Vol.3 No.2 Subject: Flow Measurement News Date: 4-24-01 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... In some industrial applications, where flowing temperatures are well above ambient, flow meter users must consider the thermal expansion of the metal in the meter. This expansion and contraction can have a significant effect on the accuracy of the flow measurement. Metals have a thermal expansion coefficient. This means the metal will expand a certain amount with every increase in temperature. For example, a typical 304 stainless steel has a linear thermal expansion coefficient of 9.500e-06 or 0.0000095 in / in * F. The steel will expand 0.0000095 inches for every inch in diameter and every Fahrenheit degree increase in temperature. With such a small number, the effect of expansion is often considered too small to include in the calculations. In certain applications, this could affect the accuracy of the flow meter. Here an example of what effect thermal expansion can have on the accuracy of a flow meter. The V-cone is a differential pressure flow meter manufactured by McCrometer. V-cones are typically made of steel and subject to thermal effects. When the meter is calibrated, the temperature is ambient, around 70 degrees F. If that meter were placed in an application where the flowing temperature was 500 degrees F, both the pipe and the cone inside would be slightly larger than when the meter was at 70 degrees F. The geometry of the meter would be different than when it was calibrated. The change in geometry is corrected with a term called the thermal expansion Fa. (Notice this is called a "factor", whereas the metal expansion is called a "coefficient." ) By changing the meter temperature from 70 to 500 degrees F, the thermal expansion factor goes from one (no change) to 1.005, or if the meter is made from 300 series stainless steel, 1.008. If the thermal expansion factor was not included in the flow calculation, the measurement would be low by 0.8%. Some meters, such as V-Cones and orifice plates, can have two types of metals in the construction. In these cases, both thermal expansion coefficients must be included in the calculations. Also, the thermal expansion coefficients of metals will change with different ranges of temperatures. In general, when calculating flow, keep these points in mind: 1) In ambient temperature applications, the effect of thermal expansions is negligible. 2) In lower and higher temperature applications, the effect should be considered for the best accuracy from your flow meter. ******************************************* 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