Thermodynamic system and its classification

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, position of boundary may change during energy exchange with the surroundings.
Everything external to the system is called surroundings or environment. 

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Thermodynamic System

A system and its surroundings together is called the universe.

Classification of Thermodynamic Systems :

Based on the mass and energy transfer between the system and the surrounding, the system can be classified as - Open system, Closed system and Isolated system.

1. Open system:

A system with mass transfer along with energy transfer across its boundaries is called an open system.
Fig a. shows open system which consists of turbine. It should be noted that the matter across the boundary of the system as the high pressure gases enter into the turbine and low pressure gases enter into the turbine and low pressure gases leave the turbine.
Also, it is not necessary that the quantity if matter within the boundaries of an open system to remain fixed.
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Open System

2. 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 its surroundings across the system boundary.
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Closed System

3. 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, universe is an isolated system
Handy example of isolated system is themos flask.
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Isolated System

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