Basic Concepts of Thermodynamics PDF-Polytropic Process, Laws of Thermodynamics(TD), Derivations for Isobaric, Isochoric, Adiabatic and Isothermal Processes: All the concepts are explained below in a detailed way. Not only the concepts but also the derivations of Isobaric, Isochoric, Adiabatic, Isothermal, Polytropic Process etc.were explained below in the form of handwritten material.

Go through them and if you have any doubts, please report us from the comments section.

Note: Download Basic Concepts of Thermodynamics PDF at the end of the article.

Energy Resources and Conversions:

• Energy is available in various forms such as Electrical, thermal, Chemical, Nuclear, Solar, Geothermal, etc.
• Energy can converts from one form to another form.

Energy Resources:

1. Wind Energy
2. Solar Energy
3. Flowing Streams of Water(Rivers)
4. Ocean Tides
5. Fossil Fuels(Coal,Petroleum,Natural Gas)
6. Nuclear Energy(Uranium, Thorium, etc.)

BASIC CONCEPTS OF THERMODYNAMICS:

• The term Thermodynamics is derived from the Greek words ‘Thermic’ which means Heat and ‘Dynamics’ which means Force.
• Thermodynamics is the science that deals with the relationship between heat and mechanical energy and conversion of one into the other.

Eg: Human body, solar heaters, sun, etc. The study of Thermodynamics is based on three general laws of nature. They are

• Zeroth Law of Thermodynamics
• First Law of Thermodynamics
• Second Law of Thermodynamics
• Third Law of Thermodynamics

MICROSCOPIC & MACROSCOPIC ANALYSIS: The behavior of matter can be studied in two viewpoints.

1.Microscopic Analysis

2.Macroscopic Analysis

The explanation is as follows.

1.Microscopic Analysis: The behavior of individual atoms or molecules. The behavior of gas is described by the sum of the behavior of each molecule (Statistical Thermodynamics).

Eg: Study of Atomic Structure in nuclear physics.

2.Macroscopic Analysis: The behavior of more number of molecules is taken into account.

Eg: Very few parameters are required to specify the state of a system like Pressure&Volume, Volume&Temp, Temp&Pressure.

What is Phase, Homogeneous, Heterogeneous, Pure Substance, Working Substance?

Phase:      A Phase is defined as the quantity of matter which is homogenous in chemical composition and physical structure.

Homogeneous:  A system which consists of a single Phase.

Eg:  Air and water vapor.

Heterogeneous:   A system which consists of two or more phases. Eg: Ice and water.

Pure Substance: A pure substance is the one that has a homogeneous and invariable chemical composition even though there is a change in phase. Eg: water or Steam or a mixture of steam and water.

Working Substance: Conversion of heat energy into work and vice-versa takes place through the agency called working substance.

What is System, Boundary, Surroundings, and Universe?

SYSTEM:        A system is defined as a finite quantity of matter or prescribed region of space.

BOUNDARY:        It is a real or imaginary envelope enclosing a system.

SURROUNDINGS:       Everything external to the system.

UNIVERSE:       System and its surroundings together comprise a Universe.

TYPES OF SYSTEMS: There are three types of System.

• Open System
• Closed System
• Isolated System

The detailed explanation of the above three systems are as follows

1.Open System: It is a system in which both energy interaction as well as mass interaction takes place with its surroundings called an open system.

Eg: Air Compressor.

2.Closed System: It is a system in which only energy interaction takes place but not mass interaction with its surroundings called a closed system.  Eg: Piston-cylinder

3.Isolated System It is a system in which neither energy interaction nor mass interaction takes place with its surroundings called an Isolated system.  Eg: Flask etc.

Types of Process:

1. Reversible Process
2. Irreversible Process

## Difference between Reversible Process and Irreversible process:

Reversible Process:

It is a process which can be made to exactly replace its path without suffering any deviation.

A process in which there are no losses is called Reversible Process.

Ex:

1.Spring-mass system

2. Electro plating

A +   B    => C  +  D

And if  the Reverse is attained i.e  C  +   D    => A  +  B      Then that process is called Reversible Process.

### Irreversible process:

It is a process which cannot be made to exactly retrace its path without suffering its deviation is called irreversible process.

Most of the processes in nature are irreversible.Any process with friction or losses is called irreversible process.

Ex:

• Sun’s  energy coming to earth.
• Hot cup of coffee kept on the table
• combustion
• Wind flow.

This is the complete explanation about the Difference between Reversible Process and irreversible process which is shown in a detailed manner. If you have any doubts, feel free to ask from the comments section. Please Share and Like this blog with the whole world so that it can reach to many.

Equilibrium and Stages of Equilibrium: A system is said to be in equilibrium if it does not tend to undergo any change. Systems under Pressure and Temperature equilibrium but not under chemical equilibrium are said to be in meta-stable equilibrium condition.

STAGES OF EQUILIBRIUM:

• Mechanical equilibrium
• Chemical equilibrium
• Thermal equilibrium and
• Thermodynamic equilibrium.

MECHANICAL EQUILIBRIUM: In a system, if there are no external and internal forces acting on the system then the system is said to be in Mechanical Equilibrium.

CHEMICAL EQUILIBRIUM: For a system to be in chemical equilibrium there should be equality of chemical potential, i.e., there should not be any chemical reactions.

THERMAL EQUILIBRIUM: For a system to be in thermal equilibrium, there should not be any temperature change in the system. (Or) The temperature across every section is same then the system is in Thermal Equilibrium.

THERMODYNAMIC EQUILIBRIUM: When a system satisfies the conditions of mechanical equilibrium, chemical equilibrium, and thermal equilibrium, it is said to be in a state of thermodynamic equilibrium.

Quasi-static process:

A system is made to undergo a series of change of states such that it is in thermodynamic equilibrium at each and every stage, then the locus of all these states is called a Quasis-static process.

• It is a very slow process.

What is Point Function, Path Function, Heat and Work?

POINT FUNCTION: When two properties locate a point on the graph (coordinate axis) then those properties are called as Point Function. Eg: Pressure, temperature, volume, etc..

PATH FUNCTION: There are certain quantities which cannot be located on a graph by a point but are given by the area under the process. Such quantities are called path functions. Eg: Work and Heat.

HEAT: It is defined as the form of energy that is transferred between two systems due to the temperature difference between them. The transfer of heat into the system is called heat addition (+ve) and heat out a system is called heat rejection (-ve).

WORK: Work is defined as energy expanded by a force through a displacement. The work transferred into the system is indicated by (-ve sign) and the work output by a system is indicated by (+ ve sign).                                                        W = F.S

PDV WORK OR DISPLACEMENT WORK:   Will be updated soon

What is Temperature, Adiabatic Process and Diathermic Process? Temperature: It is an intensive thermodynamic property related to the “hotness” or “coldness” of a body measured on a definite scale. Eg: Thermometer.

Adiabatic Process: A process in which no heat crosses the boundary of the system is called an adiabatic process.

Diathermic Process: A substance, which allows the heat to pass through it is called diathermic substance and the process is called Diathermic Process.

Laws of Thermodynamics:

• Zeroth Law of Thermodynamics
• First Law of Thermodynamics
• Second Law of Thermodynamics
• Third Law of Thermodynamics

Overview of laws: Zeroth Law of Thermodynamics:

• Thermal Equilibrium

First Law of Thermodynamics:

• Law of conservation of Energy
• Work Transfer and Heat Transfer
• Concept of Enthalpy (H)
• Concept of Internal Energy(U)

Second Law of Thermodynamics:

• The direction of Heat Transfer
• Concept of Entropy

Third Law of Thermodynamics: The entropy of a system becomes zero at Absolute Zero Temperature. The detailed explanation of all these laws is as follows.

ZEROTH LAW OF THERMODYNAMICS:

Statement:

When a body ‘A’ is in thermal equilibrium with body ‘B’ and also separately with body ‘C’ then B and C will be in thermal equilibrium with each other. (or) If two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other.

Thermal Equilibrium: The bodies A & B are said to be in thermal Equilibrium with each other if and only if, the final temperatures of both the bodies will be same when they are kept near to each other.

FIRST LAW OF THERMODYNAMICS:

• First law is a law of conservation of energy.

First law of thermodynamics for a Cyclic process:

Statement:

The first law of thermodynamics to a cyclic process is as follows.   “During any cycle that a closed system undergoes, the net work transfer is equal to the net heat transfer.”

The first law of thermodynamics for a Non-Cyclic Process:

• If a system undergoes a change of state during which both heat transfer and work transfer are involved, the net energy transfer will be stored or accumulated within the system.
• If ‘Q’ is the amount of heat transferred to the system and ‘W’ is the amount of work transferred from the system during the process as shown in the figure.
• The net Energy Transfer (Q-W) will be stored in the system. The energy in storage is neither heat nor work and is given the name Internal Energy.

Equation:

Q-W = ΔE

If there are more energy transfer quantities(i.e. Energy transfer and Work transfer) involved in the process as shown in the figure. Then the equation is as follows.

(Q+Q3 -Q1) = ΔE +(W2+W3-W1-W4)

Applications of First Law of Thermodynamics to Non-Flow Processes (or) Closed System:

The Non-Flow Processes are as follows.

1.Reversible Constant Volume Process (or) Isochoric Process

2.Reversible Constant Pressure Process (or) Isobaric Process

3.Reversible Constant Temperature Process (or) Isothermal Process

4.Reversible Adiabatic Process (or) Isentropic Process

The detailed explanation of all the Non-Flow processes is as follows.

1.Reversible Constant Volume Process (or) Isochoric Process:

 Volume (V) = Constant

In a constant Volume process, the working substance is to be placed in the container and the boundaries of the system are immovable and thereby no work is said to be done on or by the system. Fig. below shows the Isochoric Process. Considering the mass of the working substance as ‘unity’ and applying the First Law of Thermodynamics. The derivation for the Reversible Constant Volume Process is shown below.

2.Reversible Constant Pressure Process (or) Isobaric Process:

 Pressure (P) = Constant

As it is a Constant Pressure process, the gas present in the cylinder pushes the piston from its initial position to final position because of movable boundaries and it indicates the work is done by the gas on its surroundings.

3.Reversible Constant Temperature Process (or) Isothermal Process:

 Temperature (T) = Constant

4.Reversible Adiabatic Process (or) Isentropic Process:

 Heat Transfer (Q) = Zero

## Polytropic Process:

An expansion process in which the energy to do work is supplied partly from an external source and partly from the gas itself known as Polytropic Process and that follows a path which will fall in between those of Isothermal and Adiabatic Process.

For any reversible process,

Work done W =P dv

The governing equation for the polytropic process is

where n is the Polytropic Index. The detailed explanation for the Polytropic process was presented below.

In a Polytropic process, the polytropic index(n) can take the value from -∞ to +∞. Now place the values of n and get Isobaric, isothermal, adiabatic and Isochoric processes which were explained below.

Second Law of Thermodynamics: According to the second law of thermodynamics, the whole heat energy cannot be converted into work and part of the energy must be rejected to the surroundings.

The figure below shows the possible machine in which heat is supplied from the hot reservoir, work is done on the surroundings and remaining is rejected to cool reservoir(mostly the atmosphere).

The work is said to be high-grade energy and heat is low-grade energy. The complete conversion of low-grade energy into higher grade energy in a cycle is impossible.

Classius Statement:

It is impossible for a self-acting machine working in a cyclic process, unaided by any external agency to convey heat from a body at a lower temperature to a body at high temperature.

Or

It is impossible to construct a refrigerator whose only purpose is the absorption of heat from a low-temperature reservoir and its transfer to the high-temperature reservoir without any work input.

Kelvin-Planck Statement:

It is impossible to construct an engine which while operating in a cycle produce no other effect except to extract heat from a single reservoir and produce work.

Or

It is impossible to construct an engine whose only purpose is the absorption of heat from a high-temperature reservoir and its conversion to work.

Ex: Heat engine

Perpetual motion machine of the second kind:

Any device which converts 100% heat to 100% work is called Perpetual motion machine of the second kind and second law tells us that, Perpetual motion machine of the second kind is impossible.

Without violating the first law, a machine can be imagined which would continuously absorb heat from a single thermal reservoir and would convert this heat completely into work. The efficiency of such a machine would be 100%.

This machine is called Perpetual motion machine of the second kind. A machine of this kind will evidently violate the second law of thermodynamics.

Lessons for You:

Thermal Engineering Theory of Machines Non-Traditional Machining CAD/CAM Material Science Engineering Production-Casting Welding Forming Processes Machining Sheet Metal Operations Elements of Mechanical Engineering Workshop Manufacturing Practices