Introduction and Basic Concepts about Thermodynamics

THERMODYNAMICS

Thermodynamics actually includes all aspects of energy, energy transformation and relationship among the properties of matter.

Applications of Thermodynamics:

There are many applications of thermodynamics bit some of them are :

1. Human body 

2. Refrigeration system 

3. Air-conditioning system

4. Aeroplanes 

5. Power Plants 

6. Automobiles, etc.

SYSTEM AND CONTROL VOLUME:

System is any thing which is under consideration.

Volume of system or under boundary is called control volume. 

TYPES OF SYSTEM:

1. OPEN SYSTEM:

 System through which mass and energy can cross the boundary is called open system.

2. CLOSE SYSTEM:

System through which energy can transfer but mass cannot cross the boundary.

3. ISOLATED SYSTEM:

System through which mass and energy cannot transfer.

PROPERTIES OF A SYSTEM :

Any characteristic of a system defines property of a system. They are divided into several types:

1. INTENSIVE PROPERTIES:

Properties which does not depend upon the size and quantity of system. For exaqmple: temperature, pressure, density, etc.

2. EXTENSIVE PROPERTIES:

Properties which does depend upon the size and quantity of system. For example: mass, volume, mole, etc.

3. SPECIFIC PROPERTIES:

It is defined as;

Extensive properties per unit mass.

For example:
1. specific volume = volume / mass
2. Specific energy = energy / mass
3. Specfic weight = weight / volume, etc.

CONTINUUM APPROACH:

Consideration of continuity of matter that there are no holes between molecules is called Continuum Approach.
Note: At high altitudes, mean free path becomes much greater so continuum approach is not applicable. For this Rare-fied Gas Flow Theory is used.

RELATIVE DENSITY or SPECIFIC GRAVITY:

Density of solids relative to standard liquid's density that is water.

Specific Gravity = S.G. = Density of substance/Density of water

STATE OF A SYSTEM:

If a system is in equilibrium, then properties give the state of a system.

EQUILIBRIUM: 

It imlpies the state of balance. A system ion equilibrium rxperiences no change.

For example:

* Thermal equilibrium: No change in temperature.

*Mechanical equilibrium: No change in pressure.

*Chemical equilibrium: No change in composition. 

THE STATE POSTULATE:

It states that;

The state of a simple compressible system is completely specified by two independent intensive properties.

SIMPLE COMPRESSIBLE SYSTEM:

 A system in the absence of electrical, mechanical, gravitational motion and surface tension effects is called Simple Compressible System. 

PROCESS AND CYCLES:

Process is defined as; 

Any change that a system undergoes from one equilibrium state to another.

 Cycle is defined as;

If a system returns to its initial state at the end of the process.

QAUSI-EQUILIBRIUM PROCESS OR QUASI-STATIC:

When a process proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times is called Quasi-equilibrium process.

ZEROTH LAW OF THERMODYNAMICS:

It states that;

If two bodies are in thermal equilibrium with the third body then they are also in thermal equilibrium with each other.