are the activation energies for the anode and cathode electrochemical reactions, respectively。
p0 are the partial pressure of H2 and the partial pressure of H2O at the fuel channel inlet,
2respectively,
0 is the partial pressure of O at the air channel inlet,
pressure of H2 and the partial pressure of H2O at the anode three phase boundaries (TPBs), respectively
is the partial pressure of O2 at the cathode TPBs,
are the exchange transfer
current density of anode and cathode respectively。
are the anode and cathode activation loss respectively, defined as
) is the anode (cathode) concentration loss。
2。2。2。Boundary Setting for the Mass Transport Equation
At the channel inlets, the concentration of gaseous species are imposed, whereas, the convective fluxes are considered at the channel outlets, which mean diffusive component across the channel outlets is zero。 The boundaries B5 and B9 represent the interfaces between channel and electrode, where species fluxes are continuous。 As there is electrochemical reaction at boundaries B6
and B7, the normal molar flux of hydrogen, water and oxygen are
/ (4F) , respectively。 The insulation condition is set at all other boundaries, which implies the
molar flux of species is zero。
2。2。3。Boundary Setting for the Momentum Transport Equation
At the channel inlets, the uniform inlet velocity are applied, whereas, pressure and the normal flow are imposed at the channel outlets。 The no slip condition is considered at all others boundaries, which means u 0 。
2。2。4。Boundary Setting for the Heat Transport Equation
At the channel inlets, the uniform temperature are applied, whereas, the convective fluxes are considered at the channel outlets。 The boundary condition at boundary B4 and B8 become as
n NT Qohm due to contact resistance。 The boundary condition at boundary B6 and B7 are specified as
n NT Qact Qentr
due to the reaction。 Boundary B2, B3, B10 and B11 are the interfaces between rib
and channel, where the convection heat between rib and channel is considered。
For rib, convection heat transfer rate is given as
n NT h(Tchan/rib Trib/chan )
(29)
For fluid in channel, convection heat transfer rate is given as
n NT h(Tchan/rib Trib/chan )
(30)where Tchan/ rib
channel (rib) side。
( Trib/chan ) is the temperature at the interfaces between rib and the channel on
Adiabatic boundary condition is employed at all other boundaries since the simulation region is the half of one repeating unit located at the center of stack。
2。3。 Numerical Implementation
The model was implemented in the finite element commercial software COMSOL MULTIPHYSICS。 The COMSOL stationary nonlinear solver uses an affine invariant form of the damped Newton method to solve the discretized PDEs with a relative convergence tolerance of 1×10-6。 The mesh is composed of 6,540 elements with 117,279 degrees of freedom。 The values of input parameters for the base case are summarized in Table 1 and Table 2 unless otherwise stated。
Table 1。 Model parameters。
Parameter Value
Fuel channel inlet velocity, u fuel (m s-1)
0 固体氧化物燃料电池英文文献和中文翻译(5):http://www.youerw.com/fanyi/lunwen_101789.html