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Thermodynamics HW Solutions 972

# Thermodynamics HW Solutions 972 - Chapter 12 Radiation Heat...

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Unformatted text preview: Chapter 12 Radiation Heat Transfer 12-90E A sealed electronic box is placed in a vacuum chamber. The highest temperature at which the surrounding surfaces must be kept if this box is cooled by radiation alone is to be determined. Assumptions 1 Steady operating conditions exist 2 The surfaces are opaque, diffuse, and gray. 3 Convection heat transfer is not considered. 4 Heat transfer from the bottom surface of the box is negligible. Properties The emissivity of the outer surface of the box is ε = 0.95. Analysis The total surface area is 2 ft 67 . 3 ) 1 1 ( ) 12 / 1 8 ( 4 = × + × × = s A Then the temperature of the surrounding surfaces is determined to be F 43 ° = = ⎯→ ⎯ − ⋅ × = × − = − R 503 ] ) R 590 )[( R Btu/h.ft 10 1714 . )( m 67 . 3 )( 95 . ( Btu/h ) 41214 . 3 100 ( ) ( 4 4 4 2 8 2 4 4 surr surr surr s s rad T T T T A Q σ ε & T surr 8 in 100 W ε = 0.95 T s = 130 ° F 12 in 12 in 12-91 A double-walled spherical tank is used to store iced water. The air space between the two walls is A double-walled spherical tank is used to store iced water....
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