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The columns in this file record the time history of the integrals of the terms in the enthalpy transport equa-

tion. The columns are defined as follows:

t

hsdV

Q_ENTH= mbhs,b

uhs dS

Q_CONV+ qb,w+

kT dS

Q_COND+

hs,DY dS

Q_DIFF+qb,r

qr dS

Q_RADI

+

q dV HRR

+

d p

dtdV

Q_PRES

+ (qb,c qb,r qb,w) Q_PART

(16.5)

An additional column, Q_TOTAL, includes the sum of the terms on the right hand side of the equation.

Ideally, this sum should equal the term on the left,Q_ENTH. All terms are reported in units of kW. Note that

the terms that make up Q_PART are summed over the Lagrangian particles. They represent the heat absorbed

by the particles via convection, radiation, and conduction from the wall.

The other columns in the file contain the total burning rate of fuel, in units of kg/s, and the zone pres-

sures. Note that the reported value of the burning rate is not adjusted to account for the possibility that each

individual material might have a different heat of combustion. For this reason, it is not always the case that

the reported total burning rate multiplied by the gas phase heat of combustion is equal to the reported heatrelease rate.

16.9.2 Visibility and Obscuration

If you are performing a fire calculation using the simple chemistry approach, the smoke is tracked along

with all other major products of combustion. The most useful quantity for assessing visibility in a space is

the light extinction coefficient, K [34]. The intensity of monochromatic light passing a distanceL through

smoke is attenuated according to

I/I0=eKL (16.6)

The light extinction coefficient,K, is a product of the density of smoke particulate,YS, and a mass specific

extinction coefficient that is fuel dependent

K= Km YS (16.7)

Devices that output a % obscuration such as a DEVC with a QUANTITY of ASPIRATION, CHAMBER

OBSCURATION(smoke detector), orPATH OBSCURATION(beam detector) are discussed respectively in

Section15.3.7, Section15.3.5, and Section15.3.6

Estimates of visibility through smoke can be made by using the equation

S= C/K (16.8)

where Cis a non-dimensional constant characteristic of the type of object being viewed through the smoke,

i.e.,C=8 for a light-emitting sign andC=3 for a light-reflecting sign[34]. SinceKvaries from point topoint in the domain, the visibilitySdoes as well.Three parameters control smoke production and visibility. The first is the SOOT_YIELD on the REAC

line, defined as the fraction of fuel mass that is converted to soot if the simple chemistry approach is being

used. The second parameter, MASS_EXTINCTION_COEFFICIENT, is the Km in Eq. (16.7). It is defined on

one or more of the SPEClines1 for the various light absorbing gas species. Its default value is 8700 m2/kg, a

1When using the simple chemistry combustion model, you can change the default mass extinction coefficient

by adding a line to the input file of the form: &SPEC ID=SOOT, MASS_EXTINCTION_COEFFICIENT=...,

LUMPED_COMPONENT_ONLY=.TRUE. /

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