Thermodynamics System and It’s Types [With PDF]

What is a thermodynamic system? A thermodynamic system is defined as the space, region, or quantity of matter (Finite amount, measurable in kg) in which our study is focused.

It means, in that particular space or region, we are going to measure the properties of that specific region or thing.

In other word, you can say it is the space or region where the thermodynamic process happened.

To discuss further on this topic, you should know two terms. One is the system, and another one is surrounding.

So what is the system?

In thermodynamics, a system is that body or space or region where we are going to measure the properties or where thermodynamics processes are happening. That particular space or body is called system.

The system can be the finite quantity of matter or a selected region in the space. It can be liquid, solid, or gas.

And the next term what is surrounding?

Surrounding is the space outside of the system.

And also you need to know another term which is a boundary. So a boundary is an imaginary or real wall which divides the system and surrounding.

Mathematically boundary has no thickness. That means it has no volume.


A boundary can be fixed or movable.

Let clear your doubts about the system, surroundings, and body by the simple example.

You all know the flask/thermos, where you can pour warm water, milk, or tea anything.

So, in that case, the inside liquid of the flask is called system, the body of the flask is called boundary which separates the inside liquid from the outer condition or atmosphere, and outer region where the flask is placed is called surrounding, it may be a room or an open space.

So I hope you understand the concept of system, surrounding, and boundary.

There are two approaches to analysis a region or space, and that is Control mass approach and Control volume approach.

If we considered a particular mass of the system, then the process of measurement is called the control mass approach.

And if we do not need to study the mass or if we consider the mass, the analysis will be complicated, and then we will consider the control volume approach.

There are two types of interaction in the thermodynamic system.

  • Mass interaction
  • Energy interaction

Now let’s look at the types of a thermodynamic system.

A thermodynamic system is three types.

  • Open system
  • Closed system
  • Isolated system

Open system:

When in a system, mass and energy interaction is possible, then this type of system is called an open system.

That means mass can going in and mass can going out of the system as well as energy can going in and energy can going out of the system.


In mechanical engineering maximum of mechanical devices like a pump, a turbine is in the category of the open system.

Suppose you are considering a pump, in this case, pump deliver fluid from 1 section to another section then what happens? Some portion of mass will go into the pump and then go out to the particular region. That means a certain mass of water in entered and a certain mass of water is going out of the pump. So is the example of mass interaction.

As well as when the impeller rotates inside the casing of a pump, then the rotational of mechanical energy is transferred to the fluid that results in the increasing of kinetic and pressure energy of the liquid.

So this is the whole concept of an open system.

Closed system:

The closed system is a system of fixed mass. It means mass cannot cross the system boundary, but energy can cross the system boundary.

A closed system is nothing but a Control mass approach.


Let me show you the example of a closed system.

A piston-cylinder without valve that means the mass (liquid or air anything) inside the cylinder is fixed. It can not go out of the cylinder because there is no valve in the cylinder.

But when we compressed the mass, we need some energy that means energy can transfer to the fluid may be in the form of heat.

Isolated system:

In this type of system, neither mass interaction is possible, or energy interaction is possible this type of system is called Isolated system.


But in real life, this is quite hard, or you can say impossible to find this type of working system.

But at the school level, you might hear that the example of an isolated system is thermos where you can pour hot tea, milk or anything. But in a thermos, okay there is no transfer of mass, the mass inside the thermos is constant, but after a specific time, the hot tea or milk inside the thermos will be in the normal temperature, which means there is an interaction of energy with the surrounding.

So if a thermos is fully thermal insulated where mass along with temperature or energy can not cross the surrounding or no interaction of these two is possible then you can say this is the perfect example of an isolated system.

So these are the concept of Thermodynamics Sytems, feel free to comment down your doubts below in the comment section. And do share this article on your favorite social media platform.

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Anup Kumar Dey

A Mechanical Engineer with 19 years of working experience in various renowned MNCs.

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