tailieunhanh - Ebook Basics and applied thermodynamics: Part 2

(BQ) Basics and applied thermodynamics is one of the best book for Mechanical Engineers for any competitive exam like GATE, ISRO, UPSC etc. Since This subject is one of the interesting subject the book should cover all the basic concept along with their illustration this book covers that. | 11 - Thermodynamic Relations Equilibrium and Third Law Some Mathematical Theorems Theorem 1 If a relation exists among the variables X y and z then z may be expressed as a function ofX and y or dz dz Ì dz dx dy If 37Ì ÀÍ andfặ-ì N UxẶ vạdx then áz M àx Nảy vtheteZ ManAN tt functions ofx andy. Differentiating Mpartially with respect to y and N with respect to X d2z dy Jx dx-dy d2z V dx y dy-dx V đy J dx Jy This is the condition of exact or perfect differential. Theorem 2 If a quantity f is a function of X y and z and a relation exists among X y and z then is a function of any two of X y and z. Similarly any Jrheb Thermodynamic Relations Equilibrium and Third Law 397 one ofX y and z may be regarded to be a function off and any one of X y and z. Thus if x x y d 37 dv Jy uf J f Similarly if dy S7Ì d ii dz of z azjf Substituting the expression of dy in the preceding equation Theorem 3 Among the variables X y and z any one variable may be considered as a function of the other two. Thus X x y z . _ dx l f 3x A . dx -5 I dy dz UyẬ VdzẶ Similarly 398 Basic and Applied Thermodynamics Among the thermodynamic variablesp V and T the following relation holds good fiKi firi k JT k 3r Jpk dp Jv Maxwell s Equations A pure substance existing in a single phase has only two independent variables. Of the eight quantities p V T s u H F Helmholtz function and G Gibbs unction any one may be expressed as a function of any two others. For a pure substance undergoing an infinitesimal reversible process a AU TAS-pAV b dff dơ pdK Fdp rd5 rdp c AF AU-TAS-SAT -pAV-SAT d AG AH-TAS-SAT VAp-SAT Since u H F and G are thermodynamic properties and exact differentials of the type dz M dr N dy then l I 3x Jy Applying this to the four equations ỄÌ _M ÍỄ i-m X op Js X p UrJv 1L7 k or p k .