In this work, we have systematically analyzed the scaling law of droplet formation by cross-flow shear method in T-junction microfluidic devices. The droplet formation mechanisms can be distinguished by the capillary number for the continuous phase (Ca c ), which are the squeezing regime (Ca c \ 0.002), dripping regime (0.01 \ Ca c \ 0.3), and the transient regime (0.002 \ Ca c \ 0.01). Three corresponding correlations have been suggested in the different range of Ca c . In the dripping regime, we developed a modified capillary number for the continuous phase (Ca c 0 ) by considering the influence of growing droplet size on the continuous phase flow rate. And the modified model could predict droplet diameter more accurately. In the squeezing regime, the final plug length was contributed by the growth and 'squeeze' stages based on the observation of dynamic break-up process. In the transient regime, we firstly suggested a mathematical model by considering the influences of the above two mechanisms. The correlations should be very useful for the application of controlling droplet size in T-junction microfluidic devices.

In our previous work, a new flow route was developed-a so-called perpendicular shear force-induced droplet formation-in a self

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

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This work describes a novel microfluidic method to prepare monodispersed chitosan microspheres by using the solvent extraction method. Our strategy is that a chitosan/acetic acid aqueous solution is emulsified in an organic phase containing the extractant by using the co-flowing shear method in a co-axial microfluidic device. The formed droplets are in situ solidified within a synthesizing channel by the extraction of acetic acid from the chitosan aqueous droplets to the organic solution. Based on this approach, the size of chitosan microspheres can be successfully controlled from 100 mum to 700 mum in diameter with a variation of less than 4%. Furthermore, high loading efficiency (>95%) of Bovine serum albumin (BSA) can be in situ encapsulated. The present method has the advantages of actively controlling the droplet diameter, narrow size distribution, good sphericity, and having a simple and low cost process, with a high throughput. This approach for the preparation of chitosan microspheres will provide many potential applications for pharmaceutical area.

This study examines effects of the splitter plate placed in the near wake of a circular cylinder on the performance of a piezoelectric wind energy harvester through wind tunnel experiments. The kinetic energy of the harvester is gained by wind-induced vibrations of the circular cylinder. The splitter plate is attached to the leeward side of the cylinder. The ratio of the splitter plate length to the diameter of the circular cylinder (Lsp/D) ranges from 0.25 to 2.00. After attaching the splitter plate with an appropriate length, the harvester is able to sustain large amplitude vibrations beyond the wind speed range corresponding to vortex-induced vibrations. Thus, the upper bound of the wind speed range for the harvester to harness wind energy is eliminated, which significantly increases the efficiency of the harvester. Compared to the different lengths of the splitter plate, 0.65D has been found to be the optimal length for maximizing the harvested power.

This article presents a simple microfluidic method to measure the Newtonian fluid viscosity. This method is carried out in a co-axial microfluidic device. A stable liquid/liquid annular co-laminar flow in the co-axial microfluidic device has been realized, which can be described by Navier-Stokes equations. The viscosity of either fluid can be measured based on the equations when the viscosities of another fluid is known. Proper conditions to form stable annular co-laminar flow for the viscosity measurement were investigated. Several fluids were tested with viscosity ranging from 0.6 to 40 mPa s. The measured results fit very well with those measured by a commercial spinning digital viscometer. The novel method is highly controllable and reliable, and has the advantage of less time and material consumption, as well as easy fabrication of the device.