Heat and Mass Transfer: Fundamentals & Applications
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
,STEADY HEAT CONDUCTION IN PLANE WALLS
Heat transfer through the wall of a house can be
modeled as steady and one-dimensional.
The temperature of the wall in this case depends
on one direction only (say the x-direction) and
can be expressed as T(x).
for steady operation
In steady operation, the rate of heat transfer
through the wall is constant.
Fourier’s law of
heat conduction
3
, The rate of heat conduction through
a plane wall is proportional to the
average thermal conductivity, the
wall area, and the temperature
difference, but is inversely
proportional to the wall thickness.
Once the rate of heat conduction is
available, the temperature T(x) at
any location x can be determined by
Under steady conditions, the
replacing T2 by T, and L by x.
temperature distribution in a plane
wall is a straight line: dT/dx = const.
4
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
,STEADY HEAT CONDUCTION IN PLANE WALLS
Heat transfer through the wall of a house can be
modeled as steady and one-dimensional.
The temperature of the wall in this case depends
on one direction only (say the x-direction) and
can be expressed as T(x).
for steady operation
In steady operation, the rate of heat transfer
through the wall is constant.
Fourier’s law of
heat conduction
3
, The rate of heat conduction through
a plane wall is proportional to the
average thermal conductivity, the
wall area, and the temperature
difference, but is inversely
proportional to the wall thickness.
Once the rate of heat conduction is
available, the temperature T(x) at
any location x can be determined by
Under steady conditions, the
replacing T2 by T, and L by x.
temperature distribution in a plane
wall is a straight line: dT/dx = const.
4
