Non-uniform inlet flow rates of anode gas and cathode gas are practical because of the position of the manifold and the distributor geometry in a molten carbonate fuel cell. This study considered uniform, progressively increasing, and progressively decreasing profiles in the anode gas and the cathode gas, as well as combinations of
these profiles in the form of eight patterns of non-uniform inlet flow. Mass conservation, energy conservation and electrochemistry equations were considered, and the variation in the z direction ignored. Through the accuracy comparison in cell temperature and current density distribution, this study established the reliable numerical method by FORTRAN program. This study plots the temperature distribution and current density distribution on the cell plane in different patterns and draws the following conclusions. The cathode gas dominates the temperature distribution of the cell because of its flow rate exceeds that of the anode gas. The cell temperature is the highest in the corner of the outlet of the anode gas and the cathode gas in a uniform inlet flow pattern. The progressively increasing profile of the cathode gas moves the hot spot in the corner to the middle of cathode gas outlet.
The progressively decreasing profile of the cathode gas increases the temperature of the hot spot in the corner, and degrades the temperature distribution. Therefore, the position of the inlet manifold of the cathode gas must not be near the corner of the cathode gas inlet and the anode gas inlet, because it would then cause the progressively decreasing profile of inlet flow, and widen the cell temperature distribution. The anode gas dominates the current density of the cell because of the hydrogen concentration. The progressively increasing profile of the anode gas leads to the largest variation of the current density, and the progressively decreasing profile of the anode gas leads to the lowest average current density. This result implies that the uniformity of the anode gas in the inlet is important to the design of distributors.
Moreover, the non-uniform inlet flow only slightly affects the average temperature and the current density of cell, but it influences more strongly the range and contour outlines of cell temperature and current density. For example, the temperature variation on the cell plane in Pattern G and the current density variation on the cell plane in Pattern D are 12% and 37% higher than those of the uniform pattern, respectively, when the deviation of the non-uniform profile is 0.25. Therefore, the effect of the inlet flow maldistribution on the temperature and current density distribution on the cell plane is apparent, and cannot be neglected as the deviation of the profile increases.
Table 2.1 Expressions of energy source terms in Eq.X(2.5)X to Eq.X(2.11)X
Symbols Description Expression
ag s
qconv, − Heat transfer rate from separator to anode
gas by convection
( )
ha s ag−(
Ts−Tag)
cg s
qconv, − Heat transfer rate from separator to cathode
gas by convection
( )
ha s cg−(
Ts −Tcg)
qmass, − Heat transfer rate due to ion immigration
from cell to anode gas 2 p CO, 32 c
i c T
F −
c cg
qmass, − Heat transfer rate due to ion immigration
from cathode gas to cell 2 p CO, 32 cg
i c T
F −
qcont Heat transfer rate from cell to separator by
contact conduction
( ) (
c s)
qreac [49] Heat generation rate due to chemical reaction
Table 2.2 Parameters and conditions in this study Mole flow rate and molar fraction of species in anode inlet
N ag 0.0621 mol s
Mole flow rate and molar fraction of species in cathode inlet
N 0.1841 cg mol s
Inlet temperature
Tag 858 K
Tcg 867 K
Operation Pressure
P 3.5×105 Pa
Heat transfer area per unit area
aag-s=acg-s 1.26 m2 m-2
Table 2.3 Relative variation of cell temperature and current density at different non-uniform inlet flow patterns related to at uniform inlet flow
d=0.25 d=0.50 d=0.75 d=0.25 d=0.50 d=0.75 d=0.25 d=0.50 d=0.75 d=0.25 d=0.50 d=0.75 A -0.0160 -0.0676 -0.1907 -0.1833 -1.1626 -3.5033 2.4545 3.2414 2.0600 33.0081 81.0958 164.6495 B -0.0121 -0.0499 -0.0814 -0.4891 -1.8122 -4.5346 -0.0149 -2.0771 -7.2740 -15.302 35.2631 131.6049
C 0.0143 0.0582 0.1193 -0.0026 -0.0055 -0.1369 0.8594 4.5487 10.3150 3.6401 7.1689 12.0035
D 0.0063 0.0328 0.0607 -0.1659 -1.0670 -3.3795 3.3161 7.7346 9.5686 36.9351 90.1642 179.2814
E -0.0026 0.0005 0.0095 -0.5184 -1.8799 -4.7295 1.1046 3.5997 5.9902 -8.5275 46.5420 141.3524
F 0.0330 0.0992 0.2094 0.0403 0.0949 -0.0313 9.4151 23.5280 37.2358 -2.8645 -5.8102 -9.9523
G 0.0089 0.0040 -0.0438 -0.1568 -1.1202 -3.5865 11.5262 23.4491 28.7527 29.5586 73.8560 154.2792 H 0.0350 0.0888 0.1626 -0.4400 -1.6696 -4.4963 9.2487 22.6260 33.8558 -21.0292 29.8983 147.1528
Anode Eletrolyte Cathode
Cell y x
Separator
Separator Anode Gas
Cathode Gas
Fig 2.1. Schematic diagram of a molten carbonate fuel cell unit in crossflow
Fig 2.2. Patterns of non-uniform inlet flow profile in Chapter 2
Fig 2.3. Calculated node arrangement in this study
615.0 616.0 617.0 618.0 619.0 620.0 621.0 622.0 623.0 624.0 625.0
0 200 400 600 800 1000 1200
Number of grid points
Temperature (Tf, ℃)
Fig 2.4. Anode gas temperature at the central point versus grid numbers in numerical program.
615.0 616.0 617.0 618.0 619.0 620.0 621.0 622.0 623.0 624.0 625.0
0 200 400 600 800 1000 1200
Number of grid points
Temperature (Tccen, ℃)
Fig 2.5. Cell temperature at the central point versus grid numbers in numerical program.
610.0 611.0 612.0 613.0 614.0 615.0 616.0 617.0 618.0 619.0 620.0
0 200 400 600 800 1000 1200
Number of grid points
Temperature (Toxcen, ℃)
Fig 2.6. Cathode gas temperature at the central point versus grid numbers in numerical program.
615.0 616.0 617.0 618.0 619.0 620.0 621.0 622.0 623.0 624.0 625.0
0 200 400 600 800 1000 1200
Number of grid points
Temperature ( Tscen , ℃)
Fig 2.7. Separator temperature at the central point versus grid numbers in numerical program.
1650 1660 1670 1680 1690 1700 1710 1720 1730 1740 1750
0 200 400 600 800 1000 1200
Number of grid points Current density (Ir, A.m-2 )
Fig 2.8. Current density at the central point versus grid numbers in numerical program.
Fig 2.9. Cell temperature distribution calculated by the numerical method in Chapter 2 and FlexPDE software with uniform inlet flow rate
Fig 2.10. Current density distribution calculated by the numerical method in Chapter 2 and FlexPDE software with uniform inlet flow rate
Fig 2.11. Total Resistance distribution on the cell plane with uniform inlet flow
(a) Pattern A (b) Pattern B (c) Pattern C (d) Pattern D
(e) Pattern E (f) Pattern F (g) Pattern G (h) Pattern H
Fig 2.12. Cell temperature distribution of eight non-uniform patterns with deviation of 0.5
(a) Pattern B (b) Pattern F
Fig 2.13. Temperature difference related to uniform pattern on the cell plane
(a) Pattern A (b) Pattern B (c) Pattern C (d) Pattern D
(e) Pattern E (f) Pattern F (g) Pattern G (h) Pattern H
Fig 2.14. Current density distribution of eight non-uniform patterns with deviation of 0.5
(a) Pattern D (b) Pattern F
Fig 2.15. Current density difference related to uniform pattern on the cell plane
,
(a) average cell temperature (b) average current density
,
(c) cell temperature difference (d) current density difference
Fig 2.16. Relative variation of Tc and Ir at different non-uniform inlet flow patterns related to at uniform inlet flow patter