Orifice meters square-edged

Orifice Meters A square-edged or sliarp-edged orifice, as shown in Fig. 10-18, is a clean-cut square-edged hole with straight walls perpendicular to the flat upstream face of a thin plate placed crosswise of the channel. The stream issuing from such an orifice... 

Accuracy Square-edged orifices and venturi tubes have been so extensively studied and standardized that reproducibihties within 1 to 2 percent can be expected between standard meters when new and clean. This is therefore the order of reliabihty to be had, if one assumes (1) accurate measurement of meter differenfial, (2) selection of the coefficient of discharge from recommended published literature, (3) accurate knowledge of fluid density, (4) accurate measurement of critical meter dimensions, (5) smooth upstream face of orifice, and (6) proper location of the meter with respect to other flow-disturbing elements in the system. Care must also be taken to avoid even sh t corrosion or fouliug during use. 

Sharp-edged weirs have edges like those of square or sharp-edged orifices (see subsection Orifice Meters ). Notched weirs are or(iuarily sharp-edged. Weirs not in the sharp-edged class are, for the most part, those described as broad-crested weirs. 

Figure 2-18. Flow coefficient C for square edged orifices. By permission, Crane Co. [3], Technical Paper 410 Engineering Div. (1976) and Fluid Meters, Their Theory and Application Part 1, 6th Ed., 1971, American Society of Mechanical Engineers and, Tuve, G. L. and Sprenkle, R. E., Orifice Discharge Coefficients for Viscous Liquids, Instruments Nov. 1933, p. 201.

Bean, H. S., Buckingham, E., and Murphy, P. S., Discharge Coefficients of Square-Edged Orifices for Measuring the Flow of Air, U.S. National Bureau of Standards Research Paper 49, ASME Fluid Meters Report, 1931. 

FIGURE 5.23 Expansion factor for square-edged orifice and nozzle or venturi meter (a) k= 1.3, (b) k= 1.4. (From Crane Co., Flow of Fluids through Valves, Fittings, and Pipe, Technical Manual 410, Crane Co., New York (1978).)... 

This includes orifice plates, ISA nozzles, conical inlets and venturi tubes, all of which depend on the measurement of the pressure drop across a restriction through which the whole of the flow is passed. Figure 11.10 shows a sketch of a typical orifice meter which consists of a concentric square edged circular hole in a thin plate, which is clamped between the flanges of the pipe. The minimum section of the stream tube occurs downstream from the orifice with the formation of a vena contracta at section 2. A typical connection would be one diameter... 

Question by J. W. Hunt, Constock International Methane, Ltd. For metering low-temperature liquids near their boiling points, does the Venturi meter have any special advantage over a square-edged orifice plate ... 

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