2) A small metal object, initially at T; =1000 K, is cooled by radiation in a low- temperature vacuum chamber. One of two thin coatings can be applied to the object so that spectral hemispherical emissivities vary with wavelength as shown. For which coating will the object most rapidly reach a temperature of T;= 500 K?| 1.0 Coating A Coating B లో 0.5 10 100 2 (µm)

2) A small metal object, initially at T; =1000 K, is cooled by radiation in a low- temperature vacuum chamber. One of two thin coatings can be applied to the object so that spectral hemispherical emissivities vary with wavelength as shown. For which coating will the object most rapidly reach a temperature of T;= 500 K?| 1.0 Coating A Coating B లో 0.5 10 100 2 (µm)

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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The spectral, hemispherical absorptivity of an opaque surface and the spectral distribution of radiation incident on the surface are as shown. Assume that a₁ = 0.8. xx α 0 0 2 4 6 λ (μm) What is the total, hemispherical absorptivity of the surface? α = i G₂(W/m².μm) 5000 2 4 6 λ (um) If it is assumed that ε = α and that the surface is at 900 K, what is its total, hemispherical emissivity? 8 = i What is the net radiant heat flux to the surface, in W/m²? qad.net = i W/m²
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6.4 Two large diffuse parallel plates are maintained at temperatures T₁ = 1400 K and T₂ = 700 K. The plates are made from the same metal, and their spectral emissivities as a function of wavelength, &, are approximated as shown by two constant values joined by a linear decrease with wavelength. Compute the net radiant energy flux being transferred from plate 1 to plate 2. What is the energy flux if both plates are assumed gray with an approximate average emissiv- ity of 0.5 applied over the entire spectral range? 91 T₁ = 1400 K, Ex T₂ = 700 K, EX 92-91 0.85 Ex 0.15 0 Answer: q₁106,850 W/m²; 91.gray = 68,070 W/m². 2 λ (μm) 7