In-line measurements of the physical and thermodynamic properties of single and multicomponent liquids

Microfluidic devices are becoming increasingly important in various fields of pharmacy, flow chemistry and healthcare. In the embedded microchannel, the flow rates, the dynamic viscosity of the transported liquids and the fluid dynamic properties play an important role. Various functional auxiliary components of microfluidic devices such as flow restrictors, valves and flow meters need to be characterised with liquids used in several microfluidic applications. However, calibration with water does not always reflect the behaviour of the liquids used in the different applications. Therefore, several National Metrology Institutes (NMI) have developed micro-pipe viscometers for traceable inline measurement of the dynamic viscosity of liquids used in flow applications as part of the EMPIR 18HLT08 MeDDII project. These micro-pipe viscometers allow the calibration of any flow device at different flow rates and the calibration of the dynamic viscosity of the liquid or liquid mixture used under actual flow conditions. The validation of the micro-pipe viscometers has been performed either with traceable reference oils or with different liquids typically administered in hospitals, such as saline and/or glucose solutions or even glycerol-water mixtures for higher dynamic viscosities. Furthermore, measurement results of a commercially available device and a technology demonstrator for the inline measurement of dynamic viscosity and density are presented in this paper.