Heat transfer is a complex process which is achieved by the superposition of three fundamental modes: conduction, convection and radiation. In case one of these three modes is determining the effects of others are unimportant, so they can be neglected, greatly simplifying the analysis cases concerned. Taking into account these conditions, we will then present the mechanism of occurrence of each of these modes.
Conduction:
In areas where there is a material temperature gradient there is a mechanism of heat transfer from warm regions to cold regions that does not involve radiation or travel macroscopic matter is conduction.
In gases, the molecules that hot regions with more energy by collision with molecules of lower kinetic energy when they enter the colder regions. From a macroscopic point of view, it thus heat transfer. In liquids, the process is quite similar, but the molecules are closer, free electrons and lattice vibrations. It is thus understood that the body that are good conductors of electricity are also good conductors of heat. Similarly, good electrical insulators are good thermal insulators.
Heat output transmitted by conduction through a surface element dS located inside a material or temperature gradient is given by Fourier's law:
The general equation for conduction is obtained by writing that the heat stored during the time dt by a small volume element dV material at temperature T is equal to the heat generated in the item minus the heat lost by conduction:
conduction in a plane wall
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