Thermodynamics Notes 16

Thermodynamics Notes 16 - ME 311 FALL 2007 CHAPTER...

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ME 311 THERMODYNAMICS S. Masutani FALL 2007 CHAPTER 6 (continued) Gibbs Equation We have derived thermodynamic definitions of temperature and pressure (for a SCS): v u s T 1 and u v s T p Since s = s(u,v), then dv T p du T dv v s du u s ds u v + = + = 1 pdv du Tds + = Recall also that vdp dh pdv du vdp pdv du dh pv u h = + + + = + Substituting yields vdp dh Tds pdv du Tds = + = These are the Gibbs equations for a SCS. Application of the Gibbs Equation The Gibbs equation provides a means to determine changes in entropy from data on other measurable thermodynamic properties. As an example: = + = + = 2 1 1 2 2 1 2 1 s s dv T p T du ds dv T p T du ds Consider a case involving phase change where state 1 is saturated liquid and state 2 is saturated vapor. During the evaporation process, p,T = constant, so fg sat sat sat fg fg v T p T u dv T p du T s s s + = + = = 2 1 2 1 1 2 1 1
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ME 311 THERMODYNAMICS S. Masutani FALL 2007 Gibbs Equation for Other Simple Substances
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Thermodynamics Notes 16 - ME 311 FALL 2007 CHAPTER...

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