bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital Reconstruction at Femtosecond Laser-Induced Dynamic Surface Changes
Authors: Zhu Linwei , Zhou Changhe , Wu Tengfei , Jia Wei
Published: October 2010

We present the pump-probe technique and the off-axis digital holography to monitor light-induced dynamic changes in the Cr film on the glass. Femtosecond pulses from a Ti:sapphire laser oscillator were split into pump pulses and probe pulses. The pump pulses were used for inducing the phase change of the Cr film and the probe pulses were used for probing it in a Mach-Zehnder interferometer. The sample was placing in one arm of the interferometer. A delay line was used for changing the probe pulses. By changing the delay line of the probe pulses, the probe pulses were measured at different time delays between the pump and the probe pulses. A dynamic interference holography produced by the probe beam passing through the sample is then captured by a CCD camera. A reconstruction algorithm was used to obtain the sample time evolution of both amplitude and phase-contrast images. Using this setup, we study the dynamic surface deformation in a thin Cr film. Experimental results are given to show that the amplitude and phase-contrast images are well reconstructed. This technique can be used as a characterization tool to precisely monitor dynamic changes induced by femtosecond laser pulses.
Heat and Mass Transfer of a Rarefied Gas in a Driven Micro-Cavity
Authors: Gu X. J. , John B. , Tang G. H. , Emerson D. R.
Published: October 2010

A high-order moment method is employed to construct the transport model for non-equilibrium gas flow in micro-scale geometries. The motion of a gas in a two-dimensional square micro-cavity is solved using the 26 moment equations for low Reynolds and Mach number flows in the early transition regime. The computed velocity and temperature fields are compared with data obtained from the direct simulation Monte Carlo method. It is found that the 26 moment equations are able to capture the non-equilibrium phenomena in a driven micro-cavity, such as counter-gradient heat transfer, which are not embedded in the Navier-Stokes-Fourier equations.
Approach to Heat Transfer Mechanism Beneath Boiling Bubble With MEMS Sensor
Authors: Yabuki Tomohide , Nakabeppu Osamu
Published: October 2010

Temperature variation beneath isolated bubble during saturated boiling of water was measured with a MEMS (Micro-Electro-Mechanical Systems) sensor having high temporal and spatial resolution. Then, local heat transfer from the heated surface was evaluated by a transient heat conduction analysis of the wall with measured temperature data as a boundary condition. The MEMS sensor on a 20 × 20 mm2 silicon substrate includes an electrolysis trigger and eight thin film thermocouples on the top side, and two thin film heaters on the back side. The thin film thermocouple was calibrated with a thermal scan method using two alloy samples with different melting point. The condition of the sensor was smoothly controlled with the heater. The bubble is initiated with electrolysis at a gap of the trigger electrode, where slight hydrogen gasses are supplied as bubble nuclei. Then, local and fast temperature variations in wide region are measured with the thermocouples with cutoff frequency of 100 kHz arranged in a line at 40 – 2000 μm far from the trigger gap. Measured temperature data presents formation of microlayer and expansion of dryout area in bubble growth process and rewetting in bubble departure process. The numerical analysis showed that average heat flux beneath the bubble indicated the maximum value of 19 W/cm2 during the microlayer evaporation, and then after hitting a bottom slightly lower than a heat flux at the bubble nucleation, recovers to the nucleation level. The contribution of the heat transfer from the heated wall was evaluated to approximately one-fourth of latent heat in the bubble at departure.
Anisotropic Thermal Transport in Magnetic Fluids
Authors: Fang Xiaopeng , Xuan Yimin , Li Qiang
Published: October 2010

The inhomogeneous morphology of magnetic fluid may appear in the presence of an external magnetic field, which shows the structure controllability of magnetic fluid and will lead to anisotropic thermal transport inside the magnetic fluid. Based on the microstructure of magnetic fluid and considering the effect of nanolayer, a model for the thermal conductivity of the magnetic fluid has been developed. The anisotropic thermal transport inside the magnetic fluid is investigated by the present method. The results show that in the presence of an external magnetic field the particles form chainlike clusters along the magnetic field direction, which leads to an increment in the thermal conductivity along the field direction and little change in the thermal conductivity perpendicular to the magnetic field direction. The thermal conductivity of magnetic fluid presents an anisotropic feature. With the increase of the magnetic field strength the chainlike clusters in the magnetic fluid becomes more obvious and the anisotropic feature of heat conduction in the fluids becomes more evident. Comparisons show that the results predicted by the present method are well coincident with the experimental data.
The Surface-Relief Grating Produced by Interference of Femtosecond Laser
Authors: Wu Tengfei , Zhou Changhe , Zhu Linwei , Xie Jin
Published: October 2010

Since the generation of the femtosecond laser, the interaction between femtosecond pulsed laser and metal films has been extensively investigated. There are many peculiar merits of the femtosecond pulsed laser, such as precise control of micromachining sizes and minimized thermal damage to the surroundings. As we all know, a surface-relief grating can be widely applied in holographic data storage, optical communication, optical information processing and optoelectronic industry. Because the absorption coefficient of the silica glass is very low and the small nanojoule fluence of femtosecond Ti:sapphire laser oscillator, it’s difficult to micromachine the surface-relief grating on the silica glass by femtosecond Ti:sapphire laser oscillator. However, in this paper we made the surface-relief grating on the silica glass by using the intereference technique of femtosecond laser with the silica glass coated a chromium films. The optical absorption coefficient of the chromium films is much higher than that of the silica glass. So the heat energy absorbed by the chromium films should be the energy source for inducing the surface-relief grating on silica glass. Experimental results shown that this micromachining technology is simple and effective. It is helpful for us to understand the mechanism of the interaction between the femtosecond laser and chromium films.
Experimental Study of Condensation Inside a Horizontal Single Square Minichannel
Authors: Matkovic Marko , Bortolin Stefano , Cavallini Alberto , Del Col Davide
Published: October 2010

This work is aimed at presenting experimental heat transfer coefficients measured during condensation inside a single square cross section minichannel, having a 1.18 mm side length. The experimental heat transfer coefficients are compared to the ones previously obtained in a circular minitube. This subject is particularly interesting since most of the mini and microchannels used in practical applications have non circular cross sections. The test section used in the present work is obtained from a thick wall copper tube which is machined to draw a complex passage for the water; its geometry has been studied with the aim of increasing the external heat transfer area and thus decreasing the external heat transfer resistance. This experimental technique allows to measure directly the temperature in the tube wall and in the water channel. The heat flux is determined from the temperature profile of the coolant in the measuring sector. The wall temperature is measured by means of thermocouples embedded in the copper tube, while the saturation temperature is obtained from the saturation pressure measured at the inlet and outlet of the measuring sector. On the whole, more than seventy thermocouples have been placed in the 23 cm long measuring section. Tests have been performed with R134a at 40°C saturation temperature, at mass velocities ranging between 200 and 800 kg m−2s−1. As compared to the heat transfer coefficients measured in a circular minichannel, in the square minichannel the authors find a heat transfer enhancement at the lowest values of mass velocity; this must be due to the effect of the surface tension. No heat transfer coefficient increase has been found at the highest values of the mass velocity where condensation is shear stress dominated.
Analytical Study, 1-D Optimization Modeling, and Testing of Electrode Supported Solid Oxide Electrolysis Cells
Authors: Milobar Daniel G. , Li Peiwen , O’Brien James E.
Published: October 2010

The need for an infrastructure to provide hydrogen as a next generation energy carrier is ever increasing. High temperature solid oxide electrolysis cells (SOECs) have been proven to be a viable technology in the production of hydrogen [1]. With the increasing use of SOECs in various operating environments it is important to be able to specify the best SOEC for any given situation. We have developed a straightforward model to estimate cell performance in a timely and inexpensive manner. Composite electrode planer type SOEC models have been developed previously. It is a common assumption that all electrochemical reactions in these cells occur at the interface of the electrolyte and the electrode [2]. It has been shown by S. Gewies et al. [3] that the reactions occurring throughout a Ni/YSZ cermet electrode occur in a nonlinear fashion. Our one dimensional model has been developed to optimize SOECs with composite electrodes. This model takes into account ohmic, activation, and concentration polarizations. The electrochemical reaction that occurs within the electrode functional layers has been accounted for in the calculation of the concentration polarization. This is believed to give a more realistic view of the mass transfer that occurs in SOECs with composite electrodes via a simple and straightforward 1-D model.
Effects of Structural Topography on Nanofluids Droplet Evaporation on Multifarious Superhydrophobic Surfaces
Authors: Xu Wei , Choi Chang-Hwan
Published: October 2010

In this paper, we experimentally studied the evaporation kinetics and wetting dynamics of nanofluid sessile droplets on microstructured superhydrophobic surfaces of a constant air fraction but different structural topographies including arrays of pillars, lines, and wells. The dissimilar superhydrophobic surface patterns were fabricated on a silicon substrate by photolithography and deep reactive ion etching (DRIE) followed by Teflon coating. The 0.01wt% suspensions of gold (Au) nanoparticles of 250 nm in diameter were tested as nanofluids. The change of contact angle, base diameter, height, volume, and evaporation rate of the evaporating nanofluid droplet was measured in a room condition by using a goniometer. The results show that the change of structural topographies, despite the same air fraction on the surface, make significant difference in the droplet profile evolution during sequential evaporation phases. Compared to pure water tested as control, the distinctive influence of nanoparticles was especially observed in the final pinning phase with the tested nanofluid condition. This paper demonstrates that the evaporation kinetics and wetting dynamics of liquid droplets are significantly affected by the structural topography and the presences of nanoparticulates, which should be considered in the design and applications of superhydrophobic surfaces for droplet-based heat and mass transfer systems.
Quantitative DNA Hybridization Assay on a Multiplexed Surface Microfluidic Device
Authors: Prakash Ravi , Chugh Dipankar , Kaler Karan V. I. S.
Published: October 2010

A Dielectrophoresis (DEP) based Surface Microfluidic (SMF) device has been successfully configured to facilitate multiplexed DNA hybridization assay. In this paper, we have demonstrated the utility of a 2×2 multiplexed DEP based droplet dispensing and conveyance schemes to manipulate sub-nanoliter DNA sample droplets and facilitate high throughput applications. To quantify and study various aspects of the multiplexed DNA hybridization assay, a photo multiplier tube (PMT) was utilized to optically monitor the individual droplets. Applications of the proposed assay scheme are envisioned in generalization towards an MxN matrix which can conduct numerous biochemical assays in a parallel, automated fashion, consuming minimal quantities of chemical and biochemical reagents and providing means for reliable and low cost bio-diagnostics.
Molecular Dynamics Simulation of the Thermal Conductivity of Ar-Al Nanofluid Using Simplified Model
Authors: Liu Jie , Lu Wen-Qiang
Published: October 2010

Nanofluid is a colloidal solution of nano-sized solid particles in liquids. Ar-Al nanofluid is a promising heat transport fluid in the fields of low-temperature engineering. A simplified model based on the equilibrium molecular dynamics (EMD) simulation is constructed to calculate the thermal conductivity of argon suspension containing aluminum nanoparticles. The numerical method is verified by comparing the numerical results with the existing numerical results and the experimental data of the base fluid. The influence of various nanoparticle loadings is obtained and the results show that the thermal conductivity with 1% nanoparticle loading enhances up to 31% compared with the base fluid. The heat current autocorrelation functions converge well for the basefluid and nanofluid. Furthermore, interesting distinct oscillations are obtained especially at higher nanoparticle loading. The significant role of the interaction between the fluid atoms and the solid nanoparticle rather than Brownian dynamics motion of the nanoparticle in yielding the high thermal conductivity of nanofluid is numerically revealed.
Non-Fourier Heat Transport in Microscale and Nanoscale Gas Flows
Authors: Myong R. S.
Published: October 2010

It is known that heat transport in microscale and nanoscale gas flows may deviate from the classical law of Fourier. A more sophisticated model may be needed to describe the gaseous and thermal transport in these cases. In this work, computationally efficient nonlinear coupled constitutive relations are presented and their properties in states removed far from thermal nonequilibrium are examined. In order to validate the new model, the force-driven Poiseuille gas flow in microchannel is considered. The emphasis will be placed on how coupled and nonlinear relationship affects the prediction of gas flow and heat transfer in microsystem.
DSMC for Phonon Transport in Solid Thin Films
Authors: Matsumoto Mitsuhiro , Okano Masaya
Published: October 2010

As the scale of electronic devices decreases, heat transfer analysis and thermal design becomes more important. In particular, heat transfer through various solid thin films is strongly affected by thickness dependence of thermal conductivity and interfacial thermal resistance. Analysis of phonon dynamics based on a linearized Boltzmann transport equation, or the so-called relaxation time approximation, has been widely used, but detailed analysis using molecular dynamics simulation reveals that couplings among various phonon modes can affect the energy transfer. In this study, we propose a DSMC scheme to simulate phonon dynamics starting from the original Boltzmann transport equation. In contrast to the linearized model, this scheme requires no relaxation time as an input parameter, and we can investigate the couplings among phonons with different modes, although we have to assume some appropriate model of phonon-phonon collisions. As a test calculation, energy flux was evaluated for model thin films of various thicknesses, and a phenomenon similar to the Casimir limit was retrieved. This scheme will enable us to include other factors, such as phonon-electron couplings.
Development of an Efficient Particle Approach for Micro-Scale Gas Flow Simulations
Authors: Sun Quanhua , Li Feng , Fan Jing , Cai Chunpei
Published: October 2010

The micro-scale gas flows are usually low-speed flows and exhibit rarefied gas effects. It is challenging to simulate these flows because traditional CFD method is unable to capture the rarefied gas effects and the direct simulation Monte Carlo (DSMC) method is very inefficient for low-speed flows. In this study we combine two techniques to improve the efficiency of the DSMC method. The information preservation technique is used to reduce the statistical noise and the cell-size relaxed technique is employed to increase the effective cell size. The new cell-size relaxed IP method is found capable of simulating micro-scale gas flows as shown by the 2D lid-driven cavity flows.
On-Chip Particle Differentiation Utilizing Forward Scattered Light and Fluorescence Light With Passive Focusing
Authors: Wang Yao-Nan , Leong Jik Chang , Chang Chin-Lung , Tai Chang-Hsien , Tsai Chien-Hsiung , Fu Lung-Ming , Miao Jr-Ming
Published: October 2010

In this paper, a microflow cytometer for particles/cells passive focusing, fluorescence detection, and sizing is demonstrated with a convergent geometry of 50 μm detection gate channel and a pair of external optic fibers on poly-dimethylsiloxane (PDMS) microchip. A laser (635 nm) is used for fluorescent excitation. The amplitudes of the backward fluorescence signal and forward scattered light signal indicate the corresponding fluorescent intensity and size of the detected fluorescent particles and labeled white blood cells, respectively. In the experiment, the uniform fluorescent light intensity was measured by focusing the fluorescent particles in a 200×50×30μm detection gate channel. However, the emitted fluorescence and forward scattered light intensity of different size particles/cells are also measured simultaneously by external optic fibers.
On Nano Particles Traveling Into Nanochannel From a Micro Flow Field
Authors: Su Chih-Wei , Tseng Fan-gang
Published: October 2010

In this paper, we have (1) built a micro flow network that mimics micro vessels and visualized the flow inside utilizing both experimental and CFD approaches, (2) developed a model, which considering both the inertial forces caused by flow convection and the diffusion resulting from Brownian motion, to evaluate the entrapment probability of nanoparticles with various particle sizes and channel geometries from micro flow field into nanochannels. In the experimental results, the spatial resolution of about 2 μm is employed to resolve the near-wall flow field with 50% interrogation spot overlapping by using μPIV. The most significant deviation is about 5% between the experimental and simulation results. Finally we used Stokes-Einstein equation to estimate the entrapment probability of nanoparticles with various particle sizes and channel geometries.
Scale Effects and Slip Microflow Characteristics of Evaporating Thin Films in a Microchannel
Authors: Zhao J. J. , Peng X. F. , Duan Y. Y.
Published: October 2010

Micro flow, phase change and heat transfer characteristics of an evaporating thin film in a microchannel was investigated using an augmented Young-Laplace model and the kinetic theory for transverse flow in a solid-liquid-vapor triple contact line region. A model considering both wall slip and wall temperature jump was developed to explore scale effects of channel width. The results show that the average heat transfer coefficient and Reynolds number in thin film regions decrease with decreasing channel width, indicating worse flow and heat transfer characteristics. The scale effects are caused by increased far-field liquid film curvature and film thickness and consequently lower liquid superheat and lower evaporation pumping capability. Original models describing wall-affected ordered adsorbed flowing liquid microlayer and variable slip coefficient were established to give the solid-liquid interfacial resistance and wall temperature jump. Microflow and microlayer near a wall increase wall thermal resistance and thus leads to worse film spreading and heat transfer characteristics, which are significant in thin film regions. The microflow model with variable slip coefficient is logical, more reasonable in results and better than the microflow model with constant slip coefficient.
Transient Thermo-Reflectance Method for Characterization of Thermal Interface Material Based on Carbon Nanotube Array
Authors: Zhao Yang , Chu Rong-Shiuan , Majumdar Arun
Published: October 2010

Vertically aligned carbon nanotube (CNT) arrays have been explored as advanced thermal interface materials because of their compliance and high cross-plane thermal conductivity. Our previous work showed that a CNT array directly bridging two surfaces by dry contact had a surface-surface interface resistance of order of 10 m2-K/MW. With an indium bonding layer, the interface thermal resistance was reduced by a factor of ten. Therefore, a more sensitive measuring system is needed to accurately determine the thermal resistance. In this paper, we achieved a higher sensitivity measurement by applying the phase sensitive transient thermo-reflectance technique to a front side heating and detecting system. A detailed analysis is presented. We used this technique to characterize a 71-μm long CNT array with packing density of 9.4 ± 1.4%. The CNT array was sequentially wetted with chromium/gold films and was bonded to a glass surface with an indium bonding layer. We found that the CNT array-surface interface resistance is 0.35 ± 0.11 m2-K/MW and the cross-plane thermal conductivity of CNT array is 94 ± 40 W/m-K.
Concentration of Samples in Microfluidic Structure Using Joule Heating Effects
Authors: Ge Zhengwei , Yang Chun
Published: October 2010

Microfluidic concentration is achieved using temperature gradient focusing (TGF) in a microchannel with a step change in cross-section. A mathematical model is developed to describe the complex TGF processes. The proposed mathematical model includes a set of governing equations for the applied electric potential, electroosmotic flow field, Joule heating induced temperature field, and sample analyte concentration distributions as well. Scaling analysis was conducted to estimate time scales so as to simplify the mathematical model. Numerical computations were performed to obtain the temperature, velocity and sample concentration distributions. Experiments were carried out to study the effects of applied voltage, buffer concentration, and channel size on sample concentration in the TGF processes. These effects were analyzed and summarized using a dimensionless Joule number that was introduced in this study. In addition, Joule number effect in the PDMS/PDMS microdevice was compared with the PDMS/Glass microdevice. A more than 450-fold concentration enhancement was obtained within 75 seconds in the PDMS/PDMS microdevice. Overall, the numerical simulations were found in a reasonable agreement with the experimental results.
Pool Boiling CHF Enhancement on a Zircaloy-4 Surface With Micro/Nano Scale Modification
Authors: Ahn Ho Seon , Lee Chan , Kim Hyungdae , Jo Hang Jin , Kang Soon Ho , Kim Joonwon , Kim Moo Hwan
Published: October 2010

The need to operate thermal systems, including those in nuclear power plants, below the critical heat flux (CHF) requires inconvenient compromises between economy and safety. This has led to much research aimed at enhancing the CHF. CHF enhancement was recently noticed in nanofluids where the heating surface was fouled by nanoparticles. We attempted to imitate the micro/nano multi-scale structure of nanoparticle fouling by surface modification. In this study, surface treatment was used to change the surface wettability of a Zircaloy-4 heater. A pool boiling apparatus was developed based on the results of the surface treatment, and an experimental study was performed to investigate the increase in CHF.
Hydrodynamic Study of an Oscillating Meniscus in a Square Mini-Channel
Authors: Shekhawat Yajuvendra Singh , Khandekar Sameer , Panigrahi Pradipta Kumar
Published: October 2010

Miniaturized fluidic systems like MEMS may involve single-phase or multi-phase flows with oscillations/ pulsations. Understanding the hydrodynamics of such flows can help in manipulating the performance parameters and improving the efficiency of micro-systems. This work focuses on hydrodynamics of a sinusoidally oscillating meniscus in a square mini-channel. The interfacial contact line behavior of a single oscillating meniscus formed between liquid slug and air, inside the square capillary tube, has been explored. An eccentric cam follower system has been fabricated to provide sinusoidal oscillations of fluid in the square glass capillary having hydraulic diameter of 2.0 mm. Experiments are conducted with two fluids, water and silicon oil. Dynamic contact angle measurements are carried out for water at two oscillating frequencies, 0.25 Hz and 0.50 Hz using high speed videography. It is seen that an increase in the oscillating frequency increases the difference in the advancing angle and receding angle of the meniscus, with the static contact angle of water on glass surface around 21°. For silicon oil the experiments have been performed at eight different frequencies in the range of 0.20 Hz and 1.00 Hz. It is seen that the meniscus is pinned at the extreme end of the stroke, unlike that in the case of water, and there is a film of silicon oil during oscillations. The thickness of the film formed increases with increase in oscillating frequency. There is considerable difference in the hydrodynamics of silicon oil and water.
Catastrophe Optics Method to Determine the Micro-Nano Size Profiles at TPL of Liquid Films on a Solid Surface
Authors: Chao David F. , McQuillen J. B. , Sankovic J. M. , Zhang Nengli
Published: October 2010

As discovered by recent studies, the wetting and spreading is directly affected by the curvature in the micro-region rather than the macroscopic contact angle. Consequently, measuring the liquid profile in the micro-region becomes an important research topic. Recently, catastrophe optics has been applied to these measurements. Optical catastrophe occurring in far field of waves of liquid-refracted laser beam yields a wealth of information about the liquid spreading not only for liquid drops but also for films. When a parallel laser beam passes through a liquid film on a slide glass at the three-phase-line (TPL), very interesting optical image patterns occur on a screen far from the film. An analysis based on catastrophe optics discloses and interprets the formation of these optical image patterns. The analysis reveals that the caustic line manifested as the bright-thick line on the screen implies the lowest hierarchy of optical catastrophes, called fold caustic. This optical catastrophe is produced by the inflexion line on the liquid surface at the liquid foot, which is formed not only in the spreading of drops but also in spreading of films. The generalized catastrophe optics method enables the identification of the edge profiles and determine the edge foot height of liquid films.
Thermal Resistance of Semiconductor Thin Films Predicted From Lattice Dynamics Calculations and Molecular Dynamics Simulations
Authors: Landry E. S. , McGaughey A. J. H.
Published: October 2010

Semiconductor thin films are pervasive in advanced technological devices. For example, the active region in a quantum cascade laser contains films of direct bandgap semiconductors with thicknesses of 1–10 nm [1]. Superlattices, periodic materials that contain films of alternating species with thicknesses as small as 1 nm, are being studied for their potential to increase the efficiency of thermoelectric energy conversion devices [2]. Because these film thicknesses are less than the mean free paths of the phonons in the corresponding bulk material, the thermal transport properties of semiconductor thin films are different than their corresponding bulk values [3]. To aid in the design of devices employing thin films, accurate models for the thermal transport properties of the film are required.
Laser-Induced Breakdown Spectroscopy Combined With Spatial Confinement of Plasmas and Laser-Induced Fluoresence for Trace-Materials Detection
Authors: Lu Y. F. , Shen X. K. , Ling H.
Published: October 2010

Laser-induced breakdown spectroscopy (LIBS) with spatial confinement effects and LIBS combined with laser-induced fluorescence (LIBS-LIF) have been investigated to improve the detection sensitivity and element-selectivity of LIBS. An obvious enhancement in the emission intensity of aluminum (Al) atomic lines was observed when a cylindrical wall was placed to spatially confine the plasma plumes. The maximum enhance factor for the emission intensity of Al atomic lines was measured to be around 10. Assuming local thermodynamic equilibrium conditions, the plasma temperatures are estimated to be in a range from 4,000 to 5,800 K. It shows that the plasma temperature increased by around 1,000 K when the cylindrical confinement was applied. Fast images of the laser-induced Al plasmas show that the plasmas were compressed into a smaller volume with a pipe presented. LIBS-LIF has been investigated to overcome the matrix effects of LIBS for the detection of trace uranium (U) in solids. An optical parametric oscillator wavelength-tunable laser was used to resonantly excite the uranium atoms and ions within the plasma plumes generated by a Q-switched Nd:YAG laser. Both atomic and ionic lines can be selected to detect their fluorescence lines. A U concentration of 462 ppm in a glass sample can be detected using this technique at an excitation wavelength of 385.96 nm for resonant excitation of U II and a fluorescence line wavelength of 409.01 nm from U II. The mechanism of spatial confinement effects and the influence of relevant operational parameters of LIBS-LIF are discussed. In this work, detection in open air of trace phosphorus (P) in steels using LIBS-LIF has also been investigated. The optical parametric oscillator laser was used to resonantly excite the P atoms within plasma plumes generated by the Q-switched Nd:YAG laser. A set of steel samples with P concentrations from 3.9 to 720 ppm were analyzed using LIBS-LIF at wavelengths of 253.40 and 253.56 nm for resonant excitation of P atoms and fluorescence lines at wavelengths of 213.55 and 213.62 nm. The calibration curves were measured to determine the limit of detection for P in steels, which is estimated to be around 0.7 ppm.
System-Level Modeling of Surface-Immobilized Biomolecular Concentration Gradient Generation
Authors: Wang Yi , Pant Kapil
Published: October 2010

This paper presents a system-level modeling methodology for microfluidic surface-immobilized biomolecular concentration gradient generators (CGGs). The generator is broken down into a system of elemental microfluidic components with relatively simple geometries and functionality. Parameterized models for such components are developed, which hold for general biomolecular concentration profiles and arbitrary flow ratios at the component interface; hence, they are valid for a broad category of CGGs that rely on various operating mechanisms. The component models are then linked through an appropriate set of parameters at the interfaces to construct a system-level, network representation of the entire generator for simulation. The system model is extensively verified against experimental data reported in the literature. The model results are found to be in excellent agreement, and can be applied to accurately capture the overall effects of network geometry, biomolecular properties, operating parameters (e.g., flow rates and initial biomolecular concentration) on the generation of biomolecular gradients on the surfaces. The model also demonstrates salient computational efficiency (seconds of execution time) and can be used to guide fast, reliable, system-level design of CGGs and associated bioassays.
Micro and Nanofabrication of GaN by Wet-Chemical-Assisted Femtosecond Laser Ablation
Authors: Nakashima Seisuke , Sugioka Koji , Midorikawa Katsumi
Published: October 2010

For micro/nanofabrication of Gallium nitride (GaN), we developed wet-chemical-assisted fs laser ablation in which the femtosecond (fs) laser beam focused using an objective lens was directed on the surface of a GaN substrate immersed in 35% hydrochloric (HCl) acid solution. Nanocrators with a diameter as small as 320 nm (FWHM) were successfully formed on surface of a single-crystal GaN substrate by a single pulse of the second harmonic fs-laser beam (λ = 387 nm, 150 fs) focused using an objective lens with NA of 0.5. Nano scale ablation is responsible for two-photon absorption of the fs laser. The ablated craters exhibit higher quality and better uniformity with little debris formation compared with those produced by fs-laser ablation in air followed by etching in HCl (two-step processing method). The high quality ablation is presumably due to photochemical or photothermal reaction of HCl solution with ablated materials, resulting in complete removal of debris and in sharp edge and smooth surface of craters. We have demonstrated formation of 140-μm-long straight and hollow channels embedded in GaN by scanning the laser beam inside the substrate. 3D micro and nano fabrication technique of GaN has great potential for manufacture of highly-functional micro devices. We have also tried to fabricate 2D periodic nanostructures on GaN surface by scanning the sample in x-y plane. Nanocrators with uniform size periodically arranged on GaN surface can act as a two-dimensional (2D) photonic crystal which is expected to enhance a light extraction efficiency of blue LED.
Microbubble Formation in Abrupt Condensation of Vapor Bubble Exposed to Subcooled Pool
Authors: Hattori Yasusuke , Ueno Ichiro
Published: October 2010

Microbubble emission boiling (MEB) has been recognized for a potential phenomenon to be applied to devices such as next-generation heat exchanger for cooling small but high-power CPU and for long-duration exploring in the space/deep ocean; the MEB realizes higher heat flux than the critical heat flux known as ‘CHF’ accompanying with blowing out microbubbles smaller than 100 μm from the heated surface under highly subcooled condition. Invaluable information on characteristics of heat transfer and occurring condition of the MEB has been indicated by several research groups. Little knowledge on the mechanism of the MEB, however, has been accumulated; one of the reasons must be an immense complexity of the phenomenon of the boiling itself with interaction among solid-liquid-gas phases. In the present study, the authors focus on the condensing process of a vapor bubble in order to comprehend the mechanism of the microbubble formation and emitting processes in the MEB. In order to extract an interaction between the vapor and the liquid from a complex boiling phenomenon, a series of experiments of injection of superheated vapor to a subcooled pool are carried out. Comparison of the condensing process of the vapor and microbubble formation is made between the present vapor-injection experiment and conventional on-wire pool boiling experiment.
Numerical Simulation of Droplet Generation in Series Co-Flow Capillaries
Authors: Song Yanxi , Xu Jinliang
Published: October 2010

We study the production and motion of monodisperse double emulsions in microfluidics comprising series co-flow capillaries. Both two and three dimensional simulations are performed. Flow was determined by dimensionless parameters, i.e., Reynolds number and Weber number of continuous and dispersed phases. The co-flow generated droplets are sensitive to the Reynolds number and Weber number of the continuous phase, but insensitive to those of the disperse phase. Because the inner and outer drops are generate by separate co-flow processes, sizes of both inner and outer drops can be controlled by adjusting Re and We for the continuous phase. Meanwhile, the disperse phase has little effect on drop size, thus a desirable generation frequency of inner drop can be reached by merely adjusting flow rate of the inner fluid, leading to desirable number of inner drops encapsulated by the outer drop. Thus highly monodisperse double emulsions are obtained. It was found that only in dripping mode can droplet be of high mono-dispersity. Flow begins to transit from dripping regime to jetting regime when the Re number is decreased or Weber number is increased. To ensure that all the droplets are produced over a wide range of running parameters, tiny tapered tip outlet for the disperse flow should be applied. Smaller the tapered tip, wider range for Re and we can apply.
Stress and Temperature Analysis of the Copper Substrate Indented With Nanotubes and Nanocones
Authors: Wang Yun-Che , Chen Jun-Liang , Liao Ming-Liang , Chen Chuan , Chen Yan-Chi , Hwang Chi-Chuan
Published: October 2010

It has been shown that nanotubes and nanocones are most effective to make indents with large aspect ratios. Detailed studies in the heat transfer processes under the nano-scale indentation, and the accompanying stress distributions are required much attention. In this study, the copper substrate was indented with a nanotube or nano-cone. It is found that nano-cones may make indents with larger aspect ratios than the nanotubes due to the local shell buckling. Time-domain heat transfer and stress analysis was carried out by using a control-volume technique with an atomic spatial resolution, except near the boundaries. The effect of temperatures and stresses on the changes of the microstructures of the substrate will be discussed.
Ultra Fast Micropumping by Reaction Enhanced AC Electrothermal Effect
Authors: Lian Meng , Wu Jie , Mruetusatorn Prachya
Published: October 2010

AC electrothermal effect generates temperature gradients in the fluids, consequently inducing free charges that move in electric fields, and produce microflows in microchannel. This paper reports dramatic improvements in flow rate over conventional ac electrokinetic micropumps by exploiting asymmetry in electric potentials over the electrodes. A micropump consisting of planar asymmetric electrode array was tested using AC signals with and without a DC bias. The pumping velocity is much faster with a DC voltage, in some cases by an order of magnitude, reaching 3.2 mm/sec linear velocities with only 9 Vrms. Our hypothesis attributes the increase of ACET force to the ion generation near electrode by reactions and the resulting high conductivity gradient. The discovery presents an exciting opportunity for microfluidics, and further improvement can be anticipated with some optimization.
Statistical Speckle Study of Copper Nanofluids
Authors: Mansour Nastaran , Mohammad Kazemi Mehdi , Karimzadeh Rouhollah , Zamir Anvari Javid
Published: October 2010

We report on a statistical analysis of copper nanofluid speckle image patterns. The far-field speckle images are formed by illuminating the copper nanoparticle (CuNP) suspension using low power continuous wave laser light at 532 nm. The nanofluids is prepared by nanosecond pulsed laser ablation of the highly pure copper target in polysiloxane oil. A stochastic approach based on the fractional Brownian motion and the classical frequential method is applied on the speckle patterns. These methods enable us to extract statistical parameters such as mean speckle size, Hurst coefficient and saturation of variance. Our results show that the mean speckle size remains unchanged with respect to time while the Hurst exponent and the saturation of variance exhibit changes. It has been shown that the stochastic approach makes it possible to characterize the copper nanofluid. The statistical analysis indicates that the Brownian motion of nanoparticles play important role in thermal properties of the copper nanofluids. Including the Brownian motion, the thermal conductivity of the copper nanofluids is calculated.
Fabrication of Hollow Polylactic Acid Microcapsules From Microbubble Templates
Authors: Molino Jay J. , Takada Shingo , Daiguji Hirofumi , Takemura Fumio
Published: October 2010

Hollow polylactic acid (PLA) microcapsules from microbubbles templates are being generated inside methylene chloride (CH2Cl2) droplets formed in a poly-vinyl alcohol aqueous solution (PVAaq). By stably keeping the microbubbles, PLA can absorb to the bubble surface and become the shell of the microcapsules. It is desired to accurately control the final microcapsule radius size. Thus, in the following document, details on a series of experiments that aim to control the microcapsule final radius are covered. In situ, microscope imaging (ECLIPSE Ti-E, Nikon Corporation, Tokyo, Japan) was used to analyze the final radius size. PLA was also stained with Nile Red (excites at 485 nm, emits at 525 nm) for fluorescence visualization. These procedures allowed the verification of the parameters that influences the final microcapsule size. Experiments were performed at room temperature. Herein, details on the experimental arrangement, results and justification for how each parameter affects the final microcapsule radius.
Multi-Scale Simulation of Nanoparticle Transport and Deposition in Tissue During a Nanofluid Injection Process
Authors: Su Di , Ma Ronghui , Zhu Liang , Salloum Maher
Published: October 2010

In magnetic nanoparticle hyperthermia for cancer treatment, controlling nanoparticle is vital for managing heat deposition and temperature elevations in clinical applications. In this study, we first perform a numerical simulation of magnetic nanofluid transport in agarose gel during an injection process and explore the relationship between the spreading shapes of the nanofluid in gel and injection parameters. We also simulate the nanoparticle concentration distribution in tissues after being injected into the extracellular space under various injection parameters. The model consists of two components. One is a particle trajectory tracking model (PTTM) which can predict the deposition rate of nanoparticle on the porous matrix in a single pore structure by using a Lagrangian Brownian Dynamics simulation method. The other one is a macroscale transport model of nanofluid in saturated porous structures. This study provides advanced understanding of nanofluid transport behavior in a porous structure. Our results show that the gap formed surrounding the needle may cause a back flow and can significantly affect the shape of nanofluid spreading. For small-sized nanoparticle (10nm) with zero surface zeta potential, the filtration effect dominates the particle distribution. The effect of other conditions like nanoparticle size, particle surface coating, and physic-chemical properties of carrier fluid on nanoparticle concentration distribution is under study.
Effect of Hydrophobicity in Cathode Porous Media on PEM Fuel Cell Performance
Authors: Yang Lijun , Li Wenan , Du Xiaoze , Yang Yongping
Published: October 2010

The water management is a key issue for the performance of a polymer electrolyte membrane (PEM) fuel cell. Materials of the fuel cell would affect the water transportation in the flow field thus influence the overall performance of a fuel cell. Three dimensional single-channel, counter-flow model was built to analyze the performance of PEM fuel cell. Different surface contact angles were set to the liquid water droplets in the catalyst layers (CL) and gas diffusion layers (GDL) to present the different wetting property characterizations of the materials. Assuming that the contact angles range from 75° to 150°, the liquid water content and distribution in the cathode GDL were investigated in details. Numerical analysis showed that the hydrophobicity of the structure affects water transportation in the fuel cell significantly. Hydrophobic materials could lower the rate of water saturation in the flow field thus prevent the water flooding in the cathode side. When the surface contact angel of cathode CL and GDL was set to 135°, the liquid water content is least in the GDL. I-V polarization curves of the fuel cell with different materials were also developed to analyze the overall performance. As a result, proper hydrophobic material would lower the rate of cathode water flooding in PEM and benefit the performance of PEM fuel cell.
Influencing Factors for Thermal Conductivity Enhancement of Nanofluids
Authors: Xie Huaqing , Yu Wei , Li Yang , Chen Lifei
Published: October 2010

Nanofluids have attracted increasing interest for more than a decade. A number of studies have demonstrated that nanofluids presented intriguing heat transfer enhancement performances. We produced a series of nanofluids and measured their thermal conductivities. The most used heat transfer fluids including deionized water (DW), ethylene glycol (EG), glycerol, silicone oil, and the binary mixture of DW and EG were used as the base fluids. Various nanoparticles (NPs) including Al2O3 NPs with different sizes, SiC NPs with different shapes, MgO NPs, ZnO NPs, SiO2 NPs, Fe3O4 NPs, TiO2 NPs, diamond NPs (DNPs), and carbon nanotubes (CNTs) with different pretreatments have been used as additives. In the present paper, we summarized our experimental results to elucidate the influencing factors for thermal conductivity enhancement of nanofluids. The thermal transport mechanisms in nanofluids were further discussed and the promising approaches for optimizing the thermal conductivity of nanofluids were proposed.
Acoustic Driven Micro Thermal Bubble Dynamics in a Microchannel
Authors: Qu Xiaopeng , Qiu Huihe
Published: October 2010

Understanding the effects of acoustic vibration on micro thermal bubble dynamics in a microchannel is the key to develop acoustic-thermal-bubble based microfluidic devices. For that purpose, in the current research, a series of experiments were carried out to study the acoustic-thermal-bubble dynamics in a microchannel. The thermal bubble was generated by a micro heater which was fabricated by MEMS (Micro-Electro-Mechanical-System) technique. Using a high-speed digital camera, the thermal bubble dynamics was studied in two different conditions: normal condition and acoustic condition. Through theoretical analysis, the whole bubble dynamic process in two conditions can be roughly divided into four steps, which are bubble nucleation, satellite bubbles movement, bubble evolution, and bubble shrinkage and remove. The effects of acoustic vibration on all these four steps were found to be significant. The mechanisms behind these effects are discussed by analyzing the high speed video recording results. The current experimental investigation has some potential applications in microfluidic devices, and a prototype of micro mixer based on acoustic-thermal-bubble was successfully tested.
Temperature and Viscosity Effects on the Thermal Conductivity of Ferro-Nanofluid
Authors: Yang Chin-Ting , Cheng Shao-Hua
Published: October 2010

The aim of this study is to understand the temperature and viscosity effects on the thermal conductivity of ferro-nanofluid. The base-fluid of ferro-nanofluid is made of polydimethyl-siloxane (PDMS) and diesel fuel which have similar thermal property but different viscosity. The viscosity of base-fluid is controlled by changing the volume ratio of both fluids. The measured results show that the thermal conductivity is smaller when the base fluid is highly viscous, and the thermal conductivity approaches to the value predicted by the Maxwell equation. It should be that the Brownian motion effect on highly viscous fluid is not as important as on lower viscosity fluid. Usually rising temperature will decrease viscosity of base fluid. In our study, rising temperature to 58°C can reduce the viscosity of 90%diesel fuel+10%PDMS to pure diesel fuel base fluid at 23 °C. At the same viscosity condition, rising temperature will decrease the thermal conductivity of ferro-nanofluid. The reason is that the thermal conductivity of base-fluid decrease dramatically. Comparing thermal conductivity of 2% volume fraction ferro-nanofluid to base-fluid at 23°C and 58°C respectively, the value increases 8.3% at 23 °C but increases 18.8% when the temperature is 58°C. This means the Brownian motion is more active at higher temperature than lower temperature.