Problem 4Consider the very long, inclined black surfaces (A1, A2) maintained at uniform temperatures ofT₁ = 1100 K and T₂ = 700 K. Determine the net radiation exchange between these two surfacesper unit length of the surfaces. Consider the configuration when a black surface (A3), whose backside is insulated, is positioned along the dashed line shown. Calculate the net radiation transfer tosurface A2 per unit length of the surface and determine the temperature of the insulated surfaceA3.Assumption: (1) All surfaces behave as blackbodies, (2) All surfaces are very long in directionnormal to page.A2, T2-100 mmA₁, T₁100 mm.60°

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Answered: Problem 4 Consider the very long,…

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 11.29P

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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.
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.
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.
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.
11.68 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.
11.41 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.
Question #9 A circular ceramic plate that can be modelled as a blackbody is being heated by an electrical heater. The plate is 30cm in diameter and is situated in a surrounding ambient temperature of 15°C where the natural convection heat transfer coefficient is 12W/m² K. The efficiency of the electrical heater to transfer heat to the plate is 80%, the electric power is required such that the heater needs to keep the surface temperature of the plate at 200°C. Ambient 15°C Tsurr = 15°C h = 12 W/m².K Ceramic plate -T₂ = 200°C Welec (A) Determine the heat emitted from the plate, as a blackbody. (B) Determine the radiation incident on the plate from the surroundings. (C) Determine the heat transfer from the plate to the surroundings. (D) Determine the required electric power.
 Two perfectly black parallel planes 1.2 by 1.2mare separated by a distance of 1.2 m. One plane is maintained at 800 K and the other at 500 K. The plates are located in a large room whose walls are at 300 K. What is the net heat transfer between the planes?
A body at 1100ºc in a black surrounding at 550ºc has emissivity of 0.4 at 1100ºc and emissivity 0.7 at 550ºc. calculate the rate of heat loss by radiation per unit surface area; i) when the body is assumed to be grey with emissivity 0.4 ii) when the body is not grey. (assume absorptivity is independent of the surface temperature)
Two concentric spheres of diameter Di = 0.7 mand D2 = 1.2 mare separated by an air space and have surface temperatures of T = 400 K and T, = 300 K. (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? ৭12 = w (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with ɛi = 0.5 and e2 = 0.05, in W? 12 (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with e2 = 0.05, e1 = 0.5, and Di = 0.7 m, in W? 912 = i (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (e2 = 1.0) and with e = 0.5, D2 = 20 m, and D1 = 0.7 m, in W? w 912 = Physical Properties Mathematical Functions
Determine the net heat transfer by radiation between two gray surfaces, A (εA= 0.90) andB (εB= 0.25) at temperatures 500°C and 200°C, respectively if a. surfaces are infinite parallel planes b. 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 c. surfaces A and B concentric cylindrical tubes with diameters of 300 mm and 275 mm, respectively d. both surfaces are squares 2 m × 2
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