16-1
Solutions Manual
for
Fundamentals of Thermal Fluid Sciences
5th Edition
Yunus A. Çengel, John M. Cimbala, Robert H. Turner
McGraw-Hill, 2017
Chapter 16
MECHANISMS OF HEAT TRANSFER
PROPRIETARY AND CONFIDENTIAL
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16-1C The thermal conductivity of a material is the rate of heat transfer through a unit thickness of the material per unit area
16-2C No. Such a definition will imply that doubling the thickness will double the heat transfer rate. The equivalent but
16-5C Superinsulations are obtained by using layers of highly reflective sheets separated by glass fibers in an evacuated
space. Radiation heat transfer between two surfaces is inversely proportional to the number of sheets used and thus heat loss
16-6C Most ordinary insulations are obtained by mixing fibers, powders, or flakes of insulating materials with air. Heat
metals.
16-8C The mechanisms of heat transfer are conduction, convection and radiation. Conduction is the transfer of energy from
the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles.
16-3
16-9C Conduction is expressed by Fourier’s law of conduction as
dx
dT
kAQ
cond
where dT/dx is the temperature gradient,
k is the thermal conductivity, and A is the area which is normal to the direction of heat transfer.
16-7
16–24 Heat is transferred steadily to boiling water in the pan through its bottom. The inner surface temperature of the bottom
of the pan is given. The temperature of the outer surface is to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the pan remain constant at the specified
m 0.004
which gives
T2 = 106.33C
16–25E The inner and outer surface temperatures of the wall of an electrically heated home during a winter night are
measured. The rate of heat loss through the wall that night and its cost are to be determined.
Assumptions 1 Steady operating conditions exist since the surface temperatures of the wall remain constant at the specified
kWh 7.288h) kW)(8 911.0( tQQ
$0.51=
energy) ofcost it energy)(Un of(Amount =Cost
Therefore, the cost of the heat loss through the wall to the home owner that night is $0.51.
1 ft
25F
16–10
16–14
16–33 The heat flux between air with a constant temperature and convection heat transfer coefficient blowing over a pond at
a constant temperature is to be determined.
Assumptions 1 Steady operating conditions exist. 2 Convection heat transfer coefficient is uniform. 3 Heat transfer by
radiation is negligible. 4 Air temperature and the surface temperature of the pond remain constant.
16–34 Four power transistors are mounted on a thin vertical aluminum plate that is cooled by a fan. The temperature of the
aluminum plate is to be determined.
Assumptions 1 Steady operating conditions exist. 2 The entire plate is nearly isothermal. 3 Thermal properties of the wall are
constant. 4 The exposed surface area of the transistor can be taken to be equal to its base area. 5 Heat transfer by radiation is
16–17
16–38 Prob. 16–37 is reconsidered. The rate of heat transfer as a function of the heat transfer coefficient is to be
plotted.
Analysis The problem is solved using EES, and the solution is given below.
“GIVEN”
T_infinity=80 [C]
16–19
16–41 Prob. 16-40 is reconsidered. The amount of power the transistor can dissipate safely as a function of the
D=0.006 [m]
h=30 [W/m^2-C]
16–20
16–42E A 300-ft long section of a steam pipe passes through an open space at a specified temperature. The rate of heat loss
from the steam pipe and the annual cost of this energy lost are to be determined.
Assumptions 1 Steady operating conditions exist. 2 Heat transfer by radiation
is disregarded. 3 The convection heat transfer coefficient is constant and
uniform over the surface.