The shape factors with themselves of two infinitely long

The shape factors with themselves of two infinitely long black body concentric cylinders with a dia ratio of 3 are _____ for the Inner and _____ for the outer

d₂	= 3
d₁

For Body – 1
F₁₁ + F₁₂ = 1
F₁₂ = 1 (∵ F₁₁ = 0)

For Body - 2
F₂₁ + F₂₂ = 1 - (A)

By applying reciprocity theorem,
A₁ F₁₂ = A₂ F₂₁
A₁ = A₂ F₂₁

or F₂₁ =	A₁	=	πd₁l	=	d₁	=	1
	A₂		πd₂l		d₂		3

F₂₁ =	1
	3

Substituting, F₂₁ =	1	in(A),weget
	3

1	F₂₂ = 1
3

F₂₂ =	2
	3