of twenty of said tubular elements arranged into five M-shaped flow
paths for said first fluid.
12. A heat exchanger in accordance with claim 8 comprising an array
of twenty of said tubular elements arranged into ten U-shaped flow
paths for said first fluid.
13. A fuel cell assembly comprising a heat exchanger for exchanging
heat between fuel cell exhaust gas and incoming air, said exchanger
including at least one corrugated tubular element, having first and
second ends, for conveying said exhaust gas at a first starting
temperature, and jacket means surrounding said at least one tubular
element for conveying said incoming air at a second starting
temperature around said at least one tubular element, whereby heat
is transferred between said exhaust gas and said incoming air.
Description
TECHNICAL FIELD
[0001] The present invention relates to solid-oxide fuel cells
(SOFCs); more particularly, to heat exchangers for heating incoming
combustion air in an SOFC assembly; and most particularly, to an
improved heat exchanger for increasing heat exchange efficiency and
reducing heat exchanger manufacturing cost and complexity.
BACKGROUND OF THE INVENTION
[0002] Fuel cells combining hydrogen and oxygen to produce
electricity are well known. A known class of fuel cells includes a
solid oxide electrolyte layer through which oxygen anions migrate;
such fuel cells are referred to in the art as "solid-oxide" fuel
cells (SOFCs).
[0003] In some applications, for example, as an auxiliary power
unit (APU) for an automotive vehicle, an SOFC is preferably fueled
by "reformate" gas, which is the effluent from a catalytic gasoline
oxidizing reformer. Reformate typically includes amounts of carbon
monoxide (CO) as fuel in addition to molecular hydrogen. The
reforming operation and the fuel cell operation may be considered
as first and second oxidative steps of the liquid hydrocarbon,
resulting ultimately in water and carbon dioxide. Both reactions
are exothermic, and both are preferably carried out at relatively
high temperatures, for example, in the range of 700.degree. C. to
1000.degree. C.
[0004] Air enters an SOFC fuel cell at ambient temperature and
desirably is preheated before being sent to the fuel cell stacks. A
convenient and economical way to heat the air is by abstracting
heat via a heat exchanger from the fuel cell exhaust which exits
the fuel cell combustor at about 950.degree. C. In the prior art, a
typical heat exchanger employed for this purpose is of a well known
plate-and-frame design wherein a plurality of heat-exchange modules
is assembled as a stack. A plurality of alternating hot and cold
gas flow spaces are separated by heat transfer plates. A typical
prior art heat exchanger for use in an SOFC may comprise more than
100 individual plates and frames and can require more than 200 feet
of brazing to seal the edges of all the modules, and is thus
complicated and expensive to fabricate.
[0005] What is needed is an efficient heat exchanger for an SOFC
wherein the number of components and fabrication costs are
significantly reduced.
[0006] It is a principal object of the present invention to reduce
the cost and complexity of an SOFC heat exchanger.
SUMMARY OF THE INVENTION
[0007] Briefly described, a heat exchanger for a solid-oxide fuel
cell assembly includes a plurality of parallel tubes for conveying
a first gas, preferably a hot gas, from a first manifold means to a
second manifold means. The only brazing required is to attach each
tube to each manifold. Preferably, the tubes are highly corrugated
in bellows-like form to increase the wall area and decrease the
wall thickness. The tubes are disposed in a jacket through which is
passed a second gas, preferably a cool gas. The tubes may be linear
between two manifolds, or they may be curved such that the first
and second manifold functions are accommodated within a single
component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features and advantages of the invention
will be more fully understood and appreciated from the following
description of certain exemplary embodiments of the invention taken
together with the accompanying drawings, in which:
[0009] FIG. 1 is an isometric view from the front, partially
exploded, of a prior art plate-and-frame heat exchanger;
[0010] FIG.2 is an exploded isometric view from the front of a
first embodiment of a heat exchanger in accordance with the
invention;
[0011] FIG. 3 is an exploded isometric view from the front of a
second embodiment of a heat exchanger in accordance with the
invention; and
[0012] FIG. 4 is an exploded isometric view from the front of a
third embodiment of a heat exchanger in accordance with the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] Referring to FIG. 1, a prior art heat exchanger 10 comprises
a plurality of alternating hot and cold fluid flow spaces formed by
alternating rectangular plates 12 and frames 14. In an SOFC
assembly, the hot fluid is hot exhaust gas from the fuel cell stack
and the cold fluid is combustion air entering the assembly. Each
plate and frame has perforated extensions 16 at all four edges such
that, when assembled into a solid stack 18, the perforations define
inlet and exhaust manifolds 20,22 for a first fluid 23 flowing
across the plates in a first direction 24, and inlet and exhaust
manifolds 26,28 for a second fluid 29 flowing across opposite sides
of the plates in a second and orthogonal direction 30. The
extensions of first frames 14a are open on their inner edges to
permit access of first fluid 23 from manifold 20 to first sides of
plates 12, and the extensions of second frames 14b are open on
their inner edges to permit access of second fluid 29 to the
opposite sides of plates 12. It will be seen that the sequence of
plates and frames 12-14a-12-14b represents a modular repeat, and
that the full stack is simply a plurality of such modular repeats,
the number of modules being as desired for a particular heat
exchange requirement. In prior art SOFC heat exchanger 10, the
number of modules is typically about 25, requiring 100 or more
components. After the entire stack of plates and frames is
assembled, the edges of all plates and frames are sealed as by
brazing to prevent fluid leakage from the heat exchanger.
[0014] Referring to FIG. 2, a first embodiment 110 of an SOFC heat
exchanger in accordance with the invention includes a plurality of
parallel metal tubes 112 having ends 113 (one set of ends not
visible). Lower end plate 114 is provided with a plurality of
openings 116 arranged in a pattern, each opening being surrounded
by a lip 118 for receiving a first end (not visible) of a tube 112.
Upper end plate 120 is similarly provided with openings 122 and
lips (not visible). The exemplary pattern of openings and tubes is
four staggered rows of five tubes each. Obviously, other patterns
are possible within the scope of the invention. The tubes are
attached to the end plate lips as by brazing.
[0015] Metal tubes 112 preferably are axially corrugated as by
hydro-forming into bellows form such that the surface area of each
tube is substantially greater than the surface area of a
non-corrugated tube having equal length and diameter. Preferably,
the surface area is at least doubled. In addition, the
bellows-forming process, which is well known in the art, causes
thinning of the tube wall. As a result, the thermal conductance of
heat exchanger 110 can be as much as 200% greater than that of
prior art heat exchanger 10 of comparable size.
[0016] Preferably, tubes 112 are formed of a nickel-based high
temperature alloy, for example, Inconel 625.
[0017] A base plate 124 has a planar upper surface 126 for mating
against a 20 planar lower surface 128 of lower end plate 114.
Surface 126 is relieved in three areas. One is a central well 130
defining an intermediate manifold for mating with the central two
rows of ten openings 116; the other two are lateral wells
132a,132b, each of which defines an intake and exhaust manifold,
respectively, which mates with a respective lateral row of five
openings 116. Well 132a is provided with slots 134 extending
through plate 124 for mating with a supply such as an intake
manifold (not shown) of a first fluid 23, preferably the hot
exhaust gas from the fuel cell stack. Well 132b is provided with
similar slots 136 for mating with a return pathway through an
exhaust manifold (not shown) for first fluid 23.
[0018] A cover plate 138 has a planar lower surface 140 for mating
against a planar upper surface 142 of upper end plate 120. Surface
142 is relieved in two wells 144a,144b, each of which defines a
first and second crossover manifold, respectively. Each well
contains two respective lateral rows of five openings 122. Wells
144a,144b are separated by a median 146.
[0019] The result of this arrangement is an "M" shaped path for gas
through five parallel tube assemblies. A first gas (fuel cell
exhaust gas) at a first starting temperature enters through slots
134, passes through openings 116 into the first staggered row of
five tubes 112, passes upwards through openings 122 into crossover
manifold 144a, passes downwards through openings 122 into the
second staggered row of five tubes 112, passes through openings 116
into central well 130, passes upward through openings 116 into the
third staggered row of five tubes 112, passes upward through
openings 112 into second crossover manifold 144b, passes downward
through openings 112 into the fourth staggered row of five tubes
112, passes downward through openings 116 into lateral well or
manifold 132b, and passes out of heat exchanger 110 via slots
136.
[0020] Referring still to FIG. 2, tubes 112 and upper plate 120 are
surrounded by a jacket 150 defining a jacketed space 152 between
jacket 150 and the walls of tubes 112. Jacket 150 is sealed to
cover plate 138 and to lower end plate 114. Lower end plate 114 is
attached to base plate 124 as by bolts (not shown) through bores
154. Lower end plate 114 and base plate 124 are provided with slots
158,160. A second gas at a second starting temperature (air to be
heated) enters through inlet slots 158, passes into jacketed space
152, passes around corrugated tubes 112 abstracting heat therefrom,
and exits through exhaust slots 160.
[0021] Referring to FIG. 3, a second embodiment 210 is identical in
gas flow path to embodiment 110 but is substantially simplified in
construction. The "M" shaped flow path is clearly visible in five
staggered M-tubes 212 having ends 213. Each M-tube 212 preferably
is corrugated along its four linear portions as shown. Upper plate
120 and cover 138 are eliminated, their functions being cast into a
closed jacket 250 conformable with M-tubes 212. Further, lower end
plate 214 is simplified to have only ten openings 216 rather than
twenty openings 116 as in embodiment 110. The total brazing
required between tubes and plates is reduced from forty joints to
ten. When tubes 212 are one-half inch in diameter, the total length
of brazing required is about 15 inches, as compared to 200 inches
required for prior art exchanger 10 or 60 inches for first
embodiment 110. referably, bottom plate 214 is provided with a
plurality of attached fins 280 disposed adjacent M-tubes 212 for
improving air flow around the tubes. Base plate 224 is simplified
to eliminate central well 130 from embodiment 110.
[0022] The "M" flow path indicated in first and second embodiments
110,210 can give rise to undesirably high back pressures because of
the relatively long flow path. Referring to FIG. 4, a third
embodiment 310 reduces the flow path by half, albeit at a cost of
sixty joints as in first embodiment 110. The basic flow arrangement
provided by the twenty corrugated tubes 312 (shown for clarity via
a cutout in jacket 350), having tubular inserts 313, is ten
parallel U-shaped flow paths instead of five M-shaped flow paths.
Lower end plate 314 is substantially identical with plate 114 in
FIG. 2. Base plate 324 is configured as essentially a frame having
two openings 332a,332b which become inlet and exit chambers when
plate 324 is disposed between a mounting manifold (not shown) and
plate 314. Upper end plate 320 is welded to tubes 312 as in FIG. 2,
and a single upper manifold space 380 is provided by a cutout in a
new spacer frame element 382 into which tubes 312 debouch. Cover
plate 338 is similar to cover plate 138. The flow path then is
simply from inlet opening 332a upwards through the forward ten
tubes 312 into manifold space 380, then downwards through the rear
ten tubes 312 into exhaust opening 332b. Jacket 350 may be
substantially identical with jacket 150.
[0023] A potential drawback of flowing a gas through corrugated
tubing is stagnation of gas within the recesses of the
corrugations. Referring still to FIG. 4, each tube 312 preferably
is provided with an internal spiral turbulator 355 which is
installed into the tube prior to brazing. (For purposes of clarity,
each turbulator is shown partially removed from the respective
tubes). Turbulator 355 is formed from sheet metal, preferably a
high-temperature alloy, and twisted through an axial angle such as
1800 about its axis. The turbulator induces a swirling flow of gas
through the tube, promoting flushing of gas from the corrugation
recesses.
[0024] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *