Chien Hsiung Tsai

Experimental and Numerical Investigation into Mixing Efficiency of Micromixers with Different Geometric Barriers

This paper proposes a numerical and experimental investigation of mixing behaviors of two liquid samples in microchannels that are shaped into different geometric barriers. The micro-mixers utilized in this study are fabricated on low-cost glass slides using a simple and reliable fabrication process. Samples are driven by a hydrodynamic pump to lead them into the mixing section of the microchannels. The effects of mixing performance of various kinds of barrier shape are discussed in this study. The numerical and experimental results show that a better mixing efficiency can be obtained in the microchannels while using the elliptic-shape barriers in compare with the leaking side-channels. In this study, the simulated and experimental results are in good agreement. The investigation of mixing efficiency in microchannels with different geometric barriers could be crucial for microfluidic systems.

Numerical Simulation of Electromagnetic Actuator for Impedance Pumping

This study designs and analyzes an impedance pump utilizing an electromagnetic actuator. The pump is designed to have three major components, namely a lower glass substrate patterned with a copper micro-coil, a microchannel, and an upper glass cover plate attached a magnetic PDMS diaphragm. When a current is passed through the micro-coil, an electromagnetic force is established between the coil and the magnetic diaphragm. The resulting deflection of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. Overall, the simulated results reveal that a net flow rate of 52.8 μl/min can be obtained using a diaphragm displacement of 31.5 μm induced by a micro-coil input current of 0.5 A. The impedance pump proposed in this study provides a valuable contribution to the ongoing development of Lab-on-Chips (LoCs) systems.

Magnetic Microfluidic Mixer

This paper presents a novel simple Y-type micromixer based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). An electromagnet driven by an AC power source is used to induce transient interactive flows between a ferrofluid and DI water. The alternative magnetic field causes the ferrofluid to expand significantly and uniformly toward DI water associated with a great number of extremely fine fingering structures on the interface in the microchannel. Different magnetic strengths of the electromagnet were applied by adjusting the magnitude of AC supplied power at frequency of 45 Hz. The results show, due to the magnetic fields, two fluids mix with each other efficiently (mixing ratio can be as high as 95%). When the magnetic field is high enough, the labyrinthine fingering instability take place. This phenomenon is favorable for the fluid mixing. In addition, the increasing magnetic field enhances the efficiency of the mixing apparently.

Rapid Detection of Methanol in an Integration Microfluidic Chip

A rapid and simple technique was developed for detecting methanol with very small amount of sample by using PMMA (Polymethyl-Methacrylate) microfluidic chip, which fabricated by a commercially available CO2 laser scriber. The experimental results indicate that linearity expression R2 can approximate 0.936 using the proposed integrating microfluidic chip when the 2 unit methanol oxidase (MOX) and basic fuchsin to detect methanol. Hence, the current device provides a valuable tool for rapid methanol detection, while its micro mixer system delivers a simple yet effective solution for mixing problems in the micro-total-analysis -systems field.

Effects of Heating Vents in a Tunnel-Type Dryer

This work employs FDS to simulate the heating process of a tunnel-type dryer and visualizes the computational results using Smokeview. The inappropriate design of a tunnel-type dryer in a factory has motivated this work. This poorly designed dryer not only has caused terrible fuel consumption but also produced parts some of which are under- or over-cooked. These are caused by the terribly uneven temperature distribution within the dryer. In order to improve the evenness of temperature distribution, this work simulates and investigates the effects of various ventilation schemes. Based on the results, it is found that the hot air intake vent should be placed at the bottom whereas the cold air outtake vent at the top. The flow rate through the intake vents does not have a very significant effect on the temperature distribution after 40 s.

Optimal Piping Design for Enhanced Energy Saving in District Cooling System – A Case Study

This study performs a numerical investigation into the power consumption characteristics of various primary-secondary chilled water circuit designs in a district cooling system (DCS) installed in six buildings located within the same block in Taipei, Taiwan. An E20-II model is created of the DCS and a series of simulations are performed to determine the primary-secondary chilled water piping design which maximizes the energy saving obtained in the DCS over the course of a typical year. It is shown that the use of a region-pumping system or a boost-pumping system reduces the power consumption of the secondary chilled water circuit by 26.5% and 29.9%, respectively, compared to that of a common-pumping system. In addition, the results show that for a practical chilled water system in which the temperature differential on the primary side is 5.0oC while that on the secondary side is 6.5oC, an average monthly energy saving of around 5~7% is obtained compared to a DCS with equal temperature differentials in the primary-secondary circuits provided that the flow rate and the temperature differential of the chilled water in the primary circuit are a little less than those in the secondary circuit.

Numerical Investigation into Thermal Behavior of Brushless Permanent Magnet Motors

The performance of brushless permanent magnet motor for electric vehicle applications is simulated by commercial CFD codes Fluent 6.3. It is difficult to model motor winding area and to well pose the motor external boundary conditions for using CFD method. A possible approach to simplify the thermal resistance computation is to use an empirical equivalent thermal conductivity of the system winding impregnation and insulation. The empirical equivalent thermal conductivity is case sensitive and regressed in the experiment. The same is true for the boundary condition of motor. In this paper, we proposed a new model to compute equivalent thermal conductivity and overcome the above problem. This model takes advantage of the packing bed heat transfer model proposed by Zehner and Schlünder. Besides, the boundary conditions are also obtained by the numerical experiments. The validity of CFD method using in the present paper is validated utilizing the experimental data. The numerical data are concurred with the experimental data. As a result, the CFD method is shown to be a feasible method for modern thermal design for brushless permanent magnet motor.

Electrokinetic Instability Flow in Nanofilm-Coated Microfluidic Channels

This paper presented a parametric experimental study of electrokinetic instability phenomena in a cross-shaped configuration microfluidic device with varying channel depths and conductivity ratios. The flow instability is observed when applied electric field strength exceeds a certain critical value. The critical electric field strength is examined as a function of the conductivity ratio of two samples liquid, microchannel depth, and the treatment of microchannel wetted surface. It is found that the critical electric field strengths for the onset of electrokinetic instability are strongly dependent on the conductivity ratio of two samples liquid, and decrease as the channel depths increasing of microfluidic devices. In the present study, the surface inside microchannels is treated utilizing hydrophilic and hydrophobic organic-based SOG (spin-on-glass) nanofilms for glass-based microchips. The experimental results indicate that no significant difference for the critical electric fields for the onset of electrokinetic instability phenomena in both hydrophilic and hydrophobic SOG coating in the surface of microchannels. The critical electric fields for the onset of electrokinetic instability phenomena are slightly lower in both SOG coated cases in compare with that of the non-coated microchannel.

Thermal Contact Residual Stress Analysis of Elastic-Plastic Bilayer Micro-Cantilevers with Platinum Electrodes

This paper studies the residual stress distributions and tip deflections of microfabricated bilayer cantilevers of varying beam thickness and platinum electrode length. The bilayer cantilevers discussed here are composed of low-stress silicon nitride films deposited on silicon beams. Platinum electrodes are deposited and patterned on the low-stress silicon nitride layers. A thermal elastic-plastic finite element model is utilized to calculate the residual stress distribution across the cantilever cross-section and to determine the cantilever tip deflection following heat treatment. A contact model is introduced to simulate the influence of contact on the residual stress distribution. The influences of the beam thickness and the platinum electrode length on the residual stress distribution and tip deflections are thoroughly investigated. The numerical results indicate that a smaller beam thickness leads to a larger compressive residual stress within the platinum electrode and delivers a larger tip deflection. The results also indicate that a larger platinum electrode length delivers a smaller tip deflection.

Experimental investigation of high-resolution injection technique in microfluidic chips

This paper presents an experimental investigation on the use of high-resolution injection techniques to deliver sample plugs within electrophoresis microchips. Two novel injection microfluidic chips are proposed, which employ conventional cross-shaped and U-shaped injection system combined with an expander to deliver high-quality sample plugs for detection in separation channel. The valving characteristics on microfluidic devices are controlled through appropriate manipulations of the electric potential strengths during the sample injection and separation steps. These novel injection techniques developed in this study has an exciting potential for use in high-quality, high-throughput chemical analysis applications and in many other applications throughout the field of micro-total-analysis systems.