Guide alphabétique, de la thermodynamique, amplification de chaleur, transfert de masse, et dynamique des fluides
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Heat is less easily defined than work. In genera! terms, the temperature of a substance increases if heat is added to it. Therefore, heat was, for a long time, thought to be an invisible fluid named 'caloric' which flows along a temperature difference from one system to the other. We now know that this is false and that heat is not contained in a system but is manifested only as an interaction of the system with its surroundings as the system changes from one state to another. Like work, it can be considered as energy in transit. Heat is best defined through the First Law of Thermodynamics:

(1)
(2)

where U is internal energy, M mass, T temperature, cv and cp specific heat capacity at constant volume and pressure, respectively, and Q is heat, W work, p pressure, V volume, and H enthalpy.

Therefore,

(3)

If phase change occurs as a result of heat transfer, the latent heat of evaporation and/or the latent heat of solidification have to be included in Equation (3).

The sign convention is that heat transfer is positive into the system and negative out of the system.

Nombre de vues : 20260 Article ajouté : 2 February 2011 Dernière modification de l'article : 13 February 2011 © Copyright 2010-2022 Retour en haut de page
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