Transformation of energy

Thermal energy and combustion.
Effects of thermodynamics


Thermodynamic System, Types of Systems and Definition

Thermodynamic system, types of systems and definition

A thermodynamic system is a part of the physical universe with a specific limit for observation. Real or imaginary walls can define this limit.

A system contains what is called a study object. A study object is a substance with a large number of molecules or atoms. 

A thermodynamic system can undergo internal transformations and exchange energy or matter with the external environment. This concept is very interesting for mechanical engineering and thermal engines.

Definition of a Thermodynamic System

We define a thermodynamic system as a quantity of matter or a region in space on analyzing a problem.

Everything that is part of the exterior of the system is called an environment. The system is separated from its surroundings by the system boundary.

An intensive property is a local physical property of a system that does not depend on the system size or material. By contrast, extensive variables are additive for subsystems because they increase and decrease as they grow larger and smaller.

Types of a System in Thermodynamics

Within thermodynamics, there are the following types of systems: open and closed systems.

What Is an Open System in Thermodynamics?

A system is open if it can exchange mass, energy, or both between the system and surroundings. Energy can enter or leave the system.

An example of an open system is a pool filled with water. The water can enter or leave it. A wind heating and cooling system can heat it.

What Is a Closed System in Thermodynamics?

A system is closed if it allows an energy flow with the outside environment, through its boundary, but not mass.

An example is a cylinder kept closed by a valve. The cylinder can be heated or cooled; however, it does not lose mass. At the same time, the cylinder itself behaves like an open system if we open the valve.

An adiabatic system does not transfer any heat into or out of the system.

Isolated system

A system is isolated if It does not allow the exchange of matter or energy with the external environment. According to thermodynamics' zeroth law, the thermodynamic processes do not affect the system's total energy.

A system is in a thermodynamic equilibrium state if the system's condition does not change when isolated from the external environment's actions. The thermodynamic state means that there is no variation in any equation of state.

An equation of state (EOS) is a thermodynamic expression that relates pressure (​P), temperature (T), and volume (V).


Published: December 19, 2017
Last review: June 17, 2020