Environmental Engineering Reference
In-Depth Information
and partial pressure, as widely as from 0.7 to 2.8 times the heat flux under even
distributions. Consequently, there are many problems in an abridged calculation of
radiation effects using mean temperature and mean partial pressure.
Heat flux of H
2
O in Consideration of Wedge Shape Distribution (in the case
of 1-m mean effective thickness)
Tgm = 1000K Tg = 500 - 1500K
Pam = 0.5atm Pa = 0.1 - 0.9atm
2
Q kW/m
a
T
g
P
a
(Case A)
4.78
(Case B)
6.09
(Case C)
9.51
(Case D)
4.86
(Case E)
9.56
(Case F)
5.48
(Case I)
(Case G)
4.86
(Case H)
3.00
13.05
In these tables, many cases of paired boxes are shown. When high temperature
region in furnace lies and burned gas stays far from the wall, thermal radiation is
smaller, but when combustion takes place near the wall, radiative energy is larger
because of the thin optical thickness. An amount of the radiative energy from the
combusting gas reaches wall to wall. In short, the uniform distribution of temperature
and burned gas like high temperature air combustion may not be more advantageous,
but in these figures, the area of the wall is not considered.
In general, the area of high temperature wall contributes more part of total
radiative heat transfer. Uniform gas distribution makes the available wall area wide.
With regard to collision flames, the effect of convection heat transfer in the
furnace is not negligible. The total heat transfer effect in such a case can be obtained
by combining the radiation effect with the amount of convection heat transfer
calculated separately. It is, of course, important to look at it as a combined radia-
tion/convection effect, but it is sufficient for the purpose to add the convection effect
as an adjustment to the predominant radiation effect.
It is usually the case that nonluminous flames are formed in the highly preheated
air combustion with gaseous fuels, but radiation heat transfer analysis needs to take
formation of luminous flames into consideration when solid or liquid fuels are used.
In this case, existence of solid particles in the flames is regarded as the cause of the
formation of luminous flames, and radiation characteristics of the solid particles will
Search WWH ::
Custom Search