The effects of tortuosity and dispersion on porous combustion

Abstract

In this paper, the porous flow effects (tortuosity and dispersion) on the characteristics of porous combustion are numerically studied. The effects of tortuosity and dispersion are introduced in the porous diffusion coefficients to investigate the influences on the flame propagation speed and the operating range of inlet flow velocity. It is found that the ratio of thermal to mass diffusion coefficients (Le_p = α_L/D_L) due to the features of porous flow can drastically affect the flame propagation speed, which is similar to the effect of the Lewis number on the flame speed in free stream. Consequently, the results show that the operating range of inlet flow velocity (U_max–U_min) for a two-section burner can be greatly altered by the tortuosity and dispersion effects in the two porous solids. To decrease Le_p or decrease both α_L and D_L with constant Le_p in the upstream section can significantly extend the operating range by decreasing U_min; on the other hand, to increase Le_p or increase both α_L and D_L with constant Le_p can also remarkably extend the operating range by increasing U_max. Moreover, it is possible that the tortuosity effect in the upstream section (small pore) may greatly alter U_min; while the dispersion effect in the downstream section (large pore) can dominate U_max.

Keywords:

• tortuosity
• dispersion
• porous media
• radiant burner
• excess-enthalpy combustion

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

This work was supported by the Ministry of Science and Technology, Taiwan [grant number NSC101-2221-E-110-060].