Question 21-113 D2 = 0.4 m are maintained at uniform temperatures T, = 700 Kand T, = 500 K and have emissivities & = 0.5 and ɛ, = 0.7,respectively. Determine the net rate of radiation heat transferbetween the two spheres. Also, determine the convection heattransfer coefficient at the outer surface if both the surroundingmedium and the surrounding surfaces are at 30°C. Assume theemissivity of the outer surface is 0.35.21–113 Consider a circular grill whose diameter is 0.3 m.The bottom of the grill is covered with hot coal bricks at950 K, while the wire mesh on top of the grill is coveredwith steaks initially at 5°C. The distance between the coalbricks and the steaks is 0.20 m. Treating both the steaks andthe coal bricks as blackbodies, determine the initial rate ofradiation heat transfer from the coal bricks to the steaks.21–108 A spherical tank of diameter D = 2 m that is filledwith liquid nitrogen at 100 K is kept in an evacuated cubicenclosure whose sides are 3 m long. The emissivities of thespherical tank and the enclosure are ɛ = 0.1 and ɛ, = 0.8,Also, determine the initial rate of radiation heat transferto the steaks if the side opening of the grill is covered byaluminum foil, which can be approximated as a reradiatingsurface. Answers: 928 W, 2085 W914RADIATION HEAT TRANSFER21–119 The spectral emissivity of an opaque surface at 1500 Kis approximated asSteaksE = 0E, = 0.85Ez = 01< 2 µm2 λ 6 μfor0.20 mforforλ>6 μηCoalDetermine the total emissivity and the emissive flux of the-surface.bricks21–120 The spectral absorptivity of an opaque surface isas shown on the graph. Determine the absorptivity of thesurface for radiation emitted by a source at (a) 1000 K and(b) 3000 K.FIGURE P21–113

Answered: Image /qna-images/answer/945e4659-5685-446e-b737-78cdb1b0fd54.jpg

3 Consider a circular grill whose diameter is 0.3 m. pottom of the grill is covered with hot coal bricks at <, while the wire mesh on top of the grill is covered steaks initially at 5°C. The distance between the coal s and the steaks is 0.20 m. Treating both the steaks and pal bricks as blackbodies, determine the initial rate of ion heat transfer from the coal bricks to the steaks. determine the initial rate of radiation heat transfer esteaks if the side opening of the grill is covered by

3 Consider a circular grill whose diameter is 0.3 m. pottom of the grill is covered with hot coal bricks at <, while the wire mesh on top of the grill is covered steaks initially at 5°C. The distance between the coal s and the steaks is 0.20 m. Treating both the steaks and pal bricks as blackbodies, determine the initial rate of ion heat transfer from the coal bricks to the steaks. determine the initial rate of radiation heat transfer esteaks if the side opening of the grill is covered by

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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