Thermodynamics HW Solutions 937

Thermodynamics HW Solutions 937 - Chapter 12 Radiation Heat...

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Chapter 12 Radiation Heat Transfer 12-44 Two long parallel cylinders are maintained at specified temperatures. The rates of radiation heat transfer between the cylinders and between the hot cylinder and the surroundings are to be determined. Assumptions 1 Steady operating conditions exist 2 The surfaces are black. 3 Convection heat transfer is not considered. Analysis We consider the hot cylinder to be surface 1, cold cylinder to be surface 2, and the surroundings to be surface 3. Using the crossed-strings method, the view factor between two cylinders facing each other is determined to be F sD s D 12 22 2 = × = +− ∑∑ Crossed strings Uncrossed strings String on surface 1 ( / ) π or 099 . 0 ) 16 . 0 ( 5 . 0 16 . 0 5 . 0 2 2 2 2 2 2 2 1 = π + = π + = D s D s F D D (2) (1) s T 3 = 300 K ε 3 = 1 T 2 = 275 K ε 2 = 1 T 1 = 425 K ε 1 = 1 (3) The view factor between the hot cylinder and the surroundings is
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