Thermodynamic System

A Thermodynamic system is defined as a quantity of matter or a region in space upon which attention is concentrated in the analysis of a problem. Everything external to the system is called the surrounding or environment. The system is separated from the surrounding by the system boundary. Boundary may be either fixed or moving.  A system and its surrounding together comprise a universe.

Open System: The open system is one in which matter crosses the boundary of the system. There may be energy transfer also. Most of the engineering devices are generally open systems.

 Ex: An air compressor in which air enters at low pressure and leave at high pressure and there is energy transfer across the system boundary.

Closed System: A closed system is a system of fixed mass. There is no mass transfer across the system boundary.  

Ex: A certain quantity of fluid in a cylinder bounded by a piston constitutes a closed system.

Isolated System:  The isolated system is one in which there is no interaction between the system and surrounding. It is of the fixed mass and energy and there is no mass or energy transfer across the system boundary.

Homogeneous and Heterogeneous system:

A quantity of matter homogeneous throughout in chemical composition and physical structure is called a phase. Every substance can exist in any one of the three phases viz. Solid, Liquid or  gas. 

A system consisting of a single phase is called a homogeneous system while a system consisting of more than one phase is known as a heterogeneous system.