Question

7. The spectral emissivity of an opaque surface at 2000 K is approximated as: EX -0.3, for OS <3um -0.8, for 3um SX < 6um -0.4, for hum S. < 0 Determine: a) The total emissivity of the surface,

Answer 1

Revised Solution Spectral emissivity of an opaque surface at 2000k SE- 0.3 far os is 3 um EF E= 0.8 for Bunk it slum. LE3 = 0.4 far sums s<s. Total emissivity (T) Ebd (T) di OT4 Td 82 Eb (T) 865) = Ei!" finds of person E(T) = 4 OTG от 4 Ера (т). + отч - E, fo- ti () + E. ft. - tz(T) + Esfis- oo (o) = Ei funt Ez ( f82-f1) + Ez (1-fta) А, ХТ - 3 u m x 2 орто - Gooъ Цmk 12x Tz 12000 umk en x 200ok = radiation function correspondin from table (7.3, P.K Nag Heat & Masst where it, & &de au to d. XT 2 de xT , fai= 721032 Scanned with scanner 1.0432

- subsitute values 3*.721032 + '0 (1.4432 - 1721032) t '4(1-1.4432) 3 : 216309 + 157773 - 0.17728 (ECT) = .7767 salution Scanned with CamScanner

Solution al emissivity of an opaque surface at 2000k Ex = 0.3 far of de um = .8 for 3um de 64m. 0.4 far sums uso Total emissivity of surface is given by Erdt - Postcounty + 3x3 .813 + 4 oraz 3 .9 + 24 + 0 - Bar = 3.3 eum CScanned with CamScanner

Solution al emissivity of an opaque surface at 2000k Ex = 0.3 far of de um = .8 for 3um de 64m. 0.4 far sums uso Total emissivity of surface is given by Erdt - Postcounty + 3x3 .813 + 4 oraz 3 .9 + 24 + 0 - Bar = 3.3 eum CScanned with CamScanner