CA1229377A - Cooling assembly for fuel cells - Google Patents

Abstract

PATENT APPLICATION PAPERS OF

ARTHUR KAUFMAN AND JOHN WERTH

FOR: COOLING ASSEMBLY FOR FUEL CELLS

ABSTRACT OF THE DISCLOSURE

A cooling assembly for fuel cells having a simplified construction whereby coolant is efficiently circulated through a conduit arranged in serpentine fashion in a channel within a member of such assembly.
The channel is adapted to cradle a flexible, chemically inert, conformable conduit capable of manipulation into a variety of cooling patterns without crimping or oth-erwise restricting of coolant flow. The conduit, when assembled with the member, conforms into intimate con-tact with the member for good thermal conductivity.
The conduit is non-corrodible and can be constructed as a single, manifold-free, continuous coolant passage means having only one inlet and one outlet.

Description

I 7t7 COOLING ASSEMBLY FOR FUEL CELLS

BACKGROUND OF THE INVENTION

This invention relates to an improved cooling apparatus, and, more specifically, to an improved cooling assembly for use in fuel cell stacks.
Cross-reference is made to two other cop ending patent applications pertaining to related subject matter and assigned to the same assignee as this application; Canadian patent application of John Worth entitled "Fuel Cell Crimp-Resistant Coolant Device With Internal Support", Serial No. 455,653, filed on June l, 1984; and Canadian patent application of Charles Whitehall entitled "Fuel Cell Crimp-Resistant Coolant Device With Internal Coil", Serial No. 455,655, filed on June 1, 1984.
Fuel cell design and operation typically involves conversion of a hydrogen-containing fuel and some oxidant into DC electric power through an exothermic reaction. The chemistry of this reaction is well known and has established parameters and limitations.
One such limitation is that the electrochemical reaction produces, as a by-product thereof, sub Stan-trial waste heat which must be removed in a controlled manner to maintain the cells at their desired operating

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temperature. For efficient operation it is generally desirable to maintain the cells at substantially unit form temperature and at a temperature level which is consistent with a controllable rate of reaction of the fuel cells therein.
Conventional methods for removal of waste heat from the fuel cell environment have traditionally involved the use of a luminary heat exchanger asset-bites, or cooling assemblies, incorporated within and arranged parallel to the various other layers from which the fuel cells are constructed. Typically, the components of the cooling assembly take the form of passageways which contain a circulating coolant Metro-at. The heat generated within the stack is transferred to the coolant as it is circulated through the stack.
The coolant is then brought out of the stack and into a heat exchanger where the heat is removed therefrom be-fore the coolant is recirculated through the stack. In this manner the cooling assembly enables control o'er the temperature of the reaction environment of the fuel cell stack and, thus, its rate and efficiency. The pattern of distribution of the coolant passageways within the stuck, their relative size, the heat keeps-try of the coolant fluid and the volume of coolant which is circulated through the cooling assembly per unit of time determine the heat transfer capacity of the cool-in system. Because the cooling system is generally an integral part of the fuel cell stack, it should be electrically isolated from the stack and also should not be adversely affected by corrosive media within the stack such as the hot electrolyte The problems associated with corrosion as well as the undesirable flow of electrical current from , . , I ~2'~3~7 the stack into the cooling loop are described in detail in US. Patents 3,964,929; 3,964,930; and 3,969,145.
These patents address the problem of the so-called "shunt currents" and attempt to resolve it by elect tribally insulating the cooling system from ground This minimizes the driving potential of such currents relative to the coolant Other techniques for avoiding the problems associated with shunt currents include the use of dielectric coolants.
The heat exchanger configuration described in these patents is rather typical of that employed by the prior art. Generally, the configuration consists of a series of parallel tubes connected to what is generally referred to as a "plenum". The plenum is a reservoir from which coolant is simultaneously distributed into the parallel tubes which are embedded in a fuel cell cooling assembly. After passage of the coolant through the parallel tubes, it is collected in another plenum and, thereafter, returned, through a cooling loop, to I the inlet plenum.
The cooling assembly tubes are composed of electrically conductive material such as copper. Water can be used as the coolant and the metal tubes are coated either on their internal or external surfaces with a dielectric material such as polytetrafluoroethylene. This coating is used to no-dupe the possibility of shunt currents and corrosion of the tubes. The coated tubes are located in passageways formed in the plates of fuel cells in the stack. Dow-ever, due to manufacturing tolerances, it is difficult avoid voids such as spaces between the tubes and the walls of the passageways. Since air is a poor conduct ion of heat, such air spaces can be filled with a thermally-conductive grease which is compatible with the electrolyte to maximize heat transfer from the cells to the coolant. These systems also use a sacrificial anode material at the tube ends to guard against corrosion. In addition, there is the possibly-fly of discontinuities occurring in the Teflon layer such as by manufacturing imperfections, differential thermal expansion, damage during the assembly process, poor bonding, etc. This causes two problems; first the corrosive media in the fuel cell will be able to dip neatly attack the tube and second, the thermal contact will be diminished.
A variation in cooling assembly design is disclosed in US. Patent 4,233,369. In this patent, a fibrous, porous coolant tube holder, which also serves as a member through which a reactant gas can travel, is used to hold copper coolant tubes. The tubes, held in channels in the holder, are connected to a coolant in-let header and coolant outlet header. Between the I headers, the tubes pass through the stack, make a U-turn and passbook through the stack. The tubes are pressed into the channels and have caulking between the channel walls and tube. In addition to reduced Corey-soon, this system makes the separator plate thinner and easier to manufacture.
Other techniques are known for bringing coolant materials into a fuel cell stack. For in-stance, a tubeless system has been used wherein a metal plate is grooved in a pattern on its surface with one or more inlets and outlets. The grooved surface of the plate is then covered with a second ungrooved metal plate, called a brazing sheet, to create an assembly having enclosed coolant passageways and coolant inlet I I

and outlets. In addition, similar passageways can be constructed by assembling two such brazing plates with partitions there between which form coolant passageways.
It is evident that the demands upon the cooling systems for fuel cells are significantly greater and more specialized than those encountered by other devices in different heat transfer environments. US.
Patents 1,913,573; 2,819,731; 2,820,615; 2,864,591; and

3,847,194 are illustrative of some of the conventional heat transfer devices found in areas other than the fuel cell-related technologies. In virtually all the heat exchangers described in the immediately foregoing list of patents, the environmental setting contemplated for their use is much more forgiving than that encoun-toned in fuel cells SUMMARY OF THE INVENTION
According to an aspect of the invention a cooling assembly for use in removing heat from a fuel cell having means for circulating coolant through a cooling assembly adjacent the cell, the cooling assembly comprises:
(a) at least one conformable coolant conduit means for carrying the coolant through the cooling assembly and (b) means for holding the conduit means in the cooling assembly including at least one member which, when assembled with the conduit means, conforms at least a portion of the conduit means into intimate contact with the member.
According to a preferred aspect of the invent lion, the conduit can comprise a non-corroding, metal-free, dielectric material. The conduit can also be a continuous tube having periodic corrugations therein to accommodate the bends necessary to arrange the conduit I' into a serpentine configuration to maximize heat transfer in a given area while necessitating only one inlet and one outlet for the coolant.
According to another aspect of the invention cooling apparatus for removing heat from a fuel cell stack having means for circulating coolant through a cooling assembly between two adjacent fuel cell units within the stack, each fuel cell unit having a plurality of laminated plate means which include a termination plate means at the extremity thereof, the cooling assembly comprises:
(a) at least one conformable coolant conduit means, and (b) means for holding the conduit means in the cooling assembly including a member which, when assembled with the conduit means, conforms at least a portion of the conduit means into intimate contact with the member, the means for holding the conduit means being integral with and forming part of the terminal lion plate means of the fuel cell units adjacent the coolant conduit means.
according to a further aspect of the invention in a fuel cell stack assembly comprising a plurality of adjacent individual fuel cell units separated from another by a cooling plate wherein coolant is distributed to, and collected from said plate by a manifold positioned in advance of distribution of said coolant through said plate and a second manifold positioned for collection of coolant after it passes through said plate, the improvement comprises:
(a) a manifold-free heat exchanger assembly comprising a termination plate from each of two adjacent fuel cell units which, in combination, create a predetermined ,.~

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channel pattern adapted to intimately cradle a continuous crimp resistant, electrically insulating conduit, said conduit having, at its proximal end, an inlet port for introduction of a coolant fluid, and at its distal end, an outlet port for the discharge of said coolant fluid.
According to another aspect of the invention a fuel cell stack assembly comprises a plurality of individual fuel cell units and a manifold-free exchanger assembly comprising: a cooling plate separating two such individual units, the cooling plate of such manifold-free assembly having a predetermined channel pattern defined by a termination plate from each of two adjacent individual fuel cell units within the stack, said channel being adapted to intimately cradle a continuous crimp-resistant, electrically insulating conduit having at its proximal end an inlet port for the introduction owe a coolant fluid, and at its distal end, an outlet port for discharge of such fluid.

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BRIEF DESCRIPTION OF THE DRAWINGS

This invention will now be described by rev-erroneous to the following drawings and description in which like elements have been given Canaan reference numerals:
Figure 1 is a schematic representation of a fuel cell assembly comprising a plurality of stacked fuel cells with intermediate cooling plates and term-net current collecting plates.
Figure 2 is a perspective view of a portion of the fuel cell assembly of Figure 1, illustrating an individual fuel cell in greater detail.
Figures I & I are a perspective view showing two embodiments of the cooling assembly.
Figure 4 is a view in partial cross section of a cooling assembly which has been isolated from the fuel cell assembly illustrating the serpentine arrange-mint of conduit means as it weaves through the prude-termined channel pattern formed in the members which retain the conduit means.
Figure 5 is a cross section through Figure 4 at Section A-A.
Figures I and I are views of the into-mate contact between the conduit means and members of the cooling assembly.
Figures aye & (b) are schematic thus-tractions of the formation of the truncated half circle grooves.

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Figure 8 2-C are schematic illustrations of the coolant tube and the grooves at various times.
Figure 9 is a schema-tic illustration of the coil pattern after the coil material is stretched out between those sections thereof to accommodate bends in the coolant tube.
Figure 10 is a schematic illustration of the coil support in the coolant tube before the tube is bent, the tube being partiallyicut away.
Figure 11 is a schematic illustration of the coil support in a tube arranged in serpentine con fig-unction.

DETAILED DESCRIPTION OF THE PREFERRED ~IvlBODIMENT
An exemplary fuel cell stack assembly 10 em-plying the invention is shown in Figures 1 and 2. The stack assembly 10 includes a plurality of fuel cells 11. Hydrogen gas input manifolds 12 are arranged along one side of the stack assembly 10. Although a plural-try of manifolds 12 are shown for each group of fuel cells 11, a single such manifold arrangement could be used if desired. The manifolds 12 are connected to a source of hydrogen gas 14. Hydrogen gas collecting manifolds 15 are arranged along the opposing stack side in correspondence with the hydrogen gas input manifolds 12. Here again, although a plurality of manifolds 15 are shown, a single such manifold could be used if desired. The collecting manifolds 15 are connected to a hydrogen gas discharging or recirculating system 17~
The hydrogen gas from the input manifolds 12 flus through gas distribution plates 18 to the collecting manifolds 15.

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In similar fashion, a plurality of oxygen input manifolds (not shown) are arranged along another stack side connecting the one stack side and the oppose in stack side. These oxygen manifolds are connected to an oxygen source 19. The oxygen ma be supplied in the form of air rather than pure oxygen if desired. A
plurality ox oxygen collecting manifolds (not shown) are arranged along the stack side opposing the stack side having the oxygen input manifolds connecting the respective one stack side and opposing stack side. The stack sides at which the oxygen manifolds are arranged are generally stack sides other than the ones at which the hydrogen input manifold and hydrogen collecting manifold are connected. The oxygen manifolds are also connected to an oxygen storage or recirculating system (not shown). The oxygen from the input manifolds flows through the oxygen gas distribution plates 20 to the respective collecting manifolds.
Cooling assemblies 21 are arranged period-icily Belgian adjacent fuel cells 11 to effect the desired degree of cooling. In the embodiment shown in Figure 1, three cooling assemblies 21 are shown en-ranged intermediate each group of four cells 11~ The cooling material, either liquid or gas, which flows through the cooling assembly 21 can be any suitable material. For instance, it can be a dielectric fluid such as a high temperature oil coolant manufactured by Multi therm Corporation under the trade name Pal In the alternative, it can be a non-dielectric coolant such as water or water & stream mixtures.
pump 22 circulates the coolant by way of passageway 23 and distribution reservoir 24 into the respective cooling assemblies 21. The distribution reservoir 24 is joined to each individual cooling as-symbol by direct connection to the inlet port of the continuous coolant conduit 90 of cooling assembly 21.
Conduit 90 is shown in two different configurations in Figures aye and I. After passing through conduit 90, the coolant flows into the collection reservoir 25.
The reservoir 25 is connected to a heat exchanger 26 which reduces the temperature of the coolant to the desired input temperature before it is recirculated lo through the conduit 90. Collection reservoir 25 is joined to the cooling plate assemblies 21 by direct connection to the outlet port of continuous conduit 90.
A coolant passageway 27 connects the heat exchanger 26 back to the pump 22 so that the coolant can be recur-quilted through the respective cooling assemblies 21.
Reservoirs 24 and 25, referred to hereinabove, are ordinarily only present when the fuel cell stack 10 has a number of cooling assemblies 21, and even then the reservoirs are connected directly to each individual cooling assembly 21 at a single point.
Alternatively, however, cooling assembly designs could be made wherein more than one continuous conduit 90 operates in parallel to effect serial distribution of coolant throughout the plate or wherein such multiple continuous conduits are complementary to one another and each independently distributes coolant throughout the plate.
The fuel cells 11 and the cooling assemblies 21 are basically electrically conductive so that when they are stacked as shown, the fuel cells 11 are con-netted in series. In order to connect the stack asset-by 10 to a desired electrical load, current collecting plates 28 are employed at the respective ends of the -12~ 377 stack assembly 10. Positive terminal 29 and negative terminal 30 are connected to the current collecting plates 28 as shown and may be connected to the desired electrical load by any conventional means.
Any suitable fuel cell design can be utilized with the cooling assembly disclosed herein. Figure 2 depicts a cooling assembly 21 together with portions of a representative fuel cell stack shown in more detail.
This figure includes two portions of the stack l~medi-lately surrounding cooling assembly 21. Each of the stack portions includes in this embodiment, a plurality of fuel cell units 11. The stack portion to the right of the cooling assembly 21 yin solid lines) shows de-tail of the various components of the cell 11. The stack portion to the weft of cooling assembly 21 (in dotted lines) is representative of another similar fuel cell. Although the portion of the stack in dotted lines is shown slightly removed from the portion in solid lines for clarity, it is understood that these two portions are in contact with each other and conduit 90 in actual operation to provide good electrical and thermal conductivity through the two portions.
Each fuel cell 11, as depicted in Figure 2 includes a hydrogen gas distribution plate 18 and an oxygen or air distribution plate 20. Arranged interim-dilate between the respective gas distribution plates 18 and 20 are the following elements starting from the hydrogen gas distribution plate 18; anode 31, anode catalyst 32, electrolyte 33, cathode catalyst 34 and cathode 35. These elements 31-35 of the fuel cell 11 may be formed of any suitable material in accordance with conventional practice.
The hydrogen gas distribution plate 18 is arranged in contact with the anode 31. Typically, the anode comprises a carbon material having pores which allow the hydrogen fuel gas to pass through the anode to the anode catalyst 32. The anode 31 is preferably treated with Teflon (polytetrafluoroethylene) to pro-vent the electrolyte 33, which is preferably an immobilized acid, from flooding back into the area of the anode. If flooding were allowed to occur, the electrolyte would plug up the pores in the anode 31 and lessen the flow of hydrogen fuel through the fuel cell 11~ The anode catalyst 32 is preferably a platinum containing catalyst.
The fuel cell 11 is formed of an electrically conductive material, such as a carbon based material, except for the electrolyte layer which does not conduct electrons but does conduct hydrogen ions. The various elements, 18, 31-35, and 20 are compressed together under a positive pressure during the cell assembly pro-cuss. The electrolyte 33 can be made of any suitable material such as phosphoric acid. The acid can be disk pursed in a gel or paste matrix so that it is immobilized and not a free liquid. An exemplary electrolyte matrix could comprise a mixture of phosphoric acid, silicon carbide particles and Teflon particles. The cathode catalyst 34 and the cathode 35 can be formed of materials similar to the anode gala-lust 32 and anode 31.
All of the elements of the fuel cell 11 are arranged after assembly in intimate contact as shown in Figure 2. In order to provide a relatively compact electrically interconnected stack assembly of a plural-fly of adjacent individual fuel cells 11, the bipolar assembly 36 is used to easily connect together adjacent 7t~J

fuel cells 11. The bipolar assembly 36 is comprised of a hydrogen gas distribution plate 18 and an oxygen or air distribution plate 20 with the impervious inter-face layer of plate 37 arranged between them. There-fore, the bipolar assembly 36 is comprised of the ho-drogen gas distribution plate 18 of one cell 11 and the oxygen or air gas distribution plate 20 of the next adjacent cell 11. The interface layer, or plate 37, may comprise an impervious carbon plate or any other conventional interface as maybe desired. The bipolar assembly 36, the plates 18 and 20 and the interface 37 there between are securely connected together as a unit so as to have good electrical conductivity.
In order to facilitate the gas flow in the gas distribution plates 18 and 20, respective channels or grooves 38 or 39 are employed. The grooves 38 in the hydrogen gas distribution plate 18 are arranged orthogonally or perpendicularly to the grooves 39 in the oxygen or air gas distribution plate 20. This at-lows the grooves to be easily connected to respective input and output manifolds 12 and 15, for example, on opposing sides of the cell stack assembly 10. Although grooves within a particular plate, such as plates 18 or 19, are shown as extending in a unidirectional manner in Figure 2, there can be cross-channels made between these grooves to aid in the distribution of the fluidic reactants When such cross-channels are utilized, the primary flow of reactants is still in the direction of the grooves 38 and 39 as shown in Figure 2; that is, in the direction that the reactants flow between the reactant input and collecting manifolds.
The gas distribution plates 18 and 20 supply the respective hydrogen and oxygen or air gases to the -15~ 37~

surfaces of their respective anode 31 or cathode 35.
In order to more evenly distribute the respective gases at the anode 31 or cathode 35 plate surfaces, the gas distribution plates 18 and 20 are preferably formed of S a porous carbon material. This allows the gases to flow through the pores of the plates 18 and 20 between the channels 38 or 39 to provide more uniform gas disk tribution over the face of the respective anode 31 or cathode 35.
At the ends of the stack, as seen in Figure 1, there are current collecting plates 28. These can be made an integral part of the adjacent gas disk tribution plate assembly on the end cell in the stack.
Optionally, an impervious material, such as aluminum, can be placed between the gas distribution plate and current collecting plate or the current collecting plate itself can be made of such a material.
The cooling assembly 21, as shown in Figure 2 and also Figure 4, has at least one coolant conduit means such as conformable tube 90. I've conduit carries coolant through the cooling assembly 21. The cooling assemblies 21 shown in Figures 3-5 include a means for holding the conduit tube 90 in the assemblies including a member or plate 41. The member 41, when assembled I with the conduit tube, conforms at least a portion of the conduit tube into intimate contact with the member 41.
The embodiment of the cooling assembly 21 shown in Figure 2 includes the member 41 as an integral part of the gas distribution assembly 40. The assembly 40 includes hydrogen gas distribution plate 18 and a gas impervious plate 42, which is optional, assembled together with the member 41. A similar assembly is ~2~937'~

shown in dotted lines on the left side of tube 90, ox-crept that the oxygen gas distribution plate 20 is made an integral part of the assembly. The gas distribution plates I & 20 could alternatively be film bonded dip neatly onto member 41.
The improved cooling assembly 21 can take several embodiments, two of which are shown in more detail in Figures I and I. on a first embodiment shown in Figure aye, conduit is a single, continue out tube having one inlet and one outlet for coolant The tube is arranged in a serpentine or similar pattern within members 41 to effect good heat transfer between the members 41 and the tube 90. Although the tube 90 is shown as having its turning bends outside members 41 to sweep back and forth across members 41, the turning bends can alternatively be placed within the members 41. In a second embodiment shown in Figure I, con-dull 90 is actually a plurality of conduit tubes 90 passing through the members 41. Coolant, in this fat--ton embodiment, is brought in and exited through a man-infold comprising conduit feeders or headers 90' so that all conduits 90 can be fed off a single conduit feeder.
The embodiment shown in Figure I is the preferred one. This is the manifold-free arrangement which is simpler and less expensive to manufacture and assemble as compared to the arrangement shown in Figure I. The phrase "manifold-free" is intended as de-scriptive of a heat exchanger in which a coolant is distributed from the portion of the cooling loop which is remote from the fuel cells directly into the cooling assembly so as to provide for serial flow of coolant throughout the cooling assembly. This is in sharp con-tryst to the devices illustrated in the prior art I

whereby coolant is simultaneously distributed from a common manifold into a plurality of parallel, and high-lye localized, channels of the cooling plate which is served by each of these individual unconnected coolant paths.
As can be readily appreciated, the phrase "manifold-free" is not, however, intended as exclusive of a coolant distribution system wherein coolant from a common source is simultaneously distributed into two or more continuous channels or conduits arranged in penal-lot, or otherwise, within the cooling assembly. The coolant flow in this latter type system would not be of the highly localized nature as in the prior art, but rather would and could provide (a) a redundant coolant flow pattern, (b) two or more patterns which are come elementary to one another, or (c) a coolant flow pat-tern in which the direction of flow in one channel is countercurrent to the flow in the other. In any event, this predetermined pattern of distribution of a second continuous channel/conduit would not be highly lo-callused as is dictated by the prior art systems in which a manifold is an essential element for the Somali-Tunis distribution of coolant through such unconnect-Ed localized channels.
In the event a corrosion sensitive material is used in the fabrication of this cooling assembly, it should be effectively isolated from the electrolyte and other hostile chemical agents. In the most preferred embodiments of this invention, the cooling assembly is essentially metal-free; that is, none of the components thereof which are actually or potentially exposed to the corrosive environment of the fuel cell are composed of a corrosive material such as metal. For example, ~L~%~3~7 conduit 90 is preferably a fluorinated hydrocarbon polymer. In fuel cells, the gas distribution plates, such as 18 and 20 in Figure 2, are commonly made of a porous carbon material. To protect the members 41 from corrosion, an improved interracial layer configuration can be used between members 41 and gas distribution plates 18 and 20 to replace gas impervious plate 42.
This interracial configuration is described in cop ending Canadian Patent application Serial No. 437,925, filed on September 29, 1983 entitled "Film-Bonded Fuel Cell Interface Configuration", invented by A. Kaufman and PAL. Terry.
Figures 4 and 5 show further views of the cooling assembly 21. In this embodiment, the cooling assembly 21 consists of conformable coolant conducting means, the tube 90, for carrying coolant through the cooling assembly. Coolant is brought in through one end of the tube 90, the inlet 45, and removed from the assembly at the other end of tube 90, the outlet 46. A
I means similar to that described in Figure 1 is used to circulate the coolant through the cooling assembly.
The coolant assembly is located adjacent a cell or between two adjacent cells in a fuel cell stack as shown in Figure 1. The cooling apparatus includes a means for holding the tube 90, in this embodiment shown as members 41. The member 41 has means therein for holding the tube 90 such as channels 43 shown in Figure 5. When the members 41 are assembled together with the tube 90, at least a portion of the tube 90, and portico-laxly the surface area of the tube, conforms to make intimate contact with the member 41.
; The conduit means, the tube 90, is preferably 'I' I

non-corrodible and metal-free. The tube 90 can be made of any suitable material such as a dielectric material.
One material suitable for this purpose is polyp tetrafluoroethylene (Teflon). Thus, tube 90 can be a S Teflon tube having about a 0.270 inch outside diameter and a 0.015 inch wall thickness. It also is preferably a single, continuous length of tube having one inlet and one outlet to eliminate complex inlet and outlet manifolds. It can be placed in a zig-zag or serpentine configuration with periodic bends therein to sweep it back and forth across the cooling member 41. The bends in tube 90 may occur outside the member 41, as shown in Figure 4, or, alternatively, may occur within the mom-berm In the use of a Teflon tube in cooling asset-bites, some consideration should be given to the pros-sure limits of the tube. A tube such as the type de-scribed immediately above was operated in a fuel cell having a normal operating temperature of about 350-400 F. It was found that the specific tube used might burst if coolant pressures were maintained in the area of 100 psi and above. On the other hand, bursting did not occur when the pressure was maintained in a range up to approximately 50-60 psi.
The areas of the tube 90 which are bent can be made to bend as desired by any suitable means. For instance, the tube 90 can be manufactured to have pro-determined bends in it such as approximately 180 be-fore assembly with member 41. Its shape can conform to the serpentine arrangement it should follow to pass through channels 43 when the cooling assembly is put together The tube 90 can also be made of a straight section of tubing which is bent into the serpentine arrangement during assembly with members 41. To ease the bending process, corrugated segments can be period-icily arranged along its length to allele for short radius bending thereof without crimping or other damage or failure occurring to the tube as it is arranged within the predetermined channel pattern formed by mom-biers 41.
The corrugations are typically less than one or two inches in length and they permit a tight bending radius to allow a tightly-packed, zig-zag geometry that yields a high ratio of heat transfer area to total plate area. The bends can be 180 or some other angle to accommodate the pattern of sweeping the tube back and forth across members 41. One method of creating such corrugations is to apply a hot mandrel to those sections of the tube where the tube is to be bent. The tube material, such as Teflon, is thereby softened by the hot mandrel while also being constrained by the mandrel. The tube wall in this condition takes on a fluted or corrugated) configuration.
Instead of corrugating tube 90 in its portions which are to be bent, other approaches can be used in bending the tube 90 to allow short radii with out the risk of crimping the tube or causing other dam-age to it. One such approach is to provide a support means in the tube -to guard against such damage. The internal support can be placed throughout the length of the tube or only at the locations at which the tube is to be bent. Such a support can be located entirely within the tube's central passageway that carries the coolant, and it can be an additional component asset-bled to the tube.
A preferred type of internal support means is 37~

carried out by inserting wire coils inside the tube at the locations that the tube is to be bent. This is shown in Figures 9-11. Such coils 70 can have a dime-ton slightly less than the inside diameter of the tube 90 and enable the coolant to pass through inside dime-ton of the coil as well as around the coils and between the coils and tube wall. Coils have been found to pro-vent excess crimping in the tube wall when the tube is formed into short radius bends 72. The coils at the bends can be connected to one another by any suitable means such as by a straight section 74 of wire there between. The coils can be inserted into the tub-in by their leading end and fully pushed into the en-tire length of the tube. In this manner, the tight-ly-wrapped coiled portions 70 are located in the areas 72 of the tube to he bent while the straight sections 74 are located along the tube between the bends.
The coils can be made of any suitable Metro-at. For instance, they can be safely made of a metal-fig material such as steel since they are completely located in the tube and, thus, are not exposed to the corrosive materials used in the fuel cell environment.
The approach of using an internal support such as a coil in the tube is believed significantly less expend size to manufacture than the placement of corrugations in the tube material itself as described above. The shape, size and configuration of the internal support can be any suitable one so long as the coolant is at-lowed to flow in the tube as intended.
One manner of forming the metal coil internal support is to start with a length of tightly-wrapped coil or spring stock of an appropriate length and dram-ever and stretch out the coil material in conformance 3~77 with the frequency of bends in the tube. A small, still tightly-wrapped length 70 can be left between each uncoiled section 74 sufficient to accommodate a bend in the tube. The portion of the coil support structure between the bends is then simply a straight uncoiled section of coil material joined to tight-ly-wrapped sections of coil at the bends. In this man-nor, the entire internal support can be made of a sin-glue continuous length of coil material.
The coil pattern; e.g., tightly-wrapped coil sections separated by uncoiled sections, could be man-ufactured by hand with suitable coil stretching and anchoring tools to match the intended configuration of the bends of the tube in the cooling assembly. To pro-vise a coil pattern of greater dimensional control and accuracy, any conveniently available mechanism can be used For instance, an ordinary lathe was used to pro-cuss a length of tightly-wrapped coiled material into a coil pattern with sections of tightly-wrapped coil in-terspersed with uncoiled, stretched out lengths ox coil material. The lathe was used simply as a holding and stretching device and not in its usual machining kapok-fly.
The coil was placed in the chuck of the lathe with a section extending out towards the tools carriage along the lathe bed. A clamp or some other appropriate forcing device was attached to the extending section of the coil, bolt leaving a tightly coiled portion beyond.
The clamp was then moved away from the chuck to stretch jut the coil into a somewhat straight section so as to deform the coin material in that area. This provided a tightly-wrapped coil section separated from the rest of the coil by a relatively unwrapped or straight section , -23- 37~

of coil material. The coil stock was then loosened in the chuck and moved a bit to allow another tight-ly-wrapped coil section thereof to extend beyond the chuck. The clamp was then again fastened on the coil stock having a tightly-wrapped portion between it and the previously stretched out portion to be placed in a bend in the tube. after this section was stretched, the process was repeated until there were enough tight-ly-wrapped coiled sections of coil material between stretched out sections to accommodate all the bends in the tube.
The coil pattern manufactured in this manner as used in a cooling assembly with good results.
There WAS enough space within the inner diameter of the coil so as not to unduly impede the flow of coolant.
For instance, a tube having a nominal size of inch diameter was used, the inside diameter thereof being approximately 0.270 inches. A coil having an outside diameter slightly less than the inside diameter of the tube and inside diameter of approximately 0.190-0.200 inches, made in the above-described manner, was screwed into a length of tube approximately 30 feet long. In using the tube with the coil inserted therein the pros-sure drop across the entire tube length was held to less than 20 psi.
In addition to the coil-type internal sup-port, other types of internal supports can be used.
For instance, an internal cylindrical or tube or member of other configuration could be placed in the coolant tube to ease crimping in the bend areas. Such an in-vernal tube should be rigid so as not to overly no-strict or impede coolant flow yet enable small radius bends in the coolant tube. Internal tubes for this ~2~37t7 purpose can be made out of any suitable material such as plastic or metal.
The channels 43 within members 41 can take any pattern which is suitable for cooling. The contour of the channels 43 may preferably have the shape that approximately conforms with the natural peripheral shape of tubes 90. This is so that when members 41 are placed over the tubes 90, there is an intimate sun-face-to-surface contact between the two components and a minimization of any air spaces or other voids there between Any such gaps that might otherwise exist are closed by the tube conforming to the surface con-tour of the channels 43. The sizing of the channels 43 relative to the sizing of the tubes 9Q may be such that the channel at least slightly compresses the tube pew rougher when the two are assembled into operating pox sessions. Thus, the channel 43 takes on a shape which closely conforms to the tube 90 when the two are asset-bled together.
The cooling assembly I can be made as a sop-crate unit from the individual cells of the fuel cell stack so that members 41 and conduit means 90 can be placed or inserted periodically along the stack to per-mix cooling. Alternatively, members 41 can be made part of or integral with the gas distribution plates of the fuel cell adjacent to the cooling assembly. In this configuration, two such stack portions having an integral member 41 on the end cell can be assembled with the cooling tubes to form a cooling assembly with in the stack.
The function of the straight sections of tube 90 is to effect the transfer of heat from the grooved surfaces 43 in members 41 in which they are nestled ~22~37~

The members 41, containing the grooved surfaces, can be made of any solid, thermally and electrically conductive material, such as any material commonly used in hot fuel cell or battery plates.
The grooves or channels 43 in member 41 can assume any suitable cross-section profile to accomplish the result desired. The channel shape can be formed to conform the tube 90 to its shape and thereby cause in-tomato contact therewith wheniassembled. For instance, the grooves in each member 41 can be cut in an appear-mutely half-round or half-oval cross-section. The sun-faces of the members 41 can then be mechanically pressed together with the grooves over the tube 90.
The surfaces of the members between the grooves can be brought into contact, as shown in Figures 5-6, to are-ate an electrical contact over the areas adjacent to the grooves. The half oval grooves allow the cooling tube 90 to conform easily to the surface area of the grooves 43 and, thus, maintain thermal con-tact without impeding -the electrical contact between members 41 or the flow of coolant within the cooling tube 90.
The shape or contour of channels 43 are sub-jet to manufacturing variances. If non-conformable tubes 90 were used therein and large variances occurred in the dimensions and contour of the channels 43 or the tubes, rigid cooling tubes 90 would not conform to the manufactured shape of channel 43. This would create an air space produced between the tube 90 and groove 43.
This problem is addressed in the background patents mentioned herein. These patents disclose the use of caulking material in the gaps to improve heat transfer.
By using a conformable material for tube 90, such man-ufacturing variance problems would be automatically 3i37~

overcome by the tendency of the tube 90 to conform to t]le-actual contour of channels 43.
Figures I and 6~b), show a semi-circular groove 43 in member 41 and a round coolant tube 90.
If, after assembly of the cooling assembly 21, the coolant tube 90 fits perfectly within the surrounding grooves 43 in the two plates 41 r good surface-to-surface contact occurs between groove 43 and the sun-face of tube 90. This condition is shown in Figure I. However, as shown in Figure I, if groove 43 is of different contour than the natural shape of the coolant tube 90, or vise versa, the tube 90 never the-less conforms to the actual shape of groove 43 since it is conformable. Thus, intimate contact between the tube 90 and plate 41 is still accomplished after the cooling assembly is assembled for operation. The Abe normalities in the surface or contour of groove 43 shown in Figure I are greatly exaggerated for the purposes of clarity of this description.
A preferred embodiment of the grooves 43 is shown in Egress iamb and awoke. These figures which are enlarged schematic illustrations for clarity of de-ascription, are not to any scale and the components therein are not necessarily proportionally sized with accuracy with regard to one another. on this embody-mint, the groove 43, when a cross-section thereof is viewed, takes on the contour or profile of a truncated half circle in each plate. Figures Ahab and awoke are partial cross sections of the cooling assembly similar to that shown in Figure 5. When a conformable material is used for tube 90, a quasi-oval groove such as a truncated half circle, rather than a half oval or half circle has been found to be a very advantageous shape for the grooves 90 in plates 41.
The term "truncated half circle" is described in conjunction with Figures pa and b. Figure pa de-plats the cross section of a circle contour 50 which, when used as is to form the grooves, produces a half circle groove in each plate. The circle 50 has a horn-zontal center line 54 dividing the circle into upper and lower halves. In order to form the truncated half circle groove, a portion 52 of the circle 50 is cut lo away as indicated by the cross hatched section of Fig-use pa. When this is done, the remaining portions of the upper and lower portions of the circle 50 are bounded by upper half portion 56 and truncated edge 57 and lower half portion 58 and truncated edge 59, no-spectively. Each of these forms a truncated half air-ale groove.
The plates 41 of the cooling assembly are assembled as shown in Figure 7b and the upper and lower truncated half circle grooves in each plate 41, when fitted together to provide a channel for the tube (not shown), forJn a truncated circle contour for the chant not. feature of the truncated half circle grooves is that this shape provides room, at the edges 60 of the groove where the two plates 41 interface, for the walls of the tube to expand. Both the oval and truncated circle channel profiles provide much space which is used by the tube during the assembly and operation of the fuel cell. However, the use of the truncated air-ale profile in the channel provides optimum contact between the tubes' outer surface and the surface of the groove while also providing room for expansion, espy-Shelley during operation of the cell.
he interaction of the tube 90 with the ~2~3~77 truncated half circle grooves in each plate is shown in Figures awoke. Figure pa shows the shape of grooves 43 when plates 41 are assembled, but without the tube 90 within the channel provided by grooves 43. The cross section of the tube 90 is, however, superimposed in dotted lines, over the groove 43 to schematically illustrate that the natural shape of tube 90 is altered in this embodiment of the invention when it is asset-bled with plates 41. Figure ;8b shows the tube 90 as-symboled with plates 41. The tube 90 takes the approxi-mate shape shown. The fuel cell has not been placed in operation as yet and, thus, the grooves 43 still leave some room for expansion in the vicinity of edges 60.
Figure 8c shows the grooves 41 and tube 90 lo when the fuel cell has been placed in operation and has heated up to its normal operating temperature. Coolant (not shown) is also flowing through the tube 90 in this view. During the time that the fuel cell is brought up to operating temperature the materials therein expand.
when Teflon is used for the coolant tube 90, the Teflon expands Faster and to a greater degree than the rnateri-at of plates I e.g., a graphite plate. In addition, the coolant flows through the tube 90 with a pressure which tends to push against the interior wall of the tube 90 and expands its outer surface no the vicinity of edges 60.
It can be appreciated, in contrast, that when the grooves 43 are formed by half circles and the chant not for the tube 90 is in the shape of a full circle when the plates 43 are assembled, where is no room for expansion of the tube 90. Thus, if the diameter of tube 90 is approximately the same size as the groove, there is little place for the tube 90 to expand when I

the cell is brought up to operating temperature and/or coolant is passed through the tube. Such expansion could force the plates 41 apart after assembly which would deteriorate the intended performance of the cell.
On the other hand, if the outer size of tube 90 was reduced relative to the groove size to allow adequate expansion room within the groove, the smaller tube would be able to flop around in the plates after assembly whenever the cell is not at full operating temperature. This is disadvantageous in that it may cause damage to the coolant tube, such as during ship-ping and handling of the fuel cell, and little of the tube's periphery would be continuously in place against the surface of grooves 43 at all times.
The sizes of the grooves 43 and outer dime-ton of tube 90 are to be chosen so that as much of the periphery of the tube as practical is in contact with the surface of the groove during operation of the cell.
However, these sizes, necessarily, should not be such 2Q that the expansion of the tube due to the bringing of the cell to operating temperature and the passing coolant through the tube makes the tube force the plates I apart. In sizing these elements, it is prey-enable to leave a slight air gap between the groove edges 60 and the periphery of the tube 90 than risk separation of the plates. A small air gap, such as that shown in Figure 8c, does not appreciably cut down on the passage of heat from the plates 43 to the coolant in the tube 90. It does, however, provide a reasonable manufacturing tolerance for the grooves and tube.
The actual size of the tube and the profile of the groove are intimately related to provide the I
desired surface contact between the two elements.
These factors are dependent on the application also.
The selection of the size of the tube depends, among other things, on the amount of coolant required and the thickness of the tube wall. Once these factors are decided upon and the peripheral size of the tube to be used is determined, the size of the periphery of the tube at cell operating temperature and with coolant therein can be determined. This, in turn, is taken into account along with the plate material used to de-termite the size of the groove to provide optimum con-tact between the groove and tube. The optimum system results when the tube has substantial contact with the groove when the cell is not at operating temperature, as shown in Figure 8b, and almost, but not complete contact with the groove when the cell is at operating temperature, as shown in Figure 8c. In this manner, certain areas of the tube's surface are always in con-tact with the surface of the groove thereby eliminating the possibility of new gaps being generated between the two as the fuel cell is cycled on and off or over a range of operating temperatures.
In the cooling assembly embodiment shown in Figure 5, a polymeric cooling tube 90 is nestled be-tweet two grooved members 41 bonded to one another along two narrow strips adjacent to the edges parallel to the straight sections of the cooling tube. Cooling plate materials suitable for high temperature operation and corrosive environment would include strips of polyethersulfone film sandwiched between and bonded to two grooved members 41 made of graphitized or car-ionized plates. An alternative embodiment is possible which holes the same grooved members 41 together -31~ 3~7 mechanically until after they are assembled into a fuel cell stack of other device in need of cooling. Still another alternative assembly technique is to hold the plates together with the tube in the channel with a bonding medium such as dissolved polyethersulfone which is cured to an appropriate temperature.
The nature of the member 41 need not be con-strained unduly. The shape of groove 43 could be con-strutted so as to deliberately conform the tube 90 into intimate surface contact with groove 43; for instance, an elongated or oval cross-section rather than circus far. Also extremely hard materials need not be used for member 41. The materials used for member 41 in this configuration could be materials which in of them-selves conform or collapse around the tube 90 so that intimate contact is fully reached with the tube. The cooling tube can be pressed into half-oval shape grooves cut out of whatever surface or surfaces are to be cooled. In this case, the cooling assembly 21 could consist merely of a Teflon tube and cooling fluid. The complete absence of metal would give this assembly eon-rosin resistance superior to that of metallic or part-lye metallic devices whether coated or not.
The cooling tubes themselves or the entire cooling assembly, can be made of a non-corroding mate-fiat for use in a fuel cell stack. The primary ad van-taxes of this constriction are an easy and low cost fabrication, total safe-y against corrosion (non-metallic) and total elimination of shunt currents be-tweet cooling plates in the stack without having tithers electrically isolate the cooling plates. The flexibility of the cooling tube also provides good thrill conduction thereto in of itself since it tends ~L22~377 to be pressed up tightly against the surfaces of the grooves in the members 41. The tube assembly is temper-azure tolerant, totally corrosion resistant and totally impervious.
It is to be understood that the above described embodiment of the invention is illustrative only, and that modifications thereof may occur to those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiment as disclosed herein, but is to be limited only as defined by the appended claims.
Reference may be made to Engelhard Corporation's cop ending Canadian Patent Applications Serial Nos.
455,653 and 455,655, both filed June 1, 1984, wherein inventions described in the instant application are claimed.

I. Jo

Claims (25)

WHAT IS CLAIMED IS:

1. Cooling assembly for use in removing heat from a fuel cell having means for circulating coolant through a cooling assembly adjacent the cell, the cooling assembly comprising:

(a) at least one conformable coolant con-duit means for carrying the coolant through the cooling assembly and (b) means for holding the conduit means in the cooling assembly including at least one member which, when assembled with the conduit means, conforms at least a portion of the conduit means into intimate contact with the member.

2. The assembly of Claim 1 wherein the cooling conduit means is non-corrodible.

3. The assembly of Claim 2 wherein the cooling conduit means is metal-free.

4. The assembly of Claim 1 wherein the cooling conduit means is a single continuous tube means having one inlet and one outlet for coolant.

5. The assembly of Claim 4 wherein the coolant tube means is arranged in a serpentine config-uration having periodic bends therein to increase the cooling capacity thereof over an area.

6. The assembly of Claim 5 wherein the cooling tube means is corrugated at its bent portions.

7. The assembly of Claim 1 wherein the coolant conduit means is constructed of a dielectric material.

8. The assembly of Claim 7 wherein the ma-terial is polytetrafluoroethylene.

9. The assembly of Claim 1 wherein the mem-ber has channel means therein to hold the coolant con-duit means.

10. The assembly of Claim 9 wherein the channel means are shaped so as to conform the coolant conduit means to the shape of the channel automatically when the member and coolant conduit means are assem-bled.

11. Cooling apparatus for removing heat from a fuel cell stack having means for circulating coolant through a cooling assembly between two adjacent fuel cell units within the stack, each fuel cell unit having a plurality of laminated plate means which include a termination plate means at the extremity thereof, the cooling assembly comprising:

a) at least one conformable coolant conduit means, and (b) means for holding the conduit means in the cooling assembly including a member which, when assembled with the conduit means, conforms at least a portion of the conduit means into intimate contact with the member, the means for holding the conduit means being integral with and forming part of the termination plate means of the fuel cell units ad-jacent the coolant conduit means.

12. The apparatus of Claim 11 wherein the termination plate means has means for preventing the reactant gases of the fuel cell from reaching the means for holding the conduit means.

13. The apparatus of Claim 11 having more than one conformable coolant conduit means.

14. In a fuel cell stack assembly comprising a plurality of adjacent individual fuel cell units sep-arated from another by a cooling plate wherein coolant is distributed to, and collected from said plate by a manifold positioned in advance of distribution of said coolant through said plate and a second manifold posi-tioned for collection of coolant after is passes through said plate, the improvement comprising:

(a) a manifold-free heat exchanger assembly comprising a termination plate from each of two adjacent fuel cell units which, in combination, create a predetermined channel pattern adapted to intimately cradle a continuous crimp resistant, electrically insulating conduit, said conduit having, at its proximal end, an inlet port for introduction of a coolant fluid, and at its distal end, an outlet port for the discharge of said coolant fluid.

15. The improved heat exchanger of Claim 14 wherein the channel pattern provides a high ratio of heat exchange contact area relative to the total area of the coolant plate.

16. The improved heat exchanger of Claim 14 wherein the channel pattern cradles the conduit in a serpentine arrangement.

17. The heat exchanger of Claim 16 wherein two (2) conduits are arranged parallel to one another within the channels of the termination plates.

18. The improved heat exchanger of Claim 14 wherein the channel pattern cradles the conduit in a circular arrangement.

19. The improved heat exchanger of Claim 11 wherein the channel pattern cradles the conduit in a groove means having a truncated half circle contour.

20. The improved heat exchanger of Claim 14 wherein the crimp resistant conduit of the heat exchanger assembly comprises a flexible, dimensionally stable, chemically inert plastic tubing.

21. The improved heat exchanger of Claim 20 wherein the crimp resistant conduit is provided with corrugated segments to accommodate short radius bending thereof without substantial restriction of coolant flow.

22. The improved heat exchanger of Claim 14 wherein the termination plates are both thermally and electrically conductive.

23. The improved heat exchanger of Claim 22 wherein the termination plate comprises three (3) lamina, a first lamina which is permeable to the pas-sage of hydrogen or oxygen, a second lamina having an essentially flat surface and a pattern of channels formed in the opposing surface, and a third lamina disposed between said first lamina and the flat surface of said second lamina which is impermeable to the transmission of gas and corrosive fluid from the first lamina to the second lamina.

24. The improved heat exchanger of Claim 22 wherein the termination plates are of unitary con-struction.

25. A fuel cell stack assembly comprising a plurality of individual fuel cell units and a mani-fold-free exchanger assembly comprising: a cooling plate separating two such individual units, the cooling plate of such manifold-free assembly having a predetermined channel pattern defined by a termination plate from each of two adjacent individual fuel cell units within the stack, said channel being adapted to intimately cradle a continuous crimp-resistant, elec-trically insulating conduit having at its proximal end an inlet port for the introduction of a coolant fluid, and at its distal end, an outlet port for discharge of such fluid.