Ingredients for accurate flow measurement

05 Feb

Differential Pressure flow meters are, by far the most common technology in use today. Estimates are that over 50% of all liquid flow measurement applications use this type of technology. Differential pressure flow meters generate a differential pressure by means of an orifice plate, venture, flow nozzle, pitot tube or elbow tap just to name a few. The number one consideration when choosing a flow meter is a clear understanding of the requirements of a particular application.

Head type flow measurement was developed using Bernoulli’s Law an equation describing fluid flow which states that the sum of the pressure head (static energy), the velocity head (kinetic energy), and elevation head (potential energy) at one point is equal to their sum at the other point. Therefore, the energy of the fluid is conserved by continuity and flow across a constriction in the pipe.

The Bernoulli type orifice flow meter is a simple and reliable method of measuring fluid flow rate and velocity. Friction losses in the system are accounted for by calibrating the flow meter with a discharge coefficient Cd. Orifice flow meters can be very accurate if properly calibrated. For high accuracy a length of straight pipe is required upstream from the flow meter to minimize turbulent effects from bends and fittings. All of these factors play an integral part in the accuracy and range of differential pressure flow meters. The media being monitored can influence the materials of construction and service life of the flow meter which are important considerations when choosing the right flow meter.

The basic operating principle of differential pressure flow meters is based on the premise that the pressure drop across the meter is proportional to the square of the flow rate. The flow rate is obtained by measuring the pressure differential and extracting the square root.

Common applications: Power Plants, Refineries, Petrochemical Plants, Chemical Processing Facilities, Steam Flows, Chillers, Blending etc.

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