Venturi meter fluid mechanics

Differential pressure transmitters (or DP cells) are widely used in conjunction with any sensor that produces a measurement in the form of a pressure differential (e.g. orifice plate, venturi meter, flow nozzle, etc.). This pressure differential is converted by the DP cell into a signal suitable for transmission to a local controller and/or to the control room. DP cells are often required to sense small differences between large pressures and to interface with difficult process fluids. Devices are available that provide pneumatic, electrical or mechanical outputs. 

FIGURE 5.18 International standard shapes for nozzle and venturi meters. (From White, F. M., Fluid Mechanics, 3rd ed., McGraw-Hill, New York (1994).)... 

Typical Venturi meter. (Adapted from Roberson, J. A., and Crowe, T., Engineering Fluid Mechanics, p. 45, Dallas, TX Houghton Mifflin Co., 1980.)... 

So far we have considered only flows which were in one direction, as in a pipe or down a straight riverbed. In the few cases in which the fluid flow was not one-dimensional, as around a sphere or in a pipe elbow or venturi meter, we have introduced experimental data to allow us to treat the problem as if it were one-dimensional. Although this one-dimensional approach adequately covers many of the practical problems in fluid mechanics, it is not satisfactory for the complicated ones, particularly for the aerodynamics problems. To solve these more complicated problems, two additional ideas are needed potential flow and the boundary layer. 

To derive the equation for the venturi meter, friction is neglected and the pipe is assumed horizontal. Assuming turbulent flow and writing the mechanical-energy-balanCe equation (2.7-28) between points 1 and 2 for an incompressible fluid. 

Solids Metering The control valves described earlier are primarily used for the control of fluid (liquid or gas) flow. Sometimes these valves, particularly the ball, butterfly, or sliding gate valves, are used to throttle dry or slurry solids. More often, special throttling mechanisms such as venturi ejectors, conveyers, knife-type gate valves, or rotating vane valves are used. The particular solids-metering valve hardware depends on the volume, density, particle shape, and coarseness of the solids to be handled. 

Kolupada, S. (1960). John W. Ledoux. Journal of the Hydraulics Division ASCE 86(HY1 42. P Ledoux, J.W. (1913).A mechanism for metering and recording the flow of fluids through Venturi tubes, orifices, or conduits, by integrating velocity head. Trans. ASCE 76 1148-1171. Ledoux, J.W. (1914). The Pitot tube theory. Journal AWWA 1(3) 536-537. 

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