Performance evaluation of proton exchange membrane fuel cells adopting rectangular-baffle and tapered flow channels with an equivalent average depth

ABSTRACT

Optimizing the flow channel structures can improve the efficiency of proton exchange membrane fuel cells and promote the efficient utilization of clean energy. This study investigates the impacts of rectangular-baffle and tapered flow channels on electrical performance, temperature distribution and mass transfer of proton exchange membrane fuel cells, based on a 3D, multi-physical model. The equivalent average depth is adopted as the reference benchmark to mitigate the influence of channel depth. Results indicate that adopting variable-depth channels enhances convective mass transfer on the porous layer surface under higher voltage. The convective mass transfer of oxygen is dominant in the activation polarization region, while diffusion is dominant in the concentration polarization region. Variable-depth channels enhance heat and mass transfer in comparison to the straight channel. The tapered channel can improve the mass transfer flux in oxygen starvation region, and the drainage ability of the rectangular baffle channel is inferior to the tapered channel. The rectangular baffle channel demonstrates better convective heat transfer performance and temperature uniformity. A rectangular-baffle channel can increase net power by 4.31%, while a tapered channel can achieve a maximum increase of 9.27% when the pumping power is considered. Therefore, incorporating a tapered channel is an optimal strategy to boost cell efficiency.

KEYWORDS:

• Rectangular baffle
• proton exchange membrane fuel cell
• tapered flow channel
• mass transfer
• net power

Disclosure statement

No potential conflict of interest was reported by the author(s).

Nomenclatures

Abbreviate	=
CL – Catalyst layer	=
GC – Gas channel	=
GDL – Gas diffusion layer	=
ORR – Oxygen reduction reaction	=
PEMFC – Proton exchange membrane fuel cell	=
PEM – Proton exchange membrane	=
UAV – Unmanned air vehicle	=
Symbols	=
$a_{\mathrm{a}}/a_{\mathrm{c}}$ - Charge transfer coefficient of anode/cathode	=
$A_{\mathrm{act}}$ - Effective activation area of catalytic layer $({\mathrm{m}}^2)$	=
$c_{{\mathrm{H}}_2,\mathrm{ref}}/c_{{\mathrm{O}}_2,\mathrm{ref}}$ - Concentration of hydrogen/oxygen in reference to a specific context $(\mathrm{mol}\cdot {\mathrm{m}}^{-3})$	=
$C_{\mathrm{P}}$ - Specific heat capacity $(\mathrm{J}\cdot \mathrm{mo}{\mathrm{l}}^{-1}\cdot {\mathrm{K}}^{-1})$	=
$D_{\mathrm{c}}$ - Capillary diffusive coefficient $({\mathrm{m}}^2\cdot \mathrm{s})$	=
$D_{{\mathrm{H}}_2-{\mathrm{H}}_2\mathrm{O}}/D_{{\mathrm{O}}_2-{\mathrm{H}}_2\mathrm{O}}$ - Hydrogen/oxygen diffusion coefficient $({\mathrm{m}}^2\cdot \mathrm{s})$	=
$i_{0,{\mathrm{H}}_2}^{\mathrm{ref}}/i_{0,{\mathrm{O}}_2}^{\mathrm{ref}}$ - Anode/cathode reference current density $(\mathrm{A}\cdot {\mathrm{m}}^{-2})$	=
$k_{\mathrm{c}}/k_{\mathrm{e}}$ -Coefficient pertaining to the rate of condensation/evaporation $\left({\mathrm{s}}^{-1}\right)/\left(\mathrm{Pa}\cdot \mathrm{s}\right)$	=
$S_{\mathrm{i}},S_{\mathrm{m}},S_{\mathrm{T}},S_{\mathrm{vl}},S_{\mathit{\phi }}$- Species, mass, temperature, phase change, current source terms $(\mathrm{kg}\cdot {\mathrm{m}}^{-3}{\mathrm{s}}^{-1})$	=
${\mathit{u}}_g/{\mathit{u}}_{\mathrm{l}}$ - Vapor/liquid velocity$(\mathrm{m}\cdot {\mathrm{s}}^{-1})$	=
$\mathit{\eta }$- Activation over potential $(\mathrm{V})$	=
${\kappa }_{\mathrm{rg}}/{\kappa }_{\mathrm{rl}}$ - Relative permeability $({\mathrm{m}}^2)$	=
${\varphi }_{\mathrm{m}}/{\varphi }_{\mathrm{s}}$ - Electrolyte/electric phase potential $(\mathrm{V})$	=
${\mu }_{\mathrm{g}}/{\mu }_{\mathrm{l}}$ - Gas/liquid water dynamic viscosity $({\mathrm{m}}^2)$	=
$\mathit{k}$- Thermal conductivity $(\mathrm{W}\cdot {\mathrm{m}}^{-1}{\mathrm{K}}^{-1})$	=
$\mathit{\epsilon }$- Porosity	=
${\rho }_{\mathrm{g}}/{\rho }_{\mathrm{l}}$ - Vapor/liquid density $(\mathrm{kg}\cdot {\mathrm{m}}^{-3})$	=
Subscript and superscripts	=
a/c – Anode/cathode side	=
Act – Effective activation area	=
A/B – Case A/B	=
eff – effective	=
in/IN – Inlet or entrance	=
m – Ionic or mass	=
net – Net power	=
out/OUT – Outlet or exit	=
pumping – Pumping power of fuel cell	=
ref – Reference	=
s – Electric or solid	=
vl – Phase change	=

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [51976004].