Question

3. Two large, diffuse, grey, parallel surfaces are separated by a small distance. If the surface emissivities of each plate is 0.7, what emissivity should a thin radiation shield have to reduce the radiation heat transfer rate between the two surfaces by a factor of 20?

3. Two large, diffuse, grey, parallel surfaces are separated by a small distance. If the surface emissivities of each plate is 0.7, what emissivity should a thin radiation shield have to reduce the radiation heat transfer rate between the two surfaces by a factor of 20?

Answer 1

IT, k TIK (91-2) without shield Ebz Ebi 2 يت 1-EL I-E2 LEZ E, AI AiFiz & Az q A net o(1,4- T24 T Watyma 1 EL |- Ez Shield 0 E ezi 4 TT5 11 € Radiation newtork with Shield, (4-2) net Ebie with one shield лими-> I-E 1. 1-63 A, F13 6, A3 Ebs Eba um 1-E3 E₂ A3 1 Az F32 EA, I-62 E AL Since plones being very dangen we calculate flux ie pw A-A== and Fiz = f32 = 1 o(14 - Toy) wart / m² (h 1 E3 + 2 + A 1-2 with one shield Ez

>> €,- €, = 0.7 :( 9 ) As the plates have some emissivities is 0.7 - (T" -T) I+1 -1 0.7 0.7 without shield q (T - T24 (ort + 2 E3 + I 0.7 -2) As (9) homme with shield withour shield. oft 4) Soft-T 2 20 ㅗ 0.7 + + 2 E3 1 .7 -2 ) ㅗ 0.7 + 1 0.7 > 2 20 + 1 0.7 -") = 60 + 2 €3 + L 0.7 0.7 0.7 Ez = 0.055 the emissivity of the radiation shield used should be 0.055

Please rate as positive. For any doubt you can ask in comments.