1. “ BASIC CONCEPTS OF THERMODYNAMICS ”
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

2. WHAT IS THERMODYNAMIC ?
Thermodynamic is the science that deals with the energy interactions between material system.
In other words, It is the science which deals with the transformation of energy of all kinds from one form to another.
In short/in fact, thermodynamic means the science of three “Es” namely Energy, Entropy and Equilibrium.
Carnot, Joule, Kelvin and Clausius were the main scientists who developed this science in the past century.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

3. THERMODYNAMIC SYSTEM
A thermodynamic system or simply a system is defined as a quantity of matter or a region in space chosen for study.
Everything external to the system is called ‘surrounding’ or the ‘environment’.
The real or imaginary surface that separates the system from its surrounding is called boundary.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

4. TYPES OF SYSTEM Open System. Closed System. Isolated System.
(1) Open System: Open system is the one in which energy & mass transfer takes place at the system boundary. E.g. Turbine, I.C. Engine etc.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

5. (2) Closed System: Closed system is the one in which only energy transfers at its boundary. Such system have no mass transfer across it’s boundary.
Example:- Air trapped in piston cylinder arrangement.
(3) Isolated System : An isolated system is the one in which neither energy nor mass can cross the boundary.
Example:- Perfectly Insulated Thermos Flask
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

6. THERMODYNAMIC PROPERTIES, PROCESSES & CYCLES
CONTROL VOLUME
For thermodynamic analysis of an open system , like air-compressor, attention is focused on a certain volume in space which is known as ‘control volume’.
Control volume is bounded by a surface called ‘control surface’.
Every system has certain characteristics by which its physical condition may be described e.g. volume, pressure, temperature etc. Such characteristics are called properties of the system.
THERMODYNAMIC PROPERTIES, PROCESSES & CYCLES
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

7. CONTD…
Any operation in which one or more of the properties of a system changes is called change of state.
The succession of states passed through during a change of state is called the path of change of state.
When the path is completely specified , the change of state is called a process, e.g. constant volume process, constant pressure process , constant temperature process etc.
A thermodynamic cycle is defined as a series of state of changes such that final state is identical with the initial state.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

8. CONTD…
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

9. MACROSCOPIC & MICROSCOPIC POINT OF VIEW
Thermodynamic studies are undertaken by the following two different approaches.
(1) Macroscopic approach – ( macro means big or total )
(2) Microscopic approach – ( micro means small )
Macroscopic approach
Microscopic approach
In this approach a certain quantity of matter is considered without taking into account the events occurring at molecular level.
This approach is concerned with gross or overall behavior.
In this approach every quantity of matter is considered by taking into account the events occurring at molecular level. The molecules have different velocities & energies. The values of these energies are constantly changing with time.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

10. Contd… Macroscopic approach Microscopic approach
This is known as classical - thermodynamics.
This approach is known as statistical thermodynamics.
The analysis of macroscopic system requires simple mathematics formulae.
In microscopic approach, the value of the quantity changes with time so advanced statistical & mathematical methods are needed to explain the change in system.
Few properties are required to describe a system.
Large number of variables are required describe a system.
This approach is quite simple.
This approach is complicated.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

11. THERMODYNAMIC EQULIBRIUM
A system is said in thermodynamic equilibrium if the temperature and pressure at all points are same ; there should not be velocity gradient ; the chemical equilibrium is also necessary.
For attaining a state of thermodynamic equilibrium following three types of equilibrium state must be achieved:
(1) Thermal Equilibrium :- The temperature of the system does not change with time & has the same value at all points of system.
(2) Mechanical Equilibrium :- There are no unbalanced forces within the system or between the surrounding. The pressure in the system is same at all the points and does not change with respect to time.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

12. QUASI-STATIC PROCESS Contd…
(3) Chemical Equilibrium :- No chemical reaction takes place in the system and the chemical composition does not vary with time.
When process proceeds in such way that the system remains close to a thermodynamic equilibrium state at all times, it is called Quasi-Static process.
For example, consider system of gas contained in cylinder. Now, let us consider the pressure of the gas on the one face of a frictionless piston is p1 and a pressure p2 on opposite face. If two pressures are equal, the piston is in equilibrium. But if p1 is infinitesimally larger than p2 the gas on both sides still remains essentially in equilibrium . This is known as Quasi-Static process.
QUASI-STATIC PROCESS
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

13. No real process is quasistatic, but such processes can be
Contd…
This Quasi-static process only can be represented on a thermodynamic plane as shown in the below figure.
Let AB represents a quasi-static process on a thermodynamic plane, say p-V plane. Then at successive state such as 1,2,3,4, etc.; the system is very nearly in thermodynamic equilibrium.
No real process is quasistatic,
but such processes can be
approximated by performing
them very slowly.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

14. PURE SUBSTANCE CRITICAL POINT
A pure substance is the one which has a fixed chemical composition throughout. For example water, carbon dioxide, nitrogen etc.
In other words, it is a system which is
(a) Homogeneous in composition (b) Homogeneous in chemical aggregation.
The mixture of water & ice is a pure substance while the mixture of oil & water isn’t a pure substance.
The critical point may be defined as “the point at which the saturated liquid & saturated vapor states are identical.” The pressure & temperature at critical point are known as critical pressure & critical temperature respectively.
CRITICAL POINT
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

15. p-v-T Surface
The p-v-T surface is a graphical representation of the state of a pure substance which must have two independent properties and any third as the dependent property. It is relationships between pressure, specific volume and temperature which is represented by a three dimensional plot.
If any two of these state variables is specified, the third is determined.
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.

16. Thank you
Prof. Bhavesh C. Babar, Mechanical Engineering Department, SREZ - Om Shanti Engg. College, Rajkot.