Water Online

January 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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discharge heads. To create a secondary check of pump speed versus flow, pressure differential monitoring devices in the system should be recorded during testing to determine pump speed and flow versus head differential. Generated system curves can be created using any of the flow metering methods detailed above; however, there are two commonly used methods that do not require permanent installation of equipment. The two most common methods for measuring water flow in the field are the dye dilution technique and the area- velocity method using current meters. Providing details of these field techniques would require the writing of an additional article and are not detailed herein. See the following table for information on applicable pipe sizes for each technology and typical vendor-listed accuracies. Evaluation Criteria The criteria listed below should be used to evaluate the relative advantages and disadvantages of each flow monitoring alternative and to select and develop those options that are feasible for implementation. The criteria represent key aspects to any ultimately successful flow monitoring program and do not appear in order of priority. • Options should be designed to operate over the expected range of flow rates. • Options should provide an acceptable level of accuracy. • Options should function under expected debris conditions. • If applicable, options should allow continuous flow monitoring. • If applicable, options should not impact the operation of the condenser cooling system. • Options should have minimal impact, to the extent possible, on the existing civil/structural features. • Options must be commercially proven at power-generating facilities. • If applicable, options must meet all safety requirements. • If applicable, options must minimize hindrance to facility operations during the installation of the metering devices. • The technology is available and does not require further engineering development. Notes: 1. When assessing proven industry options at facilities with dissimilar physical, hydraulic, and environmental conditions than the site under consideration, best professional judgment must be used to determine applicability. 2. Available technologies are defined as alternatives that provide data in sufficient detail to develop a conceptual design and/ or technologies that have been constructed at other similar facilities. 3. Each technology must be qualitatively assessed to identify whether it has engineering advantages over the other technologies. For example, one technology would have an advantage over another if it requires fewer civil/structural modifications for its installation or if it is similar to another option but more accurate. Summary Selecting a flow meter system for industrial applications can be challenging given the myriad choices available. This is compounded when the user understands the many significant application variables that influence the choice. This may explain why, historically, industries have struggled to quantify fluid flows, especially large conduit and large flows. Where facilities rely on accurate flow measurement, an operational understanding of the principles behind each flow metering technology is crucial. n References ANSI/ASME MFC-9M, Measurement of Liquid Flow in Closed Conduits – Weighing Method, ANSI, New York, 1988. Cheremisinoff, Nicholas P., Applied Fluid Flow Measurement, Marcel Dekker, Inc., New York, 1979. Miller, Richard W., Flow Measurement Engineering Handbook, McGraw- Hill Publishing Company, New York, 1996. wateronline.com n Water Innovations Philip S. Stacy, director of calibration services at Alden Research Laboratory, is responsible for all flow meter testing performed at Alden's flow measurement facilities, providing technical and administrative supervision of its Flow Measurement Department to ensure the highest standard for calibrating fluid meters to an accredited certified uncertainty of 0.1 percent in accordance with ISO/IEC 17025:2005. About The Author INSTRUMENTATION 22 Selected Applicable Technologies Pipe Size (inches) Typical Vendor Listed Accuracy Ultrasonic Flow Meters (transit time) >0.5 ±0.2% to ±5% Ultrasonic Flow Meters (Doppler) >0.5 ±1% to ±10% Turbine Meters 0.25 to 24 ±1% to ±5% Propeller Meters 2 to 72 ±2% to ±5% Vortex Meters 1.5 to 16 ±0.75% to ±1.5% Magnetic Flow Meters >0.1 ±0.25% to ±1% Calorimetric Meters >0.5 ±1% Venturi Meters >2 ±0.7% to ±1.5% Elbow Meters >2 ±5% to ±10% Orifice Plates >0.5 ±2% to ±5% Flow Nozzles >2 ±0.75% to ±1.5% Flow Tubes >3 ±0.7% to ±1.5% Target Meters <2 ±1% to ±5% Pitot Tubes >3 ±3% to ±5% Mass Flow Meters 0.25 - 6 ±0.15% to ±10% Positive Displacement Meters <12 ±0.5% Weirs N/A ±2% to ±5% Control Flumes N/A ±2% to ±5% Precision Uncertainty Dye Dilution N/A ±1% to ±2% Current Meters N/A ±1% to 2%

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