Thermodynamics HW Solutions 943

Thermodynamics HW Solutions 943 - Chapter 12 Radiation Heat...

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Chapter 12 Radiation Heat Transfer 12-53 Two very large plates are maintained at uniform temperatures. The number of thin aluminum sheets that will reduce the net rate of radiation heat transfer between the two plates to one-fifth 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. Properties The emissivities of surfaces are given to be ε 1 = 0.2, ε 2 = 0.2, and ε 3 = 0.15. Analysis The net rate of radiation heat transfer between the plates in the case of no shield is 2 4 4 4 2 8 2 1 4 2 4 1 shield , 12 W/m 3720 1 2 . 0 1 2 . 0 1 ] ) K 800 ( ) K 1000 )[( K W/m 10 67 . 5 ( 1 1 1 ) ( = + × = ε + ε σ = T T Q no The number of sheets that need to be inserted in order to reduce the net rate of heat transfer between the two plates to onefifth can be determined from 3 = ⎯→ + + + × = ε
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This note was uploaded on 01/24/2012 for the course PHY 4803 taught by Professor Dr.danielarenas during the Fall '10 term at UNF.

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