Single pump fuel cell system

A single pump fuel cell system is provided that has multiple valves that have selective positioning to control fluidic flow throughout a fuel cell system. One of the valves provides for high and low concentration fuel dosing. Another valve or series of valves controls an unreacted fuel recirculation loop leading from the fuel cell. Another valve or series of valves control condensate collection by the fuel cell system, and allows the purging of the anode recirculation loop. Each of the valves is selectable between various positions to place the fuel cell system in a desired operating mode. A heat exchanger may also be employed to dissipate heat as desired out of the fuel cell system. A concentration sensor can also be employed to aid in achieving a desired fuel concentration within the fuel cell system.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to fuel cell systems, and more particularly, to techniques for managing fluid flow throughout the fuel cell system.

2. Background Information

Fuel cells are devices in which electrochemical reactions are used to generate electricity from fuel and oxygen. A variety of materials may be suited for use as a fuel depending upon the materials chosen for the components of the cell. Organic materials in liquid form, such as methanol are attractive fuel choices due to the their high specific energy.

Fuel cell systems may be divided into “reformer-based” systems (i.e., those in which the fuel is processed in some fashion to extract hydrogen from the fuel before the hydrogen is introduced into the fuel cell system) or “direct oxidation” systems in which the fuel is fed directly into the cell without the need for separate internal or external fuel processing. Many currently available fuel cells are reformer-based. However, because fuel processing is complex and generally requires costly components which occupy significant volume, reformer based systems are more suitable for comparatively high power applications.

Direct oxidation fuel cell systems may be better suited for applications in smaller mobile devices (e.g., mobile phones, handheld and laptop computers), as well as for somewhat larger scale applications. In direct oxidation fuel cells of interest here, a carbonaceous liquid fuel (typically methanol or an aqueous methanol solution) is directly introduced to the anode face of a membrane electrode assembly (MEA).

One example of a direct oxidation fuel cell system is the direct methanol fuel cell or DMFC system. In a DMFC system, a mixture comprised of predominantly methanol or methanol and water is used as fuel (the “fuel mixture”), and oxygen, preferably from ambient air, is used as the oxidant. The fundamental reactions are the anodic oxidation of the fuel mixture into CO2, protons, and electrons; and the cathodic combination of protons, electrons and oxygen into water. The overall reaction may be limited by the failure of either of these reactions to proceed to completion at an acceptable rate, as is discussed further hereinafter.

Typical DMFC systems include a fuel source or reservoir, fluid and effluent management systems, and air management systems, as well as the direct methanol fuel cell (“fuel cell”) itself. As used herein, the term “fuel cell system” shall include systems that include a single fuel cell, multiple fuel cells coupled in a fuel cell array, and/or a fuel cell stack. The fuel cell typically consists of a housing, hardware for current collection, fuel and air distribution, and a membrane electrode assembly (“MEA”) disposed within the housing.

The electricity generating reactions and the current collection in a direct oxidation fuel cell system take place at and within the MEA. In the fuel oxidation process at the anode, the fuel typically reacts with water and the products are protons, electrons and carbon dioxide. Protons from hydrogen in the fuel and in water molecules involved in the anodic reaction migrate through the proton conducting membrane electrolyte (“PCM”), which is non-conductive to the electrons. The electrons travel through an external circuit, which contains the load, and are united with the protons and oxygen molecules in the cathodic reaction. The electronic current through the load provides the electric power from the fuel cell. The invention set forth herein can also be implemented with any fuel cell system with a single pump and multiple valves for managing fluids within a fuel cell system including direct oxidation fuel cell systems and reformer-based systems. The invention can be implemented in fuel cell systems that use a proton exchange medium other than as described herein including but not limited to those systems that implement a silicon or liquid electrolyte.

A typical MEA includes an anode catalyst layer and a cathode catalyst layer sandwiching a centrally disposed PCM. One example of a commercially available PCM is NAFION® (NAFION® is a registered trademark of E.I. Dupont de Nemours and Company), a cation exchange membrane based on polyperflourosulfonic acid, in a variety of thicknesses and equivalent weights. The PCM is typically coated on each face with an electrocatalyst such as platinum, or platinum/ruthenium mixtures or alloy particles. A PCM that is optimal for fuel cell applications possesses a good protonic conductivity and is well-hydrated. On either face of the catalyst coated PCM, the MEA further typically includes a “diffusion layer”. The diffusion layer on the anode side is employed to evenly distribute the liquid or gaseous fuel over the catalyzed anode face of the PCM, while allowing the reaction products, typically gaseous carbon dioxide, to move away from the anode face of the PCM. In the case of the cathode side, a diffusion layer is used to allow a sufficient supply of and a more uniform distribution of gaseous oxygen to the cathode face of the PCM, while minimizing or eliminating the accumulation of liquid, typically water, on the cathode aspect of the PCM. Each of the anode and cathode diffusion layers also assist in the collection and conduction of electric current from the catalyzed PCM to the current collector.

Direct oxidation fuel cell systems for portable electronic devices ideally are as small as possible for a given electrical power and energy requirement. The power output is governed by the rates of the reactions that occur at the anode and the cathode of the fuel cell operated at a given cell voltage. More specifically, the anode process in direct methanol fuel cells, which use acid electrolyte membranes including polyperflourosulfonic acid and other polymeric electrolytes, involves a reaction of one molecule of methanol with one molecule of water. In this process, water molecules are consumed to complete the oxidation of methanol to a final CO2product in a six-electron process, according to the following electrochemical equation:
CH3OH+H2OCO2+6H++6e−1)

Generally, in order to maintain process (1) during fuel cell operation, it is important that fluid flow throughout the fuel cell system is balanced correctly. More specifically, the delivery of fuel at the appropriate concentration is a consideration and it varies with fuel cell operating conditions and ambient conditions. Secondly, water management is an important consideration because water is a reactant in the anodic process at a molecular ratio of 1:1 (water:methanol), so that the supply of water, together with methanol to the anode at an appropriate weight (or volume) ratio is critical for sustaining this process in the fuel cell system. In addition, water is generated at the cathode, and this cathode-generated water can be recirculated to the anode for use in the anodic portion of the process (1). Water is also important for maintaining adequate hydration of the membrane. However, too much water can lead to cathode flooding. Thus, it is desirable to finely control the water balance throughout the fuel cell system.

The present invention is described in conjunction with a stack comprised of more than one fuel cell, and which typically include more than one bipolar plate. However, those skilled in the art will recognize that the precise configuration of the fuel cells may comprise a single fuel cell, or a plurality of fuel cells arranged in a substantially planar system, while remaining within the scope of the present invention.

Some systems that have water management techniques have been known such as active systems which are based on feeding the cell anode with a very diluted (2%) methanol solution, pumping excess amounts of water at the cell cathode back to cell anode and dosing the recirculation liquid with neat methanol stored in a reservoir. Such active systems that include pumping can provide, in principle, maintenance of appropriate water level in the anode by dosing the methanol from a fuel delivery cartridge into a recirculation loop. The loop also receives water that is collected at the cathode and pumped back into the recirculation anode liquid. In this way, a desired water/methanol anode mix can be maintained. However, the multiple pumps that are needed to carry the various solutions throughout the fuel cell can lead to parasitic losses that ultimately result in a less efficiently operating fuel cell system. This has been particularly true in high power applications in which a fuel cell stack is employed.

Another challenge arises in a system containing a fuel cell stack when it is necessary to purge the stack of fluids. This procedure might be performed to change the fuel concentration if a lower or higher than desired concentration has developed within the stack. Other situations in which a stack purge is performed is when the system is to be shutdown for a routine maintenance check or for repairs, where the pressure within the fuel cell is greater than desired, or where it is desirable to put the fuel cell stack in a freeze tolerant state.

Temperature regulation is also a consideration in fuel cell system management. For example, fuel cell operating temperatures must be regulated so that the build up of excess heat is controlled. Sometimes excess heat must be dissipated. Ambient environmental conditions are also a factor in the dissipation of heat, and affect fuel cell performance, particularly in sub-freezing ambient environments.

Based upon all of these considerations, there remains a need for controlling the flow of fluids and controlling temperature in a fuel cell system, and specifically, there is a need for a fuel cell system in which the flow of fuel, water, effluents and other gases can be finely controlled depending upon the desired operating characteristics of the fuel cell system or the ambient environmental conditions. There remains a further need for a system that incorporates this functionality, but that does not require multiple pumps, even when the fuel cell system operates using a fuel cell stack for high power applications.

SUMMARY OF THE INVENTION

The disadvantages of prior techniques are overcome by the present invention, which is a fuel cell system that includes a fuel cell stack, a single pump and a sub-system of valves having selective positions and settings that can be adjusted by an associated microcontroller to control the flow of fluids within the system to thus manage the operation of the fuel cell stack. Several embodiments of the invention are described that include a single pump and multiple three-way valves. For example, fuel delivery from high and low concentration reservoirs is controlled by adjusting the states of the valves to deliver the desired fuel concentration via the pump and valve sub-system to the fuel cell stack, as needed. In other instances, unreacted fuel from the fuel cell stack can be delivered through an anode recirculation loop by adjusting the valves to settings that allow flow through the recirculation loop, for example. Those skilled in the art will recognize that any number of commonly known valves may be used to provide flow control to the invention set forth herein, including three-way valves, two-way valves, solenoid valves, bistable valves, proportional valves or other valves known to those skilled in the art.

In other embodiments of the invention, condensate collection is performed by providing a condensate collection point in fluid communication with a cathode output portion of the fuel cell stack. Condensate is the fluid that accumulates at the cathode plus any liquid generated by the cooling of gaseous exhaust from the fuel cell system, and is typically comprised of water, with a small amount of methanol and other substances also being present in said condensate. Condensate is collected from the cathode aspect of the fuel cell, either within the stack, or by using a separate manifold or other condenser known to those skilled in the art, and delivered to the recirculation loop or low concentration reservoir. The condensate collection can be performed even when the orientation of the fuel cell system is changed. In yet another embodiment, the system includes two condensate collection points in order to improve condensate collection in a variety of orientations and increase the condensate collection capacity. In cases in which the water loss from the fuel cell stack is sufficiently minimized so that the amount of methanol carried is sufficient for an attractive system energy density, condensate collection is not needed in such a system and, in that case, the valves can be set such that condensate collection is not performed, or the water collection subsystem can be omitted entirely from the system.

Several embodiments of the pump and valve sub-system of the present invention also allow for a stack purge state that can be activated upon system shut-down or as a recovery procedure should the fuel concentration in the stack become above or below acceptable limits or where the pressure within the fuel cell is greater than desired, or where it is desirable to put the fuel cell stack in a freeze tolerant state. The stack purge functionality of the system of the present invention benefits overall efficiency, stack control and provides the ability to put the system in a freeze-tolerant state.

A liquid/gas separator can be employed to remove undesired gas bubbles from the fluid conduits in some embodiments of the invention. An optional concentration sensor may be used to determine fuel concentration in the anode recirculation loop. In some embodiments, the system can also be operated without a concentration sensor. A pressure sensor can be included to determine if the recirculation loop is full, partially full or empty. A fuel filter may optionally be used to protect the pump and valves from any debris that may be present in the fuel mixture, the water or other effluents traveling throughout the conduits of the system. The single pump and valve sub-system yields a smaller total system size and lower electrical parasitic loss than for example, a in multi-pump design.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

Fuel Delivery

A first embodiment of the invention is illustrated inFIG. 1A, which depicts a fuel cell system100that includes a fuel cell stack102. The fuel cell stack preferably includes a bipolar fuel cell plate with integrated gas separation, including but not limited to that set forth in commonly owned U.S. patent application Ser. No. 10/384,095, by DeFilippis, for a Bipolar Plate or Assembly having Integrated Gas-Permeable Membrane, which is incorporated herein by reference. Fuel is delivered to the fuel cell stack102, in accordance with the present invention by the single pump104that is coupled to the valve sub-system, which, in the embodiment ofFIG. 1A, includes five valves V1–V5. The valves are controlled by a processor (not shown) that will retrieve information regarding system operation and will issue commands signaling the settings for valves V1–V5, depending upon the current mode of operation of the system. Those skilled in the art will recognize that the system set forth herein can be used with a planar fuel cell array, or a single fuel cell as known to those skilled in the art. The invention set forth herein can also be implemented with any fuel cell system with a single pump and multiple valves for managing fluids within a fuel cell including direct oxidation fuel cell systems and reformer-based systems The invention can be implemented in fuel cell systems that use a proton exchange medium other than as described herein including but not limited to those systems that implement a silicon or liquid electrolyte. The fuel supply for the system is contained in a low concentration reservoir110and a high concentration reservoir112. A first valve, V1, switches between the low concentration fuel in reservoir110and high concentration fuel in the reservoir112. The fuel in the high concentration reservoir112is of a concentration of greater than 5% methanol to 100% (neat) methanol, and the low concentration fuel in the reservoir110typically ranges from about 0% to 50% methanol, but the concentration in the low concentration reservoir may actually be any amount that is of a comparatively lower concentration than that contained in the high concentration reservoir. The actual concentrations in the two reservoirs will depend upon a number of factors such as, for example, the components materials and architecture of the fuel cell system being used in a particular application of the invention. As will be understood by those skilled in the art, at 0% the low concentration reservoir would contain pure water. Those skilled in the art will also recognize that there may be other instances in which only one fuel concentration is needed or desired in a particular application of the invention in which case just one reservoir would be included in the system.

Valve V1is a valve or valve assembly, including but not limited to a three-way valve, that can be positioned to allow low concentration fuel to flow from intake2to outlet1. It is within the scope of the invention that valve V1is positioned in a manner that it normally allows fuel from the low concentration reservoir110. Alternatively, the valve V1can be set to select high concentration fuel from the reservoir112so that there is fluid flow between intake3to outlet1, as illustrated in the diagram. Alternatively, to provide for a predetermined concentration that falls between the low and high values, the valve V1can be pulsed between opening intake positions2and3in such a manner that a fuel mixture is delivered via valve V1.

It may be desirable to fill the low concentration reservoir110with fuel that is of a desired initial concentration. In this case, the empty idle system is filled at startup with fuel directly from the low concentration reservoir110. As will be understood by those skilled in the art during subsequent operation of the fuel cell system, there will be other concentration values that may be desirable in particular applications of the invention depending upon operational requirements, ambient temperature requirements and other conditions that will determine whether certain concentrations are desirable under particular circumstances. Then, those other concentrations can be achieved by adjusting the valves in the accordance with the invention.

Valve V2switches between either dosing fuel from the reservoirs (via V1), or recirculating unreacted fuel from the anode recirculation loop. The terms “anode recirculation loop” and “recirculation loop”, as used herein, shall mean those components that deliver and direct fuel to the stack and remove unreacted fuel from the stack. It may also be necessary to dose fresh fuel (from reservoirs110and/or112) into the anode recirculation loop. InFIG. 1A, valves V2, V3and V4, and elements104,102,118,120and122and the conduits connecting these components comprise the anode recirculation loop116.

More particularly, an anode recirculation loop116receives unreacted fuel from the anode portions of the cells in the fuel cell stack102. The unreacted fuel exits the stack102via the conduit116and is then passed through an optional fuel filter118. The filter118removes any particulates or debris may have been picked up in the stack or through the conduits of the system. The filtered fuel is then sent through a concentration sensor120, if desired. This sensor120can be a separate fuel cell operable to act as a concentration sensor. A number of different elements can be employed for the concentration sensor, or alternatively, fuel cell characteristics can be measured and concentration can be determined from those measurements. The sensor can measure concentration, and this information can then be used to determine the whether the valves are to be set such that a low dose, or a high dose, or a recirculated fuel should be delivered to the fuel cell system. In other instances, the system can run without a concentration sensor, if desired, in a particular application of the invention. Those skilled in the art will recognize that the fuel filter118and concentration sensor120may be disposed anywhere in the recirculation loop depending on the desired form factor or operating characteristics of the fuel cell system.

After passing through the concentration sensor120, if any, the fuel then continues to conduit portion122and thus to intake2of valve V2. As noted herein, valve V2is set in position2, to deliver unreacted fuel from the recirculation loop. Or, valve V2delivers fuel from inlet3for fresh dosing from valve V1, as described herein.

Condensate Collection

The output of valve V2is one of the inputs to valve V3. Valve V3can be positioned to allow this fuel delivery from valve V2, or condensate collection. Condensate is liquid collected from the cathode aspect of the fuel cell, either within the stack, or by using a separate manifold or other condenser known to those skilled in the art, and is typically comprised of water and small amounts of methanol and other substances. More specifically, condensate collection is performed when condensate from the fuel cell102is fed via a conduit or wick130to a collection material132. Collection material132is any material that can be used to transport condensate, and may consist of foams, felts, sponges, woven or nonwoven cloth or sintered metals, though other materials are also within the scope of the invention. The conduit or wick130and collection material132preferably permit condensate collection in any orientation of the fuel cell. The collected condensate is then sent to intake3of valve V3. If condensate collection is desired, valve V3is set to receive condensate via intake3, and allows condensate to flow through to the pump104. The condensate is then delivered via the valve V4through its intake1through its second outlet3through a conduit136to a gas/liquid separator138. The condensate is then delivered into the low concentration reservoir110. In this way, condensate from the stack is retrieved and collected in the low concentration reservoir110for later use.

The gas/liquid separator138may be desirable because the pump104may draw a substantial amount of gas when drawing condensate out of the collection material132. This additional gas effluent is preferably eliminated or reduced prior to entry into the low concentration reservoir110, or used to perform other work within the system. Otherwise, volume in the low concentration reservoir110that is intended for low concentration fuel is instead taken up by a gaseous effluent which is undesirable.

As will be understood by those skilled in the art, and depending on the operating conditions there may instances in which the fuel cell stack requires the addition of water, instead of fuel. This can be accomplished with the valve V4positioned in such a mode that the condensate, which is primarily comprised of water, from the collection material132is delivered to the stack102. In such a case, valve V3is set such that condensate at intake3is delivered into the system and valve V4is set such that its outlet2is open routing the collected condensate through valve V4to the stack102.

To summarize, Table 1 indicates the valve states in various modes of operation of the fuel cell system100.

Referring to Table 1, when it is desired to operate in a recirculation mode, the valves are set as in the first row of the table. Valve V1's state is not determinative of recirculation within the fuel cell, since valve V2will not accept fluid from V1in this state, and valve V1is thus designated as “N/D” within the Table 1. It should be understood that “N/D” throughout the tables herein shall mean that the state of the relevant valve is not determinative in that mode of operation. Valve V2is in a 1-2 state meaning that the intake2is drawing recirculated fuel from the stack102and delivering it through outlet1. Valve V3is also in its 1-2 state, in which recirculated fuel is being drawn from valve V2and delivered to the pump104. Valve V4, in this instance, is also in a 1-2 state such that the recirculated fuel is flowing from the inlet1through outlet2and into the stack. Valve V5is closed.

In a low dose mode, where it is desirable to add lower concentration fuel to the recirculation loop, valve V1is in a 1-2 state so that it is drawing fuel from the low concentration fuel reservoir110, valve V3is in a 1-3 state so that fuel is drawn through valve V2and is sent to valve V3, valve V3is in a 1-2 state so that fuel from the low concentration fuel reservoir is sent to the pump104. Valve V4is again in the 1-2 state so that fuel is delivered to the stack102.

In a high dose mode, where it is desirable to add higher concentration fuel to the recirculation loop, Valve V1is in a 1-3 position so that the high concentration fuel from the reservoir112is drawn to valve V2, and the remaining positions are self-explanatory when referring to Table 1.

In a stack purge mode, where the objective is to clear the stack and the recirculation loop of at least a portion of the fluid contained therein, valve V1is in a 1-3 setting, valve V2is in a 1-2 setting so that the recirculation loop is opened and the stack volume of unreacted methanol is delivered via the conduit116via the valve V2. Then the unreacted fuel is sent via valve V3and then is pumped back around into the low concentration reservoir with valve V5being in an open state. As noted, the stack purge state is preferably activated upon system shutdown or as a recovery procedure, for example, due to a situation where the pressure within the recirculation loop is above desired tolerances. Purging the stack volume into the low concentration reservoir110will increase the overall efficiency of the system as the fuel will not be lost to crossover or evaporation. The stack purge can serve as a recovery procedure should the fuel concentration in the stack, or other operating parameters fall outside of an acceptable range.

Another advantage is that the stack purge functionality is of substantial benefit with respect to overall efficiency, stack control, and the ability to put the system in a freeze-tolerant state. In other words, if the application device and associated fuel cell system are to be used in a subfreezing ambient environment, it may be best to purge the stack when the application device is not being powered by the fuel cell system in order to preserve the fuel and put the system in a freeze-tolerant state.

It is noted that the function of valve5is to prevent ambient gases from entering the gas/liquid separator138(FIG. 1A) and going into the low concentration reservoir110. For example, when a low dose is being performed, valve V1accepts lower concentration fuel via intake2and fuel is drawn from the low concentration reservoir110. If valve V5is not closed, air could instead be pulled from the gas/liquid separator138. Thus, valve5is closed when a low dose is performed. The only time that valve5is opened is when fluid is to be passed through it.

An optional pressure sensor140may be used to determine if the recirculation loop116is full, partially full or empty, and whether or not there is appropriate pressure within the system. The optional concentration sensor120, as noted, is used to determine the fuel concentration in the recirculation loop if desired in a particular application of the invention. As noted, the system can be operated without the concentration sensor cell120.

FIG. 1Billustrates another embodiment of the invention in which the single pump fuel cell system includes a reformer150, which reforms the unreformed fuel from V4and feeds reformed fuel consisting primarily of hydrogen into a suitable fuel cell stack152. A condensate which is comprised of the products of the reaction used to reform the unreformed fuel from V4, and which typically include water, carbon monoxide, carbon dioxide and trace gases is sent via the conduit140to the collection material132. Water from stack152is delivered to the collection material132via conduit130. Gas separation, if needed, can be performed using methods known to those skilled in the art. Any methanol that is not reformed or turned into condensate is delivered into the recirculation loop116. In this case, the recirculation loop116includes the reformer150, but does not include the stack152.

FIG. 2illustrates another embodiment of the invention in which like components have the same reference characters as inFIG. 1. InFIG. 2, however, the gas separator238is located between the pump104and valve V4. The gas/liquid separator238(which is identical to gas/liquid separator138inFIG. 1A) eliminates or reduces any gas bubbles that may have been picked up when condensate is drawn by valve V3from the collection material132. This gas is separated out so that when valve V4switches between sending fluid to the stack102or to the low concentration reservoir110, any gaseous effluent has been removed. The embodiment ofFIG. 2is a more simplified system, as compared to the embodiment set forth inFIG. 1, because valve V5is eliminated. However, in order to eliminate valve5, it is assumed that the dosage is being mixed well by discrete additions of fuel and that there is not a large ripple of high concentration fuel that is going to pass through separator238. The risk is that the high concentration fuel tends to “wet out” gas/liquid separators, rendering them less effective than desired. Thus, the embodiment ofFIG. 2is preferably employed when mixing is performed adequately, or where the gas/liquid separator does not otherwise “wet out” with prolonged exposure to the fuel that is being deployed.

Table 2 below indicates the valve settings for each particular mode for the embodiment ofFIG. 2. Table 2 has the same values as Table 1, except that valve5has been eliminated.

In an alternative embodiment (not shown), it may be desirable to be able to purge the anode recirculation loop in a system where condensate is not collected. In that embodiment, conduit130, collection material132, and valve V3, as well as all conduits connecting them, may be eliminated.

Another embodiment of the invention is illustrated inFIG. 3, which shows fuel cell system300. The components illustrated inFIG. 3, which correspond with those ofFIGS. 1 and 2, have the same reference characters as in the other figures. The fuel cell system300ofFIG. 3is a simplified system for use when there is no need for water collection. In that instance, the collection material132and valve V3are not necessary, and can be eliminated to simplify the system. In addition, in this system valve V4is not necessary because there is no need to recirculate condensate back into the low concentration reservoir110. For example, if recirculation is desired, the status of valve V1is not relevant as valve V2will be in a state in which intake2is opened to deliver the effluent recirculated from the stack102, rather than accepting fuel from V1. A low dose setting involves valve V1at a 1-2 state such that the intake2draws low concentration fuel from the reservoir110and sends it to valve V2. For a high dose valve V1is in state 1-3 so that its inlet3draws high concentration fuel from the reservoir112and sends it through valve V1, through valve V2, via the pump104, into the stack102. The settings are summarized in Table 3.

Accordingly, the system300ofFIG. 3can be employed when the water loss rate from the stack is improved such that additional water is not needed to replace water loss from the stack.

Referring now toFIG. 4, the system400ofFIG. 4is a single pump six-valve fluidic system that includes an optional heat exchanger. As noted, with respect to the other figures, components that are the same or similar to those set forth in the earlier figures have the same reference characters and components that have been added or relocated are assigned new reference characters.

FIG. 4is similar to system100inFIG. 1A, but contains a heat exchanger402and associated fluid conduits and controls. It is often necessary or desirable to have controlled thermal management of the system. Heat is generated by the fuel cells in the stack, the electronics utilized to control the system, and possibly by the application to which power is being provided (not shown). A heat exchanger402can be employed that receives a fluid via valve V6. When Valve V6is in the 1-3 state, the heat exchanger is part of the recirculation loop, and when Valve V6is in the 1-2 state, the recirculation loop does not include heat exchanger402. Valve V6has an intake1and outlet2-3. In the 1-3 state, valve V6delivers unreacted fuel from the stack through heat exchanger402, which cools the fluid and returns it back to the conduit404. It then continues within the recirculation loop including416, passes through the fuel filter118and the concentration sensor120in the manners described hereinbefore. Alternatively, when heat dissipation is not needed, V6is actuated in such a manner that unreacted fuel enters the intake1, bypasses the heat exchanger402, and continues within the recirculation loop including416directly through outlet2. The heat exchanger402can be one of common design, and which uses methods well known to those skilled in the art, including a series of tubes which is exposed to the ambient environment. It is further possible to have active airflow to assist in the removal of heat from the heat exchanger via a fan or other air moving device, which may be a discrete component or integrated into heat exchanger402. The heat exchanger402and/or Valve V6can be thermally actuated, and valve V6can be any valve known to those skilled in the art. For a further simplified system, the valve V6can be eliminated, and the recirculation fluid is always sent through the heat exchanger402, but optional fan could be turned on and off in response to operating conditions to either employ active heat exchange techniques or to simply deliver the fuel from the stack102to the recirculation loop416. With respect toFIG. 4, V6and heat exchanger402are shown as being in close communication with stack102, however, they can be disposed anywhere in the recirculation loop416.

Table 4 illustrates the valve states for the various modes of operation for the system400ofFIG. 4. For example, recirculation without cooling would involve valve V1in a its 1-2 state. Valve V2would be in a 1-2 state so that it is drawing recirculated fuel via the recirculation loop416. Valve V3is then in a 1-2 state sending this recirculated fuel to the pump104. Valve V4is in its 1-2 state in which the recirculated fuel is sent to the stack102. Valve V5is closed because water collection is not being performed. Valve V6is in a 1-2 state so that the recirculated fuel from the stack102is not being sent through the optional heat exchanger 1-2.

In comparison, the “recirculation with cooling” mode involves valve V6is in a 1-3 state so that the intake1allows recirculated fuel from the stack to pass through the outlet3into the optional heat exchanger402, which cools it before it continues through the recirculation loop416. The other states of the Table 4 are similar to those described with respect to the earlier figures. It is noted that in the stack purge, valve V6is in the 1-3 state in which cooling is performed as the stack is being purged.

The embodiment illustrated inFIG. 5is a system500that includes 7 valves and the optional heat exchanger402, but also includes multiple collection points for condensate. This allows for additional condensate collection capacity and improves orientation independence of the device.

More specifically, system500ofFIG. 5includes a first collection material532and a second area of a collection material534. Valve V7switches between the condensate collection points532and534as necessary or desired in the system500and delivers the collected condensate to valve V3, in a water collection mode. Alternatively, there may be two condensate collection points in communication with V7, which is in further communication with a single collection material (not shown). This is summarized in the Table 5 below, which indicates states that are similar to those described herein with reference to the other figures. However, in the condensate collection mode, valve V7is toggled between a 1-2 state or a 1-3 state and thus condensate as collected from the desired point, is delivered to the valve V3that delivers it to the pump104. Valve V4then sends the condensate to valve V5for delivery to the low concentration fuel reservoir110. Not only does this system ofFIG. 5improve condensate collection in different orientations, but additional collection points may also be desirable in order to increase the condensate collection capacity should one collection point prove to be insufficient to support the system needs. This embodiment may be employed without the heat exchanger402and valve V6, and associated conduits.

As described herein valves V1–V7may be solenoid valves that have energized and de-energized states or three-way valves to minimize part count of the system. Other types of valves can be used similarly while remaining within the scope of the present invention. It should be understood that the embodiments illustrated herein allow for the use of a single pump in a fuel cell system that enables a smaller total system size and lower electrical parasitic loss than a multi-pump design.

The optional heat exchanger could be also employed to deliver heat to other portions of the fuel cell system if desired in a particular application of the invention. The systems shown inFIGS. 4 and 5allow improved control of the stack temperature by allowing excess waste heat to be dissipated when required. The system ofFIG. 5allows for additional condensate collection capacity.

Although specific embodiments of the invention are illustrated in the Figures, the invention can be readily adapted in such a manner so as to include or omit features and components related to the following functionality: condensate collection, active thermal management and/or purging of the recirculation loop.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details can be made without departing from the spirit and scope of the invention. Furthermore, the terms and expressions that have been employed herein are used as terms of description and not of limitation. There is not intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof. It is recognized that various modifications are possible within the scope of the invention claimed.