An efficient micro-mixer by elastic instabilities of viscoelastic fluids: Mixing performance and mechanistic analysis

Efficient mixing is one of the keen interest of many bioengineering and chemical engineering processes. In this work, we designed an efficient micro-mixer with viscoelastic fluid which can induce both strong shear and strong extension by being embedded several rhombic blocks to destabilize the viscoelastic fluid flow and can be also easily integrated. Experimental visualization and direct numerical simulation (DNS) of mixing process were conducted to evaluate the mixing performance. By adding green fluorescent particles into the fluids, apparent mixing enhancement was observed for viscoelastic fluid flow when the flow rate exceeded a threshold. The efficient micro mixing progress also shows great potential for bioengineering application with the biocompatible working fluids. Through DNS, we discussed the flow patterns and the role of polymers playing in viscoelastic fluid flow to respectively figure out the underlying mechanism of efficient mixing and the occurrence of unstable flow motions. The results show that when the elasticity is strong enough, the viscoelastic fluid flow is irregularly twisting and swinging in the channel, and as a result enhances the mixing by increasing the intersecting frequency of fluids of different concentrations. Moreover, owing to the special designed geometry, the polymers act as the energy supplier of unstable flow motions, which keeps the fluctuations from decaying towards the laminar regime.