Thermodynamic System And Its Classification

What is Thermodynamic System?

A thermodynamic system is defined as a fixed mass in space under thermodynamic consideration to analyse a problem.

The system is identified by a boundary drawn around the system which may be real or imaginary. Across the boundary, the energy transfer in the form of heat and work takes place.
Shape, volume, the position of the boundary may change during energy exchange with the surroundings.

Everything external to the system is called surroundings or environment. 

Thermodynamic System |
Thermodynamic System

A system and its surroundings together are called the universe.

Classification of Thermodynamic Systems

Many times it is asked, to classify and explain the classification of the thermodynamic system.

Based on the mass and energy transfer between the system and the surrounding, the thermodynamic system can be classified as

  1. Open system.
  2. Closed system.
  3. Isolated system.

Open system

A system with mass transfer along with energy transfer across its boundaries is called an open system.
Fig below shows an open system that consists of a turbine.
Open System |
Open System
It should be noted that the matter across the boundary of the system as the high-pressure gases enter into the turbine, low-pressure gases enter into the turbine and low-pressure gases leave the turbine.

Also, it is not necessary that the quantity of matter within the boundaries of an open system to remain fixed.

Closed system

A system without mass transfer across its boundaries is called a closed system.

Such systems have only the energy transfer in the form of heat and work with their surroundings across the system boundary.

The figure below shows a closed system.

Closed System |
Closed System

Isolated system

If there is no mass and energy transfer between the system and surroundings, the system is said to be an isolated system.
Hence, according to the definition, the universe is an isolated system.

A handy example of an isolated system is a thermos flask.

The figure below shows an isolated system.

Isolated System |
Isolated System


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