Comparison among System and Control Volume

Similarities:

(a)  Both are stated by careful in explanation of their boundaries.
(b)  Both ideas are helpful in allowing the interactions at the boundaries to be associated to the changes taking place within them.

Differences:

(a) A system represents a prescribed collection of matter whereas a control volume represents a particular area of space.
(b) The system boundary might, and generally does, change shape, location and orientation associative to the spectator. The control volume boundary does not, by statement.
(c) Matter might, and generally does, flow crossways the control volume border. The material does not cross a system border, by statement.

In view of the above contrast, some texts on thermodynamics assign the control volume as an open system, whereas the system is known as a closed system.

Problem:

Categorize, with reasons, the below as either a system or a control volume, or neither a system nor a control volume; or both a system and a control volume. 

(a) IC engine.
(b) Gases within the cylinder of an IC engine whenever both valves are closed, and the piston moves.
(c) A steam power plant, involving only the water + steam circuit.
(d) The boiler in a steam power plant.
(e) The stuffing of a toy balloon whenever there is leakage from the balloon to the environment.
(f) The contents of a firm pressure vessel whenever there is neither inflow nor outflow from the container.

Solution:

(a) Control Volume:

Fuel and air enter the IC engine, whereas exhaust gases leave the engine; the engine is of permanent shape and of preset position and orientation associative to the spectator.

(b) System:

No matter crosses the border of the IC engine, whereas the system border is moving.

(c) System and Control Volume:

The grouping of steam turbine, steam generator, condenser and boiler feed pump (exclusive of such things as the furnace & the cooling water circuit of the condenser) having same quantity of matter. All the components are of permanent shape and of fixed place and orientation associative to the spectator.

(d) Control Volume:

Fuel and air go through the furnace, whereas combustion products leave via the stack. Alongside, water is pumped in by the boiler feed pump and steam quits the boiler. All the components are of permanent shape and of fixed place and orientation associative to the spectator.

(e) Neither System nor Control Volume:

The mass within the balloon is changing, and also the shape of the boundary. 

(f) Both a System and a Control Volume:

System, as the pressure vessel is firm, and no matter crosses the border; also a control volume, as the boundary is of permanent shape, place and orientation.