Capacitive determination of wall-film thickness in liquid-liquid slug flow and its application as a non-invasive microfluidic viscosity sensor

Abstract

The knowledge of wall-film thickness in liquid-liquid slug flow can be exploited to ascertain material properties of the liquids utilized. Capacitive impedance measurement overs the cross-section of a micro-capillary allows determination of the liquid volume fractions in the biphasic flow. Wall-film thickness is determined using geometrical considerations to interpret the measurement signals of the slug flow and its disperse and continuous phases. The dimensionless Capillary Number of the system, which characterizes the viscosity of the continuous phase, can be determined from the wall-film thickness measured by employing well-known correlations. In this study, a methodology to ascertain wall film thickness from capacitive impedance measurements is presented and applied to liquid-liquid slug flows of various biphasic media with different viscosities. The determination of viscosity in a reactive system is demonstrated using the polymerization of butyl acrylate, as an illustrative reaction where viscosity depends strongly on conversion.