Over the past decade, homogeneous mixing in microfluidic devices has been a critical challenge, because of the inherently low flow rates in microfluidic channels. Although several mixer designs have been suggested to achieve efficient mixing, most of them involve intricate structures requiring a series of laborious fabrication processes. Operation at high flow rates can greatly enhance mixing by induction of turbulence, but devices that can resist such a high pressure drop to induce turbulence in microfluidic channels are difficult to fabricate, especially for commonly used poly(dimethylsiloxane) (PDMS)-based microfluidic devices. We have developed a Y-shaped, turbulent microfluidic mixer made of PDMS and a glass substrate by strong bonding of the substrates to a nanoadhesive layer deposited via initiated chemical vapor deposition. The high bonding strength of the nanoadhesive layer enables safe operation of the PDMS/glass turbulent microfluidic mixer at a total water flow rate of 40 mL min⁻¹, corresponding to a Reynolds number, Re, of ~4423, one of the highest values achieved in a microfluidic channel. The turbulence generated as a result of the high Re allows rapid mixing of the input fluids on contact. Image analysis showed that mixing started as soon as the fluids were introduced into the mixer. The experimental results matched the numerical predictions well, demonstrating that convective mixing was dominant as a result of turbulence induced in the microfluidic channel. Using the turbulent microfluidic mixer, we have demonstrated high throughput formation of emulsions with narrower size distribution. It was shown that as the flow rate increases inside the microfluidic channel, the size distribution of resulting emulsions decreases owing to the increase in the turbulent energy dissipation. The turbulent microfluidic mixer developed in this work not only enables rapid mixing of streams, but also increases throughputs of microfluidic reactors.

A new finite-element scheme to solve the Stokes–Brinkman equation for flow analyses in dual scale porous media is presented and has been applied to predict the effective permeability of dual scale fibrous media. Both continuous and discontinuous stress conditions at the interface between a porous media and a surrounding fluid are explored by introducing an equivalent momentum equation for the Brinkman equation. The proposed scheme uses a uniform structured regular rectangular mesh to discretize the domain and employs the level-set method to describe the porous media allowing for inclusion of complex geometrical features easily. Biperiodic boundary conditions have been applied to conduct the flow analysis in a representative volume of mesoscale porous structures. Numerical solutions in a parallel channel flow over a porous media are presented and compared with analytic solutions to assess the accuracy of the proposed scheme. The scheme is then applied to flow past two regular periodic geometries of elliptic porous media in two dimension, representing unidirectional fiber tow (bundle of aligned fibers) in a textile fabric, to predict the effective permeability and its dependence on the fiber volume fraction, the aspect ratio, the fiber tow permeability, and the degree of compaction of the fiber tows. In addition, we propose a simple relationship between the effective permeability and the permeability of fiber tow, based on numerical and analytic results.

A novel microfluidic method to accurately assess the cell damage under controlled extensional stress, simulating the bubble bursting process in bioreactors.