9. Consider the three-surface enclosure shown. The lower plate (A1) is a black disk of 200-mm diameter and is supplied with a heat rate of 10,000 W. The upper plate (A2), a diskcoaxial to A₁, is a diffuse, gray surface with 2 = 0.8 and is maintained at T₂ = 473 K.The diffuse, gray sides between the plates are perfectly insulated. Assume convectionheat transfer is negligible. (40 points)(a) Determine the operating temperature of the lower plate, T₁.(b) Determine the temperature of the insulated side, T3.D= 0.2 m -A2, T₂ = 473 K, &₂ = 0.8L = 0.2 mA3, T3, insulatedP = 10,000 WA₁, T₁, black surface

Let us first draw the free-body diagram:Given:Plate diameter = A1 = 200mmHeart rate = 10,000WValue…

Answered: 9. Consider the three-surface enclosure…

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 11.38P

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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.
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.
A long wire 0.7 mm in diameter with an emissivity of 0.9 is placed in a large quiescent air space at 270 K. If the wire is at 800 K, calculate the net rate of heat loss. Discuss your assumptions.
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.
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 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
 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?
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Radiation. A black body of total area 0.054m? is completely enclosed in a space bounded by 57 mm thick walls. The walls have a surface area 0.5 m² and thermal conductivity 1.05W/m.K. If the inner surface of the enveloping wall is to be maintained at 185°C and the outer wall surface is at 25°C, calculate the temperature of the black body. Neglect the difference between inner and outer surfaces areas of enveloping material. Stefan-Boltzmann constant o = 5.67x10* W/m²K'.Note: Under steady condition, the heat conducted through the wall must equal to the net radiation loss from the black body.
An enclosure has an inside area of 50 m², and its inside surface is black and is maintained at a constant temperature. A small opening in the enclosure has an area of 0.03 m². The radiant power emitted from this opening is 52 W. What is the temperature of the interior enclosure wall, in K? If the interior surface is maintained at this temperature, but is now polished so that its emissivity is 0.15, what will be the value of the radiant power emitted from the opening, in W? T, = grad = i K W
Keep in mind that both the bottom and top surfaces of the workpiece are exposed to radiation and convection. The workpiece is suspended in air in the furnace.

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