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Title: Calibration Of Nonlinear Laminar Flow Elements For Multigas Applications
Author: Chiun Wang,
Source: 2009 Measurement Science Conference
Year Published: 2009
Abstract: Laminar flow elements are frequently used in flow measurement devices either as flow splitters or to establish the pressure drop required for flow metering. All laminar flow elements suffer from the entrance effect to a certain extent, rendering the pressure versus flow relationship nonlinear. The non-linearity is sensitive to even minor differences in the entrance geometry, which is susceptible to the manufacturing tolerance. Attempts to model the nonlinear laminar-flow elements for high accuracy applications by scaling the calibration curve in native variables or to construct a universal function for the pressure-flow relationship have only seen limited success. This paper presents a method to extract the pressure-flow relationship in dimensionless variables and to derive the multi-gas model using similarity theory. Without resorting to any explicit functional forms, the method allows the flow meter to accurately predict the flow rate of any process gas once it is calibrated by using a single inert gas.