Chapter 12 Radiation Heat Transfer12-41 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. Assumptions1Steady operating conditions exist 2The surfaces are opaque, diffuse, and gray. 3Convection heat transfer is not considered.PropertiesThe emissivities are ε= 1 for all surfaces since they are black or reradiating. Steaks, T2= 278 K, ε2= 1Coal bricks, T1= 1100 K, ε1= 1 0.20 mAnalysisWe 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), 75.0m0.20m15.0====LrRRiji7778.30.7575.01112222=+=++=ijRRS2864.075.075.047778.37778.3214212/1222/12212=⎪⎭⎪⎬⎫⎪⎩⎪⎨⎧⎥⎥⎦⎤⎢⎢⎣⎡⎟⎠⎞⎜⎝⎛−−=⎪⎭⎪⎬⎫
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