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Convective heat transfer from a spherical particle suspended in air EGEE 520 Term Project Nari Soundarrajan

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Nari Soundarrajan EGEE 520 Fall 2005 2 Background Fluidized bed combustion (FBC) Ash Management Heat transfer to air and cooling of ash Air flow (pressure drop), particle size distribution of ash

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Nari Soundarrajan EGEE 520 Fall 2005 3 Problem Isolated hot particle falling down in a counter current of air Particle falls down slowly at terminal velocity Spherical particle assumption

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Nari Soundarrajan EGEE 520 Fall 2005 4 Energy Balance Radiation exchange is considered ε ash ~ 0.95 ICs and BCs: Match conduction to convection in the air boundary layer; h air averaged over the temperature range. t=0: Particle temperature T ash =1473K, conduction in air is negligible along flow axis. Assume conduction inside particle is fast compared to convection at boundary (lumped capacitance)

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Nari Soundarrajan EGEE 520 Fall 2005 5 Formulation 3D model of “spherical” particle in an air cylinder Convective Heat Transfer calculations for sphere in immersed flow using Nu = hR/k air obtained k using standard relations. C p air = 1005 (J/kg.K) at 298K = 1090 (J/kg.K) at 1000K K air = 0.026 (W/m.K) at 298K = 0.068 (W/m.K) at 1000K

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Nari Soundarrajan EGEE 520 Fall 2005 6 FEM Solution 2 D Solution 3 D Solution

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Nari Soundarrajan EGEE 520 Fall 2005 7 Results – 2D r = R, r = 10R r = 20R

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Nari Soundarrajan EGEE 520 Fall 2005 8 Results – 3D

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Nari Soundarrajan EGEE 520 Fall 2005 9 Validation: Absence of convection Biot no h air R/k ash < 0.1 x axis at z=1 along… flux Conductive x axis at z=0.98 Z axis at x=0, y=0;

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Nari Soundarrajan EGEE 520 Fall 2005 10 Findings & 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.

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Nari Soundarrajan EGEE 520 Fall 2005 11 Acknowledgements 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.

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