The radiative exchange between the walls surfaces is calculated by using the net radiation method [Siegel, 1992], in which the net radiative heat transfer is:

qrk (x, y, z) = Jj (x, y, z)- qk (x, y, z) for k & j (12)

where Jj is the radiosity and qk is the irradiation on the wall surface given by:

qk(x, y,z)= J Jj(x, y,z)dFk-J k&j and k & 2

Aj

Jj (x, y, z) = £k&Tk {x y>z) + (l -£k ))k (x, y >z) for k & J’

k and j are the wall numbers, in which the heat flux was calculated. dFk-j is the differential view factor that indicates the fraction of energy that leaves from a wall k and strikes wall j. For walls 1, 3, 4, 5 y 6 the thermal emittance is ek&1 and for wall 2, ek=1.