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RESEARCH PAPERS

Porosity and Permeability Effects on Centerline Temperature Distributions, Peak Flame Temperature, Flame Structure, and Preheating Mechanism for Combustion in Porous Media

[+] Author and Article Information
S. R. F.

School of Mechanical Engineering,  Sharif University of Technology, Tehran, I.R., Iran

B. Safavisohi, E. Sharbati

Department of Mechanical Engineering, Sharif University of Technology, Azadi Ave., Tehran 11365-8639, Irane̱sharbati@yahoo.com

J. Energy Resour. Technol 129(1), 54-65 (Mar 26, 2006) (12 pages) doi:10.1115/1.2424964 History: Received November 23, 2005; Revised March 26, 2006

The applicability and usefulness of combustion in porous media is of much interest due to its competitive combustion efficiency and lower pollutants formation. In the previous works, the focus has been on the effects of combustion and heat transfer parameters such as excess air ratio, thermal power, solid conductivity, convective heat transfer coefficient, and radiation properties on centerline temperature and pollutant formations. A premixed combustion scheme and a fixed porous medium with constant geometrical parameters have been used in these works; therefore, the effects of porous material parameters have been less considered. In this research, the effects of geometrical parameters of porous medium, namely porosity and permeability, on centerline temperature distributions, peak flame temperature, flame structure, and gas mixture preheating have been investigated by numerical methods. To this, a two-dimensional axis-symmetric physical model of porous burner is considered. As the most typical porous burners, a two stage one which has preheating porous zone (PPZ) and combustion porous zone (CPZ) is studied. The continuity, momentum, energy, turbulence, and species transport equations are solved employing a one-step chemical reaction mechanism with an eddy-dissipation model for rate of reactions. The turbulence is modeled with two transport equations which are not considered in similar works. The combustion regime is assumed to be diffusion and combustion parameters are fixed in all cases. Porosity effects on the structure and temperature characteristic of the flame are probed in a wide range for PPZ and CPZ. Critical permeability is defined and permeability effects on flame characters in both of the preheating and combustion regions are studied thoroughly.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic diagram of the physical model

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Figure 2

Pećlet number for a stoichiometric CH2 mixture as a function of δ for spherical pebbles, p=1atm, T=293K(5).

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Figure 3

Flame propagation region versus porosity and permeability variations for methane according to Carman–Cozney permeability model

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Figure 4

Effect of PPZ permeability on centerline temperature distributions

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Figure 5

Effect of CPZ permeability on centerline temperature distributions

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Figure 6

Effect of PPZ porosity on centerline temperature distributions

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Figure 7

Effect of CPZ porosity on centerline temperature distributions

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Figure 8

Effect of PPZ permeability on maximum centerline temperature

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Figure 9

Effect of PPZ porosity on maximum centerline temperature

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Figure 10

Effect of CPZ permeability on maximum centerline temperature

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Figure 11

Effect of CPZ porosity on maximum centerline temperature

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Figure 12

Effect of PPZ permeability on flame stable length

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Figure 13

Effect of PPZ porosity on flame stable length

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Figure 14

Effect of CPZ permeability on flame stable length

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Figure 15

Effect of CPZ porosity on flame stable length

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Figure 16

Effect of PPZ permeability on preheating of gas mixture

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Figure 17

Effect of PPZ porosity on preheating of gas mixture

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Figure 18

Effect of CPZ permeability on preheating of gas mixture

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Figure 19

Effect of CPZ porosity on preheating of gas mixture

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Figure 20

Comparison of a numerical result and experimental result. The parameters are presented in Table 1.

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Figure 21

Comparison of the temperature distribution obtained using one-step reaction with Eddy dissipation model and two-step reaction with finite rate-Eddy dissipation model

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