Two infinitely long plates of unequal width having a common edge with an included angle
Function F2D_13 returns the view factor between two infinitely long plates of unequal width having a common edge with an included angle alpha.
The input variables are:
b = the area per unit width into the screen of plate 1 [m or ft]
a = the area per unit width into the screen of plate 2 [m or ft]
alpha = the included angle [degrees or radians]
Example: F=F2D_13(b, a, alpha)
Reference: http://www.me.utexas.edu/~howell/sectionc/C-5.html