Transformation of energy

Definition of open system in thermodynamics

Definition of open system in thermodynamics

An open system is a system that interacts with its environment. The interaction consists of exchanging energy and matter between the system itself and the outside.

In physics, an open system often strives to maintain an energy balance in a state of equilibrium.

The open system concept was introduced in the context of thermodynamics. Its use was later extended with the development of information and computer systems theories. Today, the concept is also applied in the natural and social sciences.

In thermodynamics, an open thermodynamic system cannot exist in a state of complete equilibrium. It is like this because, by definition, there is always energy transferred to the surroundings.

In the social sciences, an open system is a process that exchanges materials, energy, people, capital, and information with its system boundary.

On this site, you can see how laws of thermodynamics affect an open system.

What is the difference between open, closed, and isolated systems?

The difference between the three thermodynamic systems depends on the interaction of energy and matter with the environment:

  • An open system can exchange energy and matter with the outside.

  • A closed system cannot exchange matter but can exchange energy with its surroundings.

  • An isolated system cannot exchange energy or matter with the environment.

This type of thermodynamic system is the most common. As a result, the only known isolated system is the entire universe. However, some systems are treated as if they were isolated to simplify specific calculations.

Open system in the natural sciences

The concept of an open system made it possible to interconnect the theory of organisms, thermodynamics, and evolutionary theory. Now the concept has applications in the natural and social sciences.

The entropy of an open system can be reduced at the expense of the environment. All or almost all natural systems are open systems with the exchange of matter and energy with the outside. 

In the natural sciences, an open system is permeable with its limits in both energy and mass.

The definition of an open system assumes that there are energy resources that cannot be exhausted. In practice, this energy is supplied by a source in the surrounding environment, which can be considered infinite.

Examples of open systems in thermodynamics

  • Planet Earth is an open system because it exchanges energy (solar energy) with the outside world. In addition, it is capable of exchanging matter such as asteroids.

  • The human body is also an open system because we exchange energy with the environment (body heat) and matter (food, air, sweat, etc.).

  • Boiling water in a kettle absorbs heat energy from the outside to increase the internal energy of the hot water. When hot water is converted into steam, it emits steam particles outside the system and surroundings.

  • Combustion engines are complex systems that generate the movement of a piston-cylinder from a constant supply of fuel: gasoline, diesel, etc.

  • Most require matter for their subsistence (in the form of water and nutrients) and energy (solar) to carry out vital photosynthesis.

  • The saunas are another example of an open system. To produce the steam contained in saunas, water (matter) and energy (fire) are required to generate the steam and allow it to accumulate in the closed area. After a period, the vapor will disappear, and a new injection of inputs to the system will be needed.

  • A composter process that produces fertilizer to fertilize crops operates based on the constant introduction of waste organic matter into the compost bin: shells, food scraps, etc. Without them, the degradation processes of matter would stop, and so would the production of fertilizer.

  • A bonfire keeps the fire burning, and it is necessary to provide it with flammable material, such as charcoal or dry branches. Without that matter to consume, the fire will go out.

  • A nuclear reactor in a nuclear power plant works as an open system. The electricity generated by the reactor is the product of the fission of uranium (or other elements) in a controlled atomic reaction that allows the generation of a lot of usable energy, but also toxic waste that must end up somewhere in the environment.

  • A steam turbine transfers energy from one system to another. It is a device that takes internal energy from steam and converts it into mechanical energy.

Publication Date: January 16, 2020
Last Revision: July 31, 2022