The document summarizes heat and mass transfer characteristics of direct methanol fuel cells (DMFCs) based on experiments and modeling. Key points: - A 3D non-isothermal model is developed to predict methanol and temperature distributions in the anode. Experimental results validate the model. - Increasing methanol concentration does not significantly impact net water generation but does increase methanol crossover, affecting cell performance. - At 1M methanol concentration and 230mA/cm2 current density, the fuel utilization efficiency is 57% despite high methanol crossover. - Temperature distribution shows methanol solution heated to 57°C from 27°C, improving cell performance. Double channel serpentine flow field aids methanol diffusion.

1. Heat and Mass Transfer Characteristics of Direct
Methanol Fuel Cell: Experiments and Model
By
B. Mullai Sudaroli
and
Prof. Ajit Kumar Kolar
Department of Mechanical Engineering
Indian Institute of Technology Madras
4th International Conference on Advances in Energy Research
(ICAER 2013)
Indian Institute of Technology Bombay, Mumbai, India.

2. Introduction
Direct Methanol Fuel Cell(DMFC)
Fuel cell is an electrochemical device which converts chemical
energy of fuel and oxidant in to electrical energy. Fuel is
methanol.
Conventional Energy
Thermal
Energy
Chemical
Energy
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Mechanical
Energy
DMFC
Electrical
Energy

3. Advantages and Applications
Advantages
 Electrical Efficiency 40-60%
 No harmful emissions
 No moving parts-no noise and less maintenance
 Low temperature
 Operates as long as fuel is supplied
 Direct use of fuel- Reformer is not required
 High energy density-10 times higher than hydrogen
 Safe, easy to handle and transport
Applications
 Portable applications (mW-W)
Mobile phones, Laptops
 Sensors (W)
 Distributed power generation(kW)
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4. Working Principle
Anode reaction
CH3OH+H2O
Cathode reaction
3/2O2+6H+ +6eOverall reaction
CH3OH+3/2O2
6H+ +6e- + CO2
3H2O
2H2O+CO2
The crossover reaction at cathode
2CH3OH+3O2
4H2O+2CO2
Methanol and water crossover
Methanol and water crosses through the membrane and affects ORR
due to oxygen deficiency at the cathode catalyst layer, hence there is
loss in potential and fuel utilization.
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5. Objective and Scope
Objective
Heat and mass transfer characteristics of DMFC and its effect on
cell performance.
Scope
 To develop a full cell model for anode side of DMFC and to
predict methanol and temperature distribution.
 To study the methanol and water transfer process through the
membrane with varying methanol concentration and cell
current density.
 The effect of double channel serpentine flow field on cell
performance
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6. Experimental Programme
Experimental Setup
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Double channel flow field plate

7. Geometric parameters
Active area of the cell (mm)
50X50
Diffusion layer thickness(mm)
0.14
Catalyst layer thickness(mm)
0.03
Membrane thickness(mm)
0.18
Chanel width, depth and rib width (mm)
1
Operating conditions
Methanol flow rate (ml/min)
Air flow rate (ml/min)
600
Cell temperature (°C)
60
Methanol concentration
7
14
0.25,0.5,1M
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8. Mathematical Model
Governing equations
Smeoh  
Mass conservation equation

( u )  m
Mmeoh
ja
6F
.
Mh 2 o
Sh 2 o  
jc
6F
.
Mco 2
Sco 2 
jc
6F
Mco 2 j
m  MmeohSmeoh  Mh 2 oSh 2 o 
6F
m  Mo 2 So 2  Mh 2 oSh 2o
Mo 2
SO 2  
jc
4F
Momentum conservation equation
 uu   P    .u   Su
Mo 2
Sh 2 o  1   
jc
2F
Species conservation equation
 uCi     Deff Ci   Si
Energy conservation equation
  CpuT     D T   ST
 u 
Su   

 K 
ST 
 Hc - Gc 
( I  Icr ) a - I
eff
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ST  I a  Icr
4F
 Ha  Ga 
6F

9. Voltage and current density relation
 Xch
ja  aia ref 
ref
 Xch

  aF 
exp 
a 


 RT

 Xo
jc  aic ref  ref
 Xo

  cF 
exp 
c 


 RT 
 I  Icr 
1
 Xo
 aic ref  ref
tc
 Xo

  cF 
exp 
c 


 RT 
Average current density
I   jadz
Effective diffusion coefficient of porous layer
Deff  D 1.5
Methanol flux in the membrane and crossover current density
m
 D m chdC
 chI
m
m
Nch 
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
F
Icr  6 FNch
Ec  E 0  a   c  IRm

10. Water crossover
icell
 dC 
Nw m   Dw eff ,m    nd
F
 dx 
Methanol crossover
Nch m
 ch icell  D m ch Cch ac / m


F
td
Net water generation
Nw  Nm  2 Nch
w
m
 icell 

 2F 

Nw  Nm w  Nmco w  Now
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 icell 
Nw  
 (  1)
 6F 

11. Assumptions and Boundary Conditions
 Steady state, non-isothermal and single phase flow
conditions
 Mass fraction and velocity of methanol at the channel
inlet is given as inlet condition.
Ambient pressure condition is given as outlet condition at
the channel outlet
Methanol at the cathode catalyst layer is completely
oxidized
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12. Temperature distribution ( C)
 The graphite plate temperature is maintained at 60 C and the
methanol is sent at 27 C. The methanol solution temperature is
raised to 57 C when it passes through the flow field plate.
 The methanol solution at high temperature is sent to the
methanol tank and circulated back to the fuel cell. This helps in
improving the cell performance.
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13. Methanol distribution (mass fraction)
Mass fraction of methanol indicates the cell current density
distribution
Double channel serpentine takes a turn and has long channel length
which helps in methanol diffusion under the rib.
Methanol distribution in anode catalyst layer controls the cell
performance which can be controlled by flow field design and
operating conditions such as cell temperature and methanol
concentration.
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14. Effect of methanol concentration on cell performance
The difference between experimental data and predicted data is
0.2 to 0.3V and it is due to cathode potential is not taken into
account for predicting cell voltage.
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15. Effect of methanol concentration on methanol crossover
and water crossover
Higher the methanol crossover leads to high mixed potential.
This affects the cell performance and fuel utilization efficiency
Net water transfer coefficient decreases from 55 to 32 as the
current density increases.
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16. At 1M, 50% of water generation is due to methanol crossover
at low current density and it decreases with increasing current
density.
 As the methanol concentration decreases, water concentration
is more in methanol solution and it leads to reduction in
methanol crossover and increase in water crossover.
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17. Conclusions
 A three dimensional non-isothermal model is developed for anode
side of DMFC. The model results are compared with experimental
data.
 Methanol and temperature distribution in anode are found.
 The methanol concentration doesn’t have significant impact on net
water generation.
 Even though the methanol crossover is high at 1M, FUE is 57% at
230mA/cm2.
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18. References
1.
2.
3.
4.
5.
18
Jiabin Ge, Hongtan Liu, 2006, “A Three-Dimensional Mathematical
Model for Liquid-Fed Direct Methanol Fuel Cells”, International Journal
of Power Sources 160: 413–421.
Marcos Vera, 2007, “A Single-phase Model for Liquid-feed DMFCs with
Non-Tafel kinetics”, International Journal of Power Sources 171: 763–
777
Li, X.Y., Yang, W.W., He, Y.L., Zhao, T.S., Qu, Z.G., “Effect of Anode
Microporous Layer on Species Crossover through the Membrane of the
Liquid-Feed Direct Methanol Fuel Cells”, International Journal of
Applied ThermalEngineering,doi:10.1016/j.applthermaleng.2011.10.051.
Yang, W.W., Zhao, T.S., Xu, C., 2007, “Three-dimensional Two-phase
Mass Transport Model for Direct Methanol Fuel Cells”, International
Journal of Electrochimica Acta 52: 6125–6140.
Nobuyoshi Nakagawa, Mohammad Ali Abdelkareem, Kazuya
Sekimoto, 2006, “Control of Methanol Transport and Separation in a
DMFC with a Porous Support” International Journal of Power Sources
160: 105–115.
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20. Experimental Results
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