The industry's most authoritative handbook on flow measurement provides a road map to the field of flow measurement. This best-seller discusses strategies for problem solving and puts the whole array of types of flowmeters at the reader's disposal. The text includes laminar flow elements, critical flowmeters, statistics for measurement, laboratory primary standards, and uncertainty in flow measurement. Emphasis is placed on the importance of accuracy in measurements and ways of ensuring accuracy and avoiding equipment damage through correct forecast of operating conditions, flowmeter selection, installation, calibration, and maintenance. Fundamental considerations such as mixed-phase flow, piping effects, and flow conditioning are examined at length. The problem of attaining a meaningful flow signal through linearization, compensation, and totalization is discussed. Join the thousands of engineers, technicians, managers, and salespeople that have found this reference text an invaluable resource.
TABLE OF CONTENTS Chapter 21 - Variable Area Flowmeters
Variable area flowmeters were invented in the nineteenth century but were not
introduced for general industrial use until the 1930s. They became very popular
and widely used since they offered a low-cost alternative to the differential pressure
flowmeter-especially in smaller pipe sizes.
The original designs introduced were available for visual indication of flow rate
only. In the 1940s designs became available with secondary functions such as
transmission, alarm, recording, and totalizing. Variable area flowmeters are available
in pipe sizes from 1/8 inch (0.3 cm) to 8 inches (20 cm) and full scale flow
rates from less than one ml/minute to over 1000 gpm (3800 lpm) of water and
approximately 30 scc/minute to 2500 scfm (71 nm3/min) of air.
Since they are in-line devices, they have been designed for a wide range of line
pressure ratings, pipe connection types, and many different materials of construction.
Operating Principle | Advantages:
|
Rotameters
In this type, a float made of a material of a density greater than that of the fluid
is contained in an upright conical tube whose smaller end is at the bottom. The
float, free to move vertically in the tube, is lifted to the position of equilibrium
between the upward force of the fluid flowing past the float and the downward
force of gravity on the float. In its simplest form the tapered tube is made of glass
that is graduated, allowing the flow rate to be read directly by observing the position
of the float (see Figure 21-1(a)). The name rotameter was originally a trade
name, which subsequently became generic in the United States.
