Browsing by Author "Chen, Ching-Yao"

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A Development of Color-filter-free Electrowetting Color Display by Using Ink Jet Printing Technology
(2010)
Kuo, Shu-Wei
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Lo, Kuo-Long
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Cheng, Wei-Yuan
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Ku, Yun-Sheng
;
Lee, Hsin-Hung
We evaluated the single layer multi-color electrowetting display (EWD) device by using various colored oils without adopting color filter. The color mediums were various colored oil that dosed into sub-pixels by ink jet printing (IJP) technique. In order to improve the color saturation of EWD, the dissolved fluxes had used to increase the solubility of various dyes. The colored saturation could increase about 50%. However, the unstable fluid movement was observed under AC square waveform driving. Therefore, simulation was utilized to analyze the phenomenon of unstable fluid movement. After optimizing the electrode pattern design of the EWD, the improvement of fluid movement was achieved.
A diffuse interface approach to injection-driven flow of different miscibility in heterogeneous porous media
(2015-08-01)
Chen, Ching-Yao
;
Yan, Pei-Yu
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機械工程學系
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Department of Mechanical Engineering
Miscible and immiscible injection flows in heterogeneous porous media, for which the permeability is characterized by a log Gaussian distribution, are simulated by a robust diffuse-interface formulation. The robust numerical method enables direct qualitative and quantitative comparisons regarding pattern formations in various fluid miscibility conditions. For miscible injections, the typical size of fingering structures depends strongly on the correlation length and forms tapered fingers with sharper tips. On the other hand, the typical size of immiscible fingers is affected less significantly by the permeability heterogeneity, and wide spreading tips are retained in the fingering patterns. Prominence of fingering instability is quantitatively evaluated by the channeling width and the interfacial length. The channeling width shows strong and monotonic dependences on the heterogeneous variance. On the contrary, maximum channeling width occurs at intermediate correlation length due to local resonant effect between the faster penetrating fingers and permeability heterogeneity. On the other hand, effects of the correlation length and the permeability variance on the interfacial lengths are generally consistent. Longer interfacial length is perturbed by smaller correlation length or higher variance. Interesting invariant evolutions of interfacial lengths are revealed regardless of the permeability variance in sufficiently large correlation length under all miscibility conditions. In addition, the regime of slower growth of interfacial length at later times experimentally observed in homogeneous miscible injection is verified in heterogeneous porous media as well. (C) 2015 AIP Publishing LLC.
A numerical study on radial Hele-Shaw flow: influence of fluid miscibility and injection scheme
(2015-02-01)
Huang, Yu-Sheng
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Chen, Ching-Yao
;
機械工程學系
;
Department of Mechanical Engineering
Fingering instability triggered by injection of a less viscous fluid in a Hele-Shaw cell is numerically investigated. Simulations are based on a diffuse-interface method, and the formulation, capable of dealing with immiscible and miscible interfaces, is presented in details. Three miscibility conditions, including immiscible with surface tension, partially miscible with effective interfacial tension and fully miscible without interfacial stresses, are simulated to verify generality of an optimal linear injection scheme proposed by Dias et al. (Phys Rev Lett 109:144502, 2012) in the limit of infinite viscosity contrast. stabilizing effects of this linear injection scheme are universally confirmed for the interfaces with the presence of interfacial stresses, such as immiscible and partially miscible conditions. On the other hand, the linear injection scheme in a fully miscible interface leads to contradictory results. Even the fingering pattern appears qualitatively more stable without the secondary phenomenon of finger merging, relevant quantitative measurements, such as longer channeling zone and interfacial length, indicate enhancement of fingering prominence. The inconsistent behaviors suggest that the coupling effects with the interfacial stresses are crucial in the applications of the optimal linear injection scheme.
A numerical study on reaction-induced radial fingering instability
(2019-01-11)
Sharma, Vandita
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Pramanik, Satyajit
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Chen, Ching-Yao
;
Mishra, Manoranjan
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機械工程學系
The dynamics of A + B -> C fronts is analysed numerically in a radial geometry. We are interested to understand miscible fingering instabilities when the simple chemical reaction changes the viscosity of the fluid locally and a non-monotonic viscosity profile with a global maximum or minimum is formed. We consider viscosity-matched reactants A and B generating a product C having different viscosity than the reactants. Depending on the effect of C on the viscosity relative to the reactants, different viscous fingering (VF) patterns are captured which are in good qualitative agreement with the existing radial experiments. We have found that, for a given chemical reaction rate, an unfavourable viscosity contrast is not always sufficient to trigger the instability. For every fixed Peclet number (Pe), these effects of chemical reaction on VF are summarized in the Damkohler number (Da) - the log-mobility ratio (R-c) parameter space that exhibits a stable region separating two unstable regions corresponding to the cases of more and less viscous product. Fixing Pe, we determine Da-dependent critical log-mobility ratios R-c(+) and R-c(-) such that no VF is observable whenever R-c(-) <= R-c <= R-c(+). The effect of geometry is observable on the onset of instability, where we obtain significant differences from existing results in the rectilinear geometry.
An experimental study on Rosensweig instability of a ferrofluid droplet
(2008-05-01)
Chen, Ching-Yao
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Cheng, Z. -Y.
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機械工程學系
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Department of Mechanical Engineering
We experimentally investigate the interfacial morphologies of Rosensweig instability on an extremely thin layer of ferrofluid droplets under a constant perpendicular magnetic field. Striking patterns consisting of numerous subscale droplets that developed from Rosensweig instability are observed. For a dry plate, on which surface tension dominates, the breaking pattern of subscale droplets can be characterized by a dimensionless magnetic Bond number Bo(m). In general, a more pronounced instability, which is evident by a greater number of breaking subscale droplets N, arises with a higher Bo(m). For a magnetic Bond number that is larger than a critical value, we identify a new mode of interfacial breakup pattern, where the central droplet is torn apart with major mass loss. In addition, we found that the volume fractions of breaking subscale droplets are strongly affected by the height variation of the initial fluid surface and appear unevenly distributed with dominance of a central droplet. On the other hand, for a prewetted plate, a nearly flat fluid surface is achieved due to a smaller contact angle, which then leads to virtually evenly distributed subscale droplets. A global size for all breaking subscale droplets is observed regardless of their initial diameters. The number of breaking subscale droplets (N) and the diameter of the initial droplet (D) can be approximated by a quadratic proportionality of N similar to D(2). (C) 2008 American Institute of Physics.
BREAKUPS OF MAGNETIC CHAINS IN AN OSCILLATING FIELD
(2014-01-01)
Li, Yan-Horn
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Bansal, Ekansh
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Chen, Ching-Yao
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機械工程學系
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Department of Mechanical Engineering
This article outlines and illustrates the manipulations and rupture mechanisms of micro magnetic chains by experimental and numerical analysis. A reversible micro-chain consisting of micro-meter superparamagnetic particles is formed under a static directional field and manipulated by an additional dynamical perpendicular field. We demonstrate the chains' different behaviors from rigid body oscillations and bending distortions to rupture failures. By calculating the induced drag and the normal force, which dominate the deformation and ruptures of the chains, we find that the distortions and ruptures occur at the position between the two particles, which sustain significant drag variation with respect to the normal force.
CHARACTERISTICS OF ELECTROMAGNETIC INDUCTION BY MOVING FERROFLUIDS
(2012-07-01)
Chen, Ching-Yao
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Wang, Sheng-Yan
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Wu, Chi-Ming
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Lin, Chung-Hao
;
Huang, Kuo-An
We have demonstrated the capabilities to catch the signals of induced electromotive force (EMF). The characteristics of EMF signals are analyzed systematically. Influences of volumes, sizes and travelling velocities of ferrofluids on the magnitudes and wave spans of the signals are presented. In addition, simulations of the induction fields are carried out to provide the physical insights of the induced EMF signals. The signals can be potentially applied as diagnostic characteristics in the measurements of travelling velocities or sizes of moving ferrofluid drops or slugs.
Control of radial miscible viscous fingering
(2020-02-10)
Sharma, Vandita
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Nand, Sada
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Pramanik, Satyajit
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Chen, Ching-Yao
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Mishra, Manoranjan
We investigate the stability of radial viscous fingering (VF) in miscible fluids. We show that the instability is determined by an interplay between advection and diffusion during the initial stages of flow. Using linear stability analysis and nonlinear simulations, we demonstrate that this competition is a function of the radius r0 of the circular region initially occupied by the less-viscous fluid in the porous medium. For each r0, we further determine the stability in terms of Peclet number (Pe) and log-mobility ratio (M). The Pe-M parameter space is divided into stable and unstable zones: the boundary between the two zones is well approximated by Mc Dff.r0 /Pe 0:55 c. In the unstable zone, the instability is reduced with an increase in r0. Thus, a natural control measure for miscible radial VF in terms of r0 is established. Finally, the results are validated by performing experiments that provide good qualitative agreement with our numerical study. Implications for observations in oil recovery and other fingering instabilities are discussed.
Controlling radial fingering patterns in miscible confined flows
(2010-11-11)
Chen, Ching-Yao
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Huang, C. -W.
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Wang, L. -C.
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Miranda, Jose A.
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機械工程學系
Injection-driven immiscible flow in radial Hele-Shaw cells results in highly ramified patterns if the injection rate is constant in time. Likewise, time-dependent gap immiscible flow in lifting Hele-Shaw cells leads to intricate morphologies if the cell's gap width grows exponentially with time. Recent studies show that the rising of these complex fingered structures can be controlled by properly adjusting the injection rate, and the time-dependent gap width. We investigate the effectiveness of these control strategies assuming that the fluids involved are miscible. Despite the absence of surface tension effects, intensive numerical simulations support the stabilizing role of these controlling protocols. Splitting, merging and competition of fingers are all inhibited. The sensitivity of the system to changes in the initial conditions and Peclet numbers is also discussed.
Controlling radial fingering patterns in miscible confined flows
(2010-11-11)
Chen, Ching-Yao
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Huang, C. -W.
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Wang, L. -C.
;
Miranda, Jose A.
;
機械工程學系
Injection-driven immiscible flow in radial Hele-Shaw cells results in highly ramified patterns if the injection rate is constant in time. Likewise, time-dependent gap immiscible flow in lifting Hele-Shaw cells leads to intricate morphologies if the cell's gap width grows exponentially with time. Recent studies show that the rising of these complex fingered structures can be controlled by properly adjusting the injection rate, and the time-dependent gap width. We investigate the effectiveness of these control strategies assuming that the fluids involved are miscible. Despite the absence of surface tension effects, intensive numerical simulations support the stabilizing role of these controlling protocols. Splitting, merging and competition of fingers are all inhibited. The sensitivity of the system to changes in the initial conditions and Peclet numbers is also discussed.
DESIGN OF MARINE VEHICLE POWERED BY MAGNETOHYDRODYNAMIC THRUSTER
(2020-01-01)
Chan, Cherng-Shyong
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Cheng, Jia-Hong
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Zeng, Cing-Hui
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Huang, Jen-Rung
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Chen, Yu-Hsuan
The present study outlines the design of a magnetohydrodynamic (MHD) thruster system which is capable to power a 3-meter ship model cruising at a speed of V = 0.5 m/s using the Lorentz force generated by the electric field and magnetic field in conducting seawater. Based on the computational fluid dynamics (CFD) simulation of a modified Delft 372 catamaran model, the thrust needed to achieve the targeted cruising speed is first estimated. To achieve the estimated magnitude of the thrust, dimensions of thruster modules are designed based on numerical simulations of magnetic field, for better distributions of the strength and uniformity of the magnetic field. Additional CFD simulations of the flows through the thruster module, coupled with magnetic and electric fields, are conducted to realize the hydrodynamics. Consequently, several configurations of thruster modules are manufactured and experimented. A particular configuration of a shielded two-unit module is chosen to power the ship model. Finally, a complete system of MHD-1 marine vehicle, including a ship model, multiple MHD thruster modules and power suppliers, is assembled and tested. The system is shown capable to cruise closely to the targeted speed.
Diffuse-interface approach to rotating Hele-Shaw flows
(2011-10-05)
Chen, Ching-Yao
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Huang, Yu-Sheng
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Miranda, Jose A.
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機械工程學系
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Department of Mechanical Engineering
When two fluids of different densities move in a rotating Hele-Shaw cell, the interface between them becomes centrifugally unstable and deforms. Depending on the viscosity contrast of the system, distinct types of complex patterns arise at the fluid-fluid boundary. Deformations can also induce the emergence of interfacial singularities and topological changes such as droplet pinch-off and self-intersection. We present numerical simulations based on a diffuse-interface model for this particular two-phase displacement that capture a variety of pattern-forming behaviors. This is implemented by employing a Boussinesq Hele-Shaw-Cahn-Hilliard approach, considering the whole range of possible values for the viscosity contrast, and by including inertial effects due to the Coriolis force. The role played by these two physical contributions on the development of interface singularities is illustrated and discussed.
Dynamics of a microchain of superparamagnetic beads in an oscillating field
(2012-10-01)
Li, Yan-Hom
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Chen, Ching-Yao
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Sheu, Shih-Tsung
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Pai, Jay-Min
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機械工程學系
The dynamics of microchains containing superparamagnetic particles in an oscillating field are studied experimentally. The chains are first formed by a static directional field, and then manipulated by an additional dynamical perpendicular field. The present methodology represents a simple reversible chaining process, whose particles can be re-dispersed after removal of the field. The motion of superparamagnetic chains is dominated by magnetic torque and induced hydrodynamic drag. The effects of key parameters, such as field strengths and the lengths of particle chains, are thoroughly analyzed. Distinct behaviors, from rigid body oscillations and bending distortions to rupture failures, are observed by increasing the amplitudes of oscillating fields or chains' lengths. Because of lower induced drag, a shorter chain follows the field trajectory closely and oscillates more synchronically with the external field. On the other hand, the influences of field strengths are not consistent. Even the overall oscillating phase trajectory in a stronger external field deviates less significantly from the corresponding field trajectory, a stronger dynamical component of the external field results in larger phase angle lags at certain points. The experimental results confirm the criterion of ruptures can be effectively determined by the value of (N*Mn (1/2)), where Mn is the Mason number defined as the ratio of induced drag to dipolar attraction, and N represents the number of particles contained in a chain.
DYNAMICS OF A SUPERPARAMAGNETIC MICROPARTICLE CHAIN IN AN OSCILLATING MAGNETIC FIELD: EFFECTS OF FIELD FREQUENCY
(2017-07-01)
Chen, Ching-Yao
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Lin, He-Ching
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Teng, Che-Jui
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Li, Yan-Hom
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機械工程學系
Dynamics of an oscillating chain consisting of several magnetic microparticles and driven by oscillating magnetic fields with different frequencies are discussed. Because of a shorter driving time by the external field with a higher field frequency, the oscillating amplitude of the chain reduces. On the other hand, the higher field frequency leads to a faster local angular velocity. These two effects result in inconsistent behavior of the structural stability of the chain, so that the chain ruptures in a field of intermediate frequency. A dimensionless parameter of the reduced frequency is proposed to generally describe the monotonic decrease of the normalized amplitude. The phenomenon of trajectory shift triggered by the higher frequency field is also demonstrated.
EFFECT OF SIZE AND STRETCH OF A MOVING FERROFLUID DROP ON INDUCED ELECTROMOTIVE FORCE
(2016-07-09)
Chen, Ching-Yao
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Wang, Sheng-Yan
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Wen, Chih-Yung
;
Jan, Cheng-Shiung
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機械工程學系
Application for obtaining useful global features, e.g. the size and stretch of a moving ferrofluid drop by analyzing the characteristics of the induced electromotive force signal is demonstrated. These features are highly relevant to two maximum magnitudes in the electromotive force signal, e.g., the positive (V-1) and the negative (V-2) peak respectively induced when the drop enters and leaves the region covered by the induction coil. Favorable induction conditions of these two maximum magnitudes are opposite. In general, V-1 increases with the size of the ferrofluid drop because of stronger magnetization. On the contrary, V-2 is more prominent for a smaller drop, whose stretch is less significant. As a result, the ratio of vertical bar V-1/V-2 vertical bar monotonically increases with the, size of the ferrofluid drop. This finding suggests that the induced EMF signal can be used as a useful tool for quantifying the flow conditions, such as the size and stretch of moving ferrofluids.
Enhanced mixing via alternating injection in radial Hele-Shaw flows
(2015-10-07)
Chen, Ching-Yao
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Huang, Yi-Cheng
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Huang, Yu-Sheng
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Miranda, Jose A.
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機械工程學系
Mixing at low Reynolds numbers, especially in the framework of confined flows occurring in Hele-Shaw cells, porous media, and microfluidic devices, has attracted considerable attention lately. Under such circumstances, enhanced mixing is limited due to the lack of turbulence, and absence of sizable inertial effects. Recent studies, performed in rectangular Hele-Shaw cells, have demonstrated that the combined action of viscous fluid fingering and alternating injection can dramatically improve mixing efficiency. In this work, we revisit this important fluid mechanical problem, and analyze it in the context of radial Hele-Shaw flows. The development of radial fingering instabilities under alternating injection conditions is investigated by intensive numerical simulations. We focus on the impact of the relevant physical parameters of the problem (Peclet number Pe, viscosity contrast A, and injection time interval Delta t) on fluid mixing performance.
Experimental and numerical study on the performance of passive heat sink having alternating layout
(2019-06-01)
Chu, Wen-Xiao
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Lin, Yu-Chieh
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Chen, Ching-Yao
;
Wang, Chi-Chuan
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機械工程學系
In this study, a novel passive heat sink with triangular fins having alternating layout to promote heat transfer performance of a passive heat sink is proposed and verified by experimental and numerical examinations. The heat sinks with rectangular fins (case A), triangular fins with right angle, 90 degrees (case B), triangular fins with right angle having alternating layout (case C), triangular fins with obtuse angle of 120 degrees (case D) and triangular fins with obtuse angle of 120 degrees having alternating layout (case E) are tested with vacuum pressure ranging from 400 Pa to atmosphere pressure. It is indicated that the triangular fin having alternating layout offer some benefits like entraining more airflow into the heat sink and a higher effective view factor, thereby showing an appreciable increase of effective heat transfer coefficient (HTC). Results obtained in low vacuum pressure show that the effective HTC of cases B, C, D and E can be improved by 1.5%, 5.5%, 3.0% and 12.1%, respectively as compared to the reference case A. Yet the effective HTC can be improved by 3.2%, 6.1%, 4.6% and 13.0%, respectively in atmosphere pressure. The numerical study is in line with the experimental results and the simulations suggest that the optimum angle of the proposed triangular fins having alternating layout can improve the effective HTC by up to 14.6% and 16.0% with obtuse angles of 150 degrees and 140 degrees when fin area is 2000 mm(2) and 3000 mm(2) , respectively. The benefits of triangular fins having alternating layout show even more superior performance when the heat sink is placed vertically and the effective heat transfer coefficient for triangular fins having alternating layout with 150 degrees is improved by up to 20.3%. (C) 2019 Elsevier Ltd. All rights reserved.
Experimental studies of labyrinthine instabilities of miscible ferrofluids in a Hele-Shaw cell
(2007-08-01)
Wen, C.-Y.
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Chen, Ching-Yao
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Kuan, D.-C.
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機械工程學系
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Department of Mechanical Engineering
The first systematic experimental studies on the labyrinthine instabilities of miscible ferrofluids in a Hele-Shaw cell are presented. Two distinct features of instabilities are observed: (i) the miscible labyrinthine fingers caused by the magnetic dipolar forces; (ii) the secondary waves dominated by the third-dimensional effects. Prominence of the labyrinthine fingers is confirmed to be affected significantly by both the magnetic field strength and the cell gap width. On the other hand, wave selection of the secondary wave numbers is mainly dominated by the gap width. The characteristic wavelength lambda of the secondary waves follows a nearly linear correlation with the gap width h, which is consistent with earlier findings on the viscous fingering instability. The wavelength can be approximated as lambda approximate to(7 +/- 1)h.
EXPERIMENTAL STUDY OF A HYBRID FERROHYDRODYNAMIC INSTABILITY IN MISCIBLE FERROFLUIDS: DROPLET SIZE EFFECTS
(2009-01-01)
Chen, Ching-Yao
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Tsai, W. -K.
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Miranda, Jose A.
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機械工程學系
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Department of Mechanical Engineering
Recently, we have performed a ferrofluid experiment that revealed the existence of a hybrid ferrohydrodynamic situation in which a three-dimensional Collapsing Rosensweig peak and effectively-two-dimensional labyrinthine structures occur simultaneously (C.-Y. Chen et al. Phys. Rev. E., vol. 77 (2008) 056306.) This has been done by immersing a ferrofluid droplet in a thin layer of a miscible nonmagnetic fluid, under the action of a vertically applied magnetic field. We extend the investigation of this new system focusing on the effects produced by ferrofluid droplets of different sizes. It, is found that; larger droplets result in a more promient manifestation of both interfacial instabilities. Moreover, the observations of the labyrinthine fingering patterns are extended into very late stages, where the decaying ferrofluid peak has been completely reimmersed into the surrounding nowmagnetic fluid.
Experiments on breakups of a magnetic fluid drop through a micro-orifice
(2009-10-01)
Chen, Ching-Yao
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Chen, C. -H.
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Lee, W. -F.
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機械工程學系
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Department of Mechanical Engineering
We experimentally study the breakups of a ferro fluid drop passing through an arrow passage under the attraction of an external field. After passing through the orifice, the fluid thread starts to neck down significantly and eventually breaks to form new droplets. The dynamics of the ferro fluid breakup are analyzed parametrically, including the diameter of the orifice and the local field strength. The patterns of fluid breakups can be characterized by two measurements of the breaking droplets, such as their sizes and stretching lengths. These two characteristic measurements mainly depend on the diameter of the orifice. Breaking droplets with less stretching and smaller sizes are resulted from a narrower orifice. On the other hand, the number of total breaking droplets that represents the transport effectiveness of ferro fluids significantly depends on both the diameter of the orifice and the local field strength. While a stronger field generates more breaking droplets, a maximum number of breaking droplets occurs at an intermediate orifice's diameter. (C) 2009 Elsevier B.V. All rights reserved.