The surface emissive power (SEP) is the heat flux due to heat radiation at surface area. It can be calculated with the Stefan-Bolzmann-equation :
SEP is surface emissive power, in W/m2 ;
e is emittance factor (emissivity)
t is constant of Stefan-Bolzmann (=5.6703.10-8 W/m2K4)
Tf is radiator surface temp of the flame (K);
Ta is ambient temperature (K).
The heat flux q at certain distance from the fire, which is experienced by the receiver per unit area, can be calculated by:
is heat flux at a certain distance, W/m2; is view factor is atmospheric transmissivity E.4.1 Fireball
In reality the radiative emission from fireball varies over its surface, but in most literature a uniform heat radiation is assumed. In PHAST, the flame is modelled as spheres (circles) (Fig. E.3). Each circle is defined by the downwind co-ordinate x and elevation z of the center of the circle, by the radius r, and by the inclination of the circle from the horizontal, as shown in the where, q
Fview illustration below . The flame radius, rflame, and flame duration, tFlame, are calculated from as:
' flame bleve
MbUve < 3700 3700 < Mbleve
Where, Mbieve is flammable mass involved in the fireball. The emissive power, E is calculated as:
J s bleve comb
Where fs is the fraction of heat radiated from the surface, given by:
and Psvp is the saturation vapour pressure of the substance, and calculated using the substance properties.
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