A thermodynamic system is defined as a quantity of matter or a region in space chosen for analysis,
surrounding or environment
is can defined as the mass or region outside the system or everything external to the system
boundary
The closed surface that separates the system from its surroundings, through which energy and mass may enter or leave the system.
Boundaries can be fixed or movable Boundaries can be real (cylinder walls and piston surfaces in an internal combustion engine) , In many cases, a thermodynamic analysis must be made of a device, such as a heat exchanger, that involves a flow of mass into and/or out of the device.
Boundaries can also be imaginary (cross sections of pipes at the entrance and exit of turbines)
It is possible to subdivide a system into subsystems, or to group several systems together into a larger system
Thermodynamic System Types
There are three kinds of systems depending on the kinds of exchanges taking place between a thermodynamic system and its environment : isolated, closed and open system
isolated systems: is one with rigid walls that has no communication (i.e., no heat, mass,or work transfer) with its surroundings. An example of an isolated system would be an insulated container, such as an insulated gas cylinder
closed systems: system is one in which the system mass cannot cross the boundary, but energy
can (heat or work). A greenhouse is an example of a closed system exchanging heat but not work with its environment. Whether a system exchanges heat, work or both is usually thought of as a property of its boundary, which can be
adiabatic boundary: not allowing heat exchange;
rigid boundary: not allowing exchange of work
so we can get conclusion the important point of closed system are :
- Consists of a fixed amount of mass
- No mass can cross its boundary
- No mass can enter or leave a closed system Volume does not have to be fixed
- But energy, in the form of heat or work can cross the boundary
- when the piston rises, the boundary of the system moves Heat and work crosses the boundary of the system during this process but not mass
open systems:system is one in which mass can cross the system boundary in addition to energy. A boundary allowing matter exchange is called permeable. The ocean would be an example of an open system
so we can get conclusion the important point of closed system are :
- The procedure in such an analysis is to specify control volume that surrounds the device under consideration
- The boundaries of a control volume are called a control surface
- Mass as well as heat and work can flow across the control surface
from picture below we can see open system and closed system, where even energy is not
allowed to cross the boundary in closed system, that system is called an isolated system.
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