1. Consider a small surface of area A₁ = 10ª m², which emits diffusely with a total,hemispherical emissive power of E₁ = 5 × 104 W/m².n₂8₁₂ = 30°A₂72 = 0.5 m0₁ = 60°(a) At what rate is this emission intercepted by a small surface of area 42 = 5 x 104m²,which is oriented as shown?(b) What is the irradiation G₂ on 42?

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Answered: 1. Consider a small surface of area A₁…

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 11.6P

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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.
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.
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.
Determine the rate of radiant heat emission in watts per square meter from a blackbody at (a) 15C, (b) 600C, and (c) 5700C.
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 .
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.
Consider a small surface of area A 0.8 × 104m?, which emits diffusely with a total, hemispherical emissive power of Ej = 5x 104 W/m². n2 02 = 30° %3D A2 r2 = 0.5 m 0 = 60° A1 (a) At what rate is this emission intercepted by a small surface of area A2 = 5x104 m², which is oriented as shown, in W? %3D 91-2 i .0014 W (b) What is the irradiation G2 on A2, in W/m2? G2 = i 2.76 W/m? Physical Properties Mathematical Functions
A small circular surface of area A1=2 cm2located at the center of a 2-m-diameter sphere emits radiation as a blackbody at T1= 1000 K. Determine the rate at which radiation energy is streaming through a D2=1-cm-diameter hole located (a) on top of the sphere directly aboveA1and (b) on the side of the sphere such that the line that connects the centres of A1 and A2 makes 45° with surface A1. (c) Repeat it for a 4-m diameter sphere.
What is the total hemispherical emissivity,, for a real surface with a temperature of T = 2900K, with the spectral emissivity shown in the graph below? ελ 0.45 0.10 λ(μm) 0 2 4
EX3 Two coaxial cylinders of diameters Di = 0.10 m and D: = 0.30 m and emissivities 1 =0.7 and 2 = 0.4 are maintained at uniforn temperatures of T1 = 750 K and T2 = 500 K. respectively. Now a coaxial radiation shield of diameter D; = 0.20 m and emissivity 3 = 0.2 is placed between the two cylinders. Determine the net rate of radiation heat transfer berween the two cylinders per unit length of the cylinders and compare the result with that without the shield.
A small surface of area A1 = 5 cm? emits radiation as a blackbody, and part of the radiation emitted by Ai strikes another small surface of area A2 = 8 cm? oriented as shown in Fig. 4. If the rate at which radiation em itted by Ai that strikes A is measured to be 274 x 106 W, determine i. the intensity of the radiation emitted by A1, and the temperature of A1. ji. Az = 8 cm? 02 = 40° 10, = 55° r = 80 cm A = 5 cm? Fig 4
A diffuse surface is characterized by the spectral hemispherical emissivity distribution shown in the figure below, where ε₁ = 0.75, ε2 = 0.10, and ε3 = 0.8. For a surface temperature of T, = 300 K, what is the emissive power for the surface? Чэ ε1 E3 ६ 0 02 4 68 10 λ (μm)

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