Introduction: Thermodynamics Notes | Study Thermodynamics - Mechanical Engineering

Introduction

  It is a science of energy transfer and its effect on the properties of a system.

System

A system is a region containing energy and/or matter that is separated from its surroundings by arbitrarily imposed walls or boundaries. In a thermodynamic analysis, the system is the subject of the investigation. 

Surrounding

Everything external to the system is the surroundings. 

Boundary

A boundary is a closed surface surrounding a system through which energy and mass may enter or leave the system. 

Closed system

•  No mass transfer to or from the system or the surrounding.
•  Energy may transfer to or from the system or the surrounding
  E.g. Piston cylinder arrangement, without valves gas in a closed container.

Open System

• Mass and energy both may transfer to or from the system or the surrounding.
  E.g. Compressor, Turbine etc.

Isolated system (Special case of Closed system)

An isolated system is a thermodynamic system that cannot exchange either energy or matter outside the boundaries of the system. There are two ways in which this may occur:

1. The system may be so distant from another system that it cannot interact with them.
2. The system may be enclosed such that neither energy nor mass may enter or exit.

Extensive Properties

An extensive property is a property that depends on the amount of matter in a sample. The mass of an object is a measure of the amount of matter that an object contains. 

Intensive Properties

An intensive property is a property of matter that depends only on the type of matter in a sample and not on the amount. 

Example: colour, temperature, density, and solubility.

Reversible Process

• A process is said to be a reversible process if when reversed follows the same path without leaving any effect on the system and surroundings.
• The quasi-static process is called a reversible process
• All reversible processes can be shown on diagrams. Ex. P–V, T–S, P–T diagrams

Irreversible Process

• A process is said to be an irreversible process if when reversed follows a different path, leaving an effect on the system & surroundings.
• All spontaneous processes are irreversible processes.
• The irreversible process cannot be shown on diagrams. They are shown as dotted lines.

Example: Heat transfer to finite temperature difference, Free expansion.

Thermodynamic Equilibrium

A system will be in a state of thermodynamic equilibrium if the condition for the following three types of equilibrium is satisfied.

(i) Mechanical equilibrium

The net force on a system should be 0, i.e. all the forces should be balanced.
(ii) Chemical equilibrium

All the chemical reactions occurring inside a system should cease after reaching an equilibrium state.
(iii) Thermal equilibrium

There should be no heat transfer between the system and surroundings.