A gray surface has an emissivity at a temperature of 550 K source. If the surface is opaque, (a) Calculate its reflectivity for black body radiation coming from a 550 K source. (b) A small 25 mm square hole is made in the thin-walled door of a furnace whose inside walls are at 920 K. if the emissivity of the walls is 0.72, calculate the rate at which radiant energy escapes from the furnace through the hole to the room.

A gray surface has an emissivity at a temperature of 550 K source. If the surface is opaque, (a) Calculate its reflectivity for black body radiation coming from a 550 K source. (b) A small 25 mm square hole is made in the thin-walled door of a furnace whose inside walls are at 920 K. if the emissivity of the walls is 0.72, calculate the rate at which radiant energy escapes from the furnace through the hole to the room.

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.30P

See similar textbooks

Similar questions

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.
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.
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 horizontal opaque flat plate is well insulated on the edges and the lower surface. The top surface has an area of 5 m2, and it experiences uniform irradiation at a rate of 5000 W. The plate absorbs 4000 W of the irradiation, and the surface is losing heat at a rate of 500 W by convection. If the plate maintains a uniform temperature of 350 K, determine the absorptivity, reflectivity, and emissivity of the plate.
Two concentric spheres of diameter D1= 0.9 m and D2= 1.2 m are separated by an air space and have surface temperatures of T1= 400 K and T2= 300 K. (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? q12= Enter your answer for part (a) in accordance to the question statement W (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with ε1= 0.5 and ε2= 0.05, in W? q12= Enter your answer for part (b) in accordance to the question statement W (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with ε2= 0.05, ε1= 0.5, and D1= 0.9 m, in W? q12= Enter your answer for part (c) in accordance to the question statement W (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (ε2= 1.0) and with ε1= 0.5, D2= 20 m, and D1= 0.9 m, in W? q12= Enter your answer for part(d) in accordance to the question statement W
Determine the view factor between two gray surfaces A and B. Their emissivities are εA = 0.90 and εB = 0.25 at temperatures 450°C and 50°C, respectively, if (1) surfaces are infinite black parallel planes, (2) surfaces are infinite gray parallel planes, (3) surface A is a spherical shell 3 m in diameter and surface B is a similar shell concentric with A and 0.3 m in diameter, (4) surfaces A and B concentric cylindrical tubes with diameters of 300 mm and 275 mm, respectively, (5) both surfaces are discs with diameter 2 m one exactly above the other, 1 m apart.