THERMODYNAMIC PROCESSES AND PROPERTIES CLASS NOTES
THERMODYNAMIC PROCESSES
AND PROPERTIES CLASS
NOTES
Any thermodynamic system works on
a closed repeatable cycle. Each cycle
consists of four processes. In these
processes, there is transfer of heat and
work into the system or out of the system.
Normally processes have one
variable as constant. Adiabatic process in
which there is no heat exchange.
Analysis use properties. Every
thermodynamic device use one fluid
or the other. The combination of the
thermodynamic fluid and device is such to
give maximum efficiency.
The equation of state is a relation between
thermodynamic properties for ideal gas.
Simple equation of state is not
applicable for thermodynamic properties
with real gases. There is a need of
more mathematical relations for the real
gases. Fundamental thermodynamic
properties temperature, pressure and
volume are measurable. Derived
thermodynamic properties namely Internal
energy, enthalpy and entropy cannot be
measured. Analysis of thermodynamic
systems use these properties. For the
determination of these properties, there is
a need to develop thermodynamic
relations.
Analysis of power producing cycles is
done with thermodynamics and transport
properties. Power consuming cycles
use these properties too.
THERMODYNAMIC PROCESSES
(a) Temperature constant process ISOTHERMAL
(b) Pressure constant processISOBARIC
(c) Enthalpy constant process ISENTHALPIC (h=constant)
(d) Entropy constant process ISENTROPIC (s=constant)
(e) Volume constant process ISOCHORIC (V=constant)
(f) No heat exchange ADIABATIC PROCESS
A thermodynamic cycle will have four processes.
Carnot cycle consists of two isothermal and two isentropic processes.
Thermodynamic and Transport Properties
THERMODYNAMIC PROPERTIES
Fundamental Properties these are measurable properties.
a. Temperature
b. Pressure
c. Volume
i. Specific volume of saturated liquid
ii. Saturated vapor specific volume
iii. Specific volume of super heated vapor
Derived Properties These are nonmeasurable properties.
Enthalpy

Specific enthalpy of saturated liquid

Enthalpy(specific) of saturated vapor

Specific enthalpy of super heated vapor
Entropy

Specific entropy of saturated liquid

Entropy(specific) of saturated vapor

Entropy(specific) of super heated vapor
INTERNAL ENERGY
Internal Energy is the sum of kinetic and potential energy. These energies are of random translation, rotational and vibratory motion of the atoms of the system. Its symbol for 1 kg is ‘u’ for 1 kg mass. U is symbol for m kg mass. Its units are kJ. From the First Law of Thermodynamics, the internal energy of a system increases with rise of temperature.
dU = Q – W= heat supplied into the system—work done by the system.
ENTROPY
Entropy is measure of disorder. More is the disorder, more will be entropy. Mathematically δV/V is a measure of disorder. It will increase in an expansion process and vice versa. Take entropy zero with respect to a datum. Various processes use difference of entropies. Take entropy of water zero at 0 ^{0 }C. Based on this, calculate the values of entropy. Similar is the case of refrigerants. Take entropy of each refrigerant zero at –40 ^{0 }C. Calculate entropy values at other temperatures and tabulate. Temperatureentropy charts are mad from the tabulated data. Units of specific entropy are k J / kg K. The symbols for specific entropy is ‘s’. S is total entropy for m kg. Read Specific entropy (k J/ kg K) values from tables and charts.
Enthalpy
It is sum of internal energy and flow work.
Mathematically
h = u+ p v
Transport properties are

Specific heat of liquid

Vapor specific heat

Thermal conductivity of liquid

Conductivity(thermal) of vapor

Viscosity of liquid

Vapor viscosity
Origin of transport properties

Internal energy comes from the First Law of Thermodynamics

Entropy comes from the Second Law of Thermodynamics. Measurement of entropy comes from the Third Law of Thermodynamics.

Definition of enthalpy comes from the total heat content which the sum of internal energy and the flow work.
SPECIFIC AND TOTAL PROPERTIES
(a) Specific property
Properties for 1 kg mass are specific properties. Refrigerant charts and tables have specific properties.
(i) specific entropy (s),
(ii) Enthalpy (specific) (h),
(iii) specific volume (v),
(iv) Humidity(specific) (w).
Specific properties are for
(i) Subcooled liquid
(ii) Saturated liquid
(iii) Wet vapor
(iv) Dry saturated vapor
(v) Superheated vapor
(vi) gas
The symbol of specific property is small alphabet.
2(b). Total properties
Total property is equal to specific property multiplied by mass (m). This represented by the corresponding capital alphabet symbol like H=m h, S=m s, V=m v.
Thermodynamic relations used in the derivation of derived properties
1. (a) f(x, y, z) =0,

(∂x/∂y)_{z} (∂y/∂z)_{x}(∂z/∂x)_{y} = 1

(∂y/∂x)_{z}(∂x/∂y)_{z}=(∂y/∂z)_{x}(∂z/∂y)_{x} =(∂z/∂x)_{y}(∂x/∂z)_{y}=1
(b)Z=z(x, y),

y =y(z, x) and x=x(y, z) z = z(x, y)

dz = (∂z/∂x)_{y} dx + (∂z/∂y)_{x} dy

For a continuous function
∂^{2}z/∂x∂y =∂^{2}z/∂y∂x

Thermodynamic characteristic functions
(i) Internal energy(U)
(ii) Helmholtz energy (A)
(iii) enthalpy (H)
(iv) Gibb’s free energy(G)
These functions use thermodynamic parameters.
4. Thermodynamic parameters
(i) Temperature (T)
(ii) Entropy (S)
(iii) Pressure (p)
(iv) Volume (V)
5. Reversible process
δq and δw use properties of the system.
δq_{rev} = T ds and δw_{rev} = p dv
For a reversible process
du = T ds—p dv
This relation combines the First and Second Law.
6. Enthalpy
For a unit mass, h = u + P v
For mass m, H = U + PV
7. Helmholtz energy at a constant temperature
A =UTS
8. Gibb’s free energy
G = UTS + pV
REFERENCES

Chemical Thermodynamics, D.J.G. Ives, University Chemistry, MacDonald Technical and Scientific, 1971

Elements of Statistical Thermodynamics (2nd Edition), L.K. Nash, AddisonWesley, 1974

Thermal Physics (2nd Edition), Kittel, Charles & Kroemer, Herbert (1980).

Encyclopedia of Physics (2nd Edition, W. H. Freeman Company. McGraw Hill,”), C.B. Parker, 1994

Thermodynamics – an Engineering Approach , Cengel, Yunus A., & Boles, Michael A, McGraw Hill, 2002

Statistical Physics (2nd Edition), F. Mandl, Manchester Physics, John Wiley & Sons, 2008

Thermodynamics, From Concepts to Applications (2nd Edition), A. Shavit, C. Gutfinger, CRC Press (Taylor and Francis Group, USA), 2009