|
The Clausius–Duhem inequality〔.〕〔.〕 is a way of expressing the second law of thermodynamics that is used in continuum mechanics. This inequality is particularly useful in determining whether the constitutive relation of a material is thermodynamically allowable.〔.〕 This inequality is a statement concerning the irreversibility of natural processes, especially when energy dissipation is involved. It was named after the German physicist Rudolf Clausius and French physicist Pierre Duhem. == Clausius–Duhem inequality in terms of the specific entropy == The Clausius–Duhem inequality can be expressed in integral form as : In this equation is the time, represents a body and the integration is over the volume of the body, represents the surface of the body, is the mass density of the body, is the specific entropy (entropy per unit mass), is the normal velocity of , is the velocity of particles inside , is the unit normal to the surface, is the heat flux vector, is an energy source per unit mass, and is the absolute temperature. All the variables are functions of a material point at at time . In differential form the Clausius–Duhem inequality can be written as : where is the time derivative of and is the divergence of the vector . (\rho~\eta)~\text \ge -\int_ \rho~\eta~(\mathbf\cdot\mathbf)~\text - \int_ \cfrac}~\text + \int_\Omega \cfrac~\text. Using the divergence theorem, we get : Since is arbitrary, we must have : Expanding out : or, : or, : Now, the material time derivatives of and are given by : Therefore, : From the conservation of mass . Hence, : |} 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Clausius–Duhem inequality」の詳細全文を読む スポンサード リンク
|