1. AHMEDABAD INSTITUTE OF TECHNOLOGY
SUBJECT : ENGINEERING THERMODYNAMICS
ENROLLMENTNO:
GUIDED BY : MR. ALPESH Parmar

2. BASIC CONCEPTS Thermodynamic can be defied as the science of ‘ENERGY’.
1) Thermo - meaning hot or heat
2) Dynamics - meaning power or powerful
The word ‘THERMODYNAMICS’ means study of heat related to matter in motion.

3. Thermodynamics may be defined as follows
It is science the deals with the interaction between energy and material systems.
It is law of science which deals with the relations among heat, work and properties of system which are in equilibrium.

4. In thermodynamics, there are four laws as
Zeroth law : It represent the concept of temperature, and deals with thermal equilibrium.
“If two bodies are each in thermal equilibrium with a third body, they are also in thermal equilibrium with each other”
Body B
Body A
Body C

5. First law : It represent the concept of internal energy.
“energy can be neither created nor be destroyed, energy can changed from one form to another form”
Second law : It indicates the limit of converting heat into work and introduce principle of increase of entropy.

6. kelvin-plank statement :
“It is impossible for any device as heat engine that operates on a cycle to receive heat from a single reservoir and produce a net amount of work.”
Third law : It concerned with the level of availability of energy and defined the absolute zero of entropy.
“The entropy of all perfect crystalline substance is zero at absolute zero temperature.”

7. MICROSCOPIC AND MACROSCOPIC POINT OF VIEW
Microscopic approach:
This approach to thermodynamics is concerned with individual behaviour of molecule.
It is known as statistical thermodynamics.
The description of system is so complicated in which larger number of variables are required.

8. Macroscopic approach:
This approach to thermodynamics is concerned with overall or gross behaviour of molecule.
It is known as classical thermodynamics.
The description of system is simple which only few properties are required.
The behaviour of the system is found by using simple mathematical formula.

9. THERMODYNAMIC SYSTEM
System
Boundary
Surroundings
system : It is defined as a quantity of matter or a region in space chosen for study.
surrounding : It is the matter of region out side of system.

10. Boundary : The boundary is contact surface shared by both system and the surrounding.
Universe : The combination of system and the surroundings together is usually refered to as the universe.
The system can be classified as
1) closed system
2) open system
3) isolated system

11. Closed system : In this system no mass transfer across the system boundary. but energy, in form of heat or work , cross the boundary as shown in fig.
Closed system Open system
2) Open system : In this system the mass as well as energy transfer across the boundary of system as shown in fig.

12. 3) Isolated system : In this system, fixed mass and fixed energy, and there is no mass or energy transfer across the system boundary as shown fig.

13. Homogeneous and heterogeneous system
Homogeneous system : A system which consists of a single phase is termed as homogeneous system.
Heterogeneous system : A system which consists of two or more phases is called heterogeneous system.
Phase : It is quantity of matter which is homogeneous through in chemical composition and physical structure.

14. THERMODYNAMIC PROPERTIES
Intensive properties : These properties do not depend on the mass of the system.
Ex. Tempreture,pressure,density
Extensive properties : These properties depend on the mass of the system.
Ex. Volume,mass,total energy

15. State : It is the condition of the system at an instant of time as described by its properties.
Process : Any change that a system undergoes from one state to another state is called a process.
Path : It is series of state through which a system passes during a process.
Cycle : It is defined as a series of state changes such that the final state is identical with the initial state.
Process B A 1 2 P V

16. THERMODYNAMIC EQUILIBRIUM
Equilibrium: A state of balance
“A system is said to be in a state of thermodynamic equilibrium if the value of properties is the same at all points in the system.”
Thermal equilibrium: If the temperature Is the same throughout the entire system.
Mechanical equilibrium: If there is no change in pressure at any point of the system with time.

17. Chemical equilibrium: If the chemical composition of a system does not change with time, that is no chemical reactions occur.

18. QUASI-STATIC PROCESS
When process proceeds in such way that the system remains close to an thermodynamic equilibrium state at all times,it is called a quasi-static process.
let consider system of gas contained in cylinder. The system initially is in an equilibrium state,and describe by properties p1,v1,T1. the upward force exerted by gas on the piston. If the weights is removed, there will be unbalanced forced between the system and the surroundings. Due to gas pressure, the piston will move up the stops.

19. Then system again comes to the equilibrium state which described by the properties p2,v2,T2. but the intermediate state through by the system are non- equilibrium and it will not be possible to describe the path.
Non-quasi-static
process
Quasi-static
process

20. gas Non quasi-static process Quasi-static process gas (Fast expansion)
(slow expansion)
Non quasi-static
process
Quasi-static process

21. Thus process 1-2 is non-quasi-static process
Thus process 1-2 is non-quasi-static process. It represent in dotted line on p-v diagram.
If above process 1-2 takes place slowly, then each step, there is only an infinitesimal (very small part) change in properties. it is possible, if single weight on the piston is replaced by number of many small pieces of weights. These weight are removed one by one very slowly from the top of the piston. If piston moved slowly, the molecule will have sufficient time to redistribute. As a result, the pressure inside the cylinder will always be uniform and will rise at the same rate at all locations. so every state passed through all the equilibrium point is called ‘QUASI-STATIC PROCESS’

22. A quasi-static process is also called a reversible process
A quasi-static process is also called a reversible process. The main characteristic of this process is a succession of equilibrium states and infinite slowness.
Example Of quasi-static process
1) iso-thermal process : Temperature constant
2) iso-baric process : pressure constant
3) iso-choric process : volume constant

23. Temperature and zeroth law of thermodynamic
The zeroth law of thermodynamics: If two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other.
By replacing the third body with a thermometer, the zeroth law can be restated as two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact.

24. Two bodies reaching thermal equilibrium after being
brought into contact in an isolated enclosure.

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