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Consider the radiation heat exchange inside an annulus between two very long concentric cylinders. The radius of the outer cylinder is Ro and that of the inner cylinder is Ri. The radiation view factor of the outer cylinder onto itself is

1. 1 - √(Ri / Ro)
2. √(1 - Ri / Ro)
3. 1 - (Ri / Ro)^(1/3)
4. 1 - Ri / Ro

Correct answer: 1 - Ri / Ro

Solution

The correct option, 1 - Ri / Ro, represents the fraction of the total radiation emitted by the outer cylinder that is not intercepted by the inner cylinder, effectively capturing the geometric relationship between the two cylinders.

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