International Symposium and School for Young Scientists INTERFACIAL PHENOMENA AND HEAT TRANSFER,
Novosibirsk, Russia, 2-4 of March 2016
Thermal and fluid issues in proton exchange membrane fuel cells
Hang GUO1,2,*, Jiaxing LIU1, Fang YE1 and Chongfang MA1
1. MOE Key Laboratory of Enhanced Heat Transfer and Energy Conservation, and Beijing Key Laboratory of Heat Transfer and Energy
Conversion, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China
2. Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081
*Corresponding author, E-mail: hangguo@sohu.com
As is known to all, hydrogen and oxygen are supplied
to proton exchange membrane fuel cells (PEMFCs) for the
electrochemical reaction, and water and heat are produced.
As a result, various fluids, i.e. hydrogen, oxygen, liquid
water, and water vapor, transport in the fuel cell. The fluids
couples with heat, which introduces complicated thermal
and fluid issues. The Thermal and fluid issues broadly exist
in the PEMFC. Examples of thermal and fluid issues show
as follows: Droplet behavior and movement in fuel cells;
gas-liquid two-phase flow in the fuel cell components; heat
transfer between fluids and components of the fuel cells;
interaction between water and heat; heat flux across the fuel
cell components and so on. All these phenomena affect the
performance of PEMFCs. Besides, the safe and stable
operation of the fuel cell highly relies on these phenomena.
Investigation of these phenomena helps to understand the
related mechanism in PEMFCs.
Water, one of the various fluids, plays a vital role in
the PEMFC. As a product of electrochemical reaction, water
involves diverse phenomena in PEMFC, such as droplet
behavior in the porous layer (Liu and Pan (2012)),
two-phase flow in the gas channel (Guo et al. 2014). Droplet
behavior and two-phase flow are important phenomena in
PEMFC, which are related to interfacial phenomena.
Interfacial phenomena are difficult to be investigated
in PEMFC because of its structure. It is well known that the
PEMFC consists of several components. The main
components are gas channel, gas diffusion layer, catalyst
layer, and membrane. Interfacial phenomena occur inside the
fuel cell, which is difficult to be directly investigated. For
example, the contact angle is difficult to be measured,
especially for droplet in the gas diffusion layer of an
operating fuel cell. In consequence, transparent window
installed in end plate of fuel cell has been developed to
visually observe the two-phase flow in the gas channel. The
gas-liquid phase boundary may be identified in the
visualization images. However, merely observation is not
enough. Although two-phase images can be obtained by high
speed camera or other instruments, interfacial phenomena
related parameters e.g. contact angle cannot be reflected in
these images. In other words, interfacial phenomena are
rarely investigated in the two-phase flow visualization. Even
though the two-phase flow can be visualization, difficulties
remain from the fluid point of view. The interfacial
phenomena such as two-phase flow coupled with
electrochemical reaction, heat transfer, and mass transport is
a complex transient process, which is rather intractable.
Electrochemical reaction produces water and heat, which
introduces interfacial phenomena and heat transfer in the
fuel cell. In turn, interfacial phenomena and heat transfer
affect electrochemical reaction by influencing mass transport
and other factors. These phenomena affect and interact with
each other, which complicates any single issue.
Heat generation and transfer is another important issue
in PEMFC. Better thermal management makes the fuel cell
operate more safe and steady. To monitor parameters related
to heat is helpful for reasonable thermal management.
However, parameters measurement in fuel cell is a huge
challenge because of the limitation of its structure.
Temperature, heat flux, and other parameters related to
thermal issue are desired to be obtained to better understand
the heat transfer inside the fuel cell. Although temperature
measurements using thermocouple (Mench et al. 2003) and
infrared thermal imaging (Guo et al. 2015) in PEMFC have
been conducted, difficulties still remain. Thermocouple is
easy to be damaged, and it needs to be inserted into fuel cell,
which deteriorates the performance of fuel cell. Fuel cells
need to be reconstructed by using infrared thermal imaging
method. Little work has been conducted on the measurement
of heat flux and thermal conductivity of components.
Similar to the temperature measurement, problem exists to
measure the heat flux inside fuel cells. The effect of
measurement methods on the performance of fuel cells and
the safety and reliability of the measurement tool are needed
to be considered. More works are still wanted in this area.
Keywords
flow field, heat and mass transfer, phase change, proton
exchange membrane fuel cells, two-phase flow
Acknowledgement
The authors are grateful to the National Natural Science
Foundation of China (Grant No.: 51476003) for the financial
support.
References
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