| Vol.2 No.1 Subject: Flow Measurement News Date: 1-11-00 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... Know your isentropic exponent Differential pressure flowmeters, like the V-Cone, use Bernoulli's principle to measure flow. If you're measuring gases however, a correction factor has to be applied to take into account changes in gas density before and after the flowmeter. This correction is known as the Y factor or adiabatic expansion factor, and depends on several parameters, including differential pressure, line pressure and isentropic exponent. While most engineers know the first two, few are familiar with the isentropic exponent. It is defined as the ratio of the specific heat at constant pressure to specific heat at constant volume and is fixed for a given gas. It has a limited effect on the Y factor but needs to be taken into account nonetheless to ensure accurate flow measurement. Fortunately, you don't need to know the Y factor or isentropic exponent of your gas in order to measure flow successfully. Your flowmeter supplier should calculate the Y factor and program the instrumentation for your particular application. If, however, your supplier says 'isentropic what?', you know you're dealing with the wrong company. Visit the McCrometer web-site www.mccrometer.com and download document #24508-20, "The Adiabatic Expansion Factor and the V-Cone", from the McCrometer library for more information on this topic. Copyright 2000 McCrometer ******************************************* |