Emissivity of flame

[fmortini]

Hi!
I need to study a radiative heat exchange inside a boiler. The combustible is wood dust, with this compostition:
C=49%
H=7%
O=44%
LHV=16700 kJ/kg

This combustible produces a luminous flame. How can I find the total emissivity of the flame, considering luminous and non-luminous effect? Is there a correlation between emissivity and the percentage of carbon and/or oxygen for this type of material? Could you give me an approximate value for this?

Thank you!

 

[davefitz]

Its a complicated issue,not easily amenable to accurate predictions based soley on first principles.

The flame and hot gases radiate heat from CO2, H20, and the entrained ash ( participating media). The ash has a complex index of refraction, which might be measured from ash samples, but it also varies as the ash temperature changes and the char combusts.

As a practical matter, furnace engineers use field test data from operating and seasoned furnaces to work backwards what the apparent flame emissivity and wall slag / fouling effects are. Practical examples are as described by the "russian normative method" , textbook by Blokh circa 1990.

The most sophisticated computer simulation , as by W Fiveland for example, assume a priaor a known ash complex index of refraction, but in fact it is not know a priori.