Thermodynamics Basics ( TYPES OF SYSTEMS )

Thermodynamics is a branch of physics dealing with matter and conversion of energy, conversion of energy into heat and work in particular. Each object of interest in engineering contains matter, therefore, thermodynamics is usually included or indirectly involved in the analysis of almost all engineering problems.

THERMODYNAMIC SYSTEM :-

A thermodynamic system, or simply a system, is defined as a certain quantity of matter or a prescribed region in space considered for thermodynamic study. The region outside the system is called the surroundings or environment. The real or imaginary surface that separates the system from its surroundings is called the boundary. The boundary of the system may be fixed or movable. The system and its surroundings constitute the universe. 

TYPES of  SYSTEMS :-

The thermodynamic systems can be classified as

 1. Closed and open systems

 2. Homogeneous and heterogeneous systems 

1) CLOSED SYSTEM :-

A closed system (also known as control mass) has the following characteristics: 

 (i) It consists of a fixed amount of mass, and no mass can cross its boundary, i.e., no mass can enter or leave a closed system.  

(ii) The volume of a closed system may vary and hence its boundary is movable. 

 (iii) The energy in the form of heat or work can cross the boundary.

2) OPEN SYSTEM :-

 An open system (or a control volume) is a properly selected region in space. It usually encloses a device which involves mass flow, such as a compressor, turbine or nozzle. Flow through these devices is best studied by selecting a region within the devices as control volume. The boundary of the control volume is called the control surface. Both mass and energy can cross the control surface. Thus, for an open system:

 (i) The system has a selected region (fixed volume), called control volume.

 (ii) The boundary of an open system is fixed. 

 (iii) Mass can cross the control surface.

 (iv) The energy, in the form of heat and work, can cross the control surface. An open system can be represented by Fig.