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Transport of Gases in Charring Solids.

Transport of Gases in Charring Solids.
(124 K)

Baum, H. R.; Atreya, A.

E1 - Fire Research/Paper E01;

Combustion Institute/Western States, Central States and
Eastern States. Fourth (4th) Joint Meeting of the U.S.
Sections. Hosted by The Eastern States Section of the
Combustion Institute and Drexel University. E1 - Fire
Research/Paper E01. March 20-23, 2005, Philadelphia, PA,
1-6 pp, 2005.

### Keywords:

combustion; solids; charring; char; thermal degradation;
combustible materials; mathematical models; equations;
flame spread

### Abstract:

*
The analysis of thermal degradation of charring solids
is complicated by the fact that the charring process
results in the release of gaseous combustible materials
at the char-virgin material interface. Initially, the
interface is at or near the surfaces of the material
being heated. Under these circumstances, it is often
assumed that the gases are instantly expelled from the
solid material into the adjacent oxidizing atmosphere,
permitting combustion to take place in the gas phase.
However, if the process goes on long enough, the
interface will no longer be adjacent to the heated
surfaces. The purpose of this document is to outline the
development of a mathematical model of the transport of
gases through the char. In the next section the basic
equations and boundary conditions controlling the gas
transport are derived. Following this, the model is used
to study the time-dependent thermal degradation of a
semi-infinite charring material heated above the
charring temperature. This onedimensional transient
analysis is the simplest possible configuration for
charring studies. A one-dimensional transient model is
also the local approximation currently used in
multi-dimensional studies of flame spread over complex
surfaces. Then, the opposed flow flame spread over a
plane surface treated by Atreya and Baum is revisited.
This permits the gas transport to be studied in a
configuration for which the temperature distribution is
already known. It also removes an assumption about the
surface distribution of the gaseous fuel that was needed
due to the absence of a physics based model of the
transport process.
*