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Title: DIFFERENTIAL METERS OTHER THAN ORIFICE: ALTERNATIVE OPTIONS AVAILABLE FOR DIFFERENTIAL MEASUREMENT
Author: Richard L. Wakeland, Cheryl D. Wakeland
Source: 2019 American School of Gas Measurement Technology
Year Published: 2019
Abstract: Flow is one of the four major physical measurements in processes. Flow meters may be classified in four categories: differential pressure, velocity, mass and positive displacement or volumetric. Each category has advantages and disadvantages however, the focus of this paper will be the differential pressure flow meters. Differential pressure (dP) flow meters include flow elements such as the orifice plate, venturi, flow nozzle, wedge meter, cone meter and proprietary devices. The elbow flow meter, pitot and annubar are also differential type flow meters, but have a different operating principle than the others and are outside of the scope of this paper. These meters may be referred to as flow elements (FE) or primary flow elements. These flow elements are called primary because an additional or secondary device must be attached to indicate the measured differential pressure. This secondary device may be an electronic transmitter, manometer, standpipe or gage. dP flow elements are often called head type, obstruction or inferential meters. The flow rate is calculated or inferred from the measured difference in pressure or head. The basic principle of operation is that an obstruction is placed in the flow stream reducing the flow area, thereby creating an increase in velocity and a decrease in the flowing pressure. The theories of dP flow meters were proposed in the 17th century. The basic concepts were established by the works by Bendetto Castilli (1578-1643) and Evangelista Torricelli (1608-1647). In 1738, Daniel Bernoulli (1700 - 1782) published his textbook on hydrodynamics in which he stated a relationship in frictionless flow between pressure, velocity and elevation. Leonhard Euler (1707-1783) offered a complete derivation of the Bernoulli Equation in 1755. The first testing of conical contraction and expansion was done by Giovanni Venturi (1746-1822). His study was published in 1797. In 1898, Clemens Herschel (1842-1930) invented the classical venturi.

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