Fundamental Numerical Analysis of a Porous Micro-Combustor Filled with Alumina Spheres: Pore-Scale vs. Volume-Averaged Models
Abstract
:1. Introduction
- (1)
- The combustion of H2/air in a regularly packed bed of alumina spheres is numerically simulated using a 3D PSM. The energy conservation equation of the solid matrix and combustor wall are combined to examine the temperature distribution in a porous micro-combustor.
- (2)
- The simulation results based on the PSM are systematically compared with those obtained by the VAM to analyze the combustion characteristics and flame stability limits.
- (3)
- The heat recirculation is examined, including preheating and heat loss, in the porous micro-combustor using the VAM and PSM.
- (4)
- A parametric study is carried out to examine the effects of solid matrix thermal conductivity (ks) on the PSM and VAM.
2. Modeling
2.1. Pore-Scale Model
2.2. Volume-Averaged Model
3. Results and Discussion
3.1. Model Validation
3.2. Fundamental Combustion Characteristics for the VAM and PSM
3.3. Heat Recirculation for VAM and PSM
3.3.1. Definition of Solid-To-Gas Preheating Zone and Heat Loss Zone
3.3.2. Heat Recirculation through Solid-To-Wall Heat Exchange
3.3.3. Ratio of Preheating to Heat Loss for VAM and PSM
3.4. Effects of Solid Matrix Thermal Conductivity (ks)
4. Conclusions
- (1)
- The VAM predicts a parabolic flame front and the highest temperature region at the centerline, but the PSM predicts a scattered flame zone in the pore areas;
- (2)
- Under the same flow conditions and properties of porous medium, the PSM gives a larger flame stability range, a lower flame temperature and peak solid matrix temperature and a higher peak wall temperature than a VAM counterpart;
- (3)
- In the PSM combustor, solid-to-wall heat exchange (qs−w) between the solid matrix and wall decreases with the decrease in Φ;
- (4)
- Ratio of preheating to heat loss (Rp-hl) of the PSM and VAM both decrease with the increase in Φ, and the PSM combustor provides a larger Rp-hl;
- (5)
- Under the same flow conditions and properties of porous media, the difference of temperature and Rp-hl between the PSM and VAM decreases with the increase in Φ, and the decrease in ks.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
Nomenclature
Ap | Contact heat transfer area between the solid matrix and wall, m2 |
ds | Alumina spheres diameter, m |
Di | Diffusion coefficient of the ith species into the mixture, m2/s |
h | Convective heat loss coefficient (non-insulated wall), W/m2-K |
hv | Volumetric heat transfer coefficient between solid and gas, W/m3-K |
H | Combustor height, m |
kg | Thermal conductivity of gas mixture, W/m-K |
ks | Thermal conductivity of solid matrix, W/m-K |
kw | Thermal conductivity of wall, W/m-K |
L | Combustor length, m |
n | Total number of the faces in the surface, |
p | Pressure, Pa |
qr | Source term due to radiation, W/m2 |
qw | Heat loss from non-insulated wall, W/m2 |
Q | Heat content of the reactive mixture, J |
t | Wall thickness, m |
T0 | Inlet flow temperature, K |
Ta | Ambient temperature, K |
Tg | Gas mixture temperature, K |
Ti | Local temperature in the facet, K |
Tw | Wall temperature, K |
Two | Outer wall temperature, K |
Averaged fluid or solid temperature, K | |
ug | Velocity in x-direction, m/s |
U0 | Inlet flow velocity, m/s |
vg | Velocity in y-direction, m/s |
wg | Velocity in z-direction, m/s |
W | Combustor width, m |
Wi | Molecular mass of the ith species, kg/mol |
Yi | Mass fraction of the ith species, kg/kg |
Greeks | |
εr | Emissivity of non-insulated wall, |
μ | Dynamic viscosity, N-s/m2 |
ρg | Density of gas mixture, kg/m3 |
σ | Stefan–Boltzmann constant, 5.67 × 10−8 W/m2-K4 |
Φ | Equivalence ratio |
ωi | Production rate of the ith species, kmol/m3-s |
Acronyms | |
PSM | Pore-scale model |
VAM | Volume-averaged model |
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Li, Q.; Wang, J.; Li, J.; Shi, J. Fundamental Numerical Analysis of a Porous Micro-Combustor Filled with Alumina Spheres: Pore-Scale vs. Volume-Averaged Models. Appl. Sci. 2021, 11, 7496. https://doi.org/10.3390/app11167496
Li Q, Wang J, Li J, Shi J. Fundamental Numerical Analysis of a Porous Micro-Combustor Filled with Alumina Spheres: Pore-Scale vs. Volume-Averaged Models. Applied Sciences. 2021; 11(16):7496. https://doi.org/10.3390/app11167496
Chicago/Turabian StyleLi, Qingqing, Jiansheng Wang, Jun Li, and Junrui Shi. 2021. "Fundamental Numerical Analysis of a Porous Micro-Combustor Filled with Alumina Spheres: Pore-Scale vs. Volume-Averaged Models" Applied Sciences 11, no. 16: 7496. https://doi.org/10.3390/app11167496