Measurement and Modelling of the Residence Time Distribution in Microfluidic Devices

An experimental method has been developed to measure the residence time distribution (RTD) in continuously operated microfluidic devices. RTD measurements are performed by a stimulus-response technique using a special dye as a tracer. The tracer concentration is spectroscopically measured at two points of the setup, one close to the inlet and the other close to the outlet. The experimental setup provides sufficient flexibility since microfluidic devices can be easily exchanged and thus individually analysed. The method was optimized in order to achieve high repeatability and to eliminate errors, such as low measuring frequencies and tracer adsorption on the microchannel walls. The measured concentration profiles were used for modeling the RTD in the microfluidic devices investigated. Since the measured overall signal is influenced by the RTD behaviour of other setup components (e.g. capillaries) has been it must be deconvoluted to obtain the RTD of the microfluidic device solely. In this work, RTD measurement and modeling was performed exemplarily for one split-and-recombine micromixer. It turned out that conventional models that are used to describe the RTD of macroscopic reactors are not suitable to describe the RTD on the micro scale adequately. The asymmetric distribution caused by the laminar flow in microchannels is better approximated by empirical models.