Flows of dry and wet granular suspensions through constrictions have long been studied, from the regular discharge of sand in antique hourglasses to the granular flows within silos or even the clogging of particles under confinement. We have designed a novel and versatile two-dimensional microfluidic hopper to investigate the flow and clogging dynamics of dense suspensions. The set-up combines an in situ microfluidic fabrication technique with a pneumatic valve at the orifice to print and concentrate particles of controllable shape. We have demonstrated that the microfluidic flow and clogging of dense suspensions of hard monodisperse disk-shaped particles are reminiscent of well-established behaviours in conventional granular hoppers. By conducting experiments under different driving forces, we report a constant particle discharge rate that depends on the flow driving mechanism and follows well-established stochastic clogging laws. Such results might contribute to bridging the gap between dry granular media and dense wet suspensions. Finally, the versatility and tunability of the microfluidic hopper pave the way for systematic experimental studies on complex granular suspensions involving particles of varying shapes and deformability, of obvious interest in practical applications.

Lars Kool*, Jules Tampier*, Philippe Bourrianne and Anke Lindner. Hopper flows of dense suspensions: a 2D microfluidic model system. Flow, 5 (E26), 2025. [pdf]