Validation of the gas flow rate measuring system with the laminar flow element
Doc. dr. Gregor Bobovnik, univ. dipl. inž., Klara Arhar, dipl. inž. str. (UN), izr. prof. dr. Jože Kutin, univ. dipl. inž., all University of Ljubljana, FME, Slovenia
The main component of a laminar flowmeter is a laminar flow element, which cross-section is made of capillary passages. The gas flows through the passageway under laminar conditions, therefore the Hagen- Poiseuille equation, in which the gas mass flow rate and the pressure drop are linearly related, could be in the ideal conditions used as the measurement model. However, the assumptions on which this equation is based on are not assured in praxis, therefore slightly modified models are applied. This article presents the measurement model based on non-dimensional parameters. Based on calibration results, the realization of such measurement model and detailed evaluation of its measurement uncertainty is shown for a concrete example. Further, the results of comparative measurements of dry gas flow rate using the laminar flowmeter and the measuring system with sonic nozzles are presented. The results are evaluated using the En number and prove the adequacy of the measurement model and respective measurement uncertainties of the measured flow rate with the laminar flowmeter.
laminar flow element, laminar flowmeter, measurement model, evaluation of measurement uncertainty, comparison measurements