Thermodynamics HW Solutions 934

Thermodynamics HW Solutions 934 - Chapter 12 Radiation Heat...

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Chapter 12 Radiation Heat Transfer 12-41 A circular grill is considered. The bottom of the grill is covered with hot coal bricks, while the wire mesh on top of the grill is covered with steaks. The initial rate of radiation heat transfer from coal bricks to the steaks is to be determined for two cases. Assumptions 1 Steady operating conditions exist 2 The surfaces are opaque, diffuse, and gray. 3 Convection heat transfer is not considered. Properties The emissivities are ε = 1 for all surfaces since they are black or reradiating. Steaks, T 2 = 278 K, ε 2 = 1 Coal bricks, T 1 = 1100 K, ε 1 = 1 0.20 m Analysis We consider the coal bricks to be surface 1, the steaks to be surface 2 and the side surfaces to be surface 3. First we determine the view factor between the bricks and the steaks (Table 12-1), 75 . 0 m 0.20 m 15 . 0 = = = = L r R R i j i 7778 . 3 0.75 75 . 0 1 1 1 2 2 2 2 = + = + + = i j R R S 2864 . 0 75 . 0 75 . 0 4 7778 . 3 7778 . 3 2 1 4 2 1 2 / 1 2 2 2 / 1 2 2 12 = =
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