Title: Convective heat transfer from a spherical particle suspended in air
1Convective heat transfer from a spherical
particle suspended in air
- EGEE 520 Term Project Nari Soundarrajan
2Background
- Fluidized bed combustion (FBC) Ash Management
- Heat transfer to air and cooling of ash
- Air flow (pressure drop), particle size
distribution of ash
3Problem
- Isolated hot particle falling down in a counter
current of air - Particle falls down slowly at terminal velocity
- Spherical particle assumption
4Energy Balance
- Radiation exchange is considered eash 0.95
- ICs and BCs Match conduction to convection in
the air boundary layer hair averaged over the
temperature range. - t0 Particle temperature Tash1473K, conduction
in air is negligible along flow axis. - Assume conduction inside particle is fast
compared to convection at boundary (lumped
capacitance)
5Formulation
- 3D model of spherical particle in an air
cylinder - Convective Heat Transfer calculations for sphere
in immersed flowusing Nu hR/kair obtained k
usingstandard relations. - Cpair 1005 (J/kg.K) at 298K 1090
(J/kg.K) at 1000K - Kair 0.026 (W/m.K) at 298K 0.068
(W/m.K) at 1000K
6FEM Solution
2 D Solution
3 D Solution
7Results 2D
r R, r 10R r 20R
8Results 3D
9Validation Absence of convection
x axis at z1
x axis at z0.98
along flux Conductive
Biot no hairR/kash lt 0.1
Z axis at x0, y0
10Findings Future Work
- Particle size (diameter greatly increases)
localized temperature gradient and downstream
convection - Radiation effects are significant
- Multiple particle interaction needs to be
evaluated - Effect of temperature air convection properties
to be evaluated thoroughly.
11Acknowledgements
- Dr. Elsworth for starting me off and the feedback
- Peter Rozelle (DOE) for information on sphericity
and FBC parameters.
Key References
Weinell, C.E., DamJohansen, K. and Johnsson,
J.E., 1997, "Single-particle behaviour in
circulating fluidized beds", Powder Technology,
92 (3), 241-252. Mihalyko C., Lakatos B.G.,
Matejdesz A. and Blickle T., Population balance
model for particle-to-particle heat transfer in
gas-solid systems, International Journal of Heat
and Mass Transfer, 47(6), pp. 1325-1334,
2004. Bird, Stewart, Lightfoot, Transport
Phenomenon, Eastern Ed. Reprint 1994, John
Wiley and Sons, Singapore, pp. 409, 1960.