please show all steps, not Ai generated 12.25 Consider the metallic surface of Example 12.7. Additional measurements of the spectral, hemispherical emissivity yield a spectral distribution which may be approximated as follows:0.4ελ (λ)0.202λ (μm)(a) Determine corresponding values of the total, hemispherical emissivity and the total emissive power E at 2000 K4

Summary/:-Total emissive power has been calculatedExplanation:

Answered: 12.25 Consider the metallic surface of…

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.9P

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11.68 Two infinitely large, black, plane surfaces are 0.3 m apart, and the space between them is filled by an isothermal gas mixture at 811 K and atmospheric pressure. The gas mixture consists of by volume. If one of the surfaces is maintained at 278 K and the other at 1390 K, calculate (a) the effective emissivity of the gas at its temperature, (b) the effective absorptivity of the gas to radiation from the 1390 K surface, (c) the effective absorptivity of the gas to radiation from the 278 K surface, and (d) the net rate of heat transfer to the gas per square meter of surface area.
11.31 A large slab of steel 0.1 m thick contains a 0.1 -m-di- ameter circular hole whose axis is normal to the surface. Considering the sides of the hole to be black, specify the rate of radiative heat loss from the hole. The plate is at 811 K, and the surroundings are at 300 K.
A tungsten filament is heated to 2700 K. At what wavelength is the maximum amount of radiation emitted? What fraction of the total energy is in the visible range (0.4to0.75m)? Assume that the filament radiates as a graybody.
Determine the total average hemispherical emissivity and the emissive power of a surface that has a spectral hemispherical emissivity of 0.8 at wavelengths less than 1.5m, 0.6 at wavelengths from 1.5to2.5m, and 0.4 at wavelengths longer than 2.5m. The surface temperature is 1111 K.
1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .
Two large parallel plates with surface conditions approximating those of a blackbody are maintained at 816C and 260C, respectively. Determine the rate of heat transfer by radiation between the plates in W/m2 and the radiative heat transfer coefficient in W/m2K.
1.28 The sun has a radius of and approximates a blackbody with a surface temperature of about 5800 K. Calculate the total rate of radiation from the sun and the emitted radiation flux per square meter of surface area.
12.37 Consider the metallic surface of Example 12.7. Addi- tional measurements of the spectral, hemispherical emissivity yield a spectral distribution which may be approximated as follows: 0.4 * 0.2 2 4 a (um) (a) Determine corresponding values of the total, hemi- spherical emissivity ɛ and the total emissive power E at 2000 K. Ez (2.)
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
An opaque surface at 1000 K if its spectral emissivity is = 0.4, 0.7, and 0.3 for 0 < < 2 µm, 2μm < 6 μm, and 6um
12.35 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 టో 0.5 1 10 100 a (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 1 10 100 A (um)

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