1. FUEL CELLS-POROUS INSERTS IN 70 CM² PEMFC IN ZIGZAG FLOW
PATTERN
RAVI SIVA MANI KANDAN
(11A248)
Dissertation submitted in partial fulfillment of the requirements for the degree of
BACHELOR OF ENGINEERING
Branch: AUTOMOBILE ENGINEERING
(08A720 Project Work - Phase I)
of Anna University
OCTOBER2014
DEPARTMENT OF AUTOMOBILE ENGINEERING
PSG COLLEGE OF TECHNOLOGY
(Autonomous Institution)
COIMBATORE – 641 004.
2. FUEL CELLS- POROUS INSERTS IN 70 CM² PEMFC IN ZIGZAG FLOW
PATTERN
Bonafide record of work done by
RAVI SIVA MANI KANDAN
(Roll No: 11A248)
Dissertation submitted in partial fulfillment of the requirements for the degree of
BACHELOR OF ENGINEERING
Branch: AUTOMOBILE ENGINEERING
(08A720 Project Work - Phase I)
of Anna University
OCTOBER 2014
-------------------- --------------------
Mr.M.Karthikeyan Dr.S.Neelakrishnan
Faculty guide Head of the Department
CONTENTS
CHAPTER Page No.
Acknowledgement………………………………………………………………………..i
List of Figures…………………………………………………………………………….ii
3. 1. PREFACE………………………………………………….………………………….1
2. FUEL CELLS......................................................................................................2
2.1 Introduction to Fuel Cells 2
2.2 Proton Exchange Membrane Fuel Cells (PEMFC) 4
3. LITERATURE REVIEW………………………………………………………...……5
4. PROJECT DESCRIPTION…………………………………………………………..6
4.1 Problem Definition 6
4.2 Incorporation of Porous Inserts 7
4.3 Modeling of Fuel Cell 8
4.4 Meshing of Fuel Cell Assembly 9
5. CONCLUSION…………………………………………………………………...……14
BIBLIOGRAPHY………………………………………………………………….......……15
4. i
ACKNOWLEDGEMENT
I wish to express my sincere gratitude to our respected Principal Dr. R. Rudramoorthy for
having given me the opportunity to undertake my project work.
I also express my sincere thanks to Dr. S. Neelakrishnan, Professor and Head, Department of
Automobile Engineering, for his encouragement and support that he had extended towards the success of
the project work.
I wish to thank Dr. P. Karthikeyan, Associate Professor, Department of Automobile
Engineering, for his evergreen ideas and motivation.
I owe a deep sense of reverence and gratitude to my guide, Mr. M. Karthikeyan, Assistant
Professor, Department of Automobile Engineering, for his efficient and excellent guidance, timely help,
encouragement, and for his sincere inspiration throughout the completion of the project.
I express my thanks and gratitude to my class tutor, Mr. R. Karthikeyan, Assistant Professor,
Department of Automobile Engineering for her help and encouragement in the duration of my course.
Finally, I would like to express my sincere thanks to my parents, all my student colleagues and
staff members in my department without whom this project would not have been completed successfully.
5. ii
LIST OF FIGURES
FIGURE NO TITLE PAGE
1 Structure of a fuel cell 2
2 Layout of a fuel cell 3
3 PEM Fuel Cell 4
4 Effect of water generation on performance 7
5 Rib area and flow channel 8
6 2mm zigzag porous inserts 8
7 5mm zigzag porous inserts 9
8 Assembled fuel cell in Ansys Workbench 9
9 Blocking -XY plane 10
10 Blocking - YZ plane 10
11 Blocking - XZ plane 11
11 Node Counts – XY plane 11
12 Node Counts – YZ plane 13
13 Node Counts – XZ plane 14
14 Meshing - XY plane 14
15 Meshing - YZ plane 15
16 Meshing - XZ plane 15
6. 1
1. PREFACE
In a world where transportation and power generation is primarily driven by use of fossil
fuel, there are two main problems. The first problem is that these fossil fuels are available in a
limited amount and eventually there will be a gap between their production and demand. The
second problem is that they are harmful to the environment, resulting in global warming,
pollution, acid rain, ozone layer depletion, land damage by continuous surface mining for coal
and so on.
There is a need for meeting the requirements of human beings in a sustainable and
efficient manner. The generation of electricity through electrochemical reactions involving
hydrogen forms the basis of fuel cell technology. The operation of fuel cell results in near zero
emission as the production of hydrogen is the only source for emissions. Additionally the
electrochemical process is not subject to Carnot cycle limitations and has high efficiency. These
advantages of fuel cell are similar to those of batteries but fuel cells have higher energy density
and also quick recharge capability for sustained usage. Also, Hydrogen is seen as a fuel which
is abundant and is very light and clean. With proper storage and utilization, hydrogen as a fuel
can replace fossil fuels.
Fuel cells have a wide range of application. Depending on the type of fuel cell used and
the stack, fuel cells can power portable electronic equipment, cars, and buses and be the
source for power generation. The prospect of high efficiency, zero emission, higher energy
density than batteries, fast recharging and quiet operation make fuel cell technology a lucrative
and sustainable choice as an energy source, especially in the fields of transportation and power
generation.
7. 2
2. FUEL CELLS
2.1 Introduction to Fuel Cell:
A fuel cell is an electrochemical energy converter which converts the chemical energy of
a fuel directly into electricity using an oxidant. Typically the process of electricity generation from
fuels consist of various stages of conversion but a fuel cell circumvents all these stages and
produces electricity in a single process, similar to a battery .In case of a PEMFC(Proton
Exchange Membrane Fuel Cell or Polymer Electrolyte Membrane Fuel Cell), the fuel is pure
hydrogen gas and the oxidant is oxygen.
The structure of a fuel cell consists of a membrane electrolyte assembly (MEA). This
consists of a membrane which is flanked by the anode and cathode. The function of the
membrane is to conduct protons (H+
) from anode to the cathode as well as act as a seal
between the fuel and oxidant. The MEA also consists of a gas diffusion layer which is coated
with a catalyst. Uniform gas distribution and proper conduction is ensured by the gas diffusion
layer and the catalyst promotes the reactions. The reactants are fed into graphite plates in
which they move along the flow channels which denotes the active area of the fuel cell. The
entire assembly is then sandwiched between end plates which hold all the components
together.
Fig 1: Structure of a fuel cell
8. 3
The conversion of chemical to electrical energy is by the electrochemical oxidation and
reduction reactions occurring at the anode and cathode respectively. The voltage produced by
these reactions depends upon the reactants (fuel and oxidant) themselves. For pure hydrogen
gas oxidized by oxygen (as in the case of a PEMFC), the resulting voltage as per the
electrochemical series is 1.23V. The hydrogen oxidation reaction results in two protons and two
electrons formed from one hydrogen molecule. This reaction is denoted as follows:
At anode(Hydrogen Oxidation Reaction):
At the cathode side the oxygen reacts with the protons (conducted through the
membrane) and the electrons (conducted through an external circuit) to form water molecules.
This reaction is denoted as:
At cathode (Oxygen Reduction Reaction):
Overall Reaction:
The reversible reaction is expressed in the equation and shows the reincorporation of the
hydrogen protons and electrons together with the oxygen molecule and the formation of one
water molecule along with 1.229V.
Fig 2: Layout of a fuel cell
2 2 2
1
2
H O H O Electricity Heat
9. 4
2.2 Proton Exchange Membrane Fuel Cells (PEMFC):
Among the types of fuel cells, the one most suited for automobile applications is the
Polymer Electrolyte Membrane or Proton Exchange Membrane Fuel Cell. In PEMFC, the fuel is
pure hydrogen gas and the oxidant is oxygen. The membrane is made of perfluro sulphonic acid
(Nafion) and the gas diffusion layer is carbon paper/cloth. Platinum is sprayed onto the gas
diffusion layer for catalysis of the electrochemical reactions. The flow plates which act as the
electrodes are made of graphite.
The PEM Fuel Cells operate at relatively low temperature range (50-100°C) which
makes them easy to contain and reduce thermal losses. They are also smaller in volume and
weight which makes them suitable for powering automobiles. They also have quick start up
compared to other types of fuel cells and high energy density compared to batteries.In addition
to these benefits, PEM Fuel Cells also have high operating efficiency and is under a lot of
research into its possible commercialization.
Key factors to consider in maximizing the utility of PEM Fuel Cells include flow channel
optimization, water management, alternatives to catalyst and the membrane, scaling up and
stacking for the required applications.
Fig 3: PEM Fuel Cell
10. 5
3. LITERATURE SURVEY:
FatamehHashemi et al studied the performance characteristics for various flow channel
designs. The study concluded that the Reaction gas distribution, current density and
temperature distributions are more uniform for serpentine flow channels.
E Birgerrson et al conducted a study on the interdigitated flow distributor. They
concluded that the interdigitated flow distributor can sustain highest current density but
requires very precise porous backing to avoid loss of power density.
Shawn Lister et al investigated the effect of porous inserts when incorporated into the
fuel cell structure. This revealed that Porous inserts in fuel cell acts as absorber for
water which increases performance compared to non-porous fuel cells.
EC Kumber studied the saturation for different pore size subjected to a constant liquid
pressure. The result was that the Liquid saturation is less for smaller pores at constant
liquid pressure.
Jer-Huan Jang observed the impact of water generation on the electrodes on the
overall performance of the fuel cell. The conclusion was that Water generation adversely
affects performance greatly at low voltage.
MM Mench conducted a study on the impact of a MPL (Micro Porous Layer) on
addressing water management issues. The result was that Micro Porous Layer acts as
water flow barrier at low liquid pressure.
Eikerling studied the effect of the reactant gas flow through the flow channels over
water. He concluded that the Gas flow (in flow channel) over water has induced drag in
gas motion.
Jixin Chen investigated the effect of air flow on water removal. This was conducted to
study the movement of water into neighboring pores depending on the flow rate of the
reactant gases.
Xianguao Li et al studied the importance and the adverse effects of water on the
operation of fuel cell. The study revealed that the Water generation adversely affects
performance but MEA requires hydration for proton conduction.
Runzhang Yuan et. Alstudied the effect of porosity on the gas diffusion layer. The result
showed that the Gas diffusion layer with porosity is more optimal for liquid water
discharge from catalyst into the gas channel than a Gas.
HuaMeng studied the effect of Micro Porous Layer through numerical models. He
concluded that the micro porous layer serves as a barrier for liquid water transport on
cathode side of a PEM Fuel cell.
Wang YL et al.performed a study by comparison on porous and non-porous fuel cells.
The performance was better for a porous fuel cell as it addressed water management by
absorption.
11. 6
4. PROJECT DESCRIPTION
4.1 Problem definition:
Although PEM Fuel Cells are most suitable for automotive applications, they are
still not able to completely propel the vehicle on their own without great costs. They are
mostly used as auxiliary power sources instead. The major problems in the
commercialization of a fuel cell are:
1. Cost – This is mainly due to the usage of platinum as the catalyst. Platinum is the
best element for the catalysis of the fuel cell reactions in the given conditions.
Alternatives include cerium oxide and some iron based alloys and this is an active
research area. Additionally the usage of Nafion membrane increases the cost.
2. Water generation –The basic electrochemical reaction results in water generation on
the cathode side. This can diffuse through to the anode side as well during operation.
This results in flooding, thus resulting in reduced overall performance (current
density, power density and voltage). An additional problem is that water should not
be completely removed from the fuel cell as some hydration is required for the
protonic conduction through the nafionmembrance.
3. Heat generation – A single fuel cell does not produce enough voltage to supply the
required power. Hence multiple fuel cells are stacked up to get the required power.
This results in heat generation which adversely affects the performance of the fuel
cells, thus reducing stack efficiency which drops the voltage per cell to around 0.6V
from a theoretical 1.23V.
In addition to addressing these problems, some of the areas to consider in increasing the
performance of fuel cells include increasing catalytic activity and reducing catalytic poisoning.
In scaling up of fuel cells (which increases the current output), the major problem is
water generation. Once this is rectified, the performance of the fuel cells increase. This reduces
the cost per unit watt of the fuel cell – thus reducing the overall cost of the fuel cell for a
particular application. Thus proper water management in the fuel cell is essential towards usage
of PEM Fuel Cells in practical applications. There are two ways of addressing this
1. Active methods – This includes usage of an external fan which causes forced
convention or using an electro-osmotic pump. Considering the power required for
these external devices, the overall increase in performance is not as high as that
achieved by passive methods.
2. Passive methods – This includes design optimization such as flow channel design,
incorporation of porosity in the gas diffusion layer or using a micro porous layer and
also the usage of porous inserts in the flow channel.
12. 7
Fig 4: Effect of water generation on performance
4.2 Incorporation of Porous Inserts:
Among the passive methods, the incorporation of porous inserts in the rib area of the
flow plates drastically reduces water formation on the surface. This leads to overall performance
of the fuel cell. This is especially true for scaled up fuel cell models such as 70cm² (active area).
The flow channel type used is serpertine 2x2. The placement of the porous inserts is in the rib
area. The water formed in the flow channel is removed by the reactant gas and the water
formed in the rib area is now removed by the porous inserts. Also the types of porous inserts
used are classified based on length and by porosity.
The classification on length is:
1. 2mm
2. 5 mm
And classification based on porosity is:
1. 60-70%
2. 70-80%
3. 80-90%
13. 8
Fig 5: Rib area and flow channel
4.3 Modeling of Fuel Cell:
The modeling of 2mm and 5mm zigzag porous inserts are done using Solidworks 2014
software. Once the flow plate is extruded, the flow channel is drawn using linear sketch pattern
and extrude-cut along with the inlet and outlet. Then the porous inserts are drawn using linear
sketch pattern and extrude cut option.
Fig6: 2mm zigzag porous inserts
14. 9
Fig 7: 5mm zigzag porous inserts
4.4 Meshing of Fuel Cell Assembly:
The assembled fuel cell geometry is imported in Ansys Workbench V14.5software and
exported as a parasolid file (.x_b)
Fig 8: Assembled fuel cell in Ansys Workbench
The fully assembled fuel cell contains 7 parts- two graphite plates, two gas diffusion
layers, two catalysts and one membrane. From the assembled model, the flow channel is made
as a single part by using the ‘Line from points’ and ‘Surface from Edges’ options found from
Tools menu.
For the meshing of the assembled fuel cell, the parasolid geometry is imported in ICEM-
CFD software. The inlets and outlets are created using ‘create part’ option found in ‘part’ list.
15. 10
The next step is blocking. Using the Blocking tab, a 3d block is first created around the
entire geometry and then split-block is used to block the fuel cell further into sections. The mesh
is created by first blocking the points along the edges. The edges and vertices are then. Thus
blocks are created for each junction on the fuel cell.
Fig 8: Blocking – XY plane
Fig 9: Blocking – YZ plane
16. 11
Fig 10: Blocking – XZ plane
Once the blocks have been created, the number of nodes on each edge can be set. The
accuracy of the results is higher when the number of node points is increased. The number of
nodes can be set using the ‘Premesh’ tool. The required edge is selected and the number of
nodes is set. For parts with short length, lesser node values can be given.
The number of nodes for individual part can be found out by clicking on blocking menu.
Right click on the ‘edge’ menu followed by ‘Counts’
Fig 11 : Node Counts – XY plane
17. 12
Fig 12: Node Counts - YZ plane
Fig 13: Node Counts - XZ plane.
After setting up the number of nodes, the meshing parameters are fed. The ’Global
mesh’ menu is clicked. Cartesian mesh type is selected. The projection factor is changed to 1.
The ‘Compute Mesh’ icon is selected and the Cartesian file is loaded. The mesh is generated
when the ‘Compute’ button is clicked.
19. 14
Fig 17: Meshing about YZ plane
The resulting mesh is saved as a mesh file (.uns). Now that the meshing is done for the
whole assembly, the mesh can be imported in FLUENT 14.5 software and analysed
5.CONCLUSION:
Fuel cells are seen as a sustainable energy source for stationary applications as well as
automotive propulsion by scaling and stacking. However, the major commercialization problems
are to be addressed. It is evident that water generation on the electrolyte surface adversely
affects overall performance. The incorporation of porous inserts is aimed at managing this
issue. From the analysis of the fuel cell assembly, the effect of various porous inserts can be
studied. This can address the water management issue and the performance parameters can
be increased. From the analysis, the most efficient assembly can be fabricated and tested for
performance measurement. A comparison with the performance for a conventional fuel cell will
show the effect of the porous inserts for water management in the 70 cm² PEM Fuel Cell.
20. 15
BIBLIOGRAPHY:
1. Fuel Cell Engines by Matthew M. Mench
2. PEM Fuel Cells – Theory and Practice by Frano Barbir
3. Wei Dai, HaijiangWanga, Xiao-Zi Yuan, Jonathan J. Martin, Daijun Yang, JinliQiao, Jianxin
Ma. “A review on water balance in the membrane electrode
assembly of proton exchange membrane fuel cells.”
4. Fuel Cell Science and Engineering: Materials, Processes, Systems and technology by
DetlefStolten and Bernd Emonts.
5. Yong Hun Park, Jerald A. Caton- “Development of a PEM stack and performance analysis
including the effects of water content in the membrane”
