Unlock document.
This document is partially blurred.
Unlock all pages and 1 million more documents.
Get Access
21-1
Solutions Manual
for
Fundamentals of Thermal Fluid Sciences
5th Edition
Yunus A. Çengel, John M. Cimbala, Robert H. Turner
McGraw-Hill, 2017
Chapter 21
RADIATION HEAT TRANSFER
PROPRIETARY AND CONFIDENTIAL
This Manual is the proprietary property of McGraw-Hill Education and protected by copyright and other
state and federal laws. By opening and using this Manual the user agrees to the following restrictions,
and if the recipient does not agree to these restrictions, the Manual should be promptly returned
unopened to McGraw-Hill Education: This Manual is being provided only to authorized professors
and instructors for use in preparing for the classes using the affiliated textbook. No other use or
distribution of this Manual is permitted. This Manual may not be sold and may not be distributed
to or used by any student or other third party. No part of this Manual may be reproduced,
displayed or distributed in any form or by any means, electronic or otherwise, without the prior
written permission of McGraw-Hill Education.
21-2
Electromagnetic and Thermal Radiation
21-1C Electromagnetic waves are caused by accelerated charges or changing electric currents giving rise to electric and
21-3C Thermal radiation is the radiation emitted as a result of vibrational and rotational motions of molecules, atoms and
21-4C Microwaves in the range of
m 10 to10 52
are very suitable for use in cooking as they are reflected by metals,
21-5C Visible light is a kind of electromagnetic wave whose wavelength is between 0.40 and 0.76 m. It differs from the
21-6C Light (or visible) radiation consists of narrow bands of colors from violet to red. The color of a surface depends on its
21-7C Infrared radiation lies between 0.76 and 100 m whereas ultraviolet radiation lies between the wavelengths 0.01 and
21-9 Electricity is generated and transmitted in power lines at a frequency of 60 Hz. The wavelength of the electromagnetic
waves is to be determined.
Analysis The wavelength of the electromagnetic waves is
m/s 10998.2 8
v
c
Power lines
21-3
21-10 The speeds of light in air, water, and glass are to be determined.
Analysis The speeds of light in air, water and glass are
m/s 100.3 8
0
c
21-4
21-13 The photon energies of an electromagnetic wave in air, water, and glass are to be determined.
Assumptions 1 The refraction index of each medium is uniform.
Properties The speed of light in a vacuum is c0 = 2.9979 × 108 m/s, and the Planck’s constant is h = 6.626069 × 10−34 J∙s.
21-5
Blackbody Radiation
21-16C Spectral blackbody emissive power is the amount of radiation energy emitted by a blackbody at an absolute
21-17C We defined the blackbody radiation function
f
because the integration
0
)(
dTEb
cannot be performed. The
21-18 The maximum thermal radiation that can be emitted by a surface is to be determined.
21-6
21-19 The peak spectral blackbody emissive power for a match flame and moonlight is to be determined.
Assumptions 1 The match and the moon behave as black bodies.
21-8
21-21 The spectral blackbody emissive power of the sun versus wavelength in the range of 0.01 m to 1000 m is to
be plotted.
Analysis The problem is solved using EES, and the solution is given below.
"GIVEN"
21-9
21-22 A small body is placed inside an evacuated spherical chamber with constant surface temperature. The radiation
incident on the small body surface is to be determined for (a) black chamber surface and (b) well-polished chamber surface.
Assumptions 1 The small body surface is much smaller than the chamber surface. 2 The chamber surface temperature is
Analysis The spherical chamber with isothermal surface temperature forms a blackbody cavity regardless of the radiation
properties of the chamber surface. The small body inside the chamber is too small to interfere with the blackbody nature of
the cavity.
Therefore, the radiation incident on any part of the small body surface is equal to the radiation emitted by a
blackbody at the surface temperature of the chamber.
(a) For chamber surface coated in black:
4
21-12
21-25 A circular plate that is modeled as a blackbody is heated by an electrical heater with an efficiency of 80%. The electric
power required to keep the plate surface temperature at 200°C is to be determined.
21-14
21-29 Prob. 21-28 is reconsidered. The effect of temperature on the fraction of radiation emitted in the visible range is
to be investigated.
Analysis The problem is solved using EES, and the solution is given below.
"GIVEN"
T
[K]
f
1000
1200
1400
1600
1800
2000
2200
2400
2600
2800
3000
3200
3400
3600
3800
4000
0.000007353
0.0001032
0.0006403
0.002405
0.006505
0.01404
0.02576
0.04198
0.06248
0.08671
0.1139
0.143
0.1732
0.2036
0.2336
0.2623
1000 1500 2000 2500 3000 3500 4000
0
0.05
0.1
0.15
0.2
0.25
0.3
T [K]
f
21-15
21-30 Radiation emitted by a light source is maximum in the blue range. The temperature of this light source and the fraction
of radiation it emits in the visible range are to be determined.
Analysis The temperature of this light source is
Km 8.2897
m 76.0 tom 40.0 21
. Noting that T = 6166 K, the blackbody radiation
functions corresponding to
TT 21 and
are determined from Table 21-2 to be
15440.0mK 2466=K) m)(6166 40.0(
1
1
λ
fT
21-18
Radiation Properties
blackbody is one for all wavelengths, the emissivity of a graybody is between zero and one. A surface whose properties
change with wavelength and direction is called a diffuse gray surface.
