27 Mechanical and Electronic Pressure Measuring Devices
Although manometers are widely used, they are not well suited for measuring very high pressures, or pressures that are changing rapidly with time. In addition, they require the measurement of one or more column heights, which, although not particularly difficult, can be time consuming. To overcome some of these problems numerous other types of pressure-measuring instruments have been developed. Most of these make use of the idea that when a pressure acts on an elastic structure the structure...
T
FIGURE 2.3 Notation for pressure variation in a fluid at rest with a free surface. The pressure head is the height of a column of fluid that would give the specified pressure difference. where h is the distance, z2 _ z1, which is the depth of fluid measured downward from the location of p2. This type of pressure distribution is commonly called a hydrostatic distribution, and Eq. 2.7 shows that in an incompressible fluid at rest the pressure varies linearly with depth. The pressure must...
29 Pressure Prism
where bh is the area of the rectangular surface, A. Pressure prism for vertical rectangular area. Graphical representation of hydrostatic forces on a vertical rectangular surface. The magnitude of the resultant fluid force is equal to the volume of the pressure prism and passes through its centroid. The resultant force must pass through the centroid of the pressure prism. For the volume under consideration the centroid is located along the vertical axis of symmetry of the surface, and at a...
212 Pressure Variation in a Fluid with RigidBody Motion
Although in this chapter we have been primarily concerned with fluids at rest, the general equation of motion Eq. 2.2 was developed for both fluids at rest and fluids in motion, with the only stipulation being that there were no shearing stresses present. Equation 2.2 in component form, based on rectangular coordinates with the positive z axis being vertically upward, can be expressed as Even though a fluid may be in motion, if it moves as a rigid body there will be no shearing stresses...
28 Hydrostatic Force on a Plane Surface
When determining the resultant force on an area, the effect of atmospheric pressure often cancels. When a surface is submerged in a fluid, forces develop on the surface due to the fluid. The determination of these forces is important in the design of storage tanks, ships, dams, and other hydraulic structures. For fluids at rest we know that the force must be perpendicular to the surface since there are no shearing stresses present. We also know that the pressure will vary linearly with depth if...
Problems
Note Unless otherwise indicated use the values of fluid properties found in the tables on the inside of the front cover. Problems designated with an are intended to be solved with the aid of a programmable calculator or a computer. Problems designated with a t are open-ended problems and require critical thinking in that to work them one must make various assumptions and provide the necessary data. There is not a unique answer to these problems. In the E-book, answers to the even-numbered...