Category: Mechanical Measurement

The orificemeter and similar devices such as venturimeter and flow nozzle work on the principle of constant area variable pressure drop. Here the area of obstruction is constant, and the pressure drop changes with flow rate. On the other hand, rotameter works as a constant pressure drop variable area meter. It can only be used…

In orificemeter, an orifice plate is placed in the pipe line, as shown in Figure 18.7. If d1 and d2 are the diameters of the pipe line and the orifice opening, then the flow rate can be obtained as: Figure 18.7 Orificemeter Volume of flow, where Cd is known as coefficient of discharge; its value ranges from 0.6 to 0.7.

Hydrodynamically, there are two types of fluid flow: laminar and turbulent. Whether a flow is viscous or turbulent can be decided by the Reynold’s number RD. If RD > 2,000, the flow is turbulent otherwise laminar. In the present case we will assume that the flow is turbulent, that is the normal case for practical situations. Let us…

Flow measurement is the quantification of volume of fluid movement. Flow can be measured in a number of ways. Positive-displacement flowmeters accumulate a fixed volume of fluid and then count the number of times the volume is filled to measure flow. Other flow measurement methods rely on forces produced by the flowing stream as it…

A hot wire anemometer involves the heat that is dissipated by a hot wire to an ambient fluid passing through it. For a fixed wire temperature, the heat dissipation from the wire will be larger with larger velocity of the fluid. Alternately, for a fixed heat dissipation rate from the wire, the wire temperature will…

The arrangement for measuring fluid velocity using a Pitot tube is shown in Figure 18.5. The Pitot tube consists of bent tube of small diameter with a rounded nose. The Pitot tube is connected to one limb of a U tube manometer. The other limb of the manometer is connected to a tap made on the tube…

When operating below the Pirani gauge range, an ion gauge can be used to measure pressure. The ion gauge consists of three distinct parts: the filament, the grid, and the collector. The filament produces electrons by thermionic emission. A positive charge on the grid attracts the electrons away from the filament; they circulate around the grid…

The Pirani gauge is a roughing pressure vacuum gauge. It uses the thermal conductivity of gases to measure pressure. The Pirani gauge head is based around a heated wire placed in a vacuum system, the electrical resistance of the wire being proportional to its temperature. At atmospheric pressure, gas molecules collide with the wire and…