Abstract:
A manifold for a fuel cell system comprises a plurality of first ports for connecting to fuel cell peripherals; a plurality of ports for connecting to a fuel cell stack; and a plurality of fluid passages within the manifold in communication with the said plurality of ports connecting to the fuel cell peripherals and with the first and second ports for providing, communication of fluids between the fuel cell stack and fuel cell peripherals. The manifold provides a higher degree of system integration, considerably reduced piping, fittings and associated hardware and hence generally reduces the size and weight of the fuel cell system. Thermal-fluid related system losses are also minimized.

Description:
FIELD OF INVENTION 
   This invention relates to a manifold for a fuel cell system, and more particularly relates to a manifold for mounting peripherals and piping to fuel cell stacks. 
   BACKGROUND TECHNOLOGY 
   Fuel cells have been proposed as a clean, efficient and environmentally friendly source of power which can be utilized for various applications. A fuel cell is an electrochemical device that produces an electromotive force by bringing the fuel (typically hydrogen) and an oxidant (typically air) into contact with two suitable electrodes and an electrolyte. A fuel, such as hydrogen gas, for example, is introduced at a first electrode, i.e. anode where it reacts electrochemically in the presence of the electrolyte to produce electrons and cations. The electrons are conducted from the anode to a second electrode, i.e. cathode through an electrical circuit connected between the electrodes. Cations pass through the electrolyte to the cathode. Simultaneously, an oxidant, such as oxygen gas or air is introduced to the cathode where the oxidant reacts electrochemically in presence of the electrolyte and catalyst, producing anions and consuming the electrons circulated through the electrical circuit; the cations are consumed at the second electrode. The anions formed at the second electrode or cathode react with the cations to form a reaction product. The anode may alternatively be referred to as a fuel or oxidizing electrode, and the cathode may alternatively be referred to as an oxidant or reducing electrode. The half-cell reactions at the two electrodes are, respectively, as follows:
 
H2 — 2H++2e−
 
1/2O 2 +2H++2e−_H 2 O
 
   The external electrical circuit withdraws electrical current and thus receives electrical power from the fuel cell. The overall fuel cell reaction produces electrical energy as shown by the sum of the separate half-cell reactions written above. Water and heat are typical by-products of the reaction. Accordingly, the use of fuel cells in power generation offers potential environmental benefits compared with power generation from combustion of fossil fuels or by nuclear activity. Some examples of applications are distributed residential power generation and automotive power systems to reduce emission levels. 
   In practice, fuel cells are not operated as single units. Rather fuel cells are connected in series, stacked one on top of the other, or placed side-by-side, to form what is usually referred to as a fuel cell stack. The fuel, oxidant and coolant are supplied through respective delivery subsystems to the fuel cell stack. Also within the stack are current collectors, cell-to-cell seals and insulation, with required piping and instrumentation provided externally to the fuel cell stack. 
   In conventional fuel cell systems, extensive piping and plumbing work is required since in operation fuel cell systems rely on peripheral preconditioning devices for optimum or even proper operation. For example, in the situation where the fuel gas of the fuel cell stack is not pure hydrogen, but rather hydrogen containing material, e.g. natural gas a reformer is usually required in the fuel delivery subsystem for reforming the hydrogen containing material to provide pure hydrogen to the fuel cell stack. Moreover, in the situation where the electrolyte of the fuel cell is a proton exchange membrane, since the membrane requires a wet surface to facilitate the conduction of protons from the anode to the cathode, and otherwise to maintain the membranes electrically conductive, a humidifier is usually required to humidify the fuel or oxidant gas before it comes into the fuel cell stack. In addition, most conventional fuel cell systems utilize several heat exchangers in gas and coolant delivery subsystems to dissipate the heat generated in the fuel cell reaction, provide coolant to the fuel cell stack, and heat or cool the process gases. In some applications, the process gases or coolant may need to be pressurized before entering the fuel cell stack, and therefore, compressors and pumps may be added to the delivery subsystems. 
   These peripheral devices require extensive piping and associated hardware, all of which leads to poor system efficiency. This results from significant energy losses occurring in lines or conduits as more power must be made available for supplementary devices such as pumps, fans, saturators etc, and hence the parasitic load is increased. In addition, hoses, pipes, valves, switches and other fittings increase the overall weight and size of the fuel cell system and complicate the commercial application thereof. This complexity poses problems in many applications, such as vehicular applications, where it is desirable that the piping and weight of the fuel cell system be minimized since strict size constraints exist. Furthermore, in vehicular applications, it is desirable for the fuel cell system to have good transient thermo-fluid response characteristics. This requirement makes it even more difficult to apply conventional fuel cell systems to vehicular applications, where relatively long pathways through hoses, valves, etc., can prevent rapid transient response characteristics being obtained. 
   Various efforts have been made to simplify the piping of fuel cell systems and hence reduce the size and weight thereof. However, to the applicants&#39; knowledge, there has yet to be disclosed any fuel cell system that solves this fundamental problem. 
   SUMMARY OF THE INVENTION 
   In accordance with a first aspect of the present invention, there is provided a manifold for a fuel cell system, comprising:
         a manifold body;   a plurality of first ports in the manifold body, for connecting to fuel cell peripherals;   a plurality of second ports in the manifold body, for connecting to a fuel cell stack comprising a plurality of fuel cells and having inlets and outlets for connection to the second ports; and   a plurality of fluid passages within the manifold providing communication between respective ones of the first ports and respective ones of the second ports, wherein at least one first port is offset from the respective second port and is connected to said respective second port by a passage extending transversely within the manifold body, whereby, in use, the fluid passages communicate fluids between the fuel cell stack and fuel cell peripherals.       

   Preferably, the body comprises a plurality of layers of plates juxtaposed together, wherein each layer has a plurality of ports and a plurality of fluid passages providing communication between the respective ones of the plurality of ports of the corresponding layer, wherein complementary pairs of ports align and face one another and at least one layer forms an external layer including at least one said first and second ports. 
   Advantageously, the manifold body comprises:
         a first plate layer, including said plurality of first ports;   a second plate layer, including said plurality of second ports;   a third plate layer sandwiched between the first and second plate layers including, a plurality of third ports and a plurality of fluid passages therein, with said plurality of fluid passages providing communication between said third ports and with at least one of said fluid passages extending transversely within the third plate layer, and with the third ports being aligned and in communication with respective ones of the said first and second ports.       

   Preferably, the third plate layer, further comprises a plurality of plate layers, each of which has a plurality of ports and a plurality of fluid passages providing communication between the ports thereof, with said plurality of ports of each plate layer of the third plate layer being aligned with and in communication with the corresponding ports of an adjacent plate layer. 
   Alternatively, the manifold body can comprise:
         a first plate layer, including said plurality of first ports;   a second plate layer, including said plurality of second ports; a plurality of third ports; and a plurality of fluid passages that communicate between said second and third ports; wherein the first ports extend through the first plate layer and each first port has two open ends, one being for a fuel cell peripheral and the other being aligned with and in communication with a corresponding third port.       

   According to the present invention, the manifold for a fuel cell system can be formed by pressing the said plates one on top of the other. The fluid passages in the manifold can be formed using the method of melting, etching, or milling. The manifold of the present invention can be manufactured with readily available, cheap materials with adequate heat durability or fluid resistance, including but not limited to, polymer, GE noryl, EN265 and aluminum. Preferably, sealing is provided between each of the said plates. Further sealing means are preferably provided around the said ports for connecting to fuel cell peripherals and said ports for connecting to a fuel cell stack. Advantageously, the manifold for a fuel cell system according to the present invention further includes coolant fluid passages for the manifold to enhance thermal management of the system. 
   In accordance with another aspect of the present invention, there is provided a fuel cell system comprising, a fuel cell stack including:
         a plurality of fuel cells and having a cathode inlet and a cathode outlet for an oxide, an anode inlet and an anode outlet for a fuel gas, and a coolant inlet and a coolant outlet;   a manifold having ports connected to the cathode inlet, the cathode outlet, the anode inlet, the anode outlet, the coolant inlet, and the coolant outlet of the fuel cell stack;   a plurality of additional ports in the manifold including at least a port for an oxidant inlet, a port for a fuel gas inlet, and inlet and outlet ports for the coolant; and   a plurality of peripheral devices connected to the additional ports of the manifold.       

   The manifold according to the present invention provides an interface between the fuel cell stack and heat exchangers, pump, fans, compressors, reformers, humidifiers etc, as well as process gases and coolant delivery components. This configuration can provide a higher degree of system integration, and hence offers a number of advantages. First, flow channels embossed into the manifold eliminate the need for bulky hoses and fittings and therefore the size and weight of the fuel cell system is considerably reduced. Moreover, thermodynamic and fluid flow related losses in the system are reduced, thus improving system efficiency, response to transient conditions and system control. In addition, since piping is minimized, control and maintenance of the system is simplified. Utilizing the invention minimizes all of the aforementioned difficulties because the compact nature of the manifold allows fuel cell systems to be developed for applications where strict size and weight constraints exist. 
   Fuel cell systems incorporating the present invention are inherently modular, and thus can be easily reproduced in large quantities at dedicated production facilities. Furthermore, the manifold of the present invention can be manufactured using currently available, inexpensive materials, which makes it suitable for manufacturing and mass production. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made to the accompanying drawings, which show, by way of example, preferred embodiments of the present invention. The features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof. 
       FIG. 1  is an exploded perspective view illustrating a manifold for a fuel cell system according to a first embodiment of the present invention, in which fluid loops are shown; 
       FIG. 2   a  is a front elevational view of a front plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 2   b  is a side elevational view of the front plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 3   a  is a front elevational view of a middle plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 3   b  is a back elevational view of the middle plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 3   c  is a left side elevational view of the middle plate of the manifold for a fuel cell system according to the first embodiment of the present invention, in which some of the fluid passages are shown; 
       FIG. 3   d  is a right side elevational view of the middle plate of the manifold for a fuel cell system according to the first embodiment of the present invention, in which some of the fluid passages are shown; 
       FIG. 4   a  is a front elevational view of a back plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 4   b  is a side elevational view of the back plate of the manifold for a fuel cell system according to the first embodiment of the present invention; 
       FIG. 5  is an exploded perspective view illustrating a manifold for a fuel cell system according to a second embodiment of the present invention, in which fluid loops are shown; 
       FIG. 6   a  is a front elevational view of a front plate of the manifold for a fuel cell system according to the second embodiment of the present invention; 
       FIG. 6   b  is a side elevational view of the front plate of the manifold for a fuel cell system according to the second embodiment of the present invention; 
       FIG. 7   a  is a front elevational view of a first middle plate of the manifold for a fuel cell system according to the second embodiment of the present invention; 
       FIG. 7   b  is a back elevational view of the first middle plate of the manifold for a fuel cell system according to the second embodiment of the present invention; 
       FIG. 7   c  is a side elevational view of the first middle plate of the manifold for a fuel cell system according to the second embodiment of the present invention; 
       FIG. 8   a  is a front elevational view of a second middle plate of the manifold a for fuel cell system according to the second embodiment of the present invention; 
       FIG. 8   b  is a side elevational view of the second middle plate of the manifold a for fuel cell system according to the second embodiment of the present invention; 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Now referring to  FIG. 1 , in which the basic arrangement of manifold assembly  70  according to the first embodiment of the present invention is shown, the manifold assembly  70  comprises of three individual plates.  FIG. 1  also shows a fuel cell stack  10  having three inlets and three outlets, specifically, an anode inlet  11  for fuel gas, typically hydrogen, an anode outlet  14  for the fuel gas, a cathode inlet  12  for oxidant gas, typically oxygen or air, a cathode outlet  13  for oxidant gas, a coolant inlet  16  and a coolant outlet  15 . It should be appreciated that the fuel cells in the fuel cell stack can be any type of fuel cell, such as, proton exchange membrane fuel cells, solid oxide fuel cells, direct methanol fuel cells, etc. The type of the fuel cells will not affect the design of the manifold according to the present invention. 
   In this embodiment, the manifold assembly  70  has three plate layers, namely a front plate  60 , a middle plate  40  and a back plate  20 . The back plate  20  is formed so that the fuel cell stack  10  can abut against it. The back plate  20  has six ports  21  provided therein, as can be best seen in  FIGS. 4   a  and  4   b . In this embodiment, the ports are in the form of six through holes  21  to  26  which penetrate the back plate  20  in the direction of thickness. For illustration only, in this embodiment, the six through holes  21  to  26  are provided in two rows each having three holes arranged in alignment in vertical direction. Each of the three holes in each row is in alignment with the corresponding hole in the other row in horizontal direction. These through holes  21  to  26  are aligned with and adapted to connect to the three inlets  11 ,  12 ,  16  and the three outlets  13 ,  14 ,  15  of the fuel cell stack  10  so that the fuel cell stack  10  can be mounted on the back plate  20  and the process gases and coolant can be supplied to the fuel cell stack  10  via the fluid passages that will be described below. Conventional sealing and clamping devices are utilized around the six through holes  21  to  26  to prevent leakage of process gases and coolant. It should be mentioned that in this embodiment, for illustration purpose only, the fuel cell stack  1  has three ports near one end and the other three ports near the other end of the stack, which is a typical arrangement in fuel cell stacks, particularly proton exchange membrane fuel cell stacks. Therefore the back plate  20  is configured accordingly. The actual number and arrangement of through holes can be different, and the back plate  20  would then be modified accordingly. 
   As shown in  FIG. 1 , the front plate  60  is adapted for fuel cell peripherals to mount on it, such as two humidifiers  110 ,  120  and three heat exchangers  111 ,  112  and  113 . Therefore, in this embodiment, fuel cell stack  10  and fuel cell peripherals are mounted on opposite sides of the manifold assembly  70 . It should be understood that the manifold plate can be adapted for mounting peripherals and the fuel cell stack on a same side thereof. The detailed structure of the front plate  60  is shown in  FIGS. 2   a  and  2   b.  The front plate  60  is provided with a plurality of ports  61 . In this embodiment, the ports are in the form of through holes  61   a  to  61   s,  which penetrate the front plate  60  in the direction of thickness. In practice the number and arrangement of the ports  61  can be varied as needed. For illustration purposes, in  FIGS. 2   a  and  2   b,  eighteen through holes  61   a  to  61   s  (with references  61   l  and  61   o  not being used for clarity) and  61   a ′,  61   b ′ are shown, with those adapted to connect to one peripheral being indicated with a rectangle in dotted lines. Some of the fuel cell peripherals, as shown in this embodiment, are the humidifiers  110 ,  120  and the heat exchangers  111 ,  112  and  113 , and these are mounted on the front plate  60  so that fluids, gases or other media can be exchanged between the fuel cell stack  10  and the peripherals via internal passages of the manifold assembly  70  as will be described in detail below; the humidifier  110  provides a first or fuel gas humidifier and the humidifier  120  provides a second or oxidant humidifier. In this embodiment, through holes  61   a ,  61   b ,  61   a ′ and  61   b  ′ are used to connect to the a first heat exchanger  113 , through holes  61   c  to  61   f  are used to connect to a first humidifier  110 , through holes in  61   g,    61   h,    61   j  and  61   k  are used to connect to a second heat exchanger  111 , through holes  61   m  and  61   n  are used to connect to the third heat exchanger  112 , and the through holes  61   p  to  61   s  are used to connect to a second humidifier  120 . As required, conventional sealing and clamping devices, such as O-rings are provided around the through holes to prevent leakage. Although in  FIGS. 2   a  and  2   b,  the through holes are shown in a particular alignment arrangement, the actual arrangement may be different considering other factors in the situation, such as the size of the fuel cell peripherals or the alignment with ports in the middle plate  40 . The arrangement of the through holes can be varied, as is required for a particular situation. 
   Referring to  FIGS. 3   a  to  3   d,  the middle plate  40  has a plurality of ports and fluid passages provided. The fluid passages can be formed by etching or milling while the ports can be formed by boring or drilling. For simplicity, in FIG.  1  and  FIGS. 3A-3D , not all the fluid passages are shown. In general only fluid passages associated with ports visible in the plane of each figure are indicated. Additionally, fluid passages are indicated in two different ways: fluid passages that are internal or below the plane of each figure indicated by dotted lines; fluid passages that are formed as open channels in one of the front and back surfaces of the middle plate  40  are indicated by solid lines, and these channels are then closed by one of the front and back plates  20 ,  60 . Thus, the various fluid passages extend transversely to connect ports that are offset from one another. Alternatively, the various plates  20 ,  40 , and  60  can be formed by molding or casting. As shown in  FIG. 1 , a complete coolant loop is shown. Coolant is supplied from a coolant source and enters the middle plate  40  through a port  41   a  provided on the side surface of the middle plate  40 , and providing a coolant inlet of the manifold assembly  70 . Then the coolant flows along a fluid passage  411  inside the middle plate  40  to a port  41   b.  As can be best seen in  FIG. 3   b,  the port  41   b  is a port provided on the surface of the middle plate  40  facing the back plate  20  that communicates with the fluid passages  411  and  412 . The fluid passage  412  is provided as an open channel on the surface of the middle plate  40  facing the back plate  20 . Therefore, the coolant flows from the port  41   b  along the fluid passage  412  to the port  41   c,  which is in alignment with the port  22  of the back plate  20 . The ports  41   b, c  are simply end portions of the passage  412  that align with the ports in the back plate  20 . These passages  411 ,  412  provide a coolant inlet path. The coolant flows through the port  22  and coolant inlet  16  into the fuel cell stack  10 . Then the coolant leaves the fuel cell stack  10  through the coolant outlet  13  after flowing through the internal coolant passages of the stack. The coolant flows through the port  25  of the back plate  20 , which is in alignment with the coolant outlet  13  and a port  42   a  provided on the surface of the middle plate  40  facing the back plate  20 . Then the coolant continues to flow into the fluid passage  421  through the port  42   a  to a port  42   b  provided on the surface of the middle plate  40  facing the front plate  60 . Port  42   a  and fluid passage  421  can be seen in FIG.  1 . From port  42   b,  the coolant flows along two separated fluid passages  422  and  423 . The two fluid passages  422  and  423  are provided as open channels on the surface of middle plate  40 , and these two streams of coolant will be described separately. 
   The first stream of the coolant flows along the fluid passage  422  to a port  42   c , which is in alignment with port  61   g  of the front plate  60 . The port  61   g  in turn aligns with an inlet  111   a  of the second or oxidant heat exchanger  111 . This stream of coolant flows through the port  61   g  and the inlet  111   a  into the second or oxidant heat exchanger  111 . The first stream of coolant then leaves the second or oxidant heat exchanger  111  through an outlet  111   b  thereof. Then the coolant flows through the port  61   k  of the front plate  60  and a port  42   f  of the middle plate  40 , both in alignment with the outlet  111   b.  Then the first stream of the coolant flows along a fluid passage  424  to a port  42   e.    
   The second stream of the coolant flows from port  42   b  along the fluid passage  423  to the port  42   d  which is in alignment with the port  61   m  of front plate  60 . The port  61   m  in turn aligns with an inlet  112   a  of the third heat exchanger  112 . Then this stream of coolant flows through the port  61  m and inlet  112   a  and enters the third heat exchanger  112 . The second stream of coolant leaves the third heat exchanger  112  through the outlet  112   b  thereof. Then the coolant continues to flow through the port  61   n  of the front plate  60  and the port  42   g  of the middle plate  40 , both in alignment with an outlet  112   b  of the third heat exchanger  112 . Then the second stream of the coolant flows along a fluid passage  425  to the port  42   e . The port  42   e  is provided on the surface of the middle plate  40  and extends into the inside of the middle plate  40 , with passages  424 ,  425  being open channels and the port  42   e  being a common end of the channels  424 ,  425 . The confluence of the first and second streams of coolant flows from the port  42   e  along an internal fluid passage  426  inside of the middle plate  40  to a port  42   h  from which it returns to the coolant pump  114  and then back to the coolant source. The passages  421 - 426  provide a return path for the coolant and the port  42   h  provides a coolant outlet for the manifold assembly  70 . 
   Now the loop of the oxidant, typically air will be described. Referring to  FIG. 1 , ambient air is usually drawn through an air filter  115  and then an air compressor  116  before it enters the middle plate  40 . The compressed air enters the middle plate  40  through a port  43   a  provided on the side surface thereof and flows along a fluid passage  431  inside of the middle plate  40  to a port  43   b . The port  43   b  is provided on the surface of the middle plate  40  facing the front plate  60  and communicates with the internal fluid passages  431  and a fluid passage  432 . The fluid passage  432  is provided as an open channel on the surface of the middle plate  40  facing the front plate  60 . Therefore, the air flows from the port  43   b  along the fluid passage  432  to a port  43   c  which is in alignment with the port  61   h  of the front plate  60  and hence an inlet  111   c  of the second or oxidant heat exchanger  111 . Then the air flows into the second or oxidant heat exchanger  111  through the port  43   c  and the inlet  111   c . After exchanging heat in the heat exchanger  111 , the air leaves the second heat exchanger  111  through an outlet  111   d  and continues to flow through the port  61   j  of the front plate  60  to a port  43   d  of the middle plate  40 . The ports  43   d ,  61   j  and the outlet  111   d  are in alignment with each other. Then the air flows from the port  43   d  along a fluid passage  433  to a port  43   e  which is provided on the surface of the middle plate  40  facing the back plate  20 . The air flows from the port  43   e  along a fluid passage  434  provided on the surface of the middle plate  40  facing the back plate  20  to a port  43   f . The port  43   f  is in alignment with the port  21  on the back plate  20  and hence the cathode inlet  12  of the fuel cell stack  10 . Therefore the air flows from the port  43   f  through the port  21  and the inlet  12  into the fuel cell stack for reaction. 
   The exhaust air flows out of the fuel cell stack  10  from the cathode outlet  13  and enters the manifold assembly through the port  26 . A port  46   a  is provided on the surface of the middle plate  40  facing the back plate  20  and in alignment with the port  26 . The exhaust air flows into the port  46   a  and along an internal fluid passage  461  which takes the exhaust air to a port  46   b  provided on the side surface of the middle plate  40 . Then the exhaust air leaves the manifold assembly  70  and returns to the environment. 
   Also, in practice, instead of flowing directly toward the fuel cell stack  10  from the port  43   e , the air may flow back to the surface of the middle plate  40  facing the front plate  60  along a fluid passage and then flow through a port on the front plate into a humidifier for humidification. Then, the air flows back into the manifold assembly  70  from the humidifier and flows along appropriate fluid passages in the manifold assembly  70  into the cathode inlet  12  of the fuel cell stack  10 . In this situation, second or oxidant humidifier  120  is provided which is mounted onto the front plate at the ports  61   p  to  61   s . The fluid passages and ports also have to be rearranged. For example, the fluid passage  434  does not extend directly from port  43   e  to  43   f . Rather, a fluid passage  435  is provided on the surface of the middle plate  40  facing the back plate  20 , as shown in  FIG. 3   b , which takes the air flow to a port  43   e ′ provided on the same surface. The port  43   e ′ is in communication with a port  43   f ′ provided on the surface of the middle plate facing the front plate  60  via an internal fluid passage. For clarity, this passage is not shown. The said port  43   f  is in alignment with the port  61   r  and hence the inlet  120   a  of the humidifier  120 . Then the air flows from the port  43   e ′ into the second oroxidant humidifier  120  through the port  43   f ′ and the inlet  120   a . After being saturated, the air leaves the humidifier  120  through the outlet  120   b  and the port  61   q  to the port  43   g ′ provided on the surface of the middle plate  40  facing the front plate  60 . The port  43   g ′ is in communication with a port  43   g  on the opposite surface of the middle plate  40  via an internal fluid passage which is not shown for clarity. A fluid passage  436  is provided on the surface of the middle plate facing the back plate  20  and communicates between the said port  43   g  and said port  43   f . Then the air flows from the port  43   g ′ to  43   f  through the port  43   g  and the fluid passage  436  and consequently flows into the cathode inlet  12  of the fuel cell stack through the port  21  in the manner described above. 
   Hydrogen enters the middle plate  40  from a hydrogen storage tank  117  through a port  44   a  provided on a top surface of the middle plate  40  and then flows along a fluid passage  441  inside the middle plate  40  to a port  44   b  provided on the surface of the middle plate  40  facing the front plate  60 . Then the hydrogen flows along a fluid passage  442  provided as a channel on the surface of the middle plate  40  facing the front plate  40  to a port  44   c  which is in alignment with the port  61   e  on the front plate  60  and hence the inlet  110   c  of the first or fuel gas humidifier  110 . Therefore, the hydrogen flows from the port  44   c  through the port  61   e  and an inlet  110   c  into the first or fuel gas humidifier  110  where it is humidified. Then, the humidified hydrogen leaves the first or fuel gas humidifier  110  through an outlet  110   d  and passes through the port  61   f  on the front plate  60 , which is in alignment with the outlet  110   d  and a port  44   d  provided on the surface of the middle plate  40  facing the front plate  60 . Then the hydrogen reaches the port  44   d  from which it continues to flow along a fluid passage  443  provided as an open channel on the surface of the middle plate  40  facing the front plate  60  to a port  44   e . The port  44   e  is a through hole on the middle plate  40  and in alignment with the port  24  of the back plate  20  and hence the anode inlet  11  of the fuel cell stack  10 . Therefore, the hydrogen flows from the port  44   e  through the port  24  and the inlet  11  into the fuel cell stack  10  for reaction. 
   After reaction, the unreacted hydrogen flows out of the fuel cell stack  10  from the anode outlet  14  and enters the manifold assembly  70  through the port  23 . A port  44   f  is provided on the surface of the middle plate  40  facing the back plate  20 . The port  44   f  is in alignment with the said port  23  and in communication with a port  44   g  provided on the side surface of the middle plate  40  via an internal fluid passage  444 , as shown in FIG.  1 . Then the hydrogen flows from the port  23  through the port  44   f , fluid passage  444  to the port  44   g  through which it leaves the manifold assembly  70 . Consequently, the hydrogen can be supplied to the inflow stream for recirculation, or vented to the environment. In practice, instead of flowing directly toward the fuel cell stack  10  from the port  44   e , the hydrogen may first flow into the first or fuelgas heat exchanger  113 . In this situation, the ports and fluid passages have to be rearranged. For example, the fluid passage  443  does not communicate port  44   d  with port  44   e . Rather, it communicates port  44   d  with a port  44   e ′ (FIG.  3 A), which is provided on the same surface and in alignment with port  61   b ′ and hence the inlet  113   b  of the first or fuel gas heat exchanger  113 . Therefore, the hydrogen flows from the port  44   d  to the first or fuel gas heat exchanger  113  through the port  44   e ′ and  61   b ′. Then the hydrogen flows back into the manifold assembly  70  from the outlet  113   a  of the first or fuel gas heat exchanger  113  and port  61   a  which is in alignment with the said outlet  113   a  and the port  44   e  on the middle plate  40 . Consequently, the hydrogen flows into the anode inlet  11  of the fuel cell stack  10  in the manner described above. 
   Typically, deionized water must be supplied to the humidifier, e.g. the humidifier  110  to humidify the process gas, i.e. air or oxygen. A loop for deionized water is also shown in FIG.  1 . The deionized water is supplied from a deionized water pump  119 . Then it passes a filter  118  and enters the middle plate  40  through a port  45   a  provided on the side surface thereof. The deionized water flows from the port  45   a  along a fluid passage  451  to a port  45   b , which is provided on the surface of the middle plate  40  facing the front plate  60  and in communication with the fluid passage  451  and a fluid passage  452 . The fluid passage  452  is provided as an open channel on the surface of the middle plate  40  and communicates between the port  45   b  and a port  45   c . Therefore the deionized water flows from the port  45   b  along the fluid passage  452  to the port  45   c  which is in alignment with the port  61   c  of the front plate  60  and hence an inlet  110   a  of the first or fuel gas humidifier  110 . The deionized water flows through the port  61   c  and the inlet  110   a  into the first or fuel gas humidifier  110  where it humidifies a process gas. Then the residual deionized water leaves the first or fuel gas humidifier  110  through an outlet  110   b  thereof and passes through a port  61   d  on the front plate  60 , which is in alignment with the outlet  110   b  and a port  45   d  provided on the surface of the middle plate  40  facing the front plate  60 . Therefore the deionized water reaches the port  45   d  and flows along a fluid passage  453  provided on the said surface to a port  45   e . The port  45   e  is in communication with an internal fluid passage  454  which in turn in communication with a port  45   f  provided on the side surface of the middle plate  40 . Therefore, the deionized water flows from the port  45   e  into the internal fluid passage  454  and exits the middle plate through the port  45   f  from which it returns to the deionized water pump  119 . 
   It is to be noted that the deionized water can also be supplied to the second or oxidant humidifier  120  via appropriate passages for humidifying the air. However, for clarity and simplicity, those passages and the humidifier for air are not shown. In fact, the supply of deionized water to the second or oxidant humidifier  120  can be effected in a manner similar to the supply to the first or fuel gas humidifier  110  for humidifying the hydrogen that has been described above and will have become apparent to those skilled in the art. It is also to be noted that although the heat exchange between the third heat exchanger  112  and any process gases is not described, the third heat exchanger  112  could be used to heat or cool the hydrogen flow. The third heat exchanger  112  could also be used to reheat air or hydrogen flow as desired, after the air or hydrogen is cooled by the second or first heat exchanger, respectively. However, for clarity, the associated arrangement of fluid passages and ports is not shown. 
   The air compressor  116 , coolant pump  114 , deionized water pump  119  can be mounted onto the manifold assembly  70  together with other peripherals. However, for a clear understanding of the present invention, they are shown in  FIG. 1  separated from manifold assembly  70 . The arrangement of the ports and fluid passages are not necessarily identical to that disclosed herein. The number and pattern of ports and fluid passages in this embodiment is only described for illustration purpose. 
   It should also be appreciated that the heat exchange process and humidification process can be arranged in any order as required in the situation. It is also possible that other fuel cell peripherals, such as enthalpy wheel, DC/AC converter, etc can be coupled to the manifold assembly  70 . The arrangement of ports and fluid passages may be varied in accordance with the particular process. 
   Now referring to  FIG. 5 , a second embodiment is shown. It should be appreciated that components similar to those in the first embodiment are indicated using the same reference numbers. 
   For simplicity and brevity, the description of these components is not repeated. In this embodiment, the manifold assembly  70  includes four layers of separated plates, namely a front plate  60 , a first middle plate  50 , a second middle plate  30  and a back plate  20 . The back plate  20  is formed so that the fuel cell stack  10  can abut against it. The back plate  20 , as in the first embodiment, has six ports provided therein, and is the same as that shown in  FIGS. 4   a  and  4   b.  In this embodiment, the ports are in the form of six through holes  21  to  26  which penetrate the back plate  20  in the direction of thickness. For illustration only, in this embodiment, the six through holes  21  to  26  penetrate the back plate  20 . The six through holes  21  to  26  are provided in two rows each having three holes arranged in alignment in vertical direction. Each of the three holes in each row is in alignment with the corresponding hole in the other row in horizontal direction. These through holes  21  to  26  are adapted to connect to the three inlets  11 ,  12 ,  16  and the three outlets  13 ,  14 ,  15  of the fuel cell stack  10  so that the fuel cell stack  10  can be mounted on the back plate  20  and the process gases and coolant can be supplied to the fuel cell stack  10  via the fluid channels that will be described below. Conventional necessary sealing means and clamping devices can be provided around the six through holes  21  to  26  to ensure proper delivery and prevent leakage of process gases and coolant. It should be mentioned that in this embodiment, for illustration purposes only, the fuel cell stack  10  has three ports near one end and other three ports near the other end thereof, which is a typical arrangement in fuel cell stacks, particularly proton exchange membrane fuel cell stacks. Therefore the back plate  20  is configured accordingly. Of course, the actual number and arrangement of through holes can be different. 
   As shown in  FIGS. 6   a  and  6   b , the front plate  60  is adapted for fuel cell peripherals to mount on it, such as the humidifiers  110 ,  120  and the three heat exchangers  111 ,  112  and  113 . Therefore, fuel cell stack  10  and fuel cell peripherals are mounted on opposite sides of the manifold assembly  70 . The detailed structure of the front plate  60  is shown in  FIGS. 6   a  and  6   b . The front plate  60  is provided with a plurality of ports. In this embodiment, the ports are in the form of through holes, which penetrate the front plate  60  in the direction of thickness. Only four through holes are numbered in this figure, namely  61 ,  62 ,  63  and  64 . In practice the number and arrangement of the said plurality of through holes can vary. For illustration purpose, in  FIGS. 6   a  and  6   b , twenty-four through holes are shown with four in one group illustrated with substantially rectangles in dotted lines. Each group of through holes is adapted to connect to ports of fuel cell peripherals. Some of the fuel cell peripherals, as shown in this embodiment, are two humidifiers  110 ,  120  and three heat exchangers  111 ,  112  and  113 , and these are mounted on the front plate  60  so that fluids, gases or other media can be exchanged between the fuel cell stack  10  and the peripherals via internal passages of the manifold assembly  70 , as will be described in details below. For example, through holes in group A 4  are used for connecting the first or fuel gas humidifier  110 , through holes in group A 5  are used for connecting the second or oxidant heat exchanger  111 , and through holes in group A 6  are used for connecting the third heat exchanger  112 . As required, conventional sealing and clamping devices are provided around the through holes to prevent leakage. In  FIGS. 6   a  and  6   b , the through holes are shown in alignment arrangement. But in practice, the arrangement of the through holes can be different as is needed in a particular situation. 
   Referring to  FIG. 5 , two middle plates  30 ,  50  are provided between the front plate  60  and the back plate  20 . Both of the two middle plates have a plurality of ports and fluid passages. The fluid passages can also be formed by etching or milling while the ports can be formed by boring or drilling; again methods of casting and molding can be used. Now referring to  FIG. 7   a , on the surface of the first middle plate  50 , which is in contact with the front plate  60 , fluid passages are provided. In this embodiment, for simplicity, not all the fluid passages are shown. On this surface, blind holes or recesses  51   a ,  52   a ,  53   a ,  54   a  are also provided. Four open channel fluid passages  51  to  54  are melted or machined on the surface from  51   a ,  52   a ,  53   a ,  54   a  to  51   b ,  52   b ,  53   b ,  54   b , respectively. In this embodiment,  51   b ,  52   b ,  53   b ,  54   b  are through holes and the blind holes  51   a ,  52   a ,  53   a ,  54   a  are positioned so that they are in alignment and hence in communication with through holes  61 ,  62 ,  63 ,  64  on the front plate  60 , respectively. When fluids, either hydrogen or air enter the manifold assembly  70  from the front plate  60  via through holes  61 ,  62 ,  63 ,  64 , they flow to holes  51   a ,  52   a ,  53   a ,  54   a  and continue to flow along each fluid passage  51 ,  52 ,  53 ,  54  to the through holes  51   b ,  52   b ,  53   b ,  54   b  from which they leave the first middle plate  50  and reach the second middle plate  30 . It will be understood that the fluid passages  51  to  54  are not necessarily melted or machined in the pattern shown in  FIG. 7   a  and other patterns are possible. 
   As also shown in  FIGS. 7   a  to  7   c , coolant passages are separately provided. The coolant herein refers to the coolant used in the management of the heat brought to the manifold assembly  70  by the process gases to ensure the proper performance of the manifold assembly  70 . As shown in  FIG. 7   b , in this embodiment, a coolant passage  55  is provided on the back surface of the first middle plate  50 , i.e. the surface in contact with the second middle plate  30 . Two openings or holes  55   a ,  56   a  are provided on one side surface of the plate  40 . On the back surface, two blind holes, or recesses  55   b ,  56   b  are provided so that the openings  55   a ,  56   a  are in communication with the sinking holes  55   b ,  56   b , respectively. The coolant passage, indicated at  55 , starts from the blind hole  55   b  and ends at the blind hole  56   b . Therefore a complete coolant loop is formed on the first middle plate  50  with coolant entering the plate via opening  55   a  and leaving the plate via opening  56   a . The coolant passages, in an actual design, are not necessarily in the pattern as shown in the drawings. But rather, the first middle plate  50  may have a large number of coolant passages and the coolant passages may extend to selected areas as needed in the situation. The coolant passages can also be formed by melting or machining. It should be mentioned that none of the fluid passages  51 ,  52 ,  53 ,  54  intercept any of the other fluid passages. Likewise, the coolant passage  55  does not intercept any of the fluid passages. 
   Now referring to  FIGS. 8   a  and  8   b , the second middle plate  30  has two large recesses  31   b,    32   b  provided on the surface which is in contact with the back plate  20 . In this embodiment, two internal coolant passages  31 ,  32  are shown, and these are different from the coolant passage  55  in  FIGS. 7   a  to  7   c , which is used for thermal management of the manifold assembly. The coolant passages  31 ,  32  are used to supply coolant to the fuel cell stack  10 . The coolant passages  31 ,  32  are formed inside of the second middle plate  20 . Coolant enters the plate  20  from a coolant source through an opening  31   a  provided on the side of the plate and flows along a passage  31  to a recess  31   b  which is in alignment with the port  22  of the back plate  20  and hence the coolant inlet  16  of the fuel cell stack  10 . Therefore the coolant flows from the slot  31  through the port  22  and the inlet  16  into the fuel cell stack  10 . Then the coolant leaves the fuel cell stack  10  through the coolant outlet  15 , which is in alignment with the port  25  of the back plate  20 . A recess  32   b  of the second middle plate  30  is in alignment with the port  25  of the back plate  20  so that the coolant reaches the recess  32   b  and flows along the passage  32  to the opening  32   a  from which it leaves the second middle plate  30 . It should be appreciated that on the second middle plate  30 , a plurality of ports are provided which are in alignment and hence in communication with the ports on the first middle plate  50  so that the fluid can flow through the ports to the second middle plate  30 . However, since the fluid communication between the two middle plates  30 ,  50  is similar to that explained in the first embodiment, those ports on the second middle plate  30  are not shown. The plurality of ports on the second middle plate  30  are in alignment and hence in communication with the through holes  21  on the back plate  20  which in turn communicate with the inlets and outlets of the fuel cell stack  10 . 
   The front plate  60 , the first and second middle plates  50 ,  30  and the back plate  20  are stacked one on top of the other and laminated together using brazing, welding, pressing and any other appropriate methods, such as casting or molding. As will be apparent to those skilled in the art, the back plate  20  can be omitted so that the second middle plate  30  is in direct contact with the fuel cell stack  10 . In this case through holes have to be provided on the second middle plate  30  so that the inlets  11 ,  12 ,  16  and outlets  13 ,  14 ,  15  of the fuel cell stack  10  can be connected onto the second middle plate  30 . Apparently, in the first embodiment, the back plate  20  could also be omitted, which results in the third embodiment described below. 
   Additionally, one or more peripheral components can be mounted to the same face of the manifold or the fuel cell stack. While the invention has been described with one manifold mounted to one fuel cell stack, other combinations are possible. For example, one manifold could be provided for a number of stack assemblies, to enable sharing of peripheral components. On the other hand, one (or more than one) fuel cell stacks could have two or more manifolds; for example, a common stack configuration provides connection ports on both ends, and it may be advantageous to provide a manifold at each end, which manifolds may have different configurations. 
   The manifold in the present invention can be manufactured with readily available, cheap materials with adequate heat durability or fluid resistance, including but not limited to polymers, such as GE noryl, and EN265, and aluminium. 
   While the invention has been described as having a number of separate plates, it is possible that a number, or all, of these plates could be integrally molded together. For example, for some applications, it may be possible to form the center manifold by investment casting on the like. In such a case, it may be necessary to provide additional access openings, for the casting process, but this can be readily closed with plugs and the like, and the sealing problems should be significantly lessened. 
   Additionally, it may be possible to integrate one or more peripheral components, particularly simple components, into the manifold. It is already suggested above that the same heat exchange facility could be provided in the manifold. Particularly, where the manifold is formed from a material with good thermal conductivity, it may be possible to eliminate one or more separate heat exchanges, and possibly integrate other peripheral components into the manifold. 
   It should be appreciated that the spirit of the present invention is concerned with a novel structure of the manifold for fuel cell systems and its use as an interface between the fuel cell stack and the peripherals. The type and internal structure of the fuel cell stack does not affect the design of the present invention. In other words, the present invention is applicable to various types of fuel cells, electrolyzers or other electrochemical cells. The position, number, size and pattern of those ports provided on the manifold assembly are not necessarily identical as disclosed herein. 
   It is anticipated that those having ordinary skill in this art can make various modification to the embodiment disclosed herein after learning the teaching of the present invention. For example, the shape of the manifold assembly, the number or arrangement of ports might be different, the materials for making the manifold assembly might be different and the manifold assembly might be manufactured using different methods as disclosed herein. However, these modifications should be considered to fall under the protection scope of the invention as defined in the following claims.