University:
North Idaho College
Course:
PHYS-211 | Engineering Physics I
Academic year:

2023
Views:

396

Pages:

3
Author:

Hani T.

Conduction At mention of the word conduction, we should immediately conjure up concepts of atomic and molecular activity, for it is processes at these levels that sustain this mode of heat transfer. Conduction may be viewed as the transfer of energy from the more energetic to the less energetic particles of a substance due to interactions between the particles. The physical mechanism of conduction is most easily explained by considering a gas and using ideas familiar from your thermodynamics background. Consider a gas in which there exists a temperature gradient and assume that there is no bulk, or macroscopic, motion. The gas may occupy the space between two surfaces that are maintained at different temperatures. We associate the temperature at any point with the energy of gas molecules in proximity to the point. This energy is related to the random translational motion, as well as to the internal rota-tional and vibrational motions of the molecules. Higher temperatures are associated with higher molecular energies, and when neighbouring molecules collide, as they are constantly doing, a transfer of energy from the more energetic to the less energetic molecules must occur. Conduction In the presence of a temperature gradient, energy transfer by conduction must then occur in the direction of decreasing temperature. This would even be true in the absence of collisions, as is evident from The hypothetical plane at is constantly being crossed by molecules from above and below due to their random motion. However, molecules with a larger temperature than those from below, in which case there must be a net transfer of energy in the posi-tive x direction. Collisions between molecules enhance this energy transfer. We may speak of the net transfer of energy by random molecular motion as a diffusion of energy. The situation is much the same in liquids, although the molecules are more closely spaced and the molecular interactions are stronger and more frequent. Similarly, in a solid, conduction may be attributed to atomic activity in the form of lat-tice vibrations. The modern view is to ascribe the energy transfer to lattice waves induced by atomic motion. In an electrical non conductor, the energy transfer is ex-exclusively via these lattice waves; in a conductor it is also due to the translational motion of the free electrons. Conduction Examples of conduction heat transfer are legion. The exposed end of a metal spoon suddenly immersed in a cup of hot coffee will eventually be warmed due to the conduction of energy through the spoon. On a winter day there is significant energy loss from a heated room to the outside air. This loss is principally due to conduction heat transfer through the wall that separates the room air from the out- side air. It is possible to quantify heat transfer processes in terms of appropriate rate equations. These equations may be used to compute the amount of energy being transferred per unit time.