**2.5. Materials for porous media combustion**

Aluminum oxide (Al2O3), silicon carbide (SiC), and zirconium dioxide (ZrO2) proposed as suitable materials for application. Al2O3 and ZrO2 were recognized as high temperature resistant materials. SiC shows good thermal shock resistance, mechanical strength, and conductive heat transport. SiC also has high melting point (3260 K), against cyclic thermal

stress and strength retention at the peak regenerator temperature (1673 K), and excellent oxidation resistance. Metallic materials were found less suitable for PM because of their inadequate thermal stability and high thermal inertia. Fe–Cr–Al-alloys and nickel-base alloys were found suitable for some applications but they were said to be comparatively less heat resistant. Structures of ceramic foams with different base materials were observed to possess high porosity, good conduction heat transport, low thermal inertia, low radiation heat transport properties and relatively high pressure drop. The effective thermal conductivity of anisotropic porous composite medium could vary largely with the component fractions.

Numerical Simulation of Combustion in Porous Media 533

*3.1.1. One-dimensional governing equations* 

be obtained in the following form.

Continuity equation:

 

density:

Radiation:

Gas phase energy equation:

Solid phase energy equation:

Species transport equation:

 

The following assumptions are made to simplify the problem:

1. Gas radiation is neglected, gas flow and heat transfer are one-dimensional. 2. PM is considered to be non-catalytic, homogeneous and optically thick. 3. The radiation of solid phase is treated using Rosseland approximation.

4. The PM consists of solid dispersed homogeneously, and the porosity variation near the tube wall is neglected. Under the above assumptions, a set of differential equations can

0. *g gu*

 


2 <sup>2</sup> (1 ) (1 ) ( ) 0. *ss r*

*t d x x*

 0. *i i g g g ii i i*

<sup>1</sup> . *<sup>d</sup> <sup>i</sup>*

ߩ = constant density. (7)

<sup>3</sup> <sup>16</sup> ( ) . <sup>3</sup>

*q x dx* 

*i*

*s s*

*T dT*

*X x* 

*X*

 

*u YV W*

 

(2)

 

(4)

(3)

 

(5)

(6)

(8)

*t x* 

*TT T T c cu YVc hW k c D h T T tx x x x*

*S S s vg s TT dq c k hT T*

*Y Y*

*r*

The following boundary conditions are considered in the computations:

 

*t xx*

 

*i im*

*V DD*

*i i*

 

 

*3.1.2 Boundary conditions for one-dimensional model* 
