## 1 January 2017

### What is thermodynamic system

The term thermodynamic system is used frequently in the subject of thermodynamics.
Let us see what the thermodynamic system is and its various types.

Introduction :

The word system is very commonly used in thermodynamics; let us know what it is. A certain quantity of matter or space which is under thermodynamic study or analysis is called a system. Let us say for example we are studying the engine of the vehicle, in this case, the engine is called the system. Similarly, the other examples of the system can be a complete refrigerator, air-conditioner, washing machine, heat exchange, a utensil with hot water etc.
Now, let us suppose that we have to analyze the performance of the engine in different conditions. Here, we will feed the engine with fuels of different grades and load it with different loads to find out its efficiency. We will also find its performance during idling, acceleration, varying speed, slow speed and high speed. A thorough analysis of the engine is carried out; hence it is called a system.
The system is covered by the boundary and the area beyond the boundary is called as universe or surroundings. The boundary of the system can be fixed or it can be movable. Between the system and surrounding the exchange of mass or energy or both can occur.
A thermodynamic system is defined as a quantity of a matter or a region in space upon which attention is concentrated in the analysis of a problem. Everything external to the system is called the surroundings or the environment. The system is separated from the surroundings by the system boundary.

There are three classes of the system :
• Closed System
• Open System
• Isolated System
The closed system is a system of fixed mass. There is no mass transfer across the system boundary. There may be energy transfer into or out of the system.

The open system is one in which matter crosses the boundary of the system.

There may be mass transfer as well as energy transfer also. Most of the engineering devices are generally open systems.

The isolated system is one in which there is no interaction between the system and the surroundings.
It is of fixed mass and energy, and there is no mass or energy transfer across the system boundary.

If a system is defined as a certain quantity of matter, then the system contains the same matter and there can be no transfer of mass across its boundary. However, if a system is defined as a region of space within a prescribed boundary, then the matter can cross the system boundary. while the former is called a closed system, the latter is an open system.