T. R. Shih

Mixing behavior of the rhombic micromixers over a wide Reynolds number range using Taguchi method and 3D numerical simulations.

A planar micromixer with rhombic microchannels and a converging–diverging element has been systematically investigated by the Taguchi method, CFD–ACE simulations and experiments. To reduce the footprint and extend the operation range of Reynolds number, Taguchi method was used to numerically study the performance of the micromixer in a L9 orthogonal array. Mixing efficiency is prominently influenced by geometrical parameters and Reynolds number (Re). The four factors in a L9 orthogonal array are number of rhombi, turning angle, width of the rhombic channel and width of the throat. The degree of sensitivity by Taguchi method can be ranked as: Number of rhombi > Width of the rhombic channel > Width of the throat > Turning angle of the rhombic channel. Increasing the number of rhombi, reducing the width of the rhombic channel and throat and lowering the turning angle resulted in better fluid mixing efficiency. The optimal design of the micromixer in simulations indicates over 90% mixing efficiency at both Re ≥ 80 and Re ≤ 0.1. Experimental results in the optimal simulations are consistent with the simulated one. This planar rhombic micromixer has simplified the complex fabrication process of the multi-layer or three-dimensional micromixers and improved the performance of a previous rhombic micromixer at a reduced footprint and lower Re.

Water-assisted CO2 laser ablated glass and modified thermal bonding for capillary-driven bio-fluidic application

The glass-based microfluidic chip has widely been applied to the lab-on-a-chip for clotting tests. Here, we have demonstrated a capillary driven flow chip using the water-assisted CO2 laser ablation for crackless fluidic channels and holes as well as the modified low-temperature glass bonding with assistance of adhesive polymer film at 300°C. Effect of water depth on the laser ablation of glass quality was investigated. The surface hydrophilic property of glass and polymer film was measured by static contact angle method for hydrophilicity examination in comparison with the conventional polydimethylsiloxane (PDMS) material. Both low-viscosity deionized water and high-viscosity whole blood were used for testing the capillary-driving flow behavior. The preliminary coagulation testing in the Y-channel chip was also performed using whole blood and CaCl2 solution. The water-assisted CO2 laser processing can cool down glass during ablation for less temperature gradient to eliminate the crack. The modified glass bonding can simplify the conventional complex fabrication procedure of glass chips, such as high-temperature bonding, long consuming time and high cost. Moreover, the developed fluidic glass chip has the merit of hydrophilic behavior conquering the problem of traditional hydrophobic recovery of polymer fluidic chips and shows the ability to drive high-viscosity bio-fluids.

Design and fabrication of an advanced rhombic micromixer with branch channels

Fluid dynamics and mixing transport of an advanced rhombic micromixer with branch channels have been designed and investigated by 3D numerical simulations and experiments. The CFD-ACE+ software was used for simulation and PDMS molding process was used for chip fabrication and experiment. Simulation results showed the advanced rhombic micromixer with branch channels enhanced much high mixing efficiency compared to cross-shape microchannels at the same Re. Compared to the pure rhombic microchannel, the branch-channel rhombic micromixer promoted the mixing efficiency at lower pressure drop at the same Re. Over 90% mixing enhanced by vortices had been achieved at Re > 80. Experimental results show this advanced rhombic micromixer enhances much mixing at Re 60 and uniform mixing at Re 120, respectively. This device is suitable to the application of high-throughput chemical production.

Design and Simulation of a Novel Micro-mixer with Baffles and Side-wall Injection into the Main Channel

A novel passive micromixer with rapid mixing and low pressure drop has been successfully demonstrated by simulations and micro-fabrication. The structure of this micro-mixer contains one main channel, two sub-channels for injecting the other specie and some baffles in the main channel to form mixing chambers. Adding baffles to the main channel will produce the recirculation to increase the contact area of the fluids and form nozzles. So, this type of design can improve mixing efficiency. The better stream mixing is attributed to the higher baffle, the more baffle number and the higher flow rates. From the design aided by simulations, the design with 3 baffles of 300 mum height is adaptive for uniform mixing ( 90% mixing) and low supplied pressure of 4750 Pa at Re of 100 in the 3D simulation.

Fabrication of a novel micro liquid flow sensor using a TaN thin film

A micro flow sensor with high temperature coefficient of resistance (TCR) is very important because of its high sensitivity of flow sensors. Different from the conventional positive-TCR Pt film used in micro flow sensor with self-heating, higher negative-TCR micro flow sensor without self-heating is developed and fabricated in this research. The novel TaN-material micro liquid flow sensors are fabricated by reactive magnetron co-sputtering system at different nitrogen flow ratios. The magnitude of negative-TCR TaN films increases with increasing nitrogen flow ratios, so the high-TCR micro flow sensor can be prepared successfully at higher N2 flow ratio. In order to understand the sensing ability, micro flow sensor is fabricated by MEMS technology. Measurement results show that this TaN micro flow sensor has high sensitivity of 407 ohm/(ml/min) at Re ≪ 5, corresponding to volume flow rate of 0.167 ml/min. This device with high-negative-TCR materials can be beneficial for the measurement of low-velocity flow of liquid because of its high sensitivity at low Reynolds number.

Characteristics of truncate-angle rhombic micromixer and rapid mold fabrication using CO 2 laser micromachining

Fluid dynamics and mixing transport of the rhombic micromixer with truncate angles have been investigated by 3D numerical simulations and experiments. Simulation result shows this rhombic microchannel with truncate angles has high mixing efficiency, compared to cross-shape microchannel. Over 90% mixing enhanced by vortices had been achieved at Re ≫ 100. Different to photolithography process, CO2 laser machine is used to fabricate the master mold rapidly. Experimental results show this rhombic micromixer enhances much mixing at Re 18.6 and uniform mixing at Re 186, respectively. This device is suitable to the application of high-throughput chemical production.

Design of a novel microreactor for microfluidic synthesis of silica nanoparticles

Conventional microreactors for nanoparticle synthesis were operated at low flow velocity as well as more residence time because of low mixing efficiency of the meander micromixer. Here, we purpose a simple obstacle micromixer to be operated at a wide range of flow velocity for increasing single-channel synthesis production rate of silica nanoparticles. Results show our obstacle micromixer has over 85% mixing efficiency covering the flow regions in both convection and diffusion mixing. This microreactor was used to synthesize silica nanoparticles with an average diameter of 200–250 nm. Enhancing fluid mixing at high flow velocity can result in high production rate.

Design of a self-stirring micromixer at low Reynolds number flow

In order to improve the complicated fabrication process and integration of 3D micromixers, we propose a novel planar self-stirring micromixer with high mixing efficiency and low pressure drop. The planar micromixer with vortices agitation for mixing enhancement had been successfully investigated by the Taguchi method, CFD-ACE simulations and experiments. The factor sensitivity test was performed by L9(34) orthogonal array in Taguchi method. Degree of sensitivity ranks as: Gap ratio > Number of mixing units > Baffle width > Chamber ratio. At Re = 20, micromixer shows 93% mixing efficiency in the adaptive design with three mixing units, H/W = 1/8, Wm/W = 1 and Wm = 80. The corresponding pressure drop of this adaptive design is only 4600 Pa at Re 20. Much improved mixing is obtained experimentally in this adaptive design at Re 20. The results of the factor sensitivity test can provide useful information for the design of the micromixers with obstacles. Merits of this design are easy fabrication and high integration capability.

Design and Simulation of a Rhombic Micromixer for Rapid Mixing

Rapid mixing is necessary in the fields of the biochemical analysis and drug delivery. In this paper, a planar micromixer featuring the rhombic microchannel had been successfully demonstrated by the CFD-ACE simulations and mixing experiments. Rhombic microchannel produces the recirculation to increase the mixing efficiency. The fluid mixing is related to the geometry parameters and Reynolds number of the rhombic micromixer. The better fluid mixing is attributed to the smaller turning angle (alpha), the more rhombi and the higher flow rates. From the design aided by the simulations, the three-rhombus mixer featuring the angle of alpha = 30deg and a converging-diverging element exhibits good mixing efficiency more than 90 %. From the experiment results of the adaptive design, nearly uniform mixing had been achieved at Re = 200. Because of the rapid and good mixing, this micromixer can be applied to the fields in need of rapid mixing, such as drug discovery and protein folding analysis.

Simulation of the novel micro-valve using dynamic analysis

In this article, the 3D dynamic analysis was used to investigate the geometrical effect on the net flow rate of the novel microvalves in comparison with the conventional nozzle/diffuser microvalves. The novel microvalves with saw-tooth structures had been investigated by 3D transient simulations in order to study the transient flow behavior at different angles. Simulation parameters are half angle α, taper angle θ and excitation frequency ƒ. Simulate results show that net flow rate is dependent on the excitation frequencies. As excitation frequency is higher than 10 Hz, net flow rate decreases with increasing excitation frequency. Net flow rate can also increase with adding circular area and increasing half angle. Better half angle is found at α = 6°. Compared to a conventional nozzle/diffuser microvalve, a novel microvalve with θ = 9.7° and α = 6° have the higher net volume flow rate of 0.256 µl/s. Besides, as width of the throat increases, net flow rate will also increase. These results are beneficial for the design of micropumps.