Vol.2 No.11 Subject: Flow Measurement News Date: 11-16-00 From: McCrometer, "The Flow Measurement Specialists" ........ http://www.mccrometer.com ........ ******************************************* This newsletter is e-mailed by McCrometer monthly to subscribers worldwide. It consists of flow measurement information of interest for professionals in this field. For More information on our complete line of flowmeters go to: http://www.mccrometer.com ******************************************* Ask The Experts... DP meters have the ability to measure a variety of fluids at various rates of flow. A DP meter, such as McCrometer's V-Cone flow meter, can not only measure the flow of water, air, steam and natural gas, but also more exotic fluids such as cryogenic neon and hydrocarbon blends. If a meter performs identically (i.e. it's unique performance characteristic or flow coefficient remains the same) in all these application and various flow conditions it becomes a simple matter to calibrate the meter - the flow coefficient is determined at any flow rate in any fluid and is usable for any other fluid at any other flow rate. No meter has that capability, however, though the V-Cone is more linear (has the same flow coefficient across a wide range of flows and conditions) than most. The next best solution is to test the meter in its application fluid across the anticipated application flow range. With all the variety of applications it becomes difficult, if not impossible, to calibrate the flow meter in its application fluid. How, then, can the performance characteristic of the meter, or flow coefficient, in the application fluid be verified? The best method, to date, is to test the meter in a common fluid across the same Reynolds Number range as the application fluid will experience. Reynolds number is a dimensionless number equal to the ratio of the inertial forces to the viscous forces acting on the flow meter. The inertial force acting on the meter is equivalent to the diameter of the pipe multiplied by the velocity of the fluid, while the viscous force acting on the meter is simply the kinematic viscosity of the fluid. The flow coefficient of a DP meter such as the V-Cone should be the same in two different fluids at like Reynolds numbers. For example: If a natural gas application is expected, from calculation, to operate roughly across a given Reynolds number range a V-Cone can be calibrated (the flow coefficient of the meter is determined) in water across the same Reynolds number range. The flow coefficient derived from testing will be the same in both applications at the same Reynolds number. Inserting the obtained flow coefficient into standard flow calculations then allows the meter, tested in water, to indicate flow in the natural gas application. Note that this does not consider such factors as gas compressibility (or expansibility), which must be accounted for separately. This is not to say the differential pressure produced by the V-Cone will be the same in both applications of the V-Cone. This process is employed to determine the meter's basic flow coefficient... one component in the equation that correlates the square root of differential pressure to the rate of fluid flow. The other variable to consider is the fluid density. Since the density of natural gas, at room temperature, is much less than the density of water, at room temperature, the differential pressure produced at the same Reynolds number will be much greater in the water test than the natural gas application. ******************************************* Copyright 2000 McCrometer ******************************************* Know anyone looking for a steady dose of flow measurement information? ****************************************** To subscribe send e-mail to <mailto:news-request@mccrometer.com>news-request@mccrometer.com with a keyword SUBSCRIBE in the subject field. To unsubscribe, send e-mail to <mailto:news-request@mccrometer.com>news-request@mccrometer.com with a keyword REMOVE in the subject field. ******************************************* To subscribe or unsubscribe online, please go to our website at: http://www.mccrometer.com/subscribe.htm ******************************************* Distributed by McCrometer "The Flow Measurement Specialists" http://www.mccrometer.com