In fluid mechanics and thermodynamics, a control volume is a mathematical abstraction employed in the process of creating mathematical models of physical processes. In an inertial frame of reference, it is a volume fixed in space or moving with constant velocity through which the fluid (gas or liquid) flows. The surface enclosing the control volume is referred to as the control surface.
At steady state, a control volume can be thought of as an arbitrary volume in which the mass of the fluid remains constant. As fluid moves through the control volume, the mass entering the control volume is equal to the mass leaving the control volume. At steady state, and in the absence of work and heat transfer, the energy within the control volume remains constant. It is analogous to the classical mechanics concept of the free body diagram.
Read more about Control Volume: Overview, Substantive Derivative
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“There has been something crude and heartless and unfeeling in our haste to succeed and be great. Our thought has been “Let every man look out for himself, let every generation look out for itself,” while we reared giant machinery which made it impossible that any but those who stood at the levers of control should have any chance to look out for themselves.”
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