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Element on longitudinal strip on inside of right circular cylinder to the exterior of concentric smaller right circular cylinder.



FDiff_13 (r1, r2, z, h) provides the view factor from a differential element (1) on a longitudinal strip on the inside of right circular cylinder with radius r2 to the exterior of a smaller concentric right circular cylinder (2) with radiation r1.

Inputs:
r1   is the radius of the smaller cylinder [m or ft]
r2  is the radius of the larger cylinder [m or ft]
z  is the height of the element above the base  [m or ft]
h is the height of the cylinders [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_4. "
$VarInfo z units=m
r1=0.5 [m]
r2=1 [m]
h=2 [m]
F_12=integral(fdiff_13(r1,r2,z, h)*2*pi*r2,z,0,h)/(2*pi*r2*h)
F_12`=f3d_4(r1, r2, h)*r1/r2     "note use of reciprocity"

{Solution: 
F_12 = F_12` = 0.4126}

Reference: Howell, http://www.me.utexas.edu/~howell/sectionb/B-57.html 

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