Title of Invention	A FUEL CELL BIPOLAR PLATE FOR IMPROVED WATER MANAGEMENT AND TO ACHIEVE MORE UNIFORM CURRENT DENSITY IN POLYMER ELECTROLYTE MEMBRANE(PEM) FUEL CELLS
Abstract	The present invention relates to fuel cell bipolar plate having multiple entry and a single exit for reactant gas flow adaptable to Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Phosphoric Acid Fuel Cells (PAFC) comprising of a plurality of gas entry ports incorporated in each bi-polar plate and emanating from a rectangular pocket such that an internal rectangular cavity or manifold is created when several bi-polar plates are stacked one below the other wherein a membrane electrode assembly or a single cell member is sandwiched between every two bi-polar plates, the complete assembly, consisting of several bi-polar plates and individual cells, enclosed between a set of insulating plates and steel clamping plates at the top and the bottom and fastened by means of a plurality of tie rods, on all the four sides of rectangular plate and each bi- polar plate having multiple gas intake ports at the front end and a single gas exit port at the rear end and the first layer of grooves being used for supplying the first reactant gas and adjacent below grooves being used for supplying the second gas to the membrane electrode assembly which is sandwiched between every two such pairs of grooves contained in the adjacent bi-polar plates assembled in such a way that every consecutive two layers of gas manifolds are disposed at 180° opposite direction.

Title of Invention

A FUEL CELL BIPOLAR PLATE FOR IMPROVED WATER MANAGEMENT AND TO ACHIEVE MORE UNIFORM CURRENT DENSITY IN POLYMER ELECTROLYTE MEMBRANE(PEM) FUEL CELLS

Abstract

The present invention relates to fuel cell bipolar plate having multiple entry and a single exit for reactant gas flow adaptable to Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Phosphoric Acid Fuel Cells (PAFC) comprising of a plurality of gas entry ports incorporated in each bi-polar plate and emanating from a rectangular pocket such that an internal rectangular cavity or manifold is created when several bi-polar plates are stacked one below the other wherein a membrane electrode assembly or a single cell member is sandwiched between every two bi-polar plates, the complete assembly, consisting of several bi-polar plates and individual cells, enclosed between a set of insulating plates and steel clamping plates at the top and the bottom and fastened by means of a plurality of tie rods, on all the four sides of rectangular plate and each bi- polar plate having multiple gas intake ports at the front end and a single gas exit port at the rear end and the first layer of grooves being used for supplying the first reactant gas and adjacent below grooves being used for supplying the second gas to the membrane electrode assembly which is sandwiched between every two such pairs of grooves contained in the adjacent bi-polar plates assembled in such a way that every consecutive two layers of gas manifolds are disposed at 180° opposite direction.

Full Text	FIELD OF INVENTION The present invention relates to a fuel cell bipolar plate having multiple entry and single exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning thereof. BACKGROUND OF THE INVENTION A fuel cell is an electrochemical device wherein a fuel gas reacts electrochemically with an oxidant gas in the presence of a catalyst, producing electricity. When operated with hydrogen as fuel and oxygen as oxidant, the operation of an "acidic" fuel cell, at the atomic level, may be understood as-stripping off of electrons from the "hydrogen" at the catalyst sites at anode, the "ionized hydrogen", known as a proton, travelling to the cathode through the "electrolyte" medium and recombining with "oxygen" which is supplied to the cathode and the "electrons" which reach the cathode through the external "load" circuit, to produce water. Several different types of fuel cells have been developed. They are generally known by the name of the "electrolyte" used in them, like Alkaline Fuel Cells (which use KOH, an alkali as an electrolyte), Phosphoric Acid Fuel Cells, Polymer Electrolyte Membrane Fuel Cells, also known as Proton Exchange Membrane Fuel Cells or even as Solid Polymer Electrolyte Fuel Cells. Fuel cells are being considered for various potential applications as portable power units and for providing clean power in transport and telecommunication applications. Stationery applications for powering homes, school buildings, hospitals, hotels, office buildings, are also becoming increasingly viable. OBJECTS OF THE INVENTION It is therefore, an object of the present invention to propose a fuel cell bipolar plate having multiple entry and single exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning thereof which eliminates the disadvantages of existing state of art bipolar plates. Another object of the present invention is to propose fuel cell bipolar plates having multiple entry and single exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning thereof which ensures availability of required amount of fuel gases to enter through multiple entries and pass through a unique flow pattern network covering the entire area of the electrodes. This is achieved by means of an inventive step whereby multiple streams of gases merge into a single stream towards the exit end of the flow field network thus making available more amounts of gases especially in those area where starvation of gases would have been felt as the original amounts of gases would have got consumed to a large extent by then. A further object of the present invention is to propose fuel cell bipolar plates having multiple entry and single exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning thereof which ensures a uniform flow of fuel gases to the electrodes. An yet further object of the present invention is to propose fuel cell bipolar plates having multiple entry and single exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning thereof which helps maintain a more uniform current density throughout the entire electrode area with almost 100% fuel utilization. SUMMARY OF THE INVENTION In order to maintain a reasonably high current density through out the cell area without having to supply excess hydrogen, thereby reducing to minimum the venting of hydrogen at the exit with consequential improvement in hydrogen utilization has been substantially resolved by developing a "multiple entry=single exit" type of flow pattern. The present invention relates, specifically to the Polymer Electrolyte Membrane Fuel Cells (PEMFC), but can also be used for other types of Fuel Cells like the Phosphoric Acid Fuel Cells. In the case of PEMFC, H2 fuel, supplied to the Anode, sheds one electron and becomes H+ ion. This H+ ion or 'proton' travels to the cathode through the 'proton conducting membrane'. The electrons (e-), shed by H2 at the anode, travel through the external 'load' up to the cathode, thus completing the electrical circuit and recombine with the proton and oxygen. The H+, O2 and e" combine with each other at cathode, to yield product "Water". Since the above process is "exothermic" in nature, some heat is also produced. "Water" and "Heat", therefore, are the only by-products of a typical fuel cell reaction, making them one of the cleanest "electricity" generating systems. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig.1 is a detailed plan view of the dual entry single exit flow field network used in the bipolar plates which can be used in assembling PEMFC and PAFC stacks. Fig.2 shows one of the sides of a typical bipolar plate containing one of the entrances, one of the Wide Canals (shorter type) and a portion of the Wide Canal (longer type). The clear arrows indicate the direction of flow of gases, the shaded arrows show the starved zone behind water droplet, reactant gas to which is supplied from the wide canal. The spherical object represents a typical condensed water droplet. Fig.3 shows the central portion of the bipolar plate where the reactant gases, coming from multiple inlets, merge together, in the longer type of wide canal. Exit port can also be seen. Fig.4 shows part assembly of a typical membrane Electrode Assembly, sandwiched between the flow fields of two adjacent bi-polar plates. Fig.5 shows a typical 5 Cells PEMFC stack assembly and the various components used in the same. DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The simplest form of fuel cell bipolar plates having a multiple entry single exit construction is a dual entry single exit flow field pattern which is used for the following description: A typical fuel cell bipolar plate comprises not only of the flow fields but also contains certain other areas which are used for accommodating tie rods, internal manifolds etc,, certain portions of these surroundings are also used for placing electrode edge seals or gaskets to avoid leakage of the fuel stream into the oxidant stream or vice versa and also to avoid their leakage into the surrounding areas. Figure 1 shows a plan view of a typical fuel cell bipolar plate (6) showing the core region where the gas flow fields are contained and the surrounding region which accommodates tie rods (3), internal gas manifolds (4) and electrode edge seals (5) etc. As can be seen in Figure 1, the rectangular pockets (4) are known as internal gas manifolds from where the reactant gases enter into the corresponding grooves (1) in the bipolar plates (6). It can be seen that out of the six rectangular pockets contained in the bipolar plate, only 3 have been used for one type of reactant gas in first row. In this case, the two pockets shown on the left side are used as entrances (1, 1) and the one shown on right side becomes the exit port (2). A typical bipolar plate (6) contains grooves on its reverse side also through which the other reactant gas flows. The three remaining pockets are connected to similar groove pattern on the other side, the two on right becoming the entrances and the one shown on left becoming the exit port for other reactant gas. The sealing of the areas (5) surrounding these rectangular pockets (4) with flexible seals like silicone rubber etc., allows the two different gases to flow from their respective pockets to the grooves which emanate from these respective pockets without intermixing or leaking out into the surrounding environment. As shown in Fig.4, a plurality of such bipolar plates are stacked one over another with Membrane Electrode Assemblies (MEAs) or single cells placed between each such pair of bipolar plates in such a manner that all the rectangular pockets are so aligned as 10 form a rectangular pipe, thereby becoming the internal manifold. The plurality of such bipolar plates and MEAs are clamped together using a pair of top and bottom steel plates which are electrically insulated from the bi-polar plates and MEAs by a pair of suitable insulating plates. The overall assembly is fastened by means of a plurality of tie rods which pass through the corresponding round holes (3) provided all along the four sides of the rectangular plate. The first layer pipe manifold (22) from the top wherein a first reactant gas takes entry from gas entry port (1) at front end and the second layer of pipe manifold (23) is engaged for a second reactant gas which takes entry in gas entry port (1) at rear end. In between the two layers of pipe manifold, a membrane electrode assembly member (24) is disposed. The reactant gas entering through the rectangular inlet manifold (22) exits through the rectangular outlet manifold (25). Similarly the other reactant gas which enters through the rectangular inlet manifold (23) exits through the outlet manifold (26), as shown in Fig.4. Fig.5 shows the arrangement of bi-polar plates, membrane electrode assemblies, insulating plates, steel clamping plates and tie rods in a typical fuel cell stack, containing 5 cells. In the flow field design shown in Fig.l, both the entry points (1) for one of the reactant gases have been positioned on the left side edge of the bipolar plate (6), one entrance being on the top and the other being at the bottom. The exit point (2) has been positioned exactly halfway away from both the entry points, but on the opposite edge i.e. in the middle portion on the right hand side edge of the bipolar plate. Figure 2 shows the details of one of the entry ports (1). It can be seen that the reactant gas contained in the rectangular internal manifold on the left side edge of the bipolar plate enters and flows to the right hand side edge through 4 parallel grooves (10,11/12,13), all of which terminate into a relatively wider canal (14). Through another set of 6 grooves emanating from this wide (shorter) canal (14), the reactant gas starts ifs journey in the opposite direction. This wider canal (14) serves as a mini storage3 of reactant gas and supplies the same to the next set of 6 parallel grooves. In addition to this, the wider canal (14) also serves another important purpose. Since water is the by- product of the reaction; some of the produced water tends to move towards the flow field in the form of droplets (7). This becomes an unwanted phenomenon since the water droplets (7) squeeze or in some cases completely block the flow path. Once a droplet comes in the way of the flowing gas in a particular groove (11) the remaining portion of the groove would suffer from starvation (9). This aspect has been effectively taken care of in this special design. Since the wider canal (14) also acts as a mini reservoir of reactant gases, the moment a particular groove (11) gets blocked with a condensed water droplet (7), gases from the wider canal (14) immediately fill the starved zone of the groove (11) from the wide canal (14), the gas flowing in the reverse direction (8) as shown in Fig.2. The second set of six parallel grooves too terminate into yet another wide canal (21) which has the same width as the earlier canal but is slightly longer to allow the grooves coming from the second entrance also to terminate in it so that double the amount of reactant gas is now available to flow through the last 4 channels leading to the exit port, as can be seen in Figure 3. This unique positioning of entry (1) and exit (2) ports makes a particular gas to travel only about half the path which it would have otherwise travelled in the case of single entry and single exit flow pattern. This reduction in path length reduces the pressure drop which the reactant gas encounters making it possible to supply the gas at a lower pressure. In the present case the flow pattern has been constituted in such a way that once the gas enters the flow field, it only travels a short distance through a set of grooves before the gas terminates into a relatively wide canal. This canal serves as a mini reservoir of the reactant gas to meet instantaneous higher demand of the reactant due to sudden load change. The canal also acts as a trap for water droplets which may be present either due to condensation of water from the humidified reactants or the condensation of product water itself, especially at low temperature of operation of the PEM Fuel Cell stack, say, below about 50°C. In the case of Phosphoric Acid Fuel cells, water condensation does not pose any problem because the temperature of operation of a typical PAFC stack is in the range of 150°C to 210°C, thereby allowing the water to escape as steam. The provision of intermediate canals has yet another advantage. The canal makes it possible to supply reactant gas to even those portions of the grooves which sometimes become inaccessible to the reactant gas due to a block created by a condensed droplet of water. In the present flow field pattern, even the starved downstream portion of such grooves, has an access to the reactant gas from the canal on the opposite end. The dimensions of the grooves are fixed in such a way that the minimum amount of gas available at any instant inside the bipolar plate is equal to or just a little more than the required amount of gas for drawing the desired current. The presence of wide canals results in reducing the pressure drop which would have otherwise occurred during change of direction of flow of the reactant gas. Apart from providing a unique pattern for gases to flow, in the effective area of the cells, the bipolar plate design also ensures that the circular holes for tie rod and rectangular pockets for gas manifolds are evenly placed, along the periphery such that the minimum clearance between the edge of the plate and beginning of any hole or pocket is sufficient for the edge seal to avoid any intermixing or leakage. WE CLAIM 1. A fuel cell bipolar plate having multiple entry and a single exit for reactant gas flow adaptable to Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Phosphoric Acid Fuel Cells (PAFC) comprising of: - a plurality of gas entry ports incorporated in each bi-polar plate and emanating from a rectangular pocket such that an internal rectangular cavity or manifold is created when several bi-polar plates are stacked one below the other wherein a membrane electrode assembly or a single cell member is sandwiched between every two bi-polar plates , the complete assembly, consisting of several bi-polar plates and individual cells, enclosed between a set of insulating plates and steel clamping plates at the top and the bottom and fastened by means of a plurality of tie rods, on all the four sides of rectangular plate; - each bi-polar plate having multiple gas intake ports at the front end and a single gas exit port at the rear end; - the first layer of grooves being used for supplying the first reactant gas and adjacent below grooves being used for supplying the second gas to the membrane electrode assembly which is sandwiched between every two such pairs of grooves contained in the adjacent bi-polar plates assembled in such a way that every consecutive two layers of gas manifolds are disposed at 180° opposite direction; 2. The process of functioning of the fuel cell comprises: - entry of first reactant gas (like H2 fuel) through the multiple intake ports in the first layer of the bi-polar plate; - entry of second reactant gas (like O2) through the multiple intake ports of the second layer of the bi-polar plate; - H2 fuel supplied to the anode sheds one electron and becomes a H+ ion, also known as a proton; - H+ ion or proton travels to cathode through the proton conducting membrane, sandwiched between an anode and a cathode; - the electrons (e-) shed by H2 at the anode, travel through the external circuit or load, up to cathode, thus completing the electrical circuit and recombine with the proton and oxygen to form product water; 3. A fuel cell as claimed in claim 1, wherein each bi-polar plate having a similar or a different groove pattern on it's reverse side, with entry and exit ports so placed that the entries and the exits on the two sides are separated from each other and do not interfere with each other. 4. A fuel cell as claimed in claim 1, wherein in a typical dual entry single exit bi- polar plate design, both the entry points for one of the reactant gases have been positioned on the front end side of bipolar plate, one entrance being on the top and the other being at the bottom and exit port has been placed exactly halfway away from both entry points but on the opposite side. 5. A fuel cell as claimed in claim 1, wherein a unique groove pattern consisting of a multiplicity of wide canals wherein the reactant gases entering through multiple entry ports merge with each other to make available more amount of reactant gas for the downstream areas of the bipolar plate. 6. A fuel cell as claimed in claim 1, wherein the wide canals acting as mini reservoirs of the reactant gases and supplying the reactant gas to even such portions of the grooves which would otherwise have been starved of any gas due to the blockage of gas groove by condensed water droplets. 7. A fuel cell as claimed in claim 1, wherein the provision of wide canals improving the availability of reactant gases to all the portions of the bipolar plate making it possible to achieve more uniform current density or voltage distribution. 8. A fuel cell as claimed in claim 1, wherein the merger of gases from multiple entries in the wide canals resulting in better availability of reactant gases throughout the total area of the bipolar plate making it possible to fully utilize the reactant gas, thereby resulting in improved efficiency and much better fuel gas and oxidant gas utilization. 9. A fuel cell as claimed in claim 1, wherein the wide canals making it possible to approach blocked portions of the gas grooves from the opposite direction such that the starved portions of the bipolar plate may also be supplied with the reactant gas. The present invention relates to fuel cell bipolar plate having multiple entry and a single exit for reactant gas flow adaptable to Polymer Electrolyte Membrane Fuel Cells (PEMFC) and Phosphoric Acid Fuel Cells (PAFC) comprising of a plurality of gas entry ports incorporated in each bi-polar plate and emanating from a rectangular pocket such that an internal rectangular cavity or manifold is created when several bi-polar plates are stacked one below the other wherein a membrane electrode assembly or a single cell member is sandwiched between every two bi-polar plates, the complete assembly, consisting of several bi-polar plates and individual cells, enclosed between a set of insulating plates and steel clamping plates at the top and the bottom and fastened by means of a plurality of tie rods, on all the four sides of rectangular plate and each bi- polar plate having multiple gas intake ports at the front end and a single gas exit port at the rear end and the first layer of grooves being used for supplying the first reactant gas and adjacent below grooves being used for supplying the second gas to the membrane electrode assembly which is sandwiched between every two such pairs of grooves contained in the adjacent bi-polar plates assembled in such a way that every consecutive two layers of gas manifolds are disposed at 180° opposite direction.

Full Text

FIELD OF INVENTION
The present invention relates to a fuel cell bipolar plate having multiple entry and single
exit flow field network for reactant gas flow adaptable to polymer electrolyte membrane
fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC) and a process of functioning
thereof.
BACKGROUND OF THE INVENTION
A fuel cell is an electrochemical device wherein a fuel gas reacts electrochemically with
an oxidant gas in the presence of a catalyst, producing electricity. When operated with
hydrogen as fuel and oxygen as oxidant, the operation of an "acidic" fuel cell, at the
atomic level, may be understood as-stripping off of electrons from the "hydrogen" at
the catalyst sites at anode, the "ionized hydrogen", known as a proton, travelling to the
cathode through the "electrolyte" medium and recombining with "oxygen" which is
supplied to the cathode and the "electrons" which reach the cathode through the
external "load" circuit, to produce water.
Several different types of fuel cells have been developed. They are generally known by
the name of the "electrolyte" used in them, like Alkaline Fuel Cells (which use KOH, an
alkali as an electrolyte), Phosphoric Acid Fuel Cells, Polymer Electrolyte Membrane Fuel
Cells, also known as Proton Exchange Membrane Fuel Cells or even as Solid Polymer
Electrolyte Fuel Cells.
Fuel cells are being considered for various potential applications as portable power units
and for providing clean power in transport and telecommunication applications.
Stationery applications for powering homes, school buildings, hospitals, hotels, office
buildings, are also becoming increasingly viable.
OBJECTS OF THE INVENTION
It is therefore, an object of the present invention to propose a fuel cell bipolar plate
having multiple entry and single exit flow field network for reactant gas flow adaptable
to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells
(PAFC) and a process of functioning thereof which eliminates the disadvantages of
existing state of art bipolar plates.
Another object of the present invention is to propose fuel cell bipolar plates having
multiple entry and single exit flow field network for reactant gas flow adaptable to
polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC)
and a process of functioning thereof which ensures availability of required amount of
fuel gases to enter through multiple entries and pass through a unique flow pattern

network covering the entire area of the electrodes. This is achieved by means of an
inventive step whereby multiple streams of gases merge into a single stream towards
the exit end of the flow field network thus making available more amounts of gases
especially in those area where starvation of gases would have been felt as the original
amounts of gases would have got consumed to a large extent by then.
A further object of the present invention is to propose fuel cell bipolar plates having
multiple entry and single exit flow field network for reactant gas flow adaptable to
polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells (PAFC)
and a process of functioning thereof which ensures a uniform flow of fuel gases to the
electrodes.
An yet further object of the present invention is to propose fuel cell bipolar plates
having multiple entry and single exit flow field network for reactant gas flow adaptable
to polymer electrolyte membrane fuel cells (PEMFC) and phosphoric acid fuel cells
(PAFC) and a process of functioning thereof which helps maintain a more uniform
current density throughout the entire electrode area with almost 100% fuel utilization.
SUMMARY OF THE INVENTION
In order to maintain a reasonably high current density through out the cell area without
having to supply excess hydrogen, thereby reducing to minimum the venting of

hydrogen at the exit with consequential improvement in hydrogen utilization has been
substantially resolved by developing a "multiple entry=single exit" type of flow pattern.
The present invention relates, specifically to the Polymer Electrolyte Membrane Fuel
Cells (PEMFC), but can also be used for other types of Fuel Cells like the Phosphoric
Acid Fuel Cells.
In the case of PEMFC, H2 fuel, supplied to the Anode, sheds one electron and becomes
H+ ion. This H+ ion or 'proton' travels to the cathode through the 'proton conducting
membrane'. The electrons (e-), shed by H2 at the anode, travel through the external
'load' up to the cathode, thus completing the electrical circuit and recombine with the
proton and oxygen. The H+, O2 and e" combine with each other at cathode, to yield
product "Water". Since the above process is "exothermic" in nature, some heat is also
produced. "Water" and "Heat", therefore, are the only by-products of a typical fuel cell
reaction, making them one of the cleanest "electricity" generating systems.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig.1 is a detailed plan view of the dual entry single exit flow field network used in the
bipolar plates which can be used in assembling PEMFC and PAFC stacks.
Fig.2 shows one of the sides of a typical bipolar plate containing one of the entrances,
one of the Wide Canals (shorter type) and a portion of the Wide Canal (longer type).

The clear arrows indicate the direction of flow of gases, the shaded arrows show the
starved zone behind water droplet, reactant gas to which is supplied from the wide
canal. The spherical object represents a typical condensed water droplet.
Fig.3 shows the central portion of the bipolar plate where the reactant gases, coming
from multiple inlets, merge together, in the longer type of wide canal. Exit port can also
be seen.
Fig.4 shows part assembly of a typical membrane Electrode Assembly, sandwiched
between the flow fields of two adjacent bi-polar plates.
Fig.5 shows a typical 5 Cells PEMFC stack assembly and the various components used in
the same.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The simplest form of fuel cell bipolar plates having a multiple entry single exit
construction is a dual entry single exit flow field pattern which is used for the following
description:
A typical fuel cell bipolar plate comprises not only of the flow fields but also contains
certain other areas which are used for accommodating tie rods, internal manifolds etc,,
certain portions of these surroundings are also used for placing electrode edge seals or
gaskets to avoid leakage of the fuel stream into the oxidant stream or vice versa and
also to avoid their leakage into the surrounding areas.

Figure 1 shows a plan view of a typical fuel cell bipolar plate (6) showing the core
region where the gas flow fields are contained and the surrounding region which
accommodates tie rods (3), internal gas manifolds (4) and electrode edge seals (5) etc.
As can be seen in Figure 1, the rectangular pockets (4) are known as internal gas
manifolds from where the reactant gases enter into the corresponding grooves (1) in
the bipolar plates (6). It can be seen that out of the six rectangular pockets contained
in the bipolar plate, only 3 have been used for one type of reactant gas in first row. In
this case, the two pockets shown on the left side are used as entrances (1, 1) and the
one shown on right side becomes the exit port (2). A typical bipolar plate (6) contains
grooves on its reverse side also through which the other reactant gas flows. The three
remaining pockets are connected to similar groove pattern on the other side, the two
on right becoming the entrances and the one shown on left becoming the exit port for
other reactant gas.
The sealing of the areas (5) surrounding these rectangular pockets (4) with flexible
seals like silicone rubber etc., allows the two different gases to flow from their
respective pockets to the grooves which emanate from these respective pockets without
intermixing or leaking out into the surrounding environment.
As shown in Fig.4, a plurality of such bipolar plates are stacked one over another with
Membrane Electrode Assemblies (MEAs) or single cells placed between each such pair
of bipolar plates in such a manner that all the rectangular pockets are so aligned as 10
form a rectangular pipe, thereby becoming the internal manifold. The plurality of such
bipolar plates and MEAs are clamped together using a pair of top and bottom steel

plates which are electrically insulated from the bi-polar plates and MEAs by a pair of
suitable insulating plates. The overall assembly is fastened by means of a plurality of tie
rods which pass through the corresponding round holes (3) provided all along the four
sides of the rectangular plate. The first layer pipe manifold (22) from the top wherein a
first reactant gas takes entry from gas entry port (1) at front end and the second layer
of pipe manifold (23) is engaged for a second reactant gas which takes entry in gas
entry port (1) at rear end. In between the two layers of pipe manifold, a membrane
electrode assembly member (24) is disposed. The reactant gas entering through the
rectangular inlet manifold (22) exits through the rectangular outlet manifold (25).
Similarly the other reactant gas which enters through the rectangular inlet manifold
(23) exits through the outlet manifold (26), as shown in Fig.4.
Fig.5 shows the arrangement of bi-polar plates, membrane electrode assemblies,
insulating plates, steel clamping plates and tie rods in a typical fuel cell stack,
containing 5 cells.
In the flow field design shown in Fig.l, both the entry points (1) for one of the reactant
gases have been positioned on the left side edge of the bipolar plate (6), one entrance
being on the top and the other being at the bottom. The exit point (2) has been
positioned exactly halfway away from both the entry points, but on the opposite edge
i.e. in the middle portion on the right hand side edge of the bipolar plate.
Figure 2 shows the details of one of the entry ports (1). It can be seen that the reactant
gas contained in the rectangular internal manifold on the left side edge of the bipolar
plate enters and flows to the right hand side edge through 4 parallel grooves

(10,11/12,13), all of which terminate into a relatively wider canal (14). Through another
set of 6 grooves emanating from this wide (shorter) canal (14), the reactant gas starts
ifs journey in the opposite direction. This wider canal (14) serves as a mini storage3 of
reactant gas and supplies the same to the next set of 6 parallel grooves. In addition to
this, the wider canal (14) also serves another important purpose. Since water is the by-
product of the reaction; some of the produced water tends to move towards the flow
field in the form of droplets (7). This becomes an unwanted phenomenon since the
water droplets (7) squeeze or in some cases completely block the flow path. Once a
droplet comes in the way of the flowing gas in a particular groove (11) the remaining
portion of the groove would suffer from starvation (9). This aspect has been effectively
taken care of in this special design. Since the wider canal (14) also acts as a mini
reservoir of reactant gases, the moment a particular groove (11) gets blocked with a
condensed water droplet (7), gases from the wider canal (14) immediately fill the
starved zone of the groove (11) from the wide canal (14), the gas flowing in the
reverse direction (8) as shown in Fig.2.
The second set of six parallel grooves too terminate into yet another wide canal (21)
which has the same width as the earlier canal but is slightly longer to allow the grooves
coming from the second entrance also to terminate in it so that double the amount of
reactant gas is now available to flow through the last 4 channels leading to the exit
port, as can be seen in Figure 3.
This unique positioning of entry (1) and exit (2) ports makes a particular gas to travel
only about half the path which it would have otherwise travelled in the case of single

entry and single exit flow pattern. This reduction in path length reduces the pressure
drop which the reactant gas encounters making it possible to supply the gas at a lower
pressure.
In the present case the flow pattern has been constituted in such a way that once the
gas enters the flow field, it only travels a short distance through a set of grooves before
the gas terminates into a relatively wide canal. This canal serves as a mini reservoir of
the reactant gas to meet instantaneous higher demand of the reactant due to sudden
load change. The canal also acts as a trap for water droplets which may be present
either due to condensation of water from the humidified reactants or the condensation
of product water itself, especially at low temperature of operation of the PEM Fuel Cell
stack, say, below about 50°C.
In the case of Phosphoric Acid Fuel cells, water condensation does not pose any
problem because the temperature of operation of a typical PAFC stack is in the range of
150°C to 210°C, thereby allowing the water to escape as steam.
The provision of intermediate canals has yet another advantage. The canal makes it
possible to supply reactant gas to even those portions of the grooves which sometimes
become inaccessible to the reactant gas due to a block created by a condensed droplet
of water. In the present flow field pattern, even the starved downstream portion of
such grooves, has an access to the reactant gas from the canal on the opposite end.
The dimensions of the grooves are fixed in such a way that the minimum amount of gas
available at any instant inside the bipolar plate is equal to or just a little more than the
required amount of gas for drawing the desired current. The presence of wide canals

results in reducing the pressure drop which would have otherwise occurred during
change of direction of flow of the reactant gas.
Apart from providing a unique pattern for gases to flow, in the effective area of the
cells, the bipolar plate design also ensures that the circular holes for tie rod and
rectangular pockets for gas manifolds are evenly placed, along the periphery such that
the minimum clearance between the edge of the plate and beginning of any hole or
pocket is sufficient for the edge seal to avoid any intermixing or leakage.

WE CLAIM
1. A fuel cell bipolar plate having multiple entry and a single exit for reactant gas
flow adaptable to Polymer Electrolyte Membrane Fuel Cells (PEMFC) and
Phosphoric Acid Fuel Cells (PAFC) comprising of:
- a plurality of gas entry ports incorporated in each bi-polar plate and
emanating from a rectangular pocket such that an internal rectangular
cavity or manifold is created when several bi-polar plates are stacked one
below the other wherein a membrane electrode assembly or a single cell
member is sandwiched between every two bi-polar plates , the complete
assembly, consisting of several bi-polar plates and individual cells,
enclosed between a set of insulating plates and steel clamping plates at
the top and the bottom and fastened by means of a plurality of tie rods,
on all the four sides of rectangular plate;
- each bi-polar plate having multiple gas intake ports at the front end and a
single gas exit port at the rear end;
- the first layer of grooves being used for supplying the first reactant gas
and adjacent below grooves being used for supplying the second gas to
the membrane electrode assembly which is sandwiched between every
two such pairs of grooves contained in the adjacent bi-polar plates
assembled in such a way that every consecutive two layers of gas
manifolds are disposed at 180° opposite direction;
2. The process of functioning of the fuel cell comprises:
- entry of first reactant gas (like H2 fuel) through the multiple intake ports
in the first layer of the bi-polar plate;
- entry of second reactant gas (like O2) through the multiple intake ports of
the second layer of the bi-polar plate;
- H2 fuel supplied to the anode sheds one electron and becomes a H+ ion,
also known as a proton;
- H+ ion or proton travels to cathode through the proton conducting
membrane, sandwiched between an anode and a cathode;
- the electrons (e-) shed by H2 at the anode, travel through the external
circuit or load, up to cathode, thus completing the electrical circuit and
recombine with the proton and oxygen to form product water;
3. A fuel cell as claimed in claim 1, wherein each bi-polar plate having a similar or a
different groove pattern on it's reverse side, with entry and exit ports so placed
that the entries and the exits on the two sides are separated from each other
and do not interfere with each other.
4. A fuel cell as claimed in claim 1, wherein in a typical dual entry single exit bi-
polar plate design, both the entry points for one of the reactant gases have been
positioned on the front end side of bipolar plate, one entrance being on the top
and the other being at the bottom and exit port has been placed exactly halfway
away from both entry points but on the opposite side.
5. A fuel cell as claimed in claim 1, wherein a unique groove pattern consisting of a
multiplicity of wide canals wherein the reactant gases entering through multiple
entry ports merge with each other to make available more amount of reactant
gas for the downstream areas of the bipolar plate.
6. A fuel cell as claimed in claim 1, wherein the wide canals acting as mini
reservoirs of the reactant gases and supplying the reactant gas to even such
portions of the grooves which would otherwise have been starved of any gas due
to the blockage of gas groove by condensed water droplets.
7. A fuel cell as claimed in claim 1, wherein the provision of wide canals improving
the availability of reactant gases to all the portions of the bipolar plate making it
possible to achieve more uniform current density or voltage distribution.
8. A fuel cell as claimed in claim 1, wherein the merger of gases from multiple
entries in the wide canals resulting in better availability of reactant gases
throughout the total area of the bipolar plate making it possible to fully utilize the
reactant gas, thereby resulting in improved efficiency and much better fuel gas
and oxidant gas utilization.
9. A fuel cell as claimed in claim 1, wherein the wide canals making it possible to
approach blocked portions of the gas grooves from the opposite direction such
that the starved portions of the bipolar plate may also be supplied with the
reactant gas.

The present invention relates to fuel cell bipolar plate having multiple entry and a single
exit for reactant gas flow adaptable to Polymer Electrolyte Membrane Fuel Cells
(PEMFC) and Phosphoric Acid Fuel Cells (PAFC) comprising of a plurality of gas entry
ports incorporated in each bi-polar plate and emanating from a rectangular pocket such
that an internal rectangular cavity or manifold is created when several bi-polar plates
are stacked one below the other wherein a membrane electrode assembly or a single
cell member is sandwiched between every two bi-polar plates, the complete assembly,
consisting of several bi-polar plates and individual cells, enclosed between a set of
insulating plates and steel clamping plates at the top and the bottom and fastened by
means of a plurality of tie rods, on all the four sides of rectangular plate and each bi-
polar plate having multiple gas intake ports at the front end and a single gas exit port
at the rear end and the first layer of grooves being used for supplying the first reactant
gas and adjacent below grooves being used for supplying the second gas to the
membrane electrode assembly which is sandwiched between every two such pairs of
grooves contained in the adjacent bi-polar plates assembled in such a way that every
consecutive two layers of gas manifolds are disposed at 180° opposite direction.

Documents:

238-KOL-2010-(28-11-2014)-ABSTRACT.pdf

238-KOL-2010-(28-11-2014)-CLAIMS.pdf

238-KOL-2010-(28-11-2014)-CORRESPONDENCE.pdf

238-KOL-2010-(28-11-2014)-DESCRIPTION PAGES.pdf

238-KOL-2010-(28-11-2014)-FORM-1.pdf

238-KOL-2010-(28-11-2014)-FORM-2.pdf

238-kol-2010-abstract.pdf

238-kol-2010-claims.pdf

238-kol-2010-correspondence.pdf

238-kol-2010-description (complete).pdf

238-kol-2010-drawings.pdf

238-kol-2010-form 1.pdf

238-KOL-2010-FORM 18.pdf

238-kol-2010-form 2.pdf

238-kol-2010-form 3.pdf

238-kol-2010-gpa.pdf

238-kol-2010-specification.pdf

abstract-238-kol-2010.jpg

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Patent Number

264653

Indian Patent Application Number

238/KOL/2010

PG Journal Number

03/2015

Publication Date

16-Jan-2015

Grant Date

14-Jan-2015

Date of Filing

10-Mar-2010

Name of Patentee

BHARAT HEAVY ELECTRICALS LIMITED

Applicant Address

REGIONAL OPERATIONS DIVISION (ROD), PLOT NO: 9/1, DJ BLOCK 3RD FLOOR, KARUNAMOYEE, SALT LAKE CITY, KOLKATA-700091, HAVING ITS REGISTERED OFFICE AT BHEL HOUSE, SIRI FORT, NEW DELHI-110049, INDIA

Inventors:

#	Inventor's Name	Inventor's Address
1	SHAILENDRA SHARMA	BHEL-CORP. RESEARCH & DEVELOPMENT VIKASNAGAR, HYDERABAD-500093, A.P., INDIA
2	ERADALA HARI BABU	BHEL-CORP. RESEARCH & DEVELOPMENT VIKASNAGAR, HYDERABAD-500093, A.P., INDIA
3	DEEPAK KUMAR KANUNGO	BHEL-CORP. RESEARCH & DEVELOPMENT VIKASNAGAR, HYDERABAD-500093, A.P., INDIA
4	AMRISH GUPTA	BHEL-CORP. RESEARCH & DEVELOPMENT VIKASNAGAR, HYDERABAD-500093, A.P., INDIA

PCT International Classification Number

C08G65/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA