Project ForgeHeat Transfer
Convection & Radiation
GATE 2012
Medium
Consider two infinitely long thin concentric tubes of circular cross section, with D1 and D2 the diameters of the inner and outer tubes respectively. The view factor F22 (outer tube to itself) is given by
- A(D2/D1) − 1
- Bzero
- CD1/D2
- 1 − (D1/D2)
Explanation
The inner tube's surface is convex, so it cannot see itself: F11=0, hence (with only two surfaces present) F12=1. By reciprocity, A1F12=A2F21, so F21=A1/A2=D1/D2 (equal-length cylinders). Since the outer tube's surface is concave, F21+F22=1, giving F22=1−D1/D2.
Source: GATE ME 2012 (Booklet Code A) (2012)
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