Thermodynamics HW Solutions 874

# Thermodynamics HW Solutions 874 - Chapter 11 Fundamentals...

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Chapter 11 Fundamentals of Thermal Radiation 11-31 A surface is subjected to radiation emitted by another surface. The solid angle subtended and the rate at which emitted radiation is received are to be determined. Assumptions 1 Surface A 1 emits diffusely as a blackbody. 2 Both A 1 and A 2 can be approximated as differential surfaces since both are very small compared to the square of the distance between them. Analysis Approximating both A 1 and A 2 as differential surfaces, the solid angle subtended by A 2 when viewed from A 1 can be determined from Eq. 11-12 to be A 1 = 4 cm 2 T 1 = 600 K θ 2 = 60 ° r = 80 cm 1 = 45 ° A 2 = 4 cm 2 sr 10 3.125 4 × = ° = θ = ω 2 2 2 2 2 2 2 , 1 2 cm) 80 ( 60 cos ) cm 4 ( cos r A r A n since the normal of A 2 makes 60 ° with the direction of viewing. Note that solid angle subtended by A 2 would be maximum if A 2 were positioned normal to the direction of viewing. Also, the point of viewing on A 1 is taken to be a point in the middle, but
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