### Control Volume of Fluids Flow Review

**Fluid Flow Table of Contents**

Hydraulic and Pneumatic Knowledge

*Control Volume of Fluids Flow *

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 **.

In thermodynamics, a *control volume *was defined as a fixed region in space where one studies the masses and energies crossing the boundaries of the region. This concept of a control volume is also very useful in analyzing fluid flow problems. The boundary of a control volume for fluid flow is usually taken as the physical boundary of the part through which the flow is occurring. The control volume concept is used in fluid dynamics applications, utilizing the continuity, momentum, and energy principles mentioned at the beginning of this chapter. Once the control volume and its boundary are established, the various forms of energy crossing the boundary with the fluid can be dealt with in equation form to solve the fluid problem. Since fluid flow problems usually treat a fluid crossing the boundaries of a control volume, the control volume approach is referred to as an "open" system analysis, which is similar to the concepts studied in thermodynamics. There are special cases in the nuclear field where fluid does not cross the control boundary. Such cases are studied utilizing the "closed" system approach.

Regardless of the nature of the flow, all flow situations are found to be subject to the established basic laws of nature that engineers have expressed in equation form. Conservation of mass and conservation of energy are always satisfied in fluid problems, along with Newtons laws of motion. In addition, each problem will have physical constraints, referred to mathematically as boundary conditions, that must be satisfied before a solution to the problem will be consistent with the physical results