Introduction to Fluid Mechanics

Introduction
          The primary objective of this chapter is to show the user the most important logical milestones and the general background of equations and formulas recommended for specific practical applications of fluid flow in pipes, nozzles, and orifices. For details, Refs. 1 through 4 or other equivalent textbooks should be consulted.


Basic Fluid Properties
          A fluid is a substance which can flow and which deforms continuously under the action of shearing forces. Fluids offer no resistance to distortion of form; they yield continuously to tangential forces, no matter how small. Ordinarily, fluids are classified as being liquids or gases. Some classifications also include the vapor form within the group of fluids. Liquids change volume and density very slightly with considerable variation in pressure, and when the pressure  is removed, they do not dilate significantly. They are practically incompressible.
           A gas is a fluid which tends to expand to fill completely any vessel in which it is contained. It is easily compressed, and a change in pressure is accompanied by a considerable change in its volume and density.


Theoretical Background Viscosity and Pressure
Some basic fluid properties used in this chapter are discussed in the following paragraphs; for more detailed information see Refs. 


Viscosity
        It is an experimental fact that a fluid in immediate contact with a solid boundary has the same velocity as the boundary itself. For the case of Fig. B8.2, in which a fluid separates closely spaced parallel plates, the force F applied to the upper, moving plate, is directly proportional to the surface area A of the upper plate and its velocity w, and is inversely proportional to the distance y between the plates. The last statement is expressed in the form of Newton’s law of viscosity: 

Pressure Variation in a Static Fluid
         The static pressure existing at a point within a fluid body is known also as the hydrostatic pressure. In the case of gaseous fluids, the density of the fluid column is relatively small unless great vertical heights are involved. In such cases the average density of fluid should be used for the static pressure calculation. With denser fluids such as liquids, the increase in pressure due to depth within the liquid can be of great significance. When applied to the two-fluid mixture in a container filled with a gas at the pressure p1.