Thesis for degree: Licentiate of Engineering

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In Figure 4.5 shows the whole modeled porous domain for the mole fraction distribution of H 2 . The inlet mole fraction is specified as x H2 = 0.9 and the mole flux is specified at the outlet. Note that no reaction effects are included in the model. The mass diffusion of hydrogen predicts, in a similar manner as the simpler channel case, the continuous reduction of hydrogen along the flow direction and the contours of the mole fraction around the obstacles normal to the surface indicates that mass diffusion occurs parallel to the surface. 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 Figure 4.6: Mole fraction distribution of H 2 O in a porous media with a porosity of 0.40. In Figure 4.6 the mole fraction distribution of H 2 O is shown for the whole modeled domain. The inlet mole fraction is specified as x H2O = 0.1 and the mole flux is specified at the outlet in a negative direction, i.e., normal to the boundary interface in opposite flow direction. Note that no reaction effects are included. This is a heavier species where the diffusion is not as fast as for the hydrogen case. Only the interaction between the two species is illustrated in this case. The local spots with higher mole fraction are because these are a closed pores and the velocity effect is very low there. For future studies, the production and consumption of species will be included and the effect of the chemical reactions on the mass density distribution. 4.2 Evaluation of kinetics at smaller scales As mentioned before, the analysis is carried out for the steam reforming reaction in the anode and the electrochemical reactions in the anode and cathode. The most significant parameters concerning the cell structure and catalytic activity, which are used for the calculations, are presented in Table 4.2, while the inlet and operating conditions are presented in Table 4.3. Note that the x-direction is the main flow direction and the direction set at the inlet. The y- direction is normal to the main flow direction. 40
Table 4.2: Parameters in the SOFC analysis. Parameter Value Cell length Anode thickness Cathode thickness Particle diameter 0.1 m 500 μm 50 μm 0.34 μm Anode TPB thickness (y-dir) 10 μm, 1 μm 2 Cathode TPB thickness (y-dir) 10 μm, 1 μm 2 Tortuosity 3 Porosity 0.3 Velocity v x,A Velocity v y,A Velocity v x,C Velocity v y,C Enthalpy change (MSR 3 ) Activation energy (MSR 3 ) Activation energy (CE 4 ) Activation energy (AE 5 ) Reaction rate (MSR 3 ), close to inlet Reaction rate (CE 4 ) Reaction rate (AE 5 ) 6.9 ∙10 -5 m/s 1.5∙10 -3 m/s 1∙10 -3 m/s 7.5 ∙10 -4 m/s 226 kJ/mol 82 kJ/mol 71 kJ/mol 185 kJ/mol 15 mol/m³/s 0.53 kmol/m³/s, 5.3 kmol/m³/s 2 1.06 kmol/m³/s, 10.1 kmol/m³/s 2 It should be noted that for the thickness of the anode and cathode TPB as well as the reaction rate for the anode and the cathode have been tested for two different values of each parameter. 2 Two different values for this parameter are tested. 3 MSR stands for methane steam reforming reaction 4 CE for the electrochemical reactions in the cathode 5 AE for the electrochemical reactions in the anode 41
Page 1 and 2: SOFC modeling from micro to macrosc
Page 3 and 4: Abstract The purpose of this work i
Page 5 and 6: katalytisk omvandling av naturgas o
Page 7 and 8: List of publications Journal public
Page 9 and 10: 3.2 Governing equations for the mac
Page 11 and 12: Q source term (heat), W/m3 q heat f
Page 13 and 14: 1 Introduction After some time of d
Page 15 and 16: 2 SOFC modeling at smaller scales T
Page 17 and 18: etween 0.3 and 1.5 mm. In this conf
Page 19 and 20: Volume Method (FVM) which adopt the
Page 21 and 22: 2.3 Lattice Boltzmann method LBM ha
Page 23 and 24: streaming [3]. The concentration ρ
Page 25 and 26: ease the correspondence between the
Page 27 and 28: applicable for a mixture of two spe
Page 29 and 30: Figure 2.6: Effective boundary arra
Page 31 and 32: Table 2.1: Comparison of previous w
Page 33 and 34: Figure 2.7: Schematic illustration
Page 35 and 36: model is presented after the data c
Page 37 and 38: 3.2.1 Mass transport In the electro
Page 39 and 40: where h v is the volume heat transf
Page 41 and 42: Achenbach [43], it was found that t
Page 43 and 44: cathode are assumed to be similar t
Page 45 and 46: (3.48) where, besides the parameter
Page 47 and 48: for an isothermal spherical particl
Page 49 and 50: Velocity carried out to check wheth
Page 51: Figure 4.4: Velocity field [lu/ts]
Page 55 and 56: eactions are safely fulfilled. This
Page 57 and 58: Figure 4.8: Mole fraction distribut
Page 59 and 60: Table 4.5: Inlet mole fractions for
Page 61 and 62: Figure 4.12: Mole fraction distribu
Page 63 and 64: 5 Conclusions The physics and the t
Page 65 and 66: 7 References [1] Andersson M., Yuan
Page 67 and 68: [25] Latt J., Hydrodynamic Limit of

Thesis for degree: Licentiate of Engineering

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