Ching-Chang Cho

Nonlinear analysis and control of the uncertain micro-electro-mechanical system by using a fuzzy sliding mode control design

This study analyzes the chaotic behavior of a micromechanical resonator with electrostatic forces on both sides and investigates the control of chaos. A phase portrait, maximum Lyapunov exponent and bifurcation diagram are used to find the chaotic dynamics of this micro-electro-mechanical system (MEMS). To suppress chaotic motion, a robust fuzzy sliding mode controller (FSMC) is designed to turn the chaotic motion into a periodic motion even when the MEMS has system uncertainties.

A NUMERICAL INVESTIGATION INTO ELECTROOSMOTIC FLOW IN MICROCHANNELS WITH COMPLEX WAVY SURFACES

This study investigates the flow characteristics of electroosmotic flow in a microchannel with complex wavy surfaces. A general method of coordinate transformation is used to solve the governing equations describing the electroosmotic flow in the microchannel. Numerical simulations are performed to analyze the effects of wave amplitude on the electrical field, flow streamlines, and flow fields in the microchannel. The simulation results show that, compared to a traditional pressure-driven flow, flow recirculation is not developed in the electroosmotic flow in a microchannel with complex wavy surfaces. The simulations also show that the electrical field and velocity profiles change along the channel in the region of wavy surfaces. Non-flat velocity profiles are observed in different cross-sections of the channel in the region of wavy surfaces.

Enhancement of microfluidic mixing using harmonic and chaotic electric fields

A novel microfluidic mixing approach is brought up in this study—the streams of species are mixed by applying harmonic or chaotic electric fields to four electrodes in the mixing chamber. For analyzing the effects of the harmonic and chaotic electric fields on the fluid flow characteristics in the microfluidic mixer, as well as evaluating the corresponding mixing performance, several numerical simulations are performed in the pursuit of the two experimental goals mentioned. In the simulation, harmonic and chaotic oscillations in the electric field are modeled by the well-known Duffing equation. Simulation results show that periodic and aperiodic perturbation effects occur within the mixing chamber when harmonic and chaotic electric fields are applied to the electrodes, respectively. These periodic and aperiodic perturbations produce strong perturbation effects, which efficiently mix species.

Numerical Investigation into Natural Convection and Entropy Generation in a Nanofluid-Filled U-Shaped Cavity

This current work studies the heat transfer performance and entropy generation of natural convection in a nanofluid-filled U-shaped cavity. The flow behavior and heat transfer performance in the cavity are governed using the continuity equation, momentum equations, energy equation and Boussinesq approximation, and are solved numerically using the finite-volume method and SIMPLE C algorithm. The simulations examine the effects of the nanoparticle volume fraction, Rayleigh number and the geometry parameters of the U-shaped cavity on the mean Nusselt number and total entropy generation. It shows that the mean Nusselt number increases and the total entropy generation reduces as the volume fraction of nanoparticles increases. In addition, the results show that the mean Nusselt number and the total entropy generation are both increased as the Rayleigh number increases. Finally, it also shows that mean Nusselt number can be increased and the total entropy generation can be reduced by extending the length of the low temperature walls or widening the width of the low temperature walls.

Enhancement of natural convection heat transfer in a U-shaped cavity filled with Al2O3-water nanofluid

This paper investigates the natural convection heat transfer enhancement of Al2O3-water nanofluid in a U-shaped cavity. In performing the analysis, the governing equations are modeled using the Boussinesq approximation and are solved numerically using the finite-volume numerical method. The study examines the effects of the nanoparticle volume fraction, the Rayleigh number and the geometry parameters on the mean Nusselt number. The results show that for all values of the Rayleigh number, the mean Nusselt number increases as the volume fraction of nanoparticles increases. In addition, it is shown that for a given length of the heated wall, extending the length of the cooled wall can improve the heat transfer performance.

NUMERICAL INVESTIGATION INTO NATURAL CONVECTION HEAT TRANSFER ENHANCEMENT OF COPPER-WATER NANOFLUID IN A WAVY WALL ENCLOSURE

Numerical investigations are performed into the natural convection heat transfer characteristics within a wavy-wall enclosure filled with Cu-water nanofluid. In the paper, the bottom wall of the enclosure has a wavy geometry and is maintained at a constant high temperature, while the top wall is straight and is maintained at a constant low temperature. The left and right walls of the enclosure are both straight and insulated. In performing the simulation, the Boussinesq approximation is used to model the governing equations. The study examines the effect of the nanoparticle volume fraction, the Rayleigh number, the wave amplitude, and the wavelength on the heat transfer characteristics. It is shown that the heat transfer performance can be enhanced as the volume fraction of nanoparticles increases. It is also shown that for a given Rayleigh number, the heat transfer effect can be optimized via an appropriate changing of the geometry conditions.

Mixing of electrokinetically-driven power-law fluids in zigzag microchannels

Purpose – The purpose of this paper is to study the mixing performance of the electrokinetically-driven power-law fluids in a zigzag microchannel. Design/methodology/approach – The Poisson-Boltzmann equation, the Laplace equation, the modified Cauchy momentum equation, and the convection-diffusion equation are solved to describe the flow characteristics and mixing performance of power-law fluids in the zigzag microchannel. A body-fitted grid system and a generalized coordinate transformation method are used to model the grid system and transform the governing equations, respectively. The transformed governing equations are solved numerically using the finite-volume method. Findings – The mixing efficiency of dilatant fluids is higher than that of pseudoplastic fluids. In addition, the mixing efficiency can be improved by increasing the width of the zigzag blocks or extending the total length of the zigzag block region. Originality/value – The results presented in this study provide a useful insight into p...

Numerical simulation of an electrokinetic micromixer using harmonic and chaotic electric fields

The study presents a novel microfluidic mixing scheme in which the fluid streams are mixed via the applications of harmonic and chaotic electric potentials to four electrodes mounted on the upper and lower surfaces of the mixing chamber. Numerical simulations are performed to analyze the effects of the resulting harmonic oscillating and chaotic oscillating electrokinetic perturbation forces. The harmonic and chaotic oscillating orbits are derived by using non-linear Duffing-Holmes equation. Simulation results indicate that periodic or aperiodic oscillations between the electrodes are obtained to perturb the fluid streams by using harmonic or chaotic oscillating electric potentials to these electrodes, respectively. The results revel that the fluid mixing are improved in the suggested micromixer.