?S of Pure Substances, Isentropic Processes, and Property Diagrams

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?S of Pure Substances,Isentropic Processes,and
Property Diagrams
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?S of Pure Substances

• Can be calculated from defining equations
• However, very complicated.
• Generally use tables or EES
• Be careful mixing methods.
• can have different reference states.

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T-s diagram for water
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Constant Volume Process
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Constant Pressure Process
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Isentropic Process
An adiabatic reversible process will be constant
entropy.
However, an isentropic process is not necessarily
an adiabatic reversible process.
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Ideal pumps, turbines, nozzles, and diffusers
are isentropic and enable us to assign idealized
efficiencies.
Because the turbine is isentropic, s2 s1 can
help us find the final state.
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Use of T-s diagrams
Entropy definition can be rearranged to dQint
rev TdS
Similar to dw Pdv is area under P-v curve.
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One Trivial Example
Isothermal processes are also easy to integrate.
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h-s diagram
?h part indicates the work out of a steady- flow
adiabatic turbine
?s part indicates the irreversibilities of
the process
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T-s diagram of a carnot heat engine
Wnet QH - QL