Pool Fire

0.32

The flame shape of the pool fire can be modelled as a cylinder sheared (Fig.E.4) in the direction of the wind with diameter D, height H and tilt angle 0 (measured from the vertical). The flame is described by three circles (ci, c2, c3) arranged along the centerline of the flame, each defined by the downwind co-ordinate x and elevation z of the center of the circle, and by the radius r. These flame-circle co-ordinates are the main input to the radiation calculations.

Wind z

Fig. E.4 Shape of pool fire flame [49]

If the release is bunded, the diameter D is given by size of the bund. Otherwise, if it release volume and the thickness of the pool can be determined, the circular pool diameter can be calculated with:

Where,

= volume of the released liquid [m ]; 5 = thickness of the pool [m]

The maximum burn rate, mmctx (in kg/s/m ), is taken from [49]:

where, DHv* is the modified heat of combustion:

and CpL is the liquid specific heat, Tb is the boiling point temperature, and Ta is the atmospheric temperature. The actual pool fire burn rate, m is then given by [49]:

Where, Lb is the burn rate characteristic scale length which is taken from the material property data. The flame length, H is given by [49] as:

m p ajgD

Where pa is the density of air and g is the acceleration due to gravity. The tilt angle 0 can be approximated with the standard quadratic formula, taking only the positive root:

d = arcsin

0.61

Where, A = 0.7Reai09.Fra428, Re is a Reynolds number (=UwD/Va), Fr is a Froude number (=Uw2/gD), Uw is the wind velocity, Va is the kinetic viscosity of the air, and g is the acceleration due to gravity.

If the flame dimension have been determined as well as the heat generated in the flame due to combustion, the surface emissive power can be calculated. The maximum surface emissive power, E (in W/m2) for a tilted cylindrical flame according to approach of the Yellowbook [230]:

Where, Fs is fraction of the generated heat radiated from flame surface, m is burning rate (in kg/m2s), DHc is heat o, and Ls is the emissive power characteristic scale length.

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