Water Formation and Flooding Phenomena in Proton Exchange Membrane Fuel Cells

Yi-Shen Chena, Chin-Hsiang Chenga,*, Chun-I Leeb, Shiauh-Ping Jungb, Chi-Chang Chenb, Ozhgibesov Mikhaila

a Dept. of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan

 b Green Energy and Environment Research Lab., Industrial Technology Research Institute,

Hsinchu, Taiwan

Fuel Cell1/50

• A Fuel Cell is a device that converts the

chemical energy from a fuel into electricity

through a chemical reaction with oxygen or

another oxidizing agent;

• Fuel Cell can produce electricity continually

for as long as fuel and oxygen are supplied;

• As the main difference among fuel cell types

is the electrolyte, fuel cells are classified by

the type of electrolyte they use.

• The energy efficiency of a fuel cell is

generally between 40-60%, or up to 85%

efficient if waste heat is captured for use.• Proton exchange membrane Fuel Cell (PEMFC) is a type of fuel cell being

developed for a wide range of applications, including stationary and portable fuel

cell based devices;

Proton Exchange Membrane Fuel Cell (PEMFC)

2/50

PEMFC Design Issues3/50

• Water and air management:The membrane must be hydrated;requiring water to be evaporated at precisely the same rate that it is produced;Quick evaporation -the membrane dries, resistance across it increases, and

eventually it will crack, creating a gas "short circuit" where hydrogen and oxygen combine directly, generating heat that will damage the fuel cell;

Slow evaporation- the electrodes will flood, preventing the reactants from reaching the catalyst and stopping the reaction;

• Temperature management:The same temperature must be maintained throughout the cell in order to prevent

destruction of the cell through thermal loading. This is particularly challenging as the 2H2 + O2 -> 2H2O reaction is highly exothermic, so a large quantity of heat is generated within the fuel cell.

• Durability, service life, and special requirements for some type of cells:Stationary fuel cell applications typically require >40,000 hours of reliable

operation at a temperature of -35 °C to 40 °C;Automotive fuel cells require a 5,000 hour lifespan under extreme temperatures.

Highlights4/50

• This work deals with the numerical simulations of liquid

water formation and migration in PEMFC;

• All calculations have been carried out by using the CFD-

ACE+ software;

• Distributions of the flow field, concentration, electric

field and pressure have been calculated;

Studied Modelparallel flow channel of fuel cell

Solution Domain

end plate of anode;

end plate of cathode;

flow channel of anode;

flow channel of cathode;

GDL;

Cathode GDL

Anode GDL

Cathode Catalyst

Membrane

Anode Catalyst

5/50

Results (Current Density)6/50

Average current density [A/m2)]versus time [s]

The distribution of current density

10s

20s

30s

45s

60s

65s

70s

75s

80s

85s

Results (Water Distribution)7/50

10s

20s

30s

45s

60s

65s

70s

75s

80s

85s

• water formation does not take place

in first 60 sec;

• Fig. (g) to Fig. (j), the liquid water is

produced at the region of rib;

• water diffuses to the region of flow

channel.

Results (Water Vapor Distribution)8/50

10s

20s

30s

45s

60s

65s

70s

75s

80s

85s

• the water vapor distribution of

the interface between the

catalyst layer and cathode

GDL;

• the water vapor concentration

decreases at the region of liquid

water formation (Fig.(e)-Fig.

(f));

• (Fig.(h)-Fig.(i)) the water vapor

concentration increases, due to

the decay on previous step.

Conclusion

• Numerical calculation of transient mode in PEMFC requires

consideration of the time term effect of electrochemical reaction,

diffusion of fuel and energy transmission.

• The system reaches steady state regime in 50s from initial state ;

• In transient mode, one should consider that the water vapor

concentration in gas increases or decreases by the water

condensation or evaporation, so adds the source of the mass flow

rate per unit volume from phase change in species diffusion equation

.

9/50

Thanks for your attention!

統御方程式 質量守恆方程式：

動量守恆方程式：

能量守恆方程式：

物種擴散方程式：

電流守恆方程式：

VOF 方程式：

水凝結 / 蒸發方程式：

源項計算：　　　　； 　

0

z

i

y

i

x

i

satwsatwwe

satwsatww

cww

PPXPPXSK

PPXPPXRT

XKMm

當

當

)(

)(

wmixmix SVt

)(

V

PVVt

V mix2

)()()(

h

eff

T Si

jVqVht

h

2

V

A)(

)(

ciii SJVYtY

i

)()(

1/50

wc mS

wSz

Fw

y

Fv

x

Fu

t

F

w

ww

mS

模型建立測試例的參數設定

Boundary conditions

ANODE CATHODE

Inlet temperature 70 ℃ 70 ℃

Outlet temperature

70 ℃ 70 ℃

Wall temperature 70 ℃ 70 ℃

relative humidity 100% 100%

stoichiometry 1.5 2.5

Inlet velocity(m/s)

0.29 1.26

Operation voltage 0.6 V

42/50