Heat 4e Chap03 Lecture
Heat 4e Chap03 Lecture
Heat 4e Chap03 Lecture
Fourth Edition
Yunus A. Cengel, Afshin J. Ghajar
McGraw-Hill, 2011
Chapter 3
STEADY HEAT CONDUCTION
Mehmet Kanoglu
University of Gaziantep
Copyright 2011 The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Objectives
Understand the concept of thermal resistance and its
limitations, and develop thermal resistance networks for
practical heat conduction problems
Solve steady conduction problems that involve multilayer
rectangular, cylindrical, or spherical geometries
Develop an intuitive understanding of thermal contact
resistance, and circumstances under which it may be
significant
Identify applications in which insulation may actually
increase heat transfer
Analyze finned surfaces, and assess how efficiently and
effectively fins enhance heat transfer
Solve multidimensional practical heat conduction problems
using conduction shape factors
2
Electrical resistance
The thermal resistance network for heat transfer through a plane wall subjected to
convection on both sides, and the electrical analogy.
Temperature drop
U overall heat
transfer coefficient
Once Q is evaluated, the
surface temperature T1 can
be determined from
Multilayer
Plane
Walls
The thermal resistance
network for heat transfer
through a two-layer plane
wall subjected to
convection on both sides.
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11
Temperature distribution and heat flow lines along two solid plates
pressed against each other for the case of perfect and imperfect contact.
12
A typical experimental
setup for the
determination of thermal
contact resistance
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hc thermal contact
conductance
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15
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Thermal
resistance
network for two
parallel layers.
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18
20
A spherical shell
with specified
inner and outer
surface
temperatures T1
and T2.
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22
23
24
27
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Fin Equation
Differential
equation
Temperature
excess
29
30
31
32
33
34
Fin Efficiency
36
37
38
39
40
41
Fin
Effectiveness
The
effectivene
ss of a fin
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Once the value of the shape factor is known for a specific geometry, the
total steady heat transfer rate can be determined from the following
equation using the specified two constant temperatures of the two
surfaces and the thermal conductivity of the medium between them.
50
Summary
Fin Equation
Fin Efficiency
Fin Effectiveness
Proper Length of a Fin