(102f) Mass Transfer Characterization Inside Reactive Droplets Flowing Throw Microchannels

In the pharmaceutical and fine chemicals industries, process fast design is a determining step for economical viability. To reduce this ?time to market? constraint, the product development phase can be reduced by improving the initial step concerned with physical and chemical data acquisition. We are particularly interested in determining chemical kinetics and mass transfer parameters. To do so, a very promising application of microtechnologies is the use of two-phase liquid-liquid flow in microchannels. In this kind of system, microdroplets of reagents are transported at constant velocity in an inert continuous phase so that they can be considered as individual nanovolume batch reactors. One of the determining parameters of this device for kinetics acquisition purpose is the mixing time inside the droplets. That is why we first focused on hydrodynamic characterisation of the droplet inner stream loops by using numerical simulations and micro PIV experiments. Then, we showed that a chemical reaction can be performed inside the droplets, and monitored with high sensibility thanks to Raman micro spectrometry. Fist, we focused on recirculation time inside the droplets. We performed numerical simulations and experimental validation of the hydrodynamics inside droplets in rectangular microchannels. We use a finite-volume/front-capturing method that allows us to perform two- and three-dimensional simulations with a reasonable cost. The numerical method is an interface-capturing technique without any interface reconstruction. Therefore no complex or expensive interface tracking is needed. Furthermore, micro-PIV measurements are used to obtain experimental velocity fields inside droplets which are compared to simulations. As it is shown on figure 1, the two approaches are in good agreement. Thanks to numerical simulations, droplet interface deformation and velocity fields inside both droplets and continuous phase can then be followed. This study leads to important results in droplet deformation and velocity fields in the droplets and in the continuous phase for mass and heat transfer studies. More particularly, the capillary number seems to have a great influence on the liquid/liquid flow hydrodynamics and no to depend on the channel scale. Secondly, we investigate the use of confocal Raman spectroscopy to obtain spatially resolved concentration maps of chemically reactive fluids flowing in two-phase channel flow. As a model chemical reaction, we use the water deuterium exchange reaction between H2O and D2O which is diffusion-controlled and whose reagents and products can be quantified depending on different the Raman signature. We are able to extract Raman images of H2O, D2O and HOD concentrations in the droplets, and we evidence the influence of wiggles on mixing efficiency inside the droplets.