Investigation of gas/shear-thinning liquids flow at high throughput in microchannels with the aim of producing biosourced foam

Abstract

The context of this work is to explore the possibility of making bio-sourced foams at high throughput in microsystems. A fundamental element for the development of new technologies based on biphasic flows in microchannels is a good characterization and knowledge of hydrodynamics. In this contribution, cross slot microsystems are tested as a promoter for the formation of train of bubbles in aqueous solutions of xanthan gum. A flow chart is proposed to present the conditions allowing a dispersed flow regime; i.e. the conditions guaranteeing the complete incorporation of the gas into the liquid phase (no gas pocket) and then the control of the void fraction. The foaming is studied under potential industrial conditions, i.e. operating with liquid flow rates up to 24 L/h. High speed imaging within the channels reveals that the mechanism of formation of bubbles is related to flow focusing. Bubbles are generated alternatively from each of the two opposite gas inlets. Using whey protein isolate to enhance foaming points out that the bubble size may be reduced along a long channel by tip streaming. The effect of the modulation of the viscosity of the liquid base (xanthan gum content) is also discussed.