The spectral, hemispherical absorptivity of an opaque surface and the spectral distribution of radiation incident on the surface are as shown. Assume that a₁ = 0.6. %20 α₁ 0 2 4 6 λ (um) What is the total, hemispherical absorptivity of the surface? α = i G₂ (W/m² μm) What is the net radiant heat flux to the surface, in W/m²? grad.net = i W/m² 5000 4 λ (μm) 2 If it is assumed that ε = a and that the surface is at 1100 K, what is its total, hemispherical emissivity? € = 6

The spectral, hemispherical absorptivity of an opaque surface and the spectral distribution of radiation incident on the surface are as shown. Assume that a₁ = 0.6. %20 α₁ 0 2 4 6 λ (um) What is the total, hemispherical absorptivity of the surface? α = i G₂ (W/m² μm) What is the net radiant heat flux to the surface, in W/m²? grad.net = i W/m² 5000 4 λ (μm) 2 If it is assumed that ε = a and that the surface is at 1100 K, what is its total, hemispherical emissivity? € = 6

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 11.3P: Determine the total average hemispherical emissivity and the emissive power of a surface that has a...

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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 .
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.
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.
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.
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.
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.
1.28 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.
11.41 Determine the steady-state temperatures of two radiation shields placed in the evacuated space between two infinite planes at temperatures of 555 K and 278 K. The emissivity of all surfaces is 0.8.