Element on longitudinal strip on inside of right circular cylinder to disk on base of cylinder
FDiff_12(r1, r2, z) provides the view factor from a differential element (1) on a longitudinal strip on the inside of right circular cylinder with radius r1 to a disk on the base of the cylinder (2) with radius r2 where r2<r1.
Inputs:
r1 is the radius of the cylinder [m or ft]
r2 is the radius of the disk at the base of the cylinder [m or ft]
z is the height of the element above the base [m or ft]
Example:
$UnitSystem SI K Pa J deg
"The following program compares the integrated view factor between the inside of a cylinder with its base to the more direct result from F3D_17. Note that this example is a limiting case since this view factor is intended to be used when r2<r1. "
r1=1 [m]
r2=1 [m]
h=.5 [m]
F_21=integral(FDiff_12(r1,r2,z)*2*pi*r1,z,0,h)/(2*pi*r1*h)
F_21`=f3d_17(r1,h)*pi*r2^2/(2*pi*r1*h)
{Solution: F_21 = F_21` = 0.390}
Reference: Howell, http://www.me.utexas.edu/~howell/sectionb/B-53.html