| Vol.2 No.6 Subject: Flow Measurement News Date: 6-9-00 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. Ask The Experts... How Turbulence Affects Flowmeters Turbulence is a critical factor to consider when choosing a flowmeter or designing a system for flow measurement. Flowmeters need non-turbulent flow to ensure accurate readings, so the designer must either use long runs of straight undisturbed pipe before and after the flow measuring element or find a way to condition the flow prior to measurement. The most common approach is to use upstream and downstream pipe runs between the flowmeter and the nearest disturbance, i.e. single elbows, double elbows out-of-plane, and tees. The exact length of pipe required depends on the pipe diameter. For example, depending on beta ratio and the type of disturbance upstream, a typical orifice plate flowmeter can require up to 50 diameters of upstream pipe run. While this may be feasible with pipe diameters of 25mm or less, requiring only a meter or two of pipe around the flowmeter, it becomes difficult or impossible to achieve with line sizes over 700mm and in restricted space installations. These applications may require more piping than is available in an existing system. Or, if it’s a new application, such an oil platform or a vehicle, space may be too limited for long straight pipe runs. Even if the distance is available, the cost of adding straight pipe before and after the flowmeter can be prohibitive. The system designer can compromise in some way to accommodate the limitations of the flowmeter. However, in doing so, he will sacrifice either accuracy or permanent pressure loss. Accuracy declines if the piping requirements are ignored, while permanent pressure loss increases if a flow conditioner is employed upstream of the meter. Neither solution is ideal. So how can the problem be solved? The solution is to use a flowmeter that “conditions” the flow prior to measurement. The V-Cone flowmeter is such a meter. Its geometry is different than that of other differential pressure devices. Rather than using a concentric opening through the center of the pipe or a multi-port insertion sensor, found in standard DP meters, the V-Cone creates an annular opening. This forces the fluid to flow around a cone suspended in the center of the pipe. The result is to “flatten” the flow profile directly upstream of the meter, “conditioning” the flow prior to measurement. In-house testing at McCrometer, manufacturer of the V-Cone, shows that within the beta ratio range of 0.363 to 0.750, the V-Cone can be installed close - even close-coupled - to either single or double elbows out-of-plane without affecting the accuracy of the meter more than 0.3%. These tests replicate those performed by the National Institute of Standards and Technology in Maryland to study installation effects on various types of differential pressure flowmeters. Other companies may make claims about reducing the need for long straight upstream and downstream pipe runs, but ask to see the data first before taking a supplier’s word for it. If there’s no data, be very skeptical of such claims! To find out more about the V-Cone flowmeter or other products in McCrometer’s line of flowmeters, please contact your nearest McCrometer flowmeter expert at 951-652-6811 or visit our web-site www.mccrometer.com Copyright 2000 McCrometer Know anyone looking for a steady dose of flow measurement information? To subscribe send e-mail to news-request@mccrometer.com <mailto:news-request@mccrometer.com> with a Distributed by McCrometer “The Flow Measurement Specialists” |