Types of Thermodynamic Systems

 The thermodynamics systems may be classified into the following three categories:

TYPES OF THERMODYNAMIC SYSTEMS

The thermodynamics systems may be classified into the following three categories:

(a) Closed system

(b) Open system

(c) Isolated system.

1. Closed System

A closed system does not permit any mass transfer but only the energy transfer takes place. The system boundary is determined by the space that the matter occupies. A closed system is also known as control mass.

Consider a system shown in Figure 1.3 (b). If heat is supplied to the system (fluid) from an external source, the temperature of the gas will raise. Therefore, the heat transfer will take place. So, the external work is done by the system because of the piston movement. But, the mass of the system remains constant.

2. Open System

In open system, both mass and energy transfers take place. The open system is often called control volume.

Example: Air compressor, turbine, etc.

Consider an air compressor system as shown in Figure 1.5 (a). In this system, the low- pressure atmospheric air is taken into the compressor and high-pressure air leaves continuously. Therefore, the mass transfer takes place in addition to the energy transfer. The work is given to the system externally to run the compressor. Hence, the work transfer takes place. The heat is produced by compressing air to high pressure and also by friction in between cylinder and piston. Hence, the heat transfer takes place. Figure 1.5 (b) is another similar example for open system. In this turbine system, the high-pressure air is given as input and air leaves at low-pressure after producing work.

3. Isolated System

A system which is not affected by surroundings is called isolated system. It can simply be stated, there is no heat, work and mass transfers. It is an imaginary system.

Example: Entire universe.

The thermodynamic relations which are applicable to closed and open systems are different. Therefore, it is very important that the types of system are well-studied before carrying out the thermodynamic analysis.