bluuebunny/crossref_metadata_2025 huggingface dataset:
A Procedure for Encapsulation in Microchannel
Authors: Yap Y. F. , Chai J. C. , Nguyen N. T. , Wong T. N. , Yobas L.
Published: April 2009

A fixed-grid approach for modeling the motion of a particle-encapsulated droplet carried by a pressure driven immiscible carrier fluid in a microchannel is presented. Three phases (the carrier fluid, the droplet and the particle), and two different moving boundaries (the droplet-carrier fluid and droplet-particle interfaces), are involved. This is a moving boundaries problem with the motion of the three phases strongly coupled. In the present article, the particle is assumed to be a fluid of high viscosity and constrained to move with rigid body motion. A combined formulation using one set of governing equations to treat the three phases is employed. The droplet-carrier fluid interface is represented and evolved using a level-set method with a mass correction scheme. Surface tension is modeled using the Continuum Surface Force model. An additional signed distance function is employed to define the droplet-particle interface. Its evolution is determined from the particle motion governed by the Newton-Euler equations. The governing equations are solved numerically using a Finite Volume method on a fixed Cartesian grid. For demonstration purpose, the flows of particle-encapsulated droplets through a constricted microchannel and through a microchannel system are presented.
Selective Synthesis of Single-Walled Carbon Nanotubes by Blending Catalysts
Authors: Inoue Shuhei , Nakajima Takeshi , Nomura Kazuya , Kikuchi Yoshihiro
Published: April 2009

Single-walled carbon nanotubes are considered the most attractive material and a lot of synthesis processes are developed. Among these synthesis processes chemical vapor deposition processes are considered to be most suitable for macroscopic production. In many CVD processes the alcohol catalytic CVD process can be the best process because it can produce very pure nanotubes without any purification. However, cobalt is essential as a catalyst that makes the flexibility of catalysts restricted. In this paper, our investigation mainly focused on as follows: The efficiency of combined catalysts with/without cobalt. The diameter distributions against catalysts density. The electrical states of catalysts near Fermi level. Consequently, almost all of cobalt containing catalysts worked well, and the diameter distributions were proportional to the particle size. Efficient catalysts had enough states around Fermi level and the cobalt-less efficient catalyst cluster model showed the similar density of state to the cobalt cluster. Thus, noticing to the DOS, other efficient catalysts can be discovered and the diameter distribution will be controllable by adjusting temperature, a catalyst size, and a catalyst combination without any complicated techniques and facilities.
Comparison of Different Formulation Methods in Phase Change Heat Transfer
Authors: Shokohmand Hossein , Jafari Alireza , Amiri Parisa
Published: April 2009

In this paper analytical solution has been used to obtain the velocity profiles and temperature field in the moving boundary problems (solidification). The Stephan model has been employed and problem has been solved by using the integral method. The results are compared and it is shown that a third order polynomial would fit quite well with the analytical result. It is assumed that physical properties for both liquid and solid phases remain constant. The most significant part is the interfacial period between two different phases which its properties should be known well. In this paper the heat transfer in this interfacial section phase has been considered. It has been supposed that domain is filled by liquid and restart to solidification from top. Governing equations have been driven for both phases and propose different solutions.
Heat Transfer Between a Heated Microcantilever and the Substrate
Authors: Park Keunhan , Cross Graham L. W. , Zhang Zhuomin M. , King William P.
Published: April 2009

This paper describes the heat transfer from a heated microcantilever to the substrate and the resultant temperature distributions. A four-point probe platinum resistive thermometer having a 140 nm lateral resolution has been fabricated on the SiO2-coated silicon substrate. The estimated temperature coefficient of resistance (TCR) of the thermometer is 0.0011 K−1, approximately one third of the bulk value. When the heated cantilever scans over the thermometer, up to 70% of the cantilever power is transferred to the substrate through the air, heating up the substrate. The maximum substrate temperature rise measured with the thermometer is around 7 K. From the force-displacement experiment, the effective contact thermal conductance was estimated to be around 40 ± 20 nW/K. The obtained results will help further understanding of thermal behavior of the heated cantilever during the scanning and its effect on the substrate.
Experimental Investigation of Flow and Heat Transfer Characteristics Using Thermo-Sensitive Magnetic Fluid in a Mini-Channel
Authors: Fumoto Koji , Ikegawa Masahiro
Published: April 2009

In the present study, the flow characteristics and heat transfer of a thermo-sensitive magnetic fluid, which is a multiphase-flow material, were investigated experimentally. Heat transport systems using magnetic fluids have been proposed by several researchers, but miniature devices of this type have not yet been developed. The mini-channels considered herein have a depth of 500 μm, with the nominal channel width being five times the width. The channel device was constructed from a Teflon tube. The operation of the device is based on the thermo-magnetic characteristics of the fluid, a suspension of Mn-Zn ferrite particles in kerosene, the magnetization of which is known to decrease with increasing temperature. The experimental parameters were magnetic force, the position of the magnet, and the temperature of the magnetic fluid. The experimental results indicated that force convection based on the magnetic characteristics of the fluid in the mini-channel exhibited excellent cooling performance. In particular, the observed variations in the flow patterns were compared with the results of a boundary layer of the flow velocity in the pipe, which is generally known. Furthermore, it was found that the flow characteristic of the thermo-sensitive magnetic fluid was strongly dependent on the magnetic condition, such as the force and the position.
A Micropump Driven by Marangoni Effect
Authors: Sugimoto Kenji , Iwamoto Kaoru , Kawamura Hiroshi
Published: April 2009

A micropump driven by the thermocapillary convection is proposed. The purpose of this study is to elucidate the flow structure in liquid region and the effect of the geometry on the performance of the present micropump. There are two significant advantages in the thermocapillary-driven system. First, the surface forces become more dominant than the volume forces with decreasing scale. The present micropump driven by the surface forces shows an advantage in the micro scale over a diaphragm pump driven by the volume forces. Secondary, the thermocapillary driven system contains no movable parts; thus, it allows a very simple structure compared to the diaphragm one. In the present micropump system, a number of ribs are distributed along the flow circuit between a heater and a cooler (see Fig. A-1). An appropriate amount of gas is trapped between the ribs; the gas-liquid interfaces formed between the ribs are the source of the pumping power. Since heat transfer from these ribs to the working liquid imposes temperature gradients along the gas-liquid interfaces, the flow from the hot to the cold side is induced by the Marangoni effect. Fundamental characteristics of the present micropump are studied on the basis of three-dimensional simulation conducted taking the gas, liquid and ribs into account. Since the surface tension is controlled by the temperature of the ribs, the equations for liquid and gas phases are formulated by coupling them with the heat conduction equation for the ribs. The intensity of the flow induced by the thermocapillary force can be described by using the Marangoni number. In this study, the flow structure corresponding to the temperature field was observed (see Fig. A-2). Since the high temperature fluid is convected downstream, the temperature of the central liquid region exceeds the temperature of the ribs at the same streamwise position. Therefore, the flow from the central field to the ribs is induced by the Marangoni effect on the gas-liquid interfaces. The present calculation has revealed that the flow field exhibits a transition from steady flow to oscillatory flow when the Marangoni number exceeds a critical value of about 2,000 – 2,500. An experiment was also performed. The liquid flow driven by the present micropump system was confirmed through the experiment.
Optimal Design of Heat Transfer and Fluid Flow Using Adjoint Sensitivity Analysis
Authors: Momose Kazunari , Ikejima Kaoru , Ishida Hideshi , Kawahara Genta
Published: April 2009

An optimization system based on adjoint sensitivity analysis has been developed for heat transfer and fluid flow design, the objective of which is, for example, the maximization of local temperature or to achieve the target temperature distributions in specific regions by controlling the flow and thermal boundary conditions as the design parameters. Using the system, the sensitivities on whole boundary can be obtained by a couple of numerical computations of the conventional forward problem and the corresponding adjoint problem. Moreover, by combining with a commercial CFD software as a front end and with the steepest descent method as an optimizer, we show that the flow and thermal boundary conditions can automatically be optimized.
MD-CFD Hybrid Simulation of a Nanobubble
Authors: Ikemoto Naofumi , Kinouchi Soichi , Matsumoto Mitsuhiro
Published: April 2009

We have developed hybrid numerical simulation codes to investigate the dynamics of nanobubbles. The idea is based on a combination of a molecular dynamics (MD) technique and a continuum dynamics with the CIP method. The MD technique enables us to examine rapid change of the bubble surface and the inside region of nanobubbles at molecular scale. The CIP method enables us to trace the mass and energy transfer processes far from the bubble surface at continuum scale. In the hybrid simulation, the simulation cell is divided into two parts. The inner region containing a bubble (or bubbles) consists of sufficiently large number of particles and is treated with the MD method. The outer region is treated with a computational fluid dynamics (CFD) scheme. The boundary between the inner and outer regions is movable and driven with the pressure difference between the two regions. To deal with the moving boundary, we adopt the CIP scheme. Two different codes have been developed, i.e., one-dimensional CFD with assuming a spherical symmetry, and full three-dimensional CFD. Examples will be given in the paper to demonstrate each code. The first example is the oscillating dynamics of a spherical bubble with one-dimensional CFD. The bubble is initially located at the center of the MD region with no translational motion. The outer (continuum) region is treated one dimensionally, with the assumption of spherical symmetry. Under the equilibrium condition, where there is no pressure difference between the two regions, we give a sudden pressure increase in the continuum region far from the bubble. The spherical pressure wave propagates through the continuum region, and the pressure difference drives the boundary to shrink the MD region. As the MD region shrinks, the bubble inside the region starts to collapse. The collapsed bubble bounces back. We have analyzed the oscillation dynamics under several different conditions, such as different initial pressures and the state of gas inside the bubble. The second one is the deformation of a non-spherical bubble. For that purpose, the continuum region is treated with full three-dimensional CIP scheme. Furthermore, we use the level set method in order to capture the interfaces (boundary) between the MD region and the continuum region.
Condensating Heat Transfer of Mixture Gases Across a Horizontal Tube
Authors: Jia Li , Wu Dongmei
Published: April 2009

This paper combined modified film model and Nusselt’s condensation theory and studies convective condensation heat transfer on a horizontal tube across which moist mixed gas flows horizontally at a certain speed. A theoretical model allowing for gas boundary layer separation was set up and how the liquid film flows and the heat transfers on the tube were presented. The effects of flowing direction on condensation heat transfer are discussed. Results predict that the condensate is so thin that the liquid phase heat resistance can be ignored.
Numerical Simulation of PSD System’s Effects on Subway Platform Air
Authors: Yang Hui , Jia Li , Yang Lixin , Huang Peng
Published: April 2009

In this paper, three dimensional air flow distributions in typical island platform both with and without PSD (platform screen door) system were simulated for the whole process of the train entering, staying in and departing from the platform. Based on the data obtained from the simulation with and without PSD system, the effects of PSD system on platform air environment were analyzed. At last, both the advantages and disadvantages of PSD system were concluded in view of improving passengers’ comfort and air quality.
Wireless Temperature Sensing System Performance Characterization
Authors: Pytel Diane , Cotoros Ingrid , Hashemi Ab
Published: April 2009

Current technology in temperature measurement and control requires labor-intensive and costly installation of sensors, wires and circuitry for thermal-vacuum (TVAC) testing of a system and/or post-deployment management of the thermal environment and performance. In addition, post-installation changes are often costly or impossible once the mission is initiated. Wireless thermal metrology is an enabling technology to obtain temperature history in an area of interest via wireless sensors. In a previous paper [1], we discussed the development of a wireless thermal sensing and mapping system designed for ground testing and in-flight use. We explained the basic instrument configuration for wireless temperature measurement and the analytical modeling for characterizing signal strength, transmission and quality. Laboratory test results indicated that the system is feasible and well-suited for aerospace applications. Predictive capabilities showed excellent agreement with fundamental physics of the signal propagation and the measured data. This paper complements the previous work. First, we describe the development of bounding analytical models to demonstrate the signal leakage from grounded and ungrounded Faraday cages at high frequencies. Then, we describe the development of a predictive model for performance characterization of a wireless thermal sensing system inside a Faraday Cage. Finally, we compare the test results with predictions and characterize the electromagnetic (EM) leakage from the cage when the equipment is placed in various configurations. Preliminary frequency response results assist in understanding EM leakage from the wireless equipment, and provide guidelines for optimal placement of equipment and sensors when tests in Faraday cage-like TVAC chambers are performed.
Experimental Investigation on Heat Transfer Characteristics of Supercritical Carbon Dioxide Inside a Horizontal Micro-Fin Copper Tube During Cooling Process
Authors: Higahiiue Shinya , Kuwahara Ken , Yanachi Satoru , Koyama Shigeru
Published: April 2009

Experimental study on cooling heat transfer of CO2 and CO2-PAG mixture flowing in a horizontal micro-fin tube under the supercritical pressure conditions was performed. The test tube having the average inner diameter of 4.76 mm, the fin height of 0.245 mm, the number of fins of 50, the area expansion ratio of 2.08 was conducted in this study. The microfins of the test tube were treated in straight along the axes of the tube on the heat transfer surface. The heat transfer coefficients of pure CO2 were measured at conditions of 8 and 10 MPa in pressure and 340 – 660 kg/(m2 s) in mass velocity. The measured heat transfer coefficients of the micro-fin tube showed 1.7 times higher than that of smooth tube with 4.42 mm inner diameter. The effect of PAG on heat transfer characteristics were investigated experimentally at 10 MPa in pressure, 510 kg/(m2 s) in mass velocity and 0.06 to 2.26% in the mass percent concentration of PAG in CO2-PAG mixture. The measured heat transfer coefficients of CO2 -PAG mixture decreased about 50% as compared with that of pure CO2 at the pseudocritical temperature.
Optical Remote Sensing of Oxygen and Water Vapor Concentration in PEMFC Channel by Using Tunable Diode Laser Absorption Spectroscopy Techniques
Authors: Fujii Yoshinobu , Tsushima Shohji , Hirai Shuichiro
Published: April 2009

In this study, we present optical remote sensing of oxygen and water vapor concentration in gas flow channels in an operating polymer electrolyte membrane fuel cell (PEMFC) by using Tunable Diode Laser Absorption Spectroscopy (TDLAS). Wavelengths of the diode laser are 1392nm for measurement of water vapor concentration and 760nm for measurement of oxygen concentration, respectively. We demonstrated that the optical remote sensing based on TDLAS techniques could detect variation of oxygen and water vapor concentration in the PEMFC channel.
Film Boiling Around a Vertical Cylinder With Top and Bottom Horizontal Surfaces
Authors: Momoki Satoru , Yamada Takashi , Shigechi Toru , Kanemaru Kuniyasu , Yamaguchi Tomohiko
Published: April 2009

Saturated and subcooled film boiling heat transfer around a vertical finite-length silver cylinder with top and bottom horizontal surfaces has been investigated, experimentally and analytically, in terms of cooling curve, and the correlations of heat transfer were proposed in the present paper. Pool film boiling experiments were carried out by quenching method. Cooling curves are obtained for saturated water at atmospheric pressure. The heated cylinder is made of silver and 18 kinds of cylinder are tested in the ranges of the diameter from 8 to 100 mm and the length from 8 to 160 mm. For subcooled water, the experiments were carried out in the similar method to the case of saturated water. The ranges of the diameter and length of the cylinder are 32 to 50 mm and 16 to 64 mm, respectively. The degree of liquid subcooling ranges from 2 to 30 K. In order to predict the film boiling characteristics, the overall heat transfer rate from a cylinder with finite length was modelled by taking into account each convective heat transfer on the bottom, side and top surfaces of the vertical cylinder. Present correlation equations for heat transfer and the lower limit of film boiling are good agreement with the experimental data for saturated and subcooled water. The values of wall heat flux and temperature at the lower limit of film boiling are obtained as the point where the cooling rate has a minimum value on the cooling curve. For the case of saturated water, wall temperature at the lower limit of film boiling is about 136 K and irrespective of the configuration of a cylinder. For subcooled water, the correlation is proposed for the effect of liquid subcooling on wall temperature at the lower limit of film boiling.
Feasibility Study of Noninvasive Measurement of Thermal Conductivity and Thermal Diffusivity for Biological Materials
Authors: Yoshida Keisuke , Uchida Satoru , Takamatsu Hiroshi , Fujii Motoo
Published: April 2009

A noninvasive technique was developed to measure the thermophysical properties of biological materials. In this technique the temperature response of a material surface heated by CO2 laser irradiation is measured with an infrared thermometry and compared with the theoretical response. The thermal conductivity and the thermal diffusivity are determined as the both values which yield the smallest deviation between the measured and analyzed temperature responses. The objective of the present study is to establish this technique by investigating the uncertainty of the method. An appropriate model of heat transfer is discussed first by taking into account of the effect of the laser absorption within the material and a heat loss from the material surface to the ambient. Then the accuracy of measurement is examined by using virtual experimental data with temperature fluctuation expected in an actual experiment. The virtual experimental data are generated by adding artificial fluctuation to a theoretical temperature response. The accuracy of measurement is estimated as a function of the standard deviation (S.D.) of the temperature fluctuation and the laser irradiation time. The effect of uncertainty in the absorption coefficient of the target material is also examined.
Flame-Spread Behavior of Fuel-Droplet Arrays With Uneven Inter-Droplet Distance at High Temperature in Microgravity
Authors: Yagi Kazuki , Shigeno Hisashi , Oyagi Hiroshi , Masato Mikami , Kojima Naoya
Published: April 2009

This research experimentally studied flame-spread behavior of fuel-droplet arrays with uneven inter-droplet distance at high temperature in microgravity. In experiments, first, n-decane droplets were generated in room-temperature air. Next, the droplet array was inserted into the combustion chamber with 600 K air. The droplet array was ignited at one end by a hot wire igniter after a certain waiting time to initiate the flame spread. Local inter-droplet distances were varied to investigate the effect of droplet interaction on local flame-spread-limit distance. Waiting time for ignition was varied to investigate the prevaporization effect on flame spread. Experimental results showed that as the inter-droplet spacing became smaller, local flame-spread-limit distance to the next droplet became larger. The local flame-spread-limit distance at high temperature was larger than that at room temperature. Flame-spread rate from the interactive droplets to the next droplet was greater with longer waiting time for ignition.
Combustion Mechanism of Rich-Lean Flame Burner Controlled Boundary Zone
Authors: Aoki Shuichi , Yamazaki Hiroshi
Published: April 2009

Rich-lean flame burners are widely used for supplying domestic hot water and heating in Japan. These burners exhaust low NOx and CO emissions, and conventionally consist of a layered structure of lean flame with two sides of rich flame. Top-runner regulation applied for the domestic hot water generator of fuel gas, is to run to achieve the CO2 reduction two years later in Japan. Not only low NOx and CO emissions, but also higher efficiency, are required for the next generation of domestic hot water generators. Kurachi et al. confirmed experimentally that a new concept, a unique burner with air supplied from the boundary zone between the rich and lean premixed gas nozzles, produces lower NOx and CO emissions (1, 2, 3). Numerous experimental and numerical simulation studies of conventional rich-lean flame burners have been reported, and the mechanism of the complex field mixed with the rich and lean premixed gas has been clarified (4). But the characteristics of the new concept burner have only been investigated experimentally. In this study, a two-dimensional numerical simulation of the new burner was executed to clarify the mechanism of the lower NOx and CO emissions compared to the conventional burner (mesh; 25,000, chemical reaction; GRI-mech II, laminar flow). Heat input was 6.5kW (half of a full load). A conventional burner, without an air supply from the boundary zone, was also calculated to compare with the new concept burner. In a conventional burner, the reaction ratio R178 (N+NO = N2+O), which is a part of the Zeldovich mechanism, is dominant at the area downstream of the rich flame. This area is almost same as the maximum temperature area of the burned gas. The maximum temperature of the new concept burner (1,923K) is approximately 50K lower than that of the conventional burner, successfully maintaining stable combustion. Because of its lower maximum temperature, the amount of NOx emission from the new concept burner is approximately 40% of that from the conventional burner. With the air supply from the boundary zone, the concentration of CO in the flue gas also is decreased by approximately 1/3. In particular, the formation of thermal NOx in the lean flame zone is suppressed by lowering the flame temperature. The amount of CO emission from the rich flame zone is also decreased due to the promotion of complete combustion with the air supply from the boundary zone. As a result, these characteristics are in relatively good agreement with the experimental results, and the dominancy of the new concept burner is also clarified.
Deposition of Various Metals on Vertically-Aligned Single-Walled Carbon Nanotubes
Authors: Ishikawa Kei , Duong Hai , Shiomi Junichiro , Maruyama Shigeo
Published: April 2009

Evaporation of different metals (Au, Ti, Al and Pd) onto Vertically-Aligned Single-Walled Carbon Nanotubes (VASWNT) has been studied. Observations through Scanning Electron Microscopy (SEM) showed a clear metal-dependence of the deposition layer structure on top of the VASWNT, reflecting the variation of wettability and cohesive energy of each metal. These characteristics also influence the structures of the metal penetrated through the top surface into VASWNT film, where metal forms particles inside VASWNT film except for Ti. A simple annealing technique to remove metals penetrated in the SWNT films is demonstrated. Some peculiar morphologies found during the processes are also presented.
Thermal Performance of a Miniature Loop Heat Pipe for Spacecraft Thermal Control System
Authors: Nagai Hiroki , Nagano Hosei , Fukuyoshi Fuyuko , Ogawa Hiroyuki
Published: April 2009

The Loop Heat Pipes (LHPs) are robust, self-starting and a passive two-phase thermal control system that uses the latent heat of vaporization of an internal working fluid to transfer heat from an evaporator (the heat source) to a condenser (the heat sink). The circulation of the working fluid is accomplished by capillary pressure gradients in a fine porous wick with very small pores. LHPs are rapidly gaining acceptance in the aerospace community and several terrestrial applications are emerging as well. In the present study, a miniature LHP is investigated the thermal performance for spacecraft thermal control system. Tests will be conducted including start-up, low power, power ramp up, high power, rapid power change, and rapid sink temperature change. Finally, we want to demonstrate the potential of LHP to become the next-generation heat transfer device to cool terrestrial devices such as advanced electronic which have high power dissipations. First of all, this paper presents the influence of the gravitational forces on the LHP performance. The present tests performed under steady state condition with three different orientations (horizontal, gravity-assisted, anti-gravity).
Thermal Performance of a Monolithic Thin-Shell Concrete Dome
Authors: Stout Roger Paul
Published: April 2009

A 3,000 sq.ft., two-story monolithic thin-shell concrete dome custom home was constructed in 2005 in Mesa, AZ, by the author. This architectural construction style represents a small, but growing, commercial and residential market, one of whose selling points is energy efficiency. During the preliminary architectural design phase, the only anecdotal and case studies available to the author were mainly related to cold-weather climates. No technically adequate thermal performance studies were found for the opposite, high temperature extreme of climate conditions. To address this need, two models are developed and explored. First, a preliminary lumped-parameter model (initially created to lend technical credence to the exuberant claims of dome aficionados and provide rationalization for the custom home construction project), is compared with actual data collected at the dome during construction. Because the correlation is not very good, a second model based on thermal two-port transmission line theory, is developed. This model provides additional insight, and in particular, comparison with the actual data suggests that model verification will require a somewhat different approach to data collection itself (and to the manner in which the model is utilized). This is confirmed using a small set of subsequent trial data. Thermal models aside, actual utility consumption data for the dome is compared with two conventional block-construction homes in the same geographic locale, showing that the dome thermal performance, at least during the hot months of the year, provides a measurable advantage. Finally, it is shown how the transmission line model makes it very easy to explore the thermal effects of reversing the order of the primary material layers (insulation and concrete).
Predictions of Field-Dependent Thermal and Electrical Transport in a Cu/CoFe Multilayer
Authors: Yang Yizhang , Jeong Taehee , Zhu Jimmy , Asheghi Mehdi
Published: April 2009

The discovery of the giant magnetoresistance effect in metallic multilayers and alloys has led to extensive theoretical and experimental investigations of this effect for the past few decades. Recently, we discovered that Cu/CoFe giant magneto-resistance layers exhibit a giant magnetothermal resistance effect (GMTR), in which the thermal conductivity shows a “giant” change under a magnetic field. In the present study, we adopted the Fuchs-So¨ndheimer extension of the semiclassical Boltzmann theory to predict the in-plane giant magneto-resistance (GMR) and giant magnetothermal resistance (GMTR) ratios in the Cu/CoFe multilayer structure. The present model has been implemented in an attempt to explain the measured differences in the giant magnetoresistance and giant magnetothermal resistance ratios, which have previously been attributed to the different mechanisms for charge and heat transport in the Cu/CoFe multilayer structure.
Numerical Investigation of Forced Convection of Nanofluids in Circular Tubes
Authors: Chiacchio Fabio , Manca Oronzio , Nardini Sergio
Published: April 2009

In this paper developing laminar forced convection flow of a water–γAl2O3 nanofluid in a circular tube submitted to a constant and uniform heat flux at the wall is numerically investigated. A single and two-phase model (discrete particles model) is employed with either constant or temperature-dependent properties. The investigation is accomplished for a size particles equal to 100 nm. Convective heat transfer coefficient for nanofluids is greater than that of the base liquid. Heat transfer enhancement is increasing with the particle volume concentration but it is accompanied by increasing wall shear stress values. The effect of Reynolds number is greater when properties depend on temperature and for higher concentrations.
Experimental Investigation of Scaling Effect on Thermal Transport in Nanoscale Hotspots
Authors: Etessam-Yazdani Keivan , Asheghi Mehdi , Hamann Hendrik F.
Published: April 2009

This paper reports experimental investigation of the scaling effect on thermal transport in platinum nanoheaters deposited on a single crystalline silicon substrate. The size dependency of the thermal resistances of nanoheaters with dimensions from 5 μm down to 100 nm is experimentally obtained. Additional Joule heating and electrical resistance thermometry in heater/sensor pairs of various dimensions and spacing (100 nm to 400nm) are carried out in order to study the temperature distribution in the vicinity of these nanoheaters. The results of these two sets of measurements confirm that the thermal resistances of smaller nanoheaters are dominated by the interface resistance between the platinum and silicon substrate. Furthermore, analytical solutions of the BTE around a hot spot are used to evaluate and examine the significance of the localized heating or sub-continuum transport around a hotspot.
Local Radiation Heating Technique of Polymeric Materials Using Functional-Dye
Authors: Saito Takushi , Satoh Isao , Kawaguchi Tatsuya
Published: April 2009

In this study, the authors added a functional dye to a material which was transparent in initial state, to locally change the radiation absorption coefficient of the material. By using this material, we proposed a radiation heating technique that can achieve a selective local heating in three-dimensional system and investigated its feasibility. Temperature change of the test sample was measured in the experiment, and the characteristic of the presenting technique was investigated. To obtain better understanding of the presenting technique, numerical simulation of the temperature distribution inside the sample was also performed. In the experiment, photochromic dye and thermochromic dye were used as functional dyes and they were individually added to thermoplastic polymeric material (polystyrene) by using organic solvent (tetrahydrofuran). Then the material containing the dye was dried and processed to give a certain shape for the experiment. He-Cd laser and Ar ion laser were properly used as the excitation and the heat sources according to the type of dye. Experimental result showed that local heating of the material was achieved only in quite thin surface region in case of photochromic dye. On the other hand, local heating inside the material was successfully achieved in case of thermochromic dye. However, it was also observed that the heating point was moved to the upstream direction of the laser beam. To examine the solution of this problem, effect of the laser irradiation conditions on the moving speed of the heating point was discussed based on the numerical simulation results.
The Effects of Inlet Flow Conditions on Gas-Liquid Two-Phase Flow in a Micro Tube
Authors: Hayashi Shota , Kasagi Nobuhide , Suzuki Yuji
Published: April 2009

In the present study, the effects of inlet geometry on the microscale two-phase flow patterns have been examined. The relationships among the flow pattern, the void fraction, the pressure loss and the heat transfer coefficient have been also investigated under different inlet flow conditions. At the inlet, a stainless steel tube is inserted into the micro glass tube, of which inner diameter is 300 and 600 μm. The gas and liquid paths and the diameter of the inner tube are interchangeable. The flow patterns are recorded at the inlet and also in the developed region in the micro tubes. The flow patterns observed in the 600 μm tube are bubbly, slug, churn and annular flows, while bubbly and churn flows are not present in the 300 μm tube. For bubbly and slug flows, bubble formation process is found to be strongly affected by the inlet conditions. Accordingly, the pressure loss as well as the heat transfer rate are changed. In addition, the bubble size is not uniquely determined; bubbles of different sizes are observed in repeated experiments under the same inlet flow conditions. On the other hand, for churn and annular flows, the flow patterns are not affected by the inlet conditions.
Laser Ablation-Induced Plasma Characteristics in Optical Near-Field
Authors: Hwang David J. , Jeon Hojeong , Grigoropoulos Costas P.
Published: April 2009

In this study, detailed characteristics of the optical near-field based ablation-induced plasma are investigated. A Cr thin metal film samples are ablated using visible and near infrared nanosecond laser pulses coupled through an optical near-field fiber probe. The ablated plasma evolution is visualized through time-resolved emission imaging and further analyzed via spectral measurement. Unveiled qualitative differences in optical near-field ablation configuration are discussed in comparison with optical far-field ablation. The measured results support implementation of laser-induced breakdown spectroscopy based on optical near-field ablation.
Behavior of Particles Suspended in Non-Coalescence Droplets Formed Between Coaxial Rods With Temperature Difference
Authors: Ueno Ichiro , Miyauchi Akira
Published: April 2009

One can realize that head-to-head droplets never coalesce if there exists a temperature gradient over the free surface under the condition of the non-zero temperature coefficient of the surface tension. The present authors focus upon unique behavior of the particles suspended in droplets formed between the coaxial cylindrical rods with a temperature difference. Several kinds of patterns emerged in the hotter droplet will be introduced. Spatio-temporal particle behaviors are reconstructed by applying three dimensional particle tracking velocimetry (3-D PTV).
Effect of Pr on the Development of Upward Laminar Mixed Convection in the Entrance Region of Vertical Quarter Circle Ducts
Authors: El Hasadi Yousef M. F.
Published: April 2009

Upward laminar mixed convection in the entrance region for vertical quarter circle ducts is investigated theoretically. The governing momentum and energy equations are solved numerically using a marching technique with finite control volume approach following the SIMPLER algorithm. Results are obtained for the thermal boundary condition of uniform heat input axially with uniform wall temperature circumferentially at any cross section (H1 boundary condition) with Pr = 7.0 and 0.7 which corresponds to water and air respectively, Re = 500 and wide range of Grashof numbers. These results include the velocity and temperature distributions, at different axial locations, axial distribution of local Nusselt number and local average wall friction factor. It is found that the local Nusselt number follows the expected behavior of monotonic decrease along the developing region down to the fully developed region. However, the axial development of the local friction factor follows a different trend than that of local Nusselt number. The effect of Grashof number is to increase the values of local Nusselt number and friction factor in the developing and fully developed regions. The effect of Pr is mainly in the entrance region where the values of Nusselt number and friction factor corresponding to air are higher than those of water; however, the flow in the fully developed region is independent of Pr.
Likelihood-ratio forensic voice comparison using parametric representations of the formant trajectories of diphthongs
Authors: Morrison Geoffrey Stewart
Published: April 2009

Non-contemporaneous speech samples from 27 male speakers of Australian English were compared in a forensic likelihood-ratio framework. Parametric curves (polynomials and discrete cosine transforms) were fitted to the formant trajectories of the diphthongs ∕aɪ∕, ∕eɪ∕, ∕oʊ∕, ∕aʊ∕, and ∕ɔɪ∕. The estimated coefficient values from the parametric curves were used as input to a generative multivariate-kernel-density formula for calculating likelihood ratios expressing the probability of obtaining the observed difference between two speech samples under the hypothesis that the samples were produced by the same speaker versus under the hypothesis that they were produced by different speakers. Cross-validated likelihood-ratio results from systems based on different parametric curves were calibrated and evaluated using the log-likelihood-ratio cost function (Cllr). The cross-validated likelihood ratios from the best-performing system for each vowel phoneme were fused using logistic regression. The resulting fused system had a very low error rate, thus meeting one of the requirements for admissibility in court.
A psychophysical evaluation of near-field head-related transfer functions synthesized using a distance variation function
Authors: Kan Alan , Jin Craig , van Schaik André
Published: April 2009

A method for synthesizing near-field head-related transfer functions (HRTFs) from far-field HRTFs measured using an acoustic point-source of sound is presented. Near-field HRTFs are synthesized by applying an analytic function describing the change in the transfer function when the location of a sound source changes from the far-field to the near-field: the distance variation function (DVF). The DVF is calculated from a rigid sphere model and approximates the change in the frequency-dependent interaural level cues as a function of the change in sound source distance. Using a sound localization experiment, the fidelity of the near-field virtual auditory space (VAS) generated using this technique is compared to that obtained by simply adjusting the intensity of the VAS stimulus to simulate changes in distance. Results show improved distance perception for sounds at simulated distances of up to 60cm using the DVF compared to simple intensity adjustment, while maintaining directional accuracy. The largest improvement for distance perception were for sound sources located to the side and within 40cm. When intensity was removed as a cue for sound source distance from near-field sounds generated using the DVF, results showed some discrimination of sound source distances but, in general, distance perception accuracy was poor.
Characteristics of air puffs produced in English “pa”: Experiments and simulations
Authors: Derrick Donald , Anderson Peter , Gick Bryan , Green Sheldon
Published: April 2009

Three dimensional large eddy simulations, microphone “pop” measurements, and high-speed videos of the airflow and lip opening associated with the syllable “pa” are presented. In the simulations, the mouth is represented by a narrow static ellipse with a back pressure dropping to 1∕10th of its initial value within 60ms of the release. The simulations show a jet penetration rate that falls within range of the pressure front of microphone pop. The simulations and high-speed video experiments were within 20% agreement after 40ms, with the video experiments showing a slower penetration rate than the simulations during the first 40ms. Kinematic measurements indicate that rapid changes in lip geometry during the first 40ms underlie this discrepancy. These findings will be useful for microphone manufacturers, sound engineers, and researchers in speech aerodynamics modeling and articulatory speech synthesis.
Fundamental constraints on the performance of broadband ultrasonic matching structures and absorbers
Authors: Acher O. , Bernard J. M. L. , Maréchal P. , Bardaine A. , Levassort F.
Published: April 2009

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at −6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.
On the Larsen effect to monitor small fast changes in materials
Authors: Lobkis Oleg I. , Weaver Richard L.
Published: April 2009

At sufficient gain an ultrasonic feedback circuit rings with a “Larsen” tone that depends on the acoustic properties of the solid body to which it is attached. Because the frequency of this tone may be measured virtually continuously and with high precision, it is potentially capable of responding to fast small changes in materials. Here a tentative theory for Larsen dynamics is introduced and compared with laboratory measurements. Larsen monitoring is then applied to observation of the curing process of a cement paste sample and to studies of “slow dynamics” in which mesoscale nonlinear materials subjected to modest loads experience a drop in modulus but then recover in a characteristic manner like log(t). The present technique, using as it does higher frequencies and the Larsen effect and brief transient loads, extends investigations of slow dynamics to earlier times. For the materials and loads investigated, it is found that log(t) behavior fails at the shortest times, recovery being faster over the first several milliseconds.
The interference component of the acoustic field corresponding to the Long-Range Ocean Acoustic Propagation Experiment
Authors: Grigorieva Natalie S. , Fridman Gregory M. , Mercer James A. , Andrew Rex K. , Wolfson Michael A. , Howe Bruce M. , Colosi John A.
Published: April 2009

Propagation of energy along the sound channel axis cannot be formally described in terms of geometrical acoustics due to repeated cusped caustics along the axis. In neighborhoods of these cusped caustics, a very complicated interference pattern is observed. Neighborhoods of interference grow with range and overlap at long ranges. This results in the formation of a complex interference wave—the axial wave—that propagates along the sound channel axis like a wave belonging to a crescendo of near-axial arrivals. The principal properties of this wave are calculated for the actual space-time configuration realized during a 2004 long-range propagation experiment conducted in the North Pacific. The experiment used M-sequences at 68.2 and 75Hz, transmitter depths from 350to800m, and ranges from 50to3200km. Calculations show that the axial wave would be detectable for an optimal geometry—both transmitter and receiver at the sound channel axis—for a “smooth” range-dependent sound speed field. The addition of sound speed perturbations—induced here by simulated internal waves—randomizes the acoustic field to the extent that the axial wave becomes undetectable. These results should be typical for mid-latitude oceans with similar curvatures about the sound speed minimum.
A realization of sound focused personal audio system using acoustic contrast control
Authors: Chang Ji-Ho , Lee Chan-Hui , Park Jin-Young , Kim Yang-Hann
Published: April 2009

A personal audio system that does not use earphone or any wire would have great interest and potential impact on the audio industries. In this study, a line array speaker system is used to localize sound in the listening zone. The contrast control [Choi, J.-W. and Kim, Y.-H. (2002). J. Acoust. Soc. Am. 111, 1695–1700] is applied, which is a method to make acoustically bright zone around the user and acoustically dark zone in other regions by maximizing the ratio of acoustic potential energy density between the bright and the dark zone. This ratio is regarded as acoustic contrast, analogous with what is used for optical devices. For the evaluation of the performance of acoustic contrast control, experiments are performed and the results are compared with those of uncontrolled case and time reversal array.
A low-noise differential microphone inspired by the ears of the parasitoid fly Ormia ochracea
Authors: Miles R. N. , Su Q. , Cui W. , Shetye M. , Degertekin F. L. , Bicen B. , Garcia C. , Jones S. , Hall N.
Published: April 2009

A miniature differential microphone is described having a low-noise floor. The sensitivity of a differential microphone suffers as the distance between the two pressure sensing locations decreases, resulting in an increase in the input sound pressure-referred noise floor. In the microphone described here, both the diaphragm thermal noise and the electronic noise are minimized by a combination of novel diaphragm design and the use of low-noise optical sensing that has been integrated into the microphone package. The differential microphone diaphragm measures 1×2mm2 and is fabricated out of polycrystalline silicon. The diaphragm design is based on the coupled directionally sensitive ears of the fly Ormia ochracea. The sound pressure input-referred noise floor of this miniature differential microphone has been measured to be less than 36dBA.