Thermodynamic System

We use cars and bikes in our daily routine to travel. To keep them going, we fill in petrol or diesel as per the design of the vehicle. The petrol or diesel in the vehicle undergoes combustion inside the engine and is an ideal example of a thermodynamic system. The system which involves the processing of heat and converting it to useful work involves thermodynamic processes. Nuclear power, electronic heat sink and rocket launch involve thermodynamics.

Thermodynamics is the branch of science that deals with heat and temperature and the inter-conversion of heat and other forms of energy. Since thermodynamics deals with the bulk system and does not deal with the molecular constitution of matter, it is known as macroscopic science.

Some examples of thermodynamic systems are washing machines, refrigerators and air-conditioners. Air-conditioner is a closed system that circulates refrigerant inside the system, altering the pressure of the refrigerant at different points to promote the transfer of heat. A refrigerator is an open system that absorbs heat from a closed space and passes it to a warmer area. In this article, let us study in detail the thermodynamic system and its types.

Thermodynamic System and Types

A system that is delimited from the surroundings by real or hypothetical boundaries is known as a thermodynamic system. A thermodynamic system refers to that part of the universe in which observations are made, and the remaining universe constitutes the surroundings. The surroundings contain everything other than the system. The system and the surroundings together make up the universe.

The universe = The system + The surroundings

A thermodynamic system is embedded in its environment or surroundings, through which it can exchange heat with, and do work on. It exchanges the heat to its surroundings through a boundary. The boundary is the wall that separates the system and the environment. Thermodynamic systems can exchange energy or matter with the external environment and can also undergo internal transformations.

The below figure shows the thermodynamic system, surroundings and boundary concept.

Example: In a car, the engine burns gasoline inside the cylinder and is considered as a thermodynamic system; the radiator, piston, exhaust system and air outside form the environment of the system. The inner surfaces of the cylinder and piston are considered as the boundary.

Thermodynamic systems are classified as :

• Open systems
• Closed systems
• Isolated Systems

Open System

If the thermodynamic system has the capacity to exchange both matter and energy with its surroundings, it is said to be an open system.

Example: Consider a beaker in the presence of reactants in an open beaker. Here the boundary is an imaginary surface enclosing the beaker and reactants.

Example: A steam turbine, a pool filled with water, where the water can enter or leave the pool.

Closed System

A system which has the ability to exchange only energy with its surroundings and cannot exchange matter is known as a closed system.

Example: Reactants placed in a closed vessel made of materials like steel, copper, and silver are an ideal example of a closed system since the material of the vessel is conducting in nature.

A cylinder in which the valve is closed is an example of a closed system. When the cylinder is heated or cooled, it does not lose its mass.

Isolated System

A system which cannot exchange matter or energy with the surroundings is known as an isolated system. The zeroth law of thermodynamics states that thermodynamic processes do not affect the total energy of the system.

Example: Reactants are present in a thermos flask or an insulated vessel, where neither energy nor matter is exchanged with the environment.

Example: If the piston and cylinder arrangement in which the fluid like air or gas is being compressed or expanded is insulated, it becomes an isolated system.

Read more about thermodynamics.

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