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Lesson
5
Review of fundamental
principles –
Thermodynamics : Part II
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.The specific objectives are to
:
1.
State principles of evaluating thermodynamic properties of pure substances using:
a)
Equations of State (
Section 5.2
)
b)
Thermodynamic charts (
Section 5.2
)
c)
Thermodynamic tables (
Section 5.2
)
2.
Derive expressions for heat and work transfer in important thermodynamic processes
such as:
a)
Isochoric process (
Section 5.3
)
b)
Isobaric process (
Section 5.3
)
c)
Isothermal process (
Section 5.3
)
d)
Isentropic process (
Section 5.3
)
e)
Isenthalpic process etc. (
Section 5.3
)
At the end of the lesson the student should be able to:
1.
Evaluate thermodynamic properties using equations of state, tables and charts
2.
Identify various regimes on T-s and P-h charts
3.
Estimate heat and work transferred in various thermodynamic processes
5.1. Thermodynamic relations
There are some general thermodynamic relations, which are useful for determination of several
thermodynamic properties from measured data on a few properties. The following relationships
are generally used for the evaluation of entropy change. These are called
T ds
equations. They
are obtained by applying first and second laws of thermodynamics
first
equation
second
equation
T
ds
du
p
dv
T ds
T
ds
dh
v
dP
T
ds
=
+
=
−
(5.1)
Two more fundamental thermodynamic relations can be obtained by defining two new
properties called Gibbs and Helmholtz functions.
5.2. Evaluation of thermodynamic properties
In order to perform thermodynamic calculations, one has to know various thermodynamic
properties of the system. Properties such as
internal energy, enthalpy and entropy cannot be
measured directly
. Thermodynamics gives mathematical relations using which one can obtain
properties, which cannot be measured directly in terms of the measurable properties such as
pressure, temperature, volume, specific heat etc.
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