Vol.3 No.1 Subject: Flow Measurement News Date: 3-13-01 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... New McCrometer Website Our website has undergone a major renovation. A new and easier user interface, expanded industry sections a new product area featuring sales and technical information on our products, a/v demonstrations and a 360-degree product viewer. Visit us at <http://www.mccrometer.com> Get a Free Flow Evaluation and see for yourself why McCrometer is the premier provider of flow measurement solutions. Regarding Gas Adiabatic Expansion Factor Flow equations for differential pressure meters such as the McCrometer V-Cone, are derived from Daniel Bernoulli's theorem of the conservation of momentum in a pipe. Bernoulli's theorem states that for a fluid moving through a closed pipe, as velocity increases, pressure decreases. The derived equation for differential pressure meters assumes the density of a fluid will not change within the meter. This assumption applies only to incompressible flows. In compressible flows, however, a correction must be made. In a gas, a change in pressure will change the density of the gas. Since the V-Cone is a differential pressure meter, the line pressure will be higher upstream of the meter than downstream. Therefore, the density upstream will also be higher than the density downstream. If not corrected, this difference in density will create a measurement error . It is corrected by a term called the "gas expansion factor." The gas expansion factor correctly identifies that the gas expands in the low pressure downstream of the meter. This, however, should not be confused with the "compressibility factor" of a gas, which is distinguished as a physical property of the gas not the meter. McCrometer uses the letter "Y" to symbolize the gas expansion factor for the V-Cone. The value of Y is always equal to or less than one. To use the factor, we simply multiply the calculated value directly into the flow equation. The expansion factor is a function of differential pressure (DP) and line pressure in the meter. As the amount of DP goes up in ratio to the line pressure, the Y factor goes down. This means the Y factor changes with any change in DP or pressure and must be calculated with each flowrate measurement. The instrumentation used to calculate flowrates through a DP meter must be capable of doing these calculations and programmed properly for gas applications. For more information regarding the gas expansion factor the following literature is available at our Website's Literature Section www.mccrometer.com <http://www.mccrometer.com> <<http://www.mccrometer.com>> : 24508-20 Regarding Gas Adiabatic Expansion Factor 24509-54 V-Cone Flow Calculations These documents, in Adobe(r) Acrobat(r) format, are easily downloadable. ******************************************* Copyright 2001 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