where 0
is the electronic conductivity of the pure material, is the porosity,
el is the
volume fraction of electronic conductor phase, B is the Bruggeman factor used to include the effects of
tortuous conduction paths (B is set as 3。5 [30]) and
pelis the probability for electronic conductor
particles to belong to the percolated clusters of electronic (ionic) conductor particles。
for Ni and LSM may be estimated as [26, 31],
The ionic conductivity of electrolyte may be estimated as
where T is the temperature。
2。1。2。Momentum Transport
Momentum transport in the fuel or air channel can be modeled by applying the Navier–Stokes equation in conjunction with the continuity equation。
where is the density, I is the identity matrix, is the viscosity coefficient of fluid, p is the pressure and u is the velocity of fluid。
2。1。3。Mass Transport
Mass transport mechanism in channel is simple, which can be described by Fick's model associated with the mass continuity equation。
Ni (DiCi Ciu) 0 (9)
whereNi is the molar flux of species i , Ci
is the molar concentration of species i ,
diffusion coefficient of species i , which equates to binary diffusion coefficient
compose of two species (H2, H2O) and the air compose of two species (O2, N2)。
by following equation。
Dijcan be evaluated
3。198108 T1。75 1 1
is diffusion volume for specie i ( 6。1210
, 13。110
, 16。310
and 18。510
m3 mol-1 for H , H O , O and
N , respectively [32]) and M ( M ) denotes molecular mass of species
2 2 2 2 i j
i ( j ) (kg mol-1)。
Mass transport mechanisms in the porous electrodes are complex, molecular diffusion and Knudsen diffusion are taken into account。
where Deff is the equivalent diffusion coefficient of species i , which can be written as
wherexi ( x j ) is the molar fraction of species i ( j ),
diffusion coefficient and the effective Knudsen diffusion coefficient of species i respectively。
can be evaluated by following equations respectively [29, 33]。
where R is the universal gas constant,
r is the pore radii and is the tortuosity factor。
2。1。4。Heat Transport
Temperature is one of the most critical factors, which significantly affects SOFC performance, because many properties of the SOFC components are temperature dependent such as the electrical and ionic conductivity, the electrochemical reaction rate, fluid properties。 For a 3D model, it is essential to take into account heat transport。
In the fluid domain, heat conduction and heat convection are must considered together。
is the thermal conductivity of the fluid,
NT is the heat flux,
Cf is the molar
concentration of the fluid, C is the molar heat capacity of the fluid, which can be written as [32] 固体氧化物燃料电池英文文献和中文翻译(3):http://www.youerw.com/fanyi/lunwen_101789.html