Abstract
The precise measurement of micro and nanoflow of incompressible liquids (below 1 μL/h) is a complex task due to several factors involved in, namely, evaporation, adsorption and the existence of air bubbles within the system. Nevertheless, the importance of its measurement is undeniable in equipment such as insulin pumps, or medical drug delivery devices for new-born, microchip flow pumps, to mention few.The work herein presented was developed in a partnership between the Volume and Flow Laboratory (LVC) of the Portuguese Institute of Quality (IPQ) and the Department of Mechanical and Industrial Engineering (DEMI) of The New University of Lisbon under the project MeDD II – Metrology for Drug Delivery. It had the main objective of conceiving a new Portuguese standard for the measurement of ultra-low flow using interferometry, with a target uncertainty of 1% (k = 2). Therefore, the new setup relies on an interferometer made up of a laser unit, two retroreflector cubes, one beam splitter, as well as a flow generator (a Nexus syringe pump) and a computer for data acquisition.Experimental tests on a Flow generator and a Coriolis flow meter were carried out at different flow rates. With the innovative methodology developed during the present research, it was possible to measure flow rates of an incompressible fluid (water) down to 1 μL/h with an uncertainty of 3% (k = 2).
Highlights
The most common calibration method used by the National Metrology Institutes (NMI) for measuring low flow rates of fluids is the gravimetric method, which consists in the determination of the mass of a liquid during a period of time
The lowest flow rate measurement capability found to date in a National Metrology Institute was achieved by the Swiss Federal Institute for Metrology (METAS), the NMI in Switzerland, down to 6 μL/h with an uncertainty of 0.7%
An innovative method that allow the determination of microflow rates lower than 1 mL/h using interferometry, developed by the Volume and Flow Laboratory of the Portuguese institute of Quality, was pre sented in this research paper
Summary
The most common calibration method used by the National Metrology Institutes (NMI) for measuring low flow rates of fluids is the gravimetric method, which consists in the determination of the mass of a liquid during a period of time. This methodology is used by the Volume and Flow Laboratory of the Portuguese Institute for Quality in a range down to 120 μL/h with a expanded uncertainty of 3% (CMC published at BIPM-JCRB website), being well defined in several publications, such as H. In the work presented, an interferometer was used to monitor the distance travelled by a pusher block of a flow generator connected to a glass syringe in order to determine the flow rate
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