文档介绍：CHAPTER 1
BASIC CONCEPTS
OF HEAT TRANSFER
Y. I. Cho
Drexel University
E. N. Ganic
University of Sarajevo
J. P. t
University of Illinois, Chicago
W. M. Rohsenow
Massachusetts Institute of Technology
HEAT TRANSFER MECHANISMS
Heat is defined as energy transferred by virtue of a temperature difference. It flows from
regions of higher temperature to regions of lower temperature. It is customary to refer to dif-
ferent types of heat transfer mechanisms as modes. The basic modes of heat transfer are con-
duction, radiation, and convection.
Conduction
Conduction is the transfer of heat from one part of a body at a higher temperature to another
part of the same body at a lower temperature, or from one body at a higher temperature to
another body in physical contact with it at a lower temperature. The conduction process takes
place at the molecular level and involves the transfer of energy from the more energetic
molecules to those with a lower energy level. This can be easily visualized within gases, where
we note that the average ic energy of molecules in the higher-temperature regions is
greater than that of those in the lower-temperature regions. The more energetic molecules,
being in constant and random motion, periodically collide with molecules of a lower energy
level and exchange energy and momentum. In this manner there is a continuous transport
of energy from the high-temperature regions to those of lower temperature. In liquids the
molecules are more closely spaced than in gases, but the molecular energy exchange process
is qualitatively similar to that in gases. In solids that are nonconductors of electricity (di-
electrics), heat is conducted by lattice waves caused by atomic motion. In solids that are good
CHAPTER ONE
conductors of electricity, this lattice vibration mechanism is only a small contribution to the
energy transfer process, the principal contributi