Code Manual for CONTAIN 2.0 - Federation of American Scientists

where N is the number of the surfaces in the enclosure, Fj~is the user-input view factor from surface
j to surface k (the fraction of radiation from surface j that is directed into the solid angle subtended ~
by surface k), e~J~is the emissivity of gas mixture, &,Jis the surface emissivity, and B~= o(T~)4is
the Planck blackbody radiation for the gas. The modeling of e~~~,which is a function of the userinput
beam length Lj~between surfaces j and k, is discussed in Section 10.3.3.
The dry surface ernissivities, view factors Fj~,and characteristic beam lengths Lj~between surfaces
are provided by the user as “emsvt,” “vufacn,” and “beaml,” respectively, in the RAD-HEAT input
block described in Section 14.3.1.5. When the surface is dry, the “emsvt” value is used for &,,j.
Whenever a water fdm is present on the surface, 0.94, the emissivity of water, is used instead of the
dry surface emissivity. Because the surface and gas temperatures of the enclosure are known, the
radiosity of each surface can be obtained from Equation (10-60) through use of a standard linear
equation solver. The flux q~~,is then obtained from Equation (10-58).
If the user has not input the beam length ~~ between surfaces for the net enclosure model, a default
value given by
3.6V;
L= (10-61)
5A.
i=l
5,1
is used, where ~ is the initial cell gas volume, and Asi is the area of surface i.
For the view factor between surfaces, the user should only supply the view factor in one direction
(say, from surface i to j). The code will then calculate the view factor in the opposite direction (from
surface j to i) according to the following equation:
A, i Fij = As,j Fji (10-62)
where ~J is the area of surface j, Fijis the view factor from surface i to j, and Fjiis the view factor
from surface j to i.
10.3.2 Direct Radiative Heat Transfer Model
The direct radiative heat transfer model in CONTAIN calculates the radiative heat transfer between
the atmosphere and each heat transfer structure, between the atmosphere and the uppermost lower
cell layer, and between the uppermost lower cell layer and each structure inner surface. The name
of this model arises from the fact that secondruy reflections involving three or more enclosure
elements are treated in an approximate fashion, in contrast to the net enclosure radiation model. A
further limitation is that direct radiation between structure surfaces is not modeled. Unlike the net
enclosure radiation model, the direct model permits radiative heat transfer from the atmosphere to
both the inner and outer surfaces of a structure if both lie within a ceil. The direct model for gas to
surface heat transfer is invoked by speci~ing either GASWAL or GEOBL in the RAD-HEAT input
block. The modeling of direct radiative exchange between the lower cell and each heat transfer ~
O 10-38 6/30/97