TABLE OF CONTENTS 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 different types of heat-transfer mechanisms as modes. The basic modes of heat transfer are conduction and radiation. In some textbooks on heat transfer, convection is also considered as a separate mechanism.
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 at a lower temperature in physical contact with it. 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 kinetic energy of molecules in the higher-temperature regions is greater than 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 conductors of electricity (dielectrics), heat is conducted by lattice...
