bluuebunny/crossref_metadata_2025 huggingface dataset:
Sub-Atmospheric Mini-Jet Impingement Boiling of Water Under Saturated and Subcooled Conditions
Authors: Cardenas Ruander , Mani Preeti , Narayanan Vinod
Published: March 2011

An experimental study of mini-jet impingement boiling is presented for saturated and subcooled conditions. Unique to this study is the documentation of boiling curves of submerged water jet impingement under sub-atmospheric conditions. Data are reported at a single sub-atmospheric pool pressure of 0.176 bar and for a fixed nozzle-to-surface distance of six jet diameters. A mini nozzle is used in the present study with an internal diameter of 1.16 mm. Jet impingement boiling at Reynolds numbers in the range of 0 to 6,800 are characterized and contrasted for both saturated and subcooled conditions. Enhancements in critical heat flux with increasing Re are observed for both saturated and subcooled conditions, with the subcooled condition of 17 °C showing approximately 2.3 times the critical heat flux as that observed for saturated conditions. Critical heat flux for subcooled jet impingement boiling is well predicted from the saturated critical heat flux data by a modified subcooled pool boiling CHF correlation presented by Inoue et al. [1]. The effect of surface finish on pool boiling is also reported.
Feasibility of Vortex Tube Air-Conditioning System
Authors: Hamdan Mohammad O. , Alawar Ahmed , Elnajjar Emad , Siddique Waseem
Published: March 2011

This paper investigates the feasibility of using vortex tube as air-conditioning device. Series of experiments are conducted to evaluate the design parameters and calculate the performances of counter-flow Ranque–Hilsch vortex tube (RHVT). The study is conducted for different inlet pressures conditions, number of nozzle inlets, vortex chamber depth and thermal insulation condition. The vortex tube performance is investigated by measuring temperatures, pressures and mass flow rates for the inlet and hot/cold exits. It is found that vortex tube has very coefficient of performance which make it inadequate to compete with conventional air conditioning system.
MD-CFD Hybrid Simulation for Microbubble Dynamics
Authors: Nabika Ryo , Matsumoto Mitsuhiro
Published: March 2011

We have developed a hybrid numerical simulation code to investigate the dynamics of nanobubbles. The idea is based on a combination of a molecular dynamics (MD) technique for the region containing a bubble and surrounding area, and the lattice Boltzmann method (LBM) for the region well away from the bubble. The boundary between the two regions is movable and driven by their pressure difference. As a test of the developed code, we have performed a simulation of a collapsing nanobubble. After equilibrating the system, we introduce a uniaxial pressure wave in the continuum region far from the bubble. The pressure wave propagates through the LBM region, and the pressure difference deforms the MD-LBM boundary. As the MD region deforms, the bubble inside the region starts to collapse non-spherically. We have analyzed the bubble collapse dynamics with several different pressure waves. Vapor bubbles and bubbles containing noncondensable particles are compared.
Molecular Dynamics Simulation of Three-Dimensional Heterogeneous Nucleation
Authors: Suh Donguk , Yasuoka Kenji
Published: March 2011

Nanoparticle growth based on three-dimensional heterogeneous nucleation was simulated by classical molecular dynamics. To collectively observe the effects of the dimension of seeds and thermodynamic conditions, seed size and system supersaturation ratio were the factors that were examined to see if they influenced the nucleation rates. Two stages were found to exist within the system, where the first stage is from the seed growth and the second from homogeneous nucleation. The Yasuoka-Matsumoto method was used to calculate the rates. The homogeneous nucleation characteristics coincided with the classical nucleation theory, but heterogeneous nucleation showed an irregular form, which at the current state cannot not be fully understood. Kinetic analysis was also performed to calculate the critical nucleus size and better understand the seed growth characteristics. All in all, the seed effects were insignificant to the overall nucleation characteristics for this system.
Thermal Conductivity Measurement of Hydrogen at High Pressure and High Temperature
Authors: Kimura Koichi , Moroe Shogo , Woodfield Peter , Fukai Jun , Shinzato Kan’ei , Kohno Masamichi , Fujii Motoo , Takata Yasuyuki
Published: March 2011

The thermal conductivities and thermal diffusivities of hydrogen were measured with a transient short hot wire method for temperature range up to 300 °C and pressure range up to 100MPa. The measured thermal conductivities showed good reproducibility and agreed with the existing values within a deviation of ±2%.
Influence of Cell Components Structure on Coupling Phenomena in Single Cell of Polymer Electrolyte Fuel Cell
Authors: Nishimura Akira , Morimoto Atsushi , Tanaka Shigeki , Oshima Atsushi , Hirota Masafumi , Tohma Eiji , Kimura Yukio , Narita Masahiko
Published: March 2011

The purpose of this study is to point out the dominant factor of heat and mass distribution in single cell of polymer electrolyte fuel cell (PEFC). The numerical simulation by simple 3D model of PEFC has been investigated to clarify the influence of cell components structure on heat and mass transfer phenomena in PEFC. In addition, the power generation experiment and the measurement of in-plane temperature distribution by thermograph were carried out. From the simulation results, the gas channel pitch of separator was the key factor to unify in-plane distribution of temperature and gas concentration on the reaction surface. The compression of gas diffusion layer (GDL) by cell binding caused wider distribution of mass concentration in GDL. According to the experimental results, the power generation performance was promoted with the decrease in gas channel pitch irrespective of relative humidity of supply gas. In addition, the temperature range in observation area was lower with the decrease in gas channel pitch.
A New Empirical Model for Bubble Growth: Boiling in an Infinite Medium and on a Wall at High Superheat
Authors: Haustein Herman D. , Dietze Georg F. , Kneer Reinhold
Published: March 2011

At high superheat bubble growth is rapid and the heat transfer is dominated by radial convection. This has been found, in the case of a droplet boiling within another liquid and in the case of a bubble growing on a heated wall, leading to similar bubble growth curves. Based on experiments conducted for the first case, an empirical model is developed for the prediction of bubble growth within the radial convection dominated regime (the RCD model), occurring only at high superheat (0.26<Ste<0.41). This model shows a dependence of R∼t1/3 equivalent to Nusselt number decreasing over time (Nu∼t1/3) as opposed to R∼t1/2 appearing in most other models, leading to a highly unlikely constant Nusselt number. The new model is shown to give accurate predictions for the first case and for the second case at medium-high superheat (0.19<Ste<0.30, experimental data taken from literature). A comparison of the RCD model to other models, shows a more consistent and accurate prediction. However, in the second case (nucleate boiling) the RCD model requires the foreknowledge of the departure diameter, for which a reliable model still is lacking.
A CFD Analysis of Transverse Airflow Around the Exterior of an Aircraft Fuselage Inside a Large Enclosure
Authors: Venkatesan Yaamunan , Paruchuri Rohitha , Ravigururajan T. S.
Published: March 2011

A model for predicting the airflow over the aircraft exterior with in a hangar is presented in this paper. The main reason behind this was to analyze the amount of air flowing over the aircraft at the time of painting, in order to dry the paint effectively and avoid possible hazardous effects on the people painting the aircraft. The air flow was supplied through the HVAC system in the hangar area. The HVAC system was available at the ceiling and air flows from the diffuser at the ceiling level. Grills were placed at the floor level in order to capture the air that flows down in the hangar area. The hangar area was split into three regions such that three aircrafts are placed for the purpose of painting. The three regions were separated with curtains between them which act as walls on the two sides for the aircraft at the center and walls on one side for aircrafts at the corner of the hangar area. A 2D model was simulated for the exterior airflow. Velocity of the air passing out of the diffuser was fixed at 0.56 m/s. The simulations were run at five different sections of the aircraft in order to simulate the airflow over the entire aircraft region on the exterior. The angle at which air flows from the diffuser is varied as 0°, 22.5°, 45°. This was performed in order to obtain the best possible angle at which air could be distributed in the hangar area, such that the aircraft is dried effectively at the time of painting. It was evident that the distribution of air along the aircraft exterior was more effective at diffuser angles of 0° and 22.5°. At 45° the airflow is directed away from the aircraft resulting in the circulation of air inside the hangar area.
Modeling Airflow Inside an Aircraft Interior With Multiple Inlets and Outlets
Authors: Paruchuri Rohitha , Venkatesan Yaamunan , Ravigururajan T. S.
Published: March 2011

A model for predicting the airflow inside an aircraft interior is presented in this paper. The objective was to optimize the amount of air flowing inside the aircraft at the time of painting, in order to dry the paint effectively and to minimize hazardous effects on the painting crew. The hangar area was split into three regions such that three aircrafts were placed for the purpose of painting. The three regions were separated with curtains between them which acted as separators between the aircraft. A 3D model of the aircraft fuselage with its openings was developed. The fuselage has two pilot doors, two escape hatches and two rear doors on each side of the aircraft. There are two dog houses at the bottom of the aircraft as doors to cargo section of the aircraft. Air flowing over the aircraft on the exterior is forced through into the aircraft through these eight openings provided. Air is forced out through the dog houses. The analysis was carried out for seven different scenarios in which the pilot and rear doors were chosen to be closed randomly. Two major constraints to maintain a minimum velocity of 100fpm (0.51 m/sec) throughout the inside of the aircraft and 12000 cfm (5.64 m3/sec) of air at each exit (dog houses). A minimum of 12000 cfm (5.64 m3/sec) at each exit was available in all scenarios, but the minimum requirement of 100 fpm (0.51 m/sec) was satisfactorily achieved only in which all the doors were open.
Initial Stage of Nucleate Boiling at Atomic Scale
Authors: Matsumoto Mitsuhiro , Yamamoto Takahiro
Published: March 2011

We investigated the initial stage of nucleate boiling on ideally smooth surface with a molecular dynamics simulation technique. Lennard-Jones model liquid was confined in a rectangular simulation cell, contacting with a flat smooth heating wall. Extra kinetic energy was given to particles in vicinity of the wall. As the temperature of liquid on the wall increases, the liquid thermally expands, which causes the pressure decrease, leading to formation of bubble nuclei, or cavitation, of atomic scale. We found that the nucleation is affected by surface wettability (hydrophobic or hydrophilic) as well as the magnitude of heat flux. When the surface is hydrophobic and the heating area is small, a size oscillation of generated bubbles was observed, which is determined by the balance among the heating flux from the wall, thermal diffusion into the surrounding liquid, and latent heat consumption during the phase change.
Effects of Heterogeneous Reaction and Slow/Rapid Volatilization Process on N2O Formation During the Combustion of Pulverized Biomass
Authors: Okumura Yukihiko , Watanabe Hirotatsu , Okazaki Ken
Published: March 2011

The purpose of this study is to clarify the fundamental and general features of N2O formation during the combustion of pulverized biomass under low temperature. First, the effect of various important factors, i.e., volatilization process (i.e., either slow or rapid dispersion), oxygen concentration, and solid-gas reaction on N2O formation were investigated by theoretical analysis. The analysis of the effect of the slow/rapid volatilization process on the formation of nitrous oxide showed that the conversion ratio of biomass-N to N2O increases with the decrease in the dispersion of volatile matter per unit time; it means that biomass-N is effectively converted to N2O during slow volatilization. The analysis of the effect of initial oxygen concentration on the formation of nitrous oxide showed that at low temperature (T = 1100K), the level of N2O emission increases, while that of NO emission decreases, with the decrease in initial oxygen concentration. In other words, there is a trade-off relationship between the formation of NO and that of N2O. With respect to the effect of solid-gas reaction, the gasification reactions between CO2, O2, and C(s) occur simultaneously on the surface of biomass particles during combustion. Further, the N2O emission level increases with the increase in N-content of the biomass, while the NO emission level remains constant during low-temperature combustion.
Response Compensation Scheme for Constant-Current Hot-Wire Anemometry Based on Frequency Response Analysis
Authors: Kaifuku Kazuhide , Minn Khine Soe , Houra Tomoya , Tagawa Masato
Published: March 2011

Hot-wire anemometry (HWA) is used for measuring velocity fluctuations such as turbulent flows. It is generally operated in three modes; constant-temperature (CT), constant-current (CC) and constant-voltage (CV) types. The constant-temperature anemometer (CTA) is the mainstream anemometer, while others are rarely used in measuring normal turbulent flows because of their insufficient response speed. However, since the constant-current anemometer (CCA) can be composed of simple circuits, the HWA can be realized at quite a low cost. In this study, the response characteristics of the CCA are theoretically analyzed, and a compensation scheme is proposed. The scheme is experimentally tested in a turbulent wake flow formed behind a cylinder. As a result, it has been confirmed that the root-mean-square (rms) velocities and the power-spectrum distributions compensated by the present scheme agree well with those measured with CTA. Hence, the CCA provides reliable measurement of turbulent velocity fluctuations.
Characterization and Convective Heat Transfer With Nanofluids
Authors: Yang Yijun , Oztekin Alparslan , Neti Sudhakar , Mohapatra Satish
Published: March 2011

Heat transfer and flow dynamics of nanofluids are investigated in developing laminar pipe flows. Characterization of nanofluids is examined by measuring resultant effective particle size, thermal conductivity and viscosity for various values of particle concentrations and temperatures. Nanofluids considered in this study are diamond-graphene (ND-50) nanoparticle in silicone oil (Syltherm 800), and Al2O3 nanoparticles in DI water with and without dispersers/stabilizers. The particle size of various nanofluids is determined quantitatively from measurements using Dynamic Light Scattering device (DLS) and also determined qualitatively from SEM images. Thermal conductivity measurements are conducted by using nano-flash LFA447 device for particle volume fractions ranging from 0.8% to 5.1%. Measured values of thermal conductivity of all fluids at low concentrations agree well with the results predicted by Maxwell model. Viscosity measurements are conducted using parallel plate geometry Rheometrics viscometer at different concentration and temperature as a function of shear rate. At low shear rates the fluid behaves as a Newtonian fluid while it becomes a shear thinning fluid at higher particle concentration of the same nanofluid. There is a significant increase in the viscosity at even low concentrations. Viscosity of nanofluids is also a strong function of temperature at all values of concentration considered in this study. The significant increase in viscosity may diminish nanofluids’ application as an advanced heat transfer fluid. The effects of nanofluid on the drag reduction and heat transfer enhancement are determined and compared with the pressure drop and heat transfer coefficient measurements with the base fluids at the same flow conditions. Our experimental measurements indicate that the pumping power to flow nanofluids is nearly the same as the pumping power required to flow the same amount of base fluid although the viscosity of nanofluids are significantly higher. Convective heat transfer enhancement with the nanofluids is limited to 5% or slightly higher as has also been reported by other workers. Hence addition of nanoparticles into heat transfer fluids could have the potential for heat transfer enhancement in pipe flow without paying the penalty of increasing pumping power.
On the Scaling of Pool Boiling Heat Flux With Gravity and Heater Size
Authors: Raj Rishi , Kim Jungho , McQuillen John
Published: March 2011

A framework for scaling pool boiling heat flux is developed using data from various heater sizes over a range of gravity levels. Boiling is buoyancy dominated for large heaters and/or high gravity conditions and the heat flux is heater size independent. The power law coefficient for gravity is a function of wall temperature. As the heater size or gravity level is reduced, a sharp transition in the heat flux is observed at a threshold value of Lh/Lc = 2.1. Below this threshold value, boiling is surface tension dominated and the dependence on gravity is smaller. The gravity scaling parameter for the heat flux in the buoyancy dominated boiling regime developed in the previous work is updated to account for subcooling effect. Based on this scaling parameter and the transition criteria, a methodology for predicting heat flux in the surface tension dominated boiling regime, typically observed under low-gravity conditions, is developed. Given the heat flux at a reference gravity level and heater size, the current framework allows the prediction of heat flux at any other gravity level and/or heater size under similar experimental conditions. The prediction is validated using data at over a range of subcoolings (7°C ≤ ΔTsub ≤ 32.6°C), heater sizes (2.1 mm ≤ Lh ≤ 7 mm), and dissolved gas concentrations (3 ppm ≤ cg ≤ 3500 ppm). The prediction errors are significantly smaller than those from correlations currently available in the literature.
Scaling of Transient Natural Convection Cooling in a Side-Cooled Cavity: The Effect of Variable Viscosity
Authors: Younis Obai , Xu Feng , Lei Chengwang , Patterson John C. , Pallares Jordi , Grau Francesc X.
Published: March 2011

The transient natural convection of variable and constant viscosity fluids in a side cooled cubical cavity is studied experimentally. The convective flow in the cavity is visualized by the shadowgraph technique. The fluid was initially preheated and enough time is allowed to assure uniform temperature distribution. Temperature difference is introduced by a sudden cooling of the two side walls. The results indicate that the transient flow development is characterized by the following distinct processes: the initial growth of the vertical boundary layer and horizontal intrusions, the interaction of the horizontal intrusions and the stratification. New scaling relations are introduced to include the effect of the viscosity variation with temperature. The new suggested scalings showed good agreement with the measurements based on the shadowgraph images.
Soot and PAH Formation Characteristics in a Micro Flow Reactor With a Controlled Temperature Profile
Authors: Tanimoto Ryu , Tezuka Takuya , Hasegawa Susumu , Nakamura Hisashi , Maruta Kaoru
Published: March 2011

To examine soot and PAH formation processes for rich methane/air and acetylene/air mixtures, a micro flow reactor with a controlled temperature profile was employed. In the experiment for a methane/air mixture, four kinds of responses to the variations of flow velocity and equivalence ratio were observed as follows: soot formation without a flame; a flame with soot formation; a flame without soot formation; and neither flame nor soot formation. Soot formations were observed in low flow velocity and high equivalence ratio. Starting point of soot formation shifted to the upstream side, i.e., low-temperature side, of the micro flow reactor with the decrease of flow velocity. One-dimensional steady-state computation was conducted by a flame code. In high flow velocity, low mole fraction of C2H2 and high mole fraction of OH were observed in the whole region of the micro flow reactor. Soot volume fraction did not increase in this case. On the other hand, in low flow velocity, high mole fraction of C2H2 and low mole fraction of OH were observed at the downstream side of the micro flow reactor. Soot volume fraction increased in this case. Since significant soot formation was observed at the low flow velocity and the high equivalence ratio, experiments with gas sampling were conducted for acetylene/air mixture to investigate temperature and equivalence ratio dependence of soot precursor production in such condition. Volume fractions of benzene increased with an increase of temperature. They were larger at higher equivalence ratio at the same temperature. Volume fractions of styrene increased with an increase of temperature. They were larger at higher equivalence ratio when the temperature is less than 1000 K. However the tendency was changed at 1000 K, styrene volume fraction at equivalence ratio of 7.0 was larger than that at equivalence ratio of 8.0.
Formation of Electro-Conductive Part on Polymeric Material Surface by CO2 Laser Irradiation
Authors: Saito Takushi , Kawaguchi Tatsuya , Satoh Isao
Published: March 2011

In this study, a method to directly form an electrically conductive layer on the surface of polymeric material by using infrared laser irradiation was investigated. Polyacrylonitrile, which was shaped into a small disk 20 mm in diameter and 5 mm thick, was used as a test specimen. The conditions for pyrolysis were obtained by referencing the conditions for commercial carbon fiber. First, the specimen was processed in air at a relatively low temperature (around 250°C) for the stabilization treatment (i.e., fireproofing), then its surface was heated at a higher temperature (above 1000°C) for the carbonization treatment (i.e., graphitizing). Both an infrared furnace and a carbon dioxide laser were used as heating devices to find optimal conditions. Property changes in the material due to the thermal treatment were measured using Fourier transform infrared spectroscopy, and the electrical conductivity of the carbonized surface was measured using a four-probe method. The results showed that an electrical conductivity of 11.4 S/cm (siemens per centimeter) was achieved with a laser intensity of 8.6 W/cm2 for 5 min for the stabilization, and a laser intensity of 34 W/cm2 for 10 s for the carbonization.
Measurement of Fluorescence Properties in Light Scattering Medium
Authors: Maruoka Shoji , Mitsui Yohei , Okawa Shinpei , Hoshi Yoko , Yamada Yukio
Published: March 2011

The purpose of this study is to measure the fluorescence properties of Indocyaninegreen (ICG) which is a fluorescence dye to be used as a fluorescence probe for the use of fluorescence imaging in biomedical applications. The fluorescence molecular imaging is expected to solve the issues in preclinical studies which require a lot of time, labors and sacrificed animals. Information of living body can be obtained by measuring the fluorescent properties of the probe in biological media. The absorption and emission spectra and the lifetime of ICG in non-scattering and scattering media were measured in this study. ICG was dissolved in water, in plasma, in Intralipid, and in a mixture of plasma and Intralipid to simulate the environment in living tissues. The absorption and emission spectra were measured using a fluorescence spectrophotometer. The fluorescence lifetimes were measured using a time-resolved measurement method. Results suggest that the fluorescent properties are affected by the reaction between ICG and biological tissues.
Numerical Study on Microwave Dehydro-Freezing of Fish Tissues
Authors: Oku Yuichiro , Tanigawa Hirofumi , Tsuruta Takaharu
Published: March 2011

In this study, a numerical simulation on the freezing process is carried out to evaluate the effects of pre-dehydration on the quality of frozen fish tissue. We use a simulation model which contains a muscle fiber to express the microscale heat and mass transfer phenomena inside the tissue cell system. Fundamental equations on heat and mass transfer are formulated in a two-dimensional coordinate system. The governing equations include phase-change terms. In order to take account of the characteristic moisture distribution produced by the microwave room-temperature drying, initial moisture distributions are given in this calculation. The numerical results indicate that the control of the water content by the pre-dehydration can shorten the freezing time. It is found that the cell shrinkage ratio is larger than that of the result using uniform distribution. As an increase of pre-dehydration, the central cell significantly shrinks but the surface-layer cell doesn’t shrink so much due to the large cooling rate.
Effect of Alkyl Chain Length on Molecular Heat Transfer Characteristics in Lipid Bilayers
Authors: Nakano Takeo , Kikugawa Gota , Ohara Taku
Published: March 2011

Nonequilibrium molecular dynamics simulations are carried out on single component lipid bilayers with ambient water in order to investigate the effect of acyl chain length on heat transport characteristics along and across the membranes. In this study, dipalmitoyl-phosphatidyl-choline (DPPC), dilauroyl-phosphatidyl-choline (DLPC), and stearoyl-myristoyl-phosphatidyl-choline (SMPC) which has two acyl chains of both sixteen C atoms, both twelve C atoms, and eighteen and fourteen C atoms, respectively, were used as lipid molecules. In the direction along the membranes, thermal conductivity corresponds with that of each membrane. On the other hand, in the direction across membrane, the highest thermal resistance exists at the center of lipid bilayer where lipid acyl chains face each other. However, asymmetric chain length reduces thermal resistance at the interface between lipid monolayers. Therefore, thermal conductivity across the membrane which consists of asymmetric chain length is higher than those which consist of symmetric chain length.
Flow-Geometry and Reynolds-Number Effects on Flame-Turbulence Interactions
Authors: Minamoto Yuki , Nada Yuzuru , Shimura Masayasu , Fukushima Naoya , Shim Youngsam , Tanahashi Mamoru , Miyauchi Toshio
Published: March 2011

Three-dimensional direct numerical simulation (DNS) with a detailed kinetic mechanism has been conducted for statistically-planar turbulent flame and turbulent V-flame of hydrogen–air mixture to clarify the effects of mean flow velocity on principal strain rates at flame front and on flame geometry. Reynolds numbers based on Taylor micro scale and turbulent intensity are selected to 60.8 and 97.1, and mean flow velocities for V-flame are 10 and 20 times laminar burning velocity. From results of DNS, eigenvalues and eigenvectors of strain tensor are evaluated to investigate characteristics of strain field near flame and flame normal alignments with the principal axes of strain in detail. It has been revealed that Reynolds number affects both magnitude of strain rates and alignment between flame normal and principal axis of strain, and that the magnitude of mean flow velocity affects flame normal alignments in turbulent V-flame.
DNS of Turbulent Premixed Flames and Heat Transfer in a Constant Volume Vessel
Authors: Fukushima Naoya , Tsunemi Akihiko , Shimura Masayasu , Shim Youngsam , Tanahashi Mamoru , Miyauchi Toshio
Published: March 2011

Three-dimensional direct numerical simulation (DNS) of turbulent hydrogen-air premixed flames in a constant volume vessel at relatively high Reynolds numbers have been conducted considering detailed kinetic mechanism and temperature dependence of the transport and thermal properties. The flame behavior and heat transfer characteristics are investigated in the vessel. The flame is strongly affected by the growth of the internal pressure which is caused by the temperature rise in the vessel. Since the pressure increase makes the flame thickness thin, the heat release rate of each flame element is augmented. The local pressure rise due to the dilatation also enhances turbulence and finer scale vortices appear, which make the flame surface more complicated and result in an increase of the flame surface area. Due to the increase of the mean pressure in the vessel, the maximum wall heat flux induced by the flame front is enhanced during the combustion.
Internal Fire Whirls Induced by Pool Fire in a Vertical Shaft
Authors: Huo Yan , Chow W. K. , Gao Ye
Published: March 2011

Internal fire whirls induced by a pool fire in a square vertical shaft were studied by experiments and numerical simulations. The burning behaviour of two pool fires in the vertical shaft and in open air was compared. The gap width of the rig is a key factor in onsetting fire whirls. Air flow field in the vertical square shaft of different gap widths were studied experimentally with nine tests. A fire whirl would not be onsetted when the gap is too narrow nor too wide. Whirling flame is not clearly observed near to the bottom of the vertical shaft when the gap width was small.
Effect of the Arrangement of Optodes for 3D Diffuse Optical Tomography
Authors: Uchida Kazuhiro , Okawa Shinpei , Masamoto Kazuto , Hoshi Yoko , Yamada Yukio
Published: March 2011

Diffuse optical tomography (DOT) can obtain tomographic images of hemodynamics such as the oxygenation state and blood volume in tissues using light in the near infrared wavelength range where tissues absorb light weakly and oxy- and deoxy-hemoglobins show different absorbing characteristics. For 3D-DOT, much more optodes than those for 2D-DOT are desirable for high quality images. But practically the number of the optodes is limited and it is necessary to find the optimum arrangement of the optodes. This paper studies the effect of the optode arrangement on the reconstructed images by simulation of 3D-DOT when the number of the optodes is 16 and the object is a sphere with a diameter of 100 mm. Simulation results show that the optode arrangement which can effectively detect the light propagating through the target is important to reconstruct the target at the correct positions.
Impact of Interstitial Mass Transport Resistance on Water Vapor Diffusion Through Southern Mills Defender™ 750 Fabric Layers
Authors: Sharma A. , Boetcher S. K. S. , Aissa W. A. , Traum M. J.
Published: March 2011

Textiles maintain wearer comfort by allowing evaporated sweat to permeate through, providing thermal management and keeping skin dry. Each textile layer presents a resistance to mass transport consistent with its physical structure (i.e., thickness, porosity, and tortuosity). However, when textiles are layered, water vapor transport becomes more complex because diffusing molecules must traverse interstitial spaces between layers. Interstitial mass transport resistances of significant magnitude can reduce rates of water vapor transport through layered textile stacks. The prevailing textile mass transport resistance interrogation method is ASTM F1868: “Standard Test Method for Thermal and Evaporative Resistance of Clothing Materials Using a Sweating Hot Plate.” A self-calibrating element of this method is to measure one, two, three, and four fabric layers. Each newly added layer is prescribed to increase the stack mass transport resistance by the integer resistance presented by a single layer with no interstitial resistance consideration. Four improvements to ASTM F1868 are recommended: 1) gravimetric mass transport measurement, 2) a Stefan flow model, 3) correct accounting for apparatus mass transport resistances, and 4) recognizing and measuring interstitial mass transport resistances. These improvements were implemented and evaluated by running tests using Southern Mills Defender™ 750 fabric, the calibration standard used for ASTM F1868, on a new gravimetric experimental apparatus. The mass transport resistance of one fabric layer measured via the gravimetric method is related to the ASTM F1868 value through working fluid properties. Using the gravimetric approach, mass transport resistance for a single layer of calibration fabric was measured at 60.3 ± 14.4 s/m, which is consistent with the prescribed result from ASTM F1868 (after the conversion factor), 73.1 ± 7.3 s/m. The diffusion coefficient for water vapor in air in the fabric pores measured by gravimetric experiment, (2.02 ± 0.59) × 10−5 m2/s, agrees (within experimental uncertainty) with the theoretical value for the experimental conditions, 2.54 × 10−5 m2/s. However, for stacks of two or more calibration fabric layers, the gravimetric approach does not agree with the prescribed ASTM F1868 result due to interstitial mass transport resistance between fabric layers. The measured interstitial resistance value is 23.6 s/m, 39.1% of a single fabric layer, a value too significant to be ignored in engineering analysis.
Femtogram-Level Thermophysical Property Measurement of Polymeric Samples Using Heated Microcantilevers
Authors: Gauffreau Andrew M. , Park Keunhan
Published: March 2011

This article investigates thermophysical property measurement of femtogram-level polymeric samples by using the 3ω method on a heated microcantilever probe. A localized thermal scooping method was employed to acquire 449 fg of polyethylene terephthalate (PET) sample, measured gravimetrically, directly onto the heater of the cantilever. It is shown that the sample case has a 3ω signal that is smaller in magnitude than the bare case, suggesting that sample properties could be determined using the processes discussed here. A finite element analysis (FEA) model was also developed to compute the steady periodic behavior of the cantilever in the frequency domain. In order to drastically reduce the computational cost and consider the transient effect of the surrounding air, the FEA model implements the complex thermal conductance of the air as the boundary condition rather than modeling the air as a separate domain. The comparison of the modified model with the model that includes the air in the system reveals that the running time has improved by one order of magnitude while showing excellent agreement. The obtained results will expand the characterization and functionality of microcantilevers leading to advancements in localized thermal analysis.
Impact of Surface Micro-Structures on Liquid Micro-Jet Array Impingement Cooling: Comparison Between Single-Phase and Phase Change Heat Transfer
Authors: Bhunia Avijit , Chen Ya-Chi , Chen Chung-Lung
Published: March 2011

This article investigates liquid micro-jet array impingement cooling of a micro-structured surface. An array of 16 free-surface DI water jets, each 125 μm in diameter, and jet Reynolds number ranging between 816 and 2124, is used. A parametric study is carried out with micro-studs of varying size and spacing, implemented on a 1 cm2 base area surface. Based on the decades of research on heat transfer enhancement by surface modification, one would intuitively think that impingement cooling of a micro-structured surface will always be better than that of a plain surface. The current results are in contrary. The micro-structures actually degrade single-phase impingement heat transfer, compared to a plain surface. On the other hand, in the phase change regime they significantly enhance heat transfer, leading to a clear choice of optimal structure. The results are explained in the light of thin film dynamics, heat transfer surface area enhancement and nucleation site density.
An Experimental Study of Heat Transfer From Small Horizontal Cylinders at Near-Critical Pressures
Authors: Rousselet Yohann , Warrier Gopinath R. , Dhir Vijay K.
Published: March 2011

An experimental study of the free convection heat transfer from horizontally held wires to carbon dioxide at near-critical pressures has been performed. In the experiments, platinum wires of 25.4 μm, 76.2 μm and 100 μm, as well as a 101.6 μm diameter nichrome 60/20 wire were used. The pressure (P) and bulk temperature (Tb) of the fluid were varied in the range: 6.34 MPa ≤ P ≤ 9.60 MPa and 10 °C ≤ Tb ≤ 33.3 °C, respectively. Visual observation of the flow was realized using a high speed camera. The bulk fluid temperature is introduced as a new reference temperature for the calculation of fluid properties. Correlations were developed to predict the natural convection heat transfer rate at both subcritical and supercritical pressures. The correlations developed predict almost all the experimental data from the current study and those reported in the literature to within ± 15%. No bubble-like flow pattern was observed for both platinum and nichrome wires.
Concerning the Effect of Surface Material on Nucleate Boiling Heat Transfer of R-113
Authors: Hosseini R. , Gholaminejad A. , Nabil Mahdi , Samadinia Mohammad Hossein
Published: March 2011

This paper presents results of an experimental investigation carried out to determine the effects of surface material on nucleate pool boiling heat transfer of refrigerant R113. Experiments were performed on horizontal circular plates of brass, copper and aluminum. The heat transfer coefficient was evaluated by measuring wall superheat and effective heat flux removed by boiling. The experiments were carried out in the heat flux range of 8 to 200kW/m2. The obtained results have shown significant effect of surface material, with copper providing the highest heat transfer coefficient among the samples, and aluminum the least. There was negligible difference at low heat fluxes, but copper showed 23% better performance at high heat fluxes than aluminum and 18% better than brass.
Effects of Local Concentration on Freezing Solutions of Winter Flounder Antifreeze Protein
Authors: Hagiwara Yoshimichi , Sakurai Ryo , Yamamoto Daichi , Kitagawa Atsuhide
Published: March 2011

We have carried out experiments on the one-directional freezing of an aqueous solution of winter flounder antifreeze protein in a narrow gap between two cover glasses. The motion of the ice/solution interface has been observed with an inverted microscope. The solution has been cooled by a Peltier device. The local change in protein concentration has been estimated from the measured intensity of fluorescence from molecules tagged to the protein. It is found that highly-concentrated regions of the protein can be observed in the bottom edge of the serrated interface. These regions interact with the interface, though most of the protein diffuses due to the concentration gradient. The diffusion velocity is much lower than the interface velocity. Thus, the protein is accumulated near the interface.
Multiple Droplet Impingements on Nanostructured Surfaces for Enhanced Spray Cooling
Authors: Alvarado Jorge L. , Lin Yen-Po
Published: March 2011

Spray cooling has been studied thoroughly over the years in an effort to understand its unique heat transfer potential. Spray cooling is characterized by its ability to dissipate high heat transfer rates while maintaining relatively uniform surface temperatures. Despite of all the recent developments, liquid-surface properties such as contact angle and surface tension have been shown to limit the ability of spray cooling to dissipate high heat flux. Recent high-speed images of multiple droplet impingent events have revealed that liquid film thickness, impact crown morphology, and tangential velocity gradients tend to dominate the overall heat transfer process. All these aspects are intrinsically linked to surface morphology. Therefore, enhancement of heat transfer should be preceded by the design, fabrication and use of surfaces that reduce film thickness, promote constructive impact crown morphology, and facilitate greater tangential velocity gradients. Recently, a new type of nanostructured surface has been designed, fabricated, and tested that reduces film thickness and contact angle by at least 30%. The nanostructured surface consists of nanopillars of 100 nm in height and 200 nm in diameter. The combination of spacing and nanopillar size has resulted in a thinner liquid film. The nanostructured surface was fabricated using the Step and Flash Imprinting Lithography (S-FIL) technique. Current work also includes the study of the relationship between the effective thermal diameter and heat flux when using nanostructured and bare surfaces.
Photovoltaic Generation of Electricity Using Near-Field Radiation
Authors: Hanamura Katsunori , Fukai Hirofumi , Srinivasan Elaiyaraju , Asano Masao , Masuhara Teppei
Published: March 2011

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1 μm or 1.8 μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.
Experimental and Numerical Study on Growth of Single Vapor Bubble in Upward Flow Through Vertical Mini-Tube
Authors: Iwai Hiroshi , Saito Motohiro , Kami Yuichi , Niina Yasuhiro , Yoshida Hideo
Published: March 2011

A slug flow with phase change in a vertical mini-tube is numerically simulated on the basis of a scheme of continuum mechanics. To formulate two-phase flow, the volume of fluid, VOF, method is employed; the advection of the gas-liquid surface is expressed by the piecewise linear interface calculation, PLIC, scheme, while the effect of surface tension is evaluated by the continuum surface force, CSF, model. Since the treatment of liquid film between a bubble and tube wall is crucially important to properly predict both heat transfer and resulting fluid flow in a mini-tube, a semi-empirical approach based on subsidiary knowledge estimated from a preliminary experiment is newly proposed. Further, an additional numerical procedure is introduced to obtain allowable mass conservation even in the thin-film region with intense evaporation. Consequently, by introducing only one parameter, the physical meaning of which is clear, the bubble behavior is reasonably predicted, and its detailed mechanism is clarified.
Thermal Radiation From a Photonic Crystal of Silica-Particles
Authors: Ikemachi Nozomi , Nakano Ryota , Kurogi Shohei , Miyazaki Koji
Published: March 2011

Thermal radiation properties, such as reflectivity and emissivity, have been well modified by using a photonic crystal in this decade. In this paper we fabricated three-dimensional photonic crystals by self-assembled silica particles with 3 μm diameter. The close-packed hexagonal photonic crystal with defects is observed by SEM. The measured specular reflectance explained by modified Bragg’s law is measured with a diffuse reflectance by FT-IR. The near normally incident diffuse reflectance is measured by using paraboloidal mirrors to understand the diffuse reflection. We experimentally confirmed the strong diffuse reflectance in the near infrared regions. We numerically calculated reflectance of the three-dimensional photonic crystals by RCWA. The diffuse reflectance in near infrared is calculated only in the photonic crystal with defects. The numerically calculated diffuse reflectance is roughly explained by Mie scattering theory. The directional emissivity of the photonic crystal is measured by FT-IR with collimator. The normal emittance is suppressed in the photonic gap, but the directional emittance is enhanced in 30 degrees. The absorptance is numerically calculated to understand the experimental results. The numerical results show that the directional absorptance is increased in narrow direction. The directional sharp peak in 30 degrees is calculated although the monocrystalline photonic crystal is assumed in the numerical model. The effects of the defects in the photonic crystal on the emittance should be considered to explain the experimental results.
Thermal Rectification in Graphene and Carbon Nanotube Systems Using Molecular Dynamics Simulations
Authors: Vallabhaneni Ajit K. , Hu Jiuning , Chen Yong P. , Ruan Xiulin
Published: March 2011

We investigate the thermal rectification phenomena in asymmetric graphene and carbon nanotube systems using molecular dynamics (MD) simulations. The effects of various parameters, including mean temperature, temperature difference, and system size on rectification factor have been studied. In homogenous triangular graphene nanoribbons (T-GNR), the heat current is normally higher from wide to narrow end than that in the opposite direction, resulting in a positive rectification factor. The rectification factor increases further for a double layered T-GNR. It is also found that varying the parameters like mean temperature can result in reverse of the sign of thermal rectification factor. In the case of carbon nanotube (CNT)–silicon system, the heat current is higher when heat flows from CNT to silicon. The thermal rectification factor is almost independent of the diameter of CNT. In both cases, the rectification factor increases with the imposed temperature difference.
The Characteristics of Recycled-NO Reduction in O2/CO2 Coal Combustion
Authors: Marumo Takashi , Yamamoto Jun-ichiro , Watanabe Hirotatsu , Okazaki Ken
Published: March 2011

O2/CO2 coal combustion is a promising technology for easy CO2 recovery and low NOx emission. O2/CO2 coal combustion system has very high CO2 concentration, and so O2/CO2 ratio is very important parameter in this system. In this study, the effect of CO2 concentration on recycled NO reduction was investigated experimentally and numerically. It was revealed that the recycled NO reduction ratio was increased with decreasing CO2 concentration. This was because high CO2 concentration enhanced the reaction to produce OH radical (CO2 + H → CO + OH). Both calculations and experiments showed OH radical increased with an increase in CO2 concentration. However, increasing OH radical enhanced the consumption of H2 which is needed for the reduction of secondary NO. It was shown that high CO2 concentration inhibits recycled-NO reduction from the new point of CO2 reactivity.
Effect of Skin Structure Change With Age on Optical Characteristics of Human Skin
Authors: Yamada Jun , Ogawa Tatsuya , Kawai Hirokazu , Yoshikawa Hironobu , Takata Sadaki
Published: March 2011

It is considered that the surface structure of human skin changes with age, affecting the appearance of skin. However, the effect of skin structure on its appearance has not yet been clarified. In this study, we measured the geometric structure of the skin of eight women in the age group of 21 to 45 years using the latest confocal scanning laser microscope, and clarified the change in skin structure with age. In addition, based on the geometric data of the skin structure, we numerically investigated the optical characteristics of the skin surface by using a numerical model developed by us. Numerical results reveal that the optical characteristics of skin surface do not depend on the age-induced change in the skin structure very much.