13-47 A dryer is shaped like a long semicylindrical duct of diameter 2 m. The base of the dryer is occupied with water-soaked materials that are to be dried. The dome of the dryer has a constanttemperature of 500°C, while the materials at the base are at 40°C. Both surfaces can be approximated as blackbodies. Determine the length of the dryer so that the materials are dried at a rate of 0.1 kg/s.FIGURE P13–47Tz = 500°C------D= 2.0 m -T = 40°C

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Answered: 13-47 A dryer is shaped like a 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 11.27P

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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.
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.
11.41 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.
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 .
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.

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