Jik Chang Leong

Analysis of Fluid Film Lubrication of an MHD Journal Bearing Subjected to an Axially Applied External Magnetic Field

This work simulates the steady-state flow field in a magnetohydrodynamic journal bearing. A uniform magnetic field is applied in the axial direction across the bearing. Current results indicate that a crescent-shape secondary flow will develop at E = 0.8. The velocity profiles at the location of the minimum and maximum film thickness are almost independent of the strength of the external magnetic field unless the eccentricity ratio is relatively small and magnetic field is strong. There exists an eccentric dependent threshold Ha beyond which the shear stress on the journal increases with Ha while that on the bearing decreases.

Finite Element Simulations of Thermal Affected Zone during Bone Drilling

In this study, an elastic-plastic finite element model is used to simulate the thermal affected bone (TAZ) during bone drilling process under the condition of constant applied drilling force. Various drilling times and measurement depths are investigated to explore the size of TAZ and stress distributions within the bone. The results indicate that the maximum TAZ occurs at the interface of cortical bone and cancellous bone. The maximum diameter of TAZ is found to be 3.5 mm in this study.

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.

MHD Couette Flow in Cylindrical Porous Annulus with Perfectly Conducting Walls

This work obtained an analytical solution for a steady cylindrical MHD Couette flow in a porous medium between two perfectly conducting rotating cylinders under the influence of a non-uniform radial magnetic field. Since part of the analytical solution is expressed in terms of the integral of the Modified Bessel function of the first and second kinds of variable order, numerical integration was performed. Current results indicate that the flow may become more uniform when the strength of the external magnetic field is increased. The magnetic fluid tends to slow down if the permeability of the porous medium decreases. If the porous annulus is thick, the momentum of the flow is more difficult to propagate from the outer cylinder into the inner part of the annulus. If both the inner and outer cylinders rotate, the shear effect the inner cylinder imposes is only relatively influential in the region close to it. A decrease in Da no less than 10-2 may increase the amount of magnetic field induced. The transfer of momentum across the annular space is easier in a thin porous annulus than a thick one and hence induces a stronger magnetic field. If the inner cylinder rotates in the direction opposite of the outer one, the magnetic field in the clockwise direction will be induced in some region.

HCPV Module Temperature Prediction: A Case Study Based on Measurements at NPUST

The subject of study in this work is a 135 Wp high concentration photovoltaic module with III-V solar cells. The module is currently installed in NPUST. Three equation forms for module temperature prediction were investigated. The simplest form predicts the module temperature quite well. Among these forms, the third form which takes into account the direct normal radiation yields the least error. The efficiency of the module was about 21% between 10:00 a.m. and 3:00 p.m. and the amount of power the module generates was linearly dependent on the electricity current.

Smoke Propagation in an Inclined Semi-Circular Long Tunnel

This work used FDS to simulate tunnel fires occur in a semi-circular longitudinally ventilated tunnel. By varying the parameters such as the tunnel gradient, the fire size, and the ventilation velocity, their influence on the backlayering effect and downstream propagation rate can be recognized. Under weak ventilation, the backlayering effect either advances or vanishes depending on the slope of the tunnel. Under stronger ventilation, the backlayering effect would break up. The temperature distributions may become less and less dependent on the tunnel gradient when the ventilation velocity is increased. Although the hot gases and smoke in uphill tunnels propagate faster than those in downhill tunnels, their difference reduces with ventilation velocity.

Rapid Microfluidc Biochips Fabrication by Femtosecond Laser on Glass Substrate

This paper uses a femtosecond laser scriber to perform the direct-writing ablation of glass substrate for the development of microfluidic biochips. The surface quality of the ablated microchannels was examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurement techniques. The developed femtosecond laser ablation system provides a versatile and economic approach for the fabrication of glass-base microfluidic chips. In the laser writing process, the desired microfluidic patterns are designed using commercial computer software and are then transferred to the laser scriber to ablate the trenches. The results show that a very smooth channel wall can be achieved through the annealing process at the temperature 650°C and 5 hours. The system provides an economic and powerful means of rapid glass microfluidic biochips development.

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.