Horn-Jiunn Sheen

Correlation of Swirl Number for a Radial-Type Swirl Generator

An experimental investigation was undertaken to derive a new correlation for the swirl number of a radial-type swirl generator under various Reynolds numbers and various vane angle conditions. A radial-type swirl generator with 16 rotary guide vanes was used to generate an annular swirling jet flow. The Reynolds numbers ranged from 60 to 6000, and the vane angles from 0° to 56°. Quantitative measurements for the velocities were made by using an optical method of laser-Doppler anemometry (LDA). Three-component velocity profiles of axial, radial, and azimuthal components at the swirling jet exit were measured for various flow conditions. A flow visualization method using smoke-wire and still photography was also applied to observe the flow patterns of the recirculation region behind the circular bluff body. Under low Reynolds number conditions, the swirl strength was found to be strongly dependent on the Reynolds number as well as on the guide vane angle. Based on the experimental results, a modified swirl number S is derived to characterize the swirling flow, which is useful for the design of a swirl generator.

Penetration force measurement of thin plates by laser doppler anemometry

An experimental method is developed by applying laser-Doppler anemometry (LDA) to measure the velocity history of a projectile impact on a target. The force history was obtained by assuming the projectile to be rigid and by differentiating a polynomial which best fitted the obtained velocity data. This method was then applied to the impact of a hemispherically tipped striker on 1-mm thick aluminum plates. The initial velocity of the projectile ranged from several m/s to 93.5 m/s. When these velocities were low enough not to produce cracks on the plate, double-force peaks were observed in each test, and the value corresponding to the higher peak was proportional to the initial velocity of the projectile. Further, this peak force occurred when the projectile just started to rebound, and spring-back behavior of the plate always occurred. Once the cracks on the target started to form, the peak impact force dropped, and the double-peak phenomenon disappeared. It was also found that the peak force was at approximately the same level for impact speeds above the ballistic limit of the plate. On the other hand, a power law was found to perfectly fit the relationship between the absorbed kinetic energy and the initial velocity of the projectile when it was lower than the ballistic limit.

Ultraviolet-enhanced room-temperature gas sensing by using floccule-like zinc oxide nanostructures

The self-aggregation of floccule-like ZnO nanostructures that were shaped by an anodic aluminum oxidation (AAO) template to improve photoactivation and sensing performance was demonstrated. Because of differences in the surface energy between the densely distributed nanopores of AAO templates, sputtered ZnO materials were located in constricted regions and aggregated into roughened nanostructures with a high surface-to-volume ratio. Because of the generation of oxygen ions by ultraviolet illumination, the room-temperature-sensing responses showed a high degree of linearity with a resistance variation of 1.758% per 100 ppm of octane gas. The optimized sensing performance of the self-organized ZnO nanostructures was increased and was 15.4 times higher than that of an unpatterned ZnO thin film.

Fabrication and testing of surface ratchets primed with hydrophobic parylene and hexamethyldisilazane for transporting droplets

We demonstrate a way to transport droplets by an arrowed micropillar array surface with hydrophobic parylene. The lightly hydrophilic parylene surface could be changed to hydrophobic one by treating with fluorine-based plasma (CF4 or SF6). The droplet on this hydrophobic parylene surface with arrowed ratchets could be transported by a speaker, and the average measured velocity was 29 mm/s. Moreover, the authors compared driving performance of the parylene surface ratchets with the ones modified by the hexamethyldisilazane (HMDS) vapor. Both the results of using hydrophobic parylene and HMDS were better than the previous work.

The development of a triple-channel separator for particle removal with self-pumping oscillating flow

The results of a new triple-channel separator with dual functions of fluid pumping and particle removal are presented in this paper. The separator was made through a MEMS fabrication process using only one photo mask. A valve-less micropump was connected to a triple-channel at a downstream position, and the oscillating flow in the micro-channel was produced by the micropump. An important characteristic of the separator is its oscillating flow, which produces two vortices at the trifurcate zone. These vortices served as obstacles to increase the flow resistance of the center channel. Based on the rotating direction of these vortices, the particles were driven towards side channels to achieve the removal effect. Micro-particle image velocimetry (μ-PIV) with an external trigger was used to measure the flow characteristics of the vortices. Streamtrace patterns were obtained at the trifurcate zone in a time period. Image processing was used to count the number of particles and to analyze the removal efficiency. The optimal removal efficiency (close to 100%) is obtained at a driving frequency of 1.5 kHz and a divaricated angle of 25°. This study indicates that the positions of the vortices provided improved removal performance with respect to the driving frequency of the PZT (piezoelectric zirconium titanate) plate and the divaricated angle of the triple-channel.

The arrowed surface ratchets with hydrophobic parylene for droplet transportation

In this article we demonstrated a way to transport droplets by an arrowed micro-pillar array surface with hydrophobic parylene. We developed successfully that the lightly hydrophilic parylene surface can be changed to hydrophobic one treated with fluorine-based plasma (CF4 and SF6) for 10 seconds. Otherwise, we designed the ratchet pattern similar to the one proposed by A. Shasty in 2007. The droplet can be up or back transported by advancing or recessive arrowed surface ratchets, and the average velocity is 23 mm/sec. Moreover, we also compared the case modified by hexamethyldisilazane (HMDS) vapor and showed the better performance of our work.

Velocity measurements of the laminar flow through a rotating straight pipe

Some measurements have been obtained for the axial velocity of the fully developed laminar flow in a circular straight pipe with radius a, which is rotating with constant angular speed Ω about an axis perpendicular to its own axis. A diode laser LDA system was mounted together with a circulating pipe flow system on a rotating table for the experiment. According to previous analyses and calculations, there exist four types of axial velocity distributions that result from the various effects of the secondary flow on the main stream via the convection and Coriolis effect for different values of R( = wm’a/ν) and RΩ(=Ωa2/ν), where wm’ is the mean axial velocity and ν is the kinematic viscosity of the fluid. The present study provides experimental validation for the previous theoretical and numerical analyses. Experiments have also been carried out for studying the asymptotic nature of the slow flow in a rapidly rotating pipe (RΩ≫1 and RΩ≫R) and the rapid flow in a slowly rotating pipe (RRΩ≫1 and R≫RΩ).

A Novel Thermal Bubble Valve Integrated Nanofluidic Preconcentrator for Highly Sensitive Biomarker Detection

In this study, we developed a new immunosensor that can achieve an ultralow detection limit and high sensitivity. This new device has an electrokinetic trapping (EKT)-based nanofluidic preconcentrator, which was integrated with oscillating bubble valves, to trap concentrated antigen and immunobeads. During the immunoassay process, oscillating bubbles rapidly grew and acted as control valves and to block the microchannel. Thereafter, the trapped preconcentrated antigen plug and antibody-coated nanobeads were preserved in the region between these two valves. Finally, the antigen concentration was quantitatively analyzed by a real-time measurement of Brownian diffusion of the immunobeads. In this work, the test sample used was C-reactive protein (CRP) which is a risk indicator of coronary heart disease and atherosclerosis.

Micro-wing and pore design in an implantable FPC-based neural stimulation probe for minimally invasive surgery

This paper presents a bipolar porous probe for implantable nerve stimulation treatment utilizing minimally invasive surgery. The probes design features micro-wings and pores for cell growth that promote long term fixation in the body. Two recording pairs detect whether cells grow into the pores, and one pair of stimulating pads stimulates the target nerve. The probe is composed of three layers: two SU-8 layers and one flexible printed circuit (FPC) layer. Results show that SU-8 films can increase the product of the area moment of inertia and Youngs Modulus by 9.04% from 5.86×10-6 N·m2 to 6.93×10-6 N·m2 and that micro-wings can increase the force of fixation by 38.58% from 0.114 N to 0.158 N. From the impedance test, the impedance of the pores in gelatin is shown to be lower than the ones in air, demonstrating that the two recording pairs are promising for detecting cells growth.

Integrating Instant Response System (IRS) as an In-Class Assessment Tool into Undergraduate Chemistry Learning Experience: Student Perceptions and Performance

Since being introduced nearly a decade ago, the use of instant response systems (IRS) (also referred to as a “clicker”) has been extensively adopted on college campuses, and is particularly popular among instructors of large lecture classes. The available evidence supports that IRS offers a promising avenue for future developments in pedagogy, though findings on advantages of effective use of IRS in relation to improving or enhancing student learning are inconclusive. Considering this unique attribute of IRS, the main purpose of the present study aims to examine the degree to which students perceive or believe that using IRS in class has an effect on their understanding of course content, engagement in classroom learning, and preparation to take class tests. Moreover, multiple student performance evaluation results are used to explore correlations between student perceptions of IRS and their actual learning outcomes. This chapter presents 151 undergraduate students’ learning experiences of a basic chemistry class incorporating IRS as an in-class assessment tool at National Chung Hsing University in Taiwan. Based on research findings, overall student perceptions on the use of IRS in class were positive. In addition, certain interactions between students’ perceptions on IRS use and their performance in learning basic chemistry were identified in the present study. Although students’ perceived benefits and effectiveness of IRS use are revealed, the research indicates that further studies are needed to probe what specifically about the use of IRS contributes to certain learning outcomes of a large chemistry class in higher education.