Tzong Shyng Leu

Recovering Estimates of Fluid Flow from Image Sequence Data

This paper presents an approach to measuring fluid flow from image sequences. The approach centers around a motion-recovery algorithm that is based on principles from fluid mechanics: The algorithm is constrained so that recovered flows observe conservation of mass as well as physically motivated boundary conditions. Empirical results from application of the algorithm to transmittance imagery of fluid flows, where the fluids contained a contrast medium, are presented. In these experiments, the algorithm recovered accurate and precise estimates of the flow. The significance of this work is twofold. First, from a theoretical point of view it is shown how information derived from the physical behavior of fluids can be used to motivate a flow-recovery algorithm. Second, from an applications point of view the developed algorithm can be used to augment the tools that are available for the measurement of fluid dynamics; other imaged flows that observe compatible constraints might benefit in a similar fashion.

Physically based fluid flow recovery from image sequences

This paper presents an approach to measuring fluid flow from image sequences. The approach centers around a motion recovery algorithm that is based on principles from fluid mechanics: The algorithm is constrained so that recovered flows observe conservation of mass as well as physically motivated boundary conditions. Results are presented from application of the algorithm to transmittance imagery of fluid flows, where the fluids contained a contrast medium. In these experiments, the algorithm recovered accurate and precise estimates of the flow. The significance of this work is two fold. First, from a theoretical point of view it is shown how information derived from the physical behavior of fluids can be used to motivate a flow recovery algorithm. Second, from an applications point of view the developed algorithm can be used to augment the tools that are available for the measurement of fluid dynamics; other imaged flows that observe compatible constraints might benefit in a similar fashion.

OPERATIONAL CHARACTERISTICS OF CATALYTIC COMBUSTION IN A PLATINUM MICROTUBE

Catalytic combustion of hydrogen in a platinum microtube, or subquenching diameter tube, is studied via theoretical analysis, experiments, and numerical simulation in terms of the major operation and design parameters. Fine-thermocouple, laser-induced fluorescence (LIF) and Raman scattering are used to measure the temperature and major species and OH concentration data at the tube exit. The experimental results show that the tube-exit temperature increases with fuel concentration, velocity, and tube size. For high fuel concentration and velocity cases in the 1000- and 500-µm tubes, an obvious gas-phase reaction behind the exit can be detected by thermocouple and LIF-OH images. Numerical simulation results show that smaller tube sizes and lower velocities would enhance the conversion ratio on the catalytic surface due to the enhanced diffusion of surface species of H2 and O2. Based on the current results and analysis, the characteristic operation regions of hydrogen catalytic combustion in microtubes are quantitatively identified in terms of parameters related to heat generation and heat loss characteristics, competition among the timescales, and tube size. Decreasing the tube size will shift the operation region toward the high-concentration and high-velocity portion of the domain with a smaller operation area.

Flow distortion in a circular-to-rectangular transition duct

Experiments were made for three circular-to-rectangular transition ducts with different transition lengths at Reynolds numbers which ranged from 4 × 10 3 to 2 × 10 4 . The Reynolds number is based on the inlet boundary-layer thickness and a reference freestream velocity measured upstream of the transition duct. The secondary flow pattern developed at the exit cross-sectional plane was mapped out in detail by a three-dimensional velocity measurement technique

Design and Simulation of a Microfluidic Blood-Plasma Separation Chip Using Microchannel Structures

Current clinical methods for the separation of whole blood into blood cells and cell-free plasma are currently based on large facility equipment, such as centrifuges. The disadvantage of this process is that the patients must have assays performed at the hospital or laboratory where the separation facility is located. The present study presents a design for microfluidic chips with different microchannel structures, which utilizes backward facing step geometry and centrifugal force to extract the cell-free plasma from whole blood samples at the branch of the microchannel for further assay, avoiding the influence of blood cells. Numerical simulation was performed on a personal computer to analyze the effects of inlet velocity and the structures of the microchannel on the flow field and back–flow in the microchannel, as well as the efficiency of separation and the volumetric fraction of the flowrate of plasma extraction. The minimum radius of particles (R) that can be excluded from the side channel, and fraction of the volumetric flowrate were obtained to evaluate the efficiency of plasma extraction. Based on the numerical simulations, the design with both converging and bending channels was the best design among the four layouts proposed. In this design, the value of R could be set to less than the critical value (set as 1 µm because of the radius of platelets), and the volumetric fraction of the extraction flowrate was approximately 8.4% when Re was about 20. The preliminary experiments indicated the fluorescent particles with 2.5 µm in radius were successfully excluded from side (plasma outlet) channel of the microfluidic chip with converging a inlet channel and the bent microchannel, when the Reynolds number of the inlet flowrate equals 50.

Experimental Study of Free Stream Turbulent Effects on Dynamic Stall of Pitching Airfoil by Using Particle Image Velocimetry

The unsteady flow fields above NACA 0015 airfoil pitching with/without upstream turbulence generator are investigated in a water tunnel by mean of particle image velocimetry (PIV). The turbulence was generated by a square bar mesh situated at the inlet of the test section. The airfoil pitching waveform is performed under the condition calculated from the angle of attack histogram of a vertical axis wind turbine (VAWT). By using PIV, the instantaneous vortex structures above the pitching airfoil can be revealed. It allows us to study the free stream turbulence effects on dynamic stall over an airfoil at pitching waveform the same as VAWT. It is found that the free stream turbulence intensity has significant impacts on the dynamic stall process. The dynamic stall process is delayed to higher incidence angles on increasing the turbulence intensity.

Design and Test of a Vertical-Axis Wind Turbine with Pitch Control

The concept of pitch control has been implemented in the design of a small vertical-axis wind turbine. Benefits gained can be shown by the experimental and numerical results presented in this paper. As found, the method of variable pitch control outperforms the one of fixed pitch control. The present results show that the former can make remarkable improvement on the starting torque as well as the aerodynamic characteristics at low tip speed ratios.

Unsteady Analysis of Microvalves With No Moving Parts

No-moving-parts valves (NMPV) pumps produce the net volume flow due to the difference of pressure resistances between forward and reverse flow of a microchannel structure. NMPV has been developed by a number of research groups. However, most of NMPV in these studies are designed and based on steady state flow conditions. Little data is available regarding the NMPV in unsteady flow conditions. In this study, the performances of NMPV under both steady and unsteady flow conditions are investigated numerically. The NMPV used in this study is a diffuser-type microchannel with diffuser angle of 20° because of its outstanding production of net volume flow. By a series of numerical simulations, some useful results would be addressed for the performance of NMPV micropumps. First, Reynolds number confirmed by steady analysis should be greater than 10 (Re > 10) for the NMPV pumps to be more effective. Second, an optimal Strouhal number with maximum net volume flow rate is found at St = 0.013 for the unsteady flow condition. In addition, the relation between the driving pressure amplitude and net volume flow rate with a linear behavior found was helpful to the performance of the micropump system. According to these findings, it was easy for users to operate and design of NMPV micropumps.

NOVEL EHD-PUMP DRIVEN MICRO MIXERS

Novel electrohydrodynamic (EHD) pump driven micro mixers are fabricated to study fluidic mixing in micro channels experimentally. Microscopic flow visualization experiments are presented to visualize microscale mixing in micro mixers. Mixing is achieved in a laminar flow by perturbing the main flow with EHD pumps in a micro channel. EHD pumps operate in a way to form cross-stream mixing mechanism by using either dc voltage or traveling wave signals. Experimental results show transverse or vortical cross-stream flows are generated within hundreds microns distance in the micro mixers, thereby increasing mixing.

SEPARATING PLASMA AND BLOOD CELLS BY DIELECTROPHORESIS IN MICROFLUIDIC CHIPS

In this paper, a dielectrophoretic (DEP) micro separator is studied for plasma-blood separation. DEP forces created by non-uniform electric fields are used as deflected forces to deplete blood cells from side walls at a given inlet flow rate (Qin). Then one can extract plasma through a microchannel on side wall at certain extraction flow rate (Qp). In this experiment, saline isotonic solution is chosen as dilute solution for whole blood. The minimum dilute ratio (whole blood: saline dilute) is found to be 1:3 for DEP to substantially deplete blood cells from side walls. Exraction of plasma from whole blood sample by DEP force is also investigated. Experimental results show blood cells do not enter side channel by DEP force at inlet flow rate Qin=0.5 μ1/min when plasma extract flow rates is Qp ≤ 0.3 μ1/min. By calculating pure plasma extraction volume fraction, the efficiency in current experiment can reach as high as 20% if dilute ratio 1:3 of whole blood sample is considered.