Fire And Explosion Models

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 [230]:

Where,

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 [49]. The flame radius, rflame, and flame duration, tFlame, are calculated from as:

' flame bleve

Fig. E.3 Shape of fireball [49]

12.59Mbl

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:

I SVP

atm svP

atm svP

and Psvp is the saturation vapour pressure of the substance, and calculated using the substance properties.

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