bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastic Wave Suppression of Permanent Magnetic Motors by Pole/Slot Combination
Authors: Wang Shiyu , Xu Jinyou , Xiu Jie , Liu Jianping , Zhang Ce , Yang Yuhu
Published: March 2011

This work investigates the influence of the pole/slot combination on the elastic wave deformation of permanent magnetic motors. To this aim, the local wave superposition and distributed wave interaction methods are used during investigation. The methods borrow ideas from other fields such as the planetary gears, the turbines, and so on because of the inherent mechanical and magnetic symmetry of the motor. More precisely, the symmetry naturally presents some interesting and useful results without specifying the magnetic pulls/waves or even their magnitudes. The analysis results explicitly show that the elastic wave deformations only depend on whether particular algebraic relations are satisfied by the combination of pole number, slot number, magnetic pull order, and wave number. The predicted relationship and the wave suppression effectiveness are verified by the finite element method and a comparison with an existing literature. The relationship naturally provides simple guidelines for the elastic wave deformation suppression only by using the proper pole/slot combination.
Modeling of Strain-Stress Relationship for Carbon Steel Deformed at Temperature Exceeding Hot Rolling Range
Authors: Hojny Marcin , Glowacki Miroslaw
Published: March 2011

The subject of the presented paper is the modeling of strain-stress relationship, which is the main mechanical property characteristic of the behavior of steel subjected to plastic deformation. The major challenge of the research is the temperature of the deformation, which significantly exceeds the hot rolling temperature range. This paper presents the results of work leading to the development of a rheological model describing the phenomena accompanying the deformation of 18G2A grade steel at temperature 1420°C and higher. Such temperature is a characteristic of the central parts of steel strands subjected to latest, very high temperature rolling technologies such as integrated rolling and casting processes. Rheological models have crucial influence on the results of the computer simulation of the mentioned processes. The methodology of yield stress curves development requires high accuracy systems of tension and compression test simulation. Hence, the proposed testing procedure is related to dedicated hybrid finite element method system with variable density, which was developed by the authors. The experimental work has been done using the Gleeble® 3800 thermomechanical simulator in the Institute for Ferrous Metallurgy in Gliwice, Poland. The testing machine allows the physical deformation of samples while solidification of their central part is still in progress. The essential goal of the simulation was the computer reconstruction of both temperature changes and strain evolution inside a specimen subjected to simultaneous deformation and solidification. In order to verify the predictive ability of the developed rheological model, a number of compression tests using Gleeble® 3800 simulator have been done, as well. The comparison between the numerical and the experimental results is also a part of the presented paper.
Experimental Study on Model Predictive Control to Minimize Temperature Change of Vertical Plate With Varying Heat Generation
Authors: Hirasawa Shigeki , Kawanami Tsuyoshi
Published: March 2011

Precise temperature control of 0.001°C under noise-temperature change of 0.1°C is required in semiconductor manufacturing process. We made an experimental apparatus of a vertical steel plate placed in an atmosphere with a varying noise-heat-generation and a control-heater. The noise-heat-generation is that the heating-OFF and ON every 300 s, and it makes temperature change of 3°C at an object position in the plate without control. The control-heater is controlled with the model predictive control method of 5 s interval with two monitoring temperatures to minimize temperature change at the object position in the plate. In this work, we study the effect of the dynamic predictive model on the temperature change at the object position and examine how to make the best dynamic predictive model. Three methods to make the dynamic predictive model are examined: (1) dynamic step responses are obtained by experiment, (2) dynamic step responses are obtained by calculation with a network model of the object, and (3) both step response patterns are combined. When the step response patterns obtained by experiment and calculation are combined to use, the minimum temperature change at the object position is 0.06°C and 1/50 times smaller than that without control. Also, the effect of artificial error in the dynamic predictive model on temperature change at the object position is examined by numerical simulation.
Space-Time-Structure Map for As Cast Massive Rolls
Authors: Wołczyn´ski Waldemar S. , Kania Bogusz , Wajda Wojciech , Kostrzewa Mirosław
Published: March 2011

A thermal gradients’ field was studied for an as cast massive roll. Three ranges within the thermal gradients field were differentiated. The thermal gradient is constant along with the second range of thermal gradients’ field. Thus, columnar into equiaxed structure transition (CET) is to be expected within the second range. This statement is in good qualitative agreement with a similar observation given by Hunt’s theory. The columnar structure formation was significantly slowed down within the second range of thermal gradients field. At beginning of the second range the liquidus isotherm tears away from columnar structure / liquid interface. The columnar structure is still formed within the time adequate to the second range of thermal gradients but its growth vanishes due to lost competition, and at the end of the second range the equiaxed structure growth dominates, exclusively. In fact, the extrapolation of the velocity of the columnar structure / liquid interface to its value equal with zero confirms the appropriate location of the end of the second range within which the CET is observed. The detailed analysis of the solidus isotherm / liquidus isotherm movements allows a development of the Space-Time-Structure Map for a solidifying massive roll. The Map shows the location of the CET in time (solidification time) and in space (along the roll radius). Moreover a proper locations of structural zones are drawn in the Map. The simulation of the thermal gradients’ field is a very useful tool in the industrial practice. The results of simulation can be used to predict the Space-Time-Structure Map (STSM) for a given massive roll or a massive ingot. Additionally, the equation for solute redistribution after back-diffusion was formulated on the basis of the new theory for microsegregation. It allows formulating the so-called macrosegregation index dealing with the whole ingot/roll volume.
A Microstructure Device for Single Phase Surface Cooling
Authors: Brandner Juergen J. , Kamaruzaman Natrah binti , Maikowske Stefan
Published: March 2011

A microstructure device for cooling of hot surfaces at liquid single phase laminar flow is presented. The initial design as well as the theoretical background is described in detail. It consists of numerous short micro channels acting as overflow structures and providing a relatively large hydraulic diameter, used in parallel between large inlet and outlet channels. The design was chosen to be scalable as well as appropriate for mass production in different materials. The fluid distribution was optimized as well as the dimensions of the overflow structures in terms of heat transfer, both by CFD simulations. Several devices were tested. They provide very high heat flux at reasonably low pressure drop. The temperature difference to achieve, heat flux and pressure drop can be adjusted easily by control of the applied mass flow. The design was tested as liquid-liquid heat exchanger in a simple lab-scale test facility. Moreover, using a copper electrically powered surface heat focus, some devices were tested as surface coolers.
Investigation of the Working Processes in a Gas Turbine Combustor With Steam Injection
Authors: Serbin Serhiy , Mostipanenko Anna , Matveev Igor
Published: March 2011

Theoretical and experimental investigations of the working processes in a gas turbine combustor with steam injection have been conducted. Selected concept of a gas turbine combustor can provide higher performance, wider turn down ratios, lower emission of nitrogen oxides, demonstrate satisfactory major gravimetric and volumetric parameters. Obtained results and recommendations can be used for the gas turbine combustor operation modes modeling, geometry optimization, prospective propulsion and power generation units design and engineering.
Numerical Analysis of Microdroplet Impact and Evaporation on a Solid Surface
Authors: Son Gihun
Published: March 2011

Microdroplet impact and evaporation on a solid surface, which is an integral part of an inkjet printing process, is studied numerically by solving the equations governing the conservation of mass, momentum, energy and mass fraction in the liquid and gas phases. The deformed droplet shape is tracked by a sharp-interface level-set method which is modified to include the effects of evaporation at the liquid-gas interface and dynamic contact angle at the liquid-gas-solid interline. The numerical results show that the droplet impact and evaporation pattern depends significantly on the advancing and receding contact angles. Also, the effect of cavity sidewall on the droplet motion is investigated.
Defect-Induced Thermal Rectification: Numerical Study on Carbon Nanotube and FPU-Beta Lattice
Authors: Hayashi Hiroyuki , Takahashi Koji
Published: March 2011

The thermal properties of a half-defective single-walled carbon nanotube, and one-dimensional (1D) nonlinear lattices were investigated to unveil the mechanism of defect-induced thermal rectification. We propose a model of an asymmetrically defective low-dimensional material to explain the underlying mechanism of thermal rectification obtained in a past experiment in which C9H16Pt was asymmetrically deposited on a nanotube. These numerical approaches show the applicability of asymmetrically defective low-dimensional material to solid-state thermal rectification.
Determination of Heat of Reaction in Supercritical Water
Authors: Matsumura Yukihiko , Tsujimoto Go , Konishi Takuro
Published: March 2011

The heat of reactions in supercritical water is difficult to measure. Our group fabricated a new reactor to enable the measurement of this heat with extremely high accuracy. The system consisted of a single, insulated tube reactor. The reaction heat was determined by the temperature change of the flow caused by the heat. We found, however, that the heat loss of the reactor compromised the measurements accuracy. Though small, this factor was impossible to completely remove, especially when the reaction was fast or the flow was slow. To compensate, we measured the heat loss and used the measured value to correct our calculation of the reaction heat. The direct measurements of the reaction heat agreed well with the calculated values, with relative error of only around 5% up to reaction heats as large as 100 kJ/kg-water.
Analysis of Laminar Slip-Flow Thermal Transport in Microchannels With Transverse Rib and Cavity Structured Superhydrophobic Walls at Constant Heat Flux
Authors: Maynes D. , Webb B. W. , Soloviev V.
Published: March 2011

This paper presents an analytical investigation of the thermally developing and periodically fully-developed flow in a parallel-plate channel comprised of superhydrophobic walls. The superhydrophobic walls considered in this paper exhibit alternating micro-ribs and cavities positioned perpendicular to the flow direction and the transport scenario analyzed is that of constant wall heat flux through the rib surfaces with negligible thermal transport through the vapor cavity interface. Axial conduction is neglected in the analysis and the problem is one of Graetz flow with apparent slip-flow and periodicity of constant heating. Closed form solutions for the local Nusselt number and wall temperature are presented and are in the form of infinite series expansions. Previously it has been shown that significant reductions in the overall frictional pressure drop can be expected relative to the classical smooth channel laminar flow. The present results reveal that the overall thermal transport is markedly influenced by the relative cavity region (cavity fraction), the relative rib/cavity module width, and the flow Peclet number. The following conclusions can be made regarding thermal transport for a constant heat flux channel exhibiting the superhydrophobic surfaces considered: 1) Increases in the cavity fraction lead to decreases in the average Nusselt number; 2) Increasing the relative rib/cavity module length yields a decrease in the average Nusselt number; and 3) as the Peclet number increases the average Nusselt number increases. For all parameters explored, the limiting upper bound on the fully-developed average Nusselt number corresponds to the limiting case scenario of classical laminar flow through a smooth-walled channel with constant heat flux.
Hybrid SN-PN Solution of the Radiative Transfer Equation in Multi-Dimensional Media
Authors: Sankar Maathangi , Mazumder Sandip
Published: March 2011

The Modified Differential Approximation (MDA) was originally proposed for solution of the radiative transfer equation (RTE) in order to remove the shortcomings of the P1 approximation in scenarios where the radiation intensity is strongly directionally dependent. In the original MDA approach, the wall-emitted component of the intensity is determined using a surface-to-surface exchange formulation that makes use of geometric viewfactors. Such an approach is computationally very expensive for complex geometry and/or inhomogeneous media. This article presents a new formulation in which the wall-emitted component is solved using the Discrete Ordinates Method (SN approximation), while the medium-emitted component is solved using the P1 approximation, resulting in a hybrid SN-PN RTE solver. Results show that the hybrid Discrete Ordinates-P1 method (DOM-P1) is computationally very efficient, but its accuracy is poor in optically thin situations where ray effects, inherent in the Discrete Ordinates Method, are pronounced. To circumvent this problem, the control-angle Discrete Ordinates Method (CADOM) is finally employed, and the accuracy of the hybrid CADOM-P1 method is found to be far superior to the hybrid DOM-P1 method.
Dryout Studies of Carbon Nanotube Bi-Porous Structure
Authors: Cai Qingjun , Chen Ya-Chi , Chen Chung-lung
Published: March 2011

Dryout occurring in a heat pipe evaporator section is caused by insufficient coolant supply of wick structure, and generally considered as a failure mode of heat pipe operation. However, traditional dryout theory does not fit the bi-porous (bi-wick) wick structure research on the new mass transfer mechanism, such as liquid splash at high heat flux. The reported maximum heat flux on the similar wick structure may show a large deviation. Accordingly, dryout studies of bi-wick structures become critical and necessary to understand the limitation of the heat and mass transfer. In this article, carbon nanotube (CNT) clusters are used to investigate dryout of bi-wick structures. Within a closed system, evaporation and boiling phase change on CNT bi-wick structures is visualized to provide direct views on the occurrence and expansion of dryout zone. At the same time, the evaporator temperature variations versus heat flux are measured to characterize the temperature responses upon the bi-wick dryout. Investigations based on both visualization and measurement results show that dryout of CNT bi-wick structures are caused by insufficient liquid supply to create temperature elevation and in-plane heat transfer increase of the evaporator substrate. On the curvatures of heat flux versus the evaporator temperature, dryout can be defined as the appearance of the inflexion point on the heating section, and associated by the existence of large hysteresis of heat transfer performance. Numerical modeling of the temperature distribution on dried wick structure further indicates that traditional temperature measurement approaches are hardly to detect the occurrence of dryout and to provide the maximum temperature. High temperature hotspot on dried wick structure can be more destructive than temperature sensor measured.
Enhancing the Heat Transfer in Energy Systems From a Volumetric Approach
Authors: Otanicar Todd P.
Published: March 2011

Many energy systems rely on flat surfaces for energy conversion. The simplest example is the solar thermal collector which absorbs solar irradiance on a flat plate and then transfers heat via conduction, convection and radiation to both the surroundings and more importantly to the working fluid. Conversely a night-sky radiator tries to lose heat via convection and radiation to ambient and night sky respectively while being coupled either via convection or conduction to higher temperature system. The recent advent of nanoparticles, particularly liquid-nanoparticle suspensions termed nanofluids, have led to novel systems that can reduce some of these heat transfer steps by utilizing the whole fluid volume directly. This study looks at the advantages afforded by using the volumetric approach on both the radiative properties of the system and the simplification of the heat transfer networks within these systems.
Liquid Film Thickness of Oscillating Flow in a Micro Tube
Authors: Han Youngbae , Shikazono Naoki , Kasagi Nobuhide
Published: March 2011

Oscillating flow is encountered frequently in many two-phase flow systems such as pulsating heat pipe, refrigerator with reciprocating compressor, etc. Thickness of liquid film formed between the tube wall and the vapor bubble is one of the crucial parameters to develop two-phase flow systems using micro tubes. However, liquid film formation and variation of oscillating flows are very complicated phenomena coupled with acceleration, deceleration, evaporation, condensation, etc. In the previous research, liquid film thickness in accelerating flow under adiabatic conditions was measured and compared with the correlation developed under steady condition [5]. In the present study, liquid film thickness in decelerating flow in a micro tube is investigated under adiabatic condition. Circular tubes with diameter, D = 1.0 mm, is used. Laser focus displacement meter is used to measure the liquid film thickness. Two-phase flow is obtained by introducing air from the open end of the test tube. Ethanol is used as a working fluid. At small capillary numbers, the effect of deceleration is negligible similar to the trend under accelerated condition. As capillary number increases, liquid film thicknesses in decelerated conditions become larger than the predictions of adiabatic steady correlation. However, liquid film thickness does not exceed the critical thickness at Re > Recrit. It is considered that liquid film thickness is affected by the altered velocity profiles in the liquid slug ahead of air-liquid interface according to accelerated or decelerated condition.
Prediction of Turbulent Convective Heat Transfer to Supercritical CH4/N2 Mixture in a Vertical Circular Tube
Authors: Du Zhongxuan , Lin Wensheng , Gu Anzhong
Published: March 2011

Cooling of supercritical CH4/N2 mixture is the most important heat transfer process during coalbed methane (CBM) liquefaction. In this paper, numerical studies of the turbulent convective heat transfer of supercritical CH4/N2 flowing inside a vertical circular tube has been conducted with Lam-Bremhorst low Reynolds turbulence model. The present numerical investigations focus on the effects of the nitrogen content, heat flux and flow orientation. Results indicate that as nitrogen content increases, the maximum heat transfer coefficient gradually decreases and corresponds to lower temperature. Heat transfer coefficient is slightly affected by heat flux in the liquid-like region, and increases with increasing heat flux in the gas-like region. Buoyancy effect gradually increases with decreasing bulk temperature, and reaches its maximum at the pseudo-critical point, and then drops as bulk temperature further decreases. It is significant in the liquid-like region, and negligible in the gas-like region. At the same time, buoyancy effect enhances heat transfer in the upward flow and impairs it in the downward flow.
Effects of Pitch and Depth on the Condensation Heat Transfer of R-134a Flowing Through Corrugated Tubes
Authors: Laohalertdecha Suriyan , Wongwises Somchai
Published: March 2011

The effects of pitch and depth on the condensation heat transfer of R-134a flowing inside corrugated tubes are experimentally investigated. The test section is a horizontal tube-in-tube heat exchanger. The refrigerant flows in the inner tube and the water flows in the annulus. The length of heat exchanger is 2 m. A smooth tube and corrugated tubes having inner diameters of 8.7 mm are used as an inner tube. The corrugation pitches used in this study are 5.08, 6.35, and 8.46 mm. Similarly, the corrugation depths are 1, 1.25, and 1.5 mm. The effects of corrugation pitch and depth on tube wall temperature, heat transfer coefficient and frictional pressure drop are discussed. The results illustrate that the maximum heat transfer coefficient and frictional pressure drop obtained from the corrugated tube are up to 50% and 70% higher than those obtained from the smooth tube, respectively.
Measurement Technique of In-Plane Thermal Resistance of PCB
Authors: Hatakeyama Tomoyuki , Ishizuka Masaru , Nakagawa Shinji , Nakano Yuta , Hirokawa Masataka , Tomimura Toshio
Published: March 2011

Nowadays, thermal design of electrical packages is a key issue for the development of electronics. One of the most important thermal design is the estimation of temperature distribution on Printed Circuit Board (PCB). However, estimated temperature distribution by Computational Fluid Dynamics (CFD) analysis has not enough accuracy because of unknown in-plane thermal conductivity of PCB. PCB has complex wiring pattern and the effect of copper wire on heat diffusion has not been investigated. In this study, we developed measurement technique of thermal resistance of PCB without and with in-plane heat diffusion effect. Measured PCB consists of Glass-Epoxy of 1.6 mm thickness and various copper wiring patterns of 35 μm thickness. Measurement results showed that thermal resistance without inplane heat diffusion effect was not dependent on the wiring patterns. On the other hand, thermal resistance including in-plane heat diffusion effect became smaller with increasing the amount of copper. Further, we compared the experimental results with the results of Thermal Network Method (TNM).
Estimation of Cooling Performance of PCM Module by Using CFD Analysis With Enthalpy Porosity Method
Authors: Hatakeyama Tomoyuki , Ishizuka Masaru , Nakagawa Shinji , Takakuwa Sadakazu
Published: March 2011

This paper describes transient cooling technology for electronic equipment using Phase Change Material (PCM). In previous our report, we can estimate the cooling performance of PCM by using thermal network method, which can not calculate melted PCM flow. In this paper, we further consider the heat transfer phenomena of PCM more deeply by using Computational Fluid Dynamics (CFD) analysis with Enthalpy Porosity Method. By using this method, we can calculate phase change phenomena and flowing phenomena of melted PCM with CFD analysis. The calculation results showed that, high temperature and low temperature location exist on the substrate in the case that PCM module is set vertically. If several devices are cooled with PCM module, most power consuming device must be set in lower part of PCM module. Further, we discussed the reason why the thermal network method can predict PCM module performance though natural convective flow can not be expressed in the thermal network method.
Geometric Optimization of Multiple-Arrays of Micropin-Fins
Authors: Ighalo Fervent Urebho , Bello-Ochende Tunde , Meyer Josua Petrus
Published: March 2011

This study concerns the geometric design of a cylindrical micropin-fin heat sink with multiple row configurations. The objective is to maximize the rate of heat transfer from the solid to the fluid subject to total fin volume and manufacturing constraints. A heat sink with dimensions of 1 mm × 0.6 mm × 1 mm is used for the computational analysis. An automated gradient-based optimization algorithm, which effectively handles an objective function obtained from a computational fluid dynamics simulation is implemented. The optimal design is obtained as results of balance of conductive heat transfer along the pin-fins with laminar forced convection. In the first case, the fins are arranged in two rows of pin-fins with different geometric sizes (diameter, height, and spacing between the fins). The optimal configurations obtained as a function of thermal conductivity ratio and Reynolds number are found to be in good agreement with those obtained from theory and numerical optimization. In the second case, the fins are arranged in rows of three, the effect of thermal conductivity and Reynolds number on the optimal configuration and the maximized heat transfer rate from the arrays of cylinders is reported.
Effects of Diluent Gases on Combustion of Coal Gasification Gas: Comparison Between N2 and CO2 Dilutions
Authors: Nagano Yukihide , Kado Kunihoro , Takeo Tomohiro , Miki Yukito , Kitagawa Toshiaki
Published: March 2011

Combustion properties of coal gasification gas with CO2 dilution were investigated for a newly proposed IGCC power generation system with CO2 capture. In this system, the gasification gas was burned under high CO2 concentration atmosphere. In order to clarify the properties of the flames under such atmosphere, the laminar and turbulent burning velocities were investigated for outwardly propagating stoichiometric H2/O2/CO2 and H2/O2/N2 flames under the two conditions, 1: the same amount of diluent of CO2 or N2, 2: the constant flame temperature irrespective of diluents. Under the condition1 of the same amount of diluents, the unstretched laminar burning velocities, ul of CO2 diluted flames were smaller than those of N2 diluted flames. The ratios of the turbulent burning velocity at the flame radius 30mm, utn(30mm) to ul of the CO2 diluted flames were found to be larger than those of N2 diluted flames. Under the condition2 of the constant flame temperature, it was set to 1300, 1500, 1700, and 2135 degrees Celsius. At the flame temperatures except for 2135 degrees Celsius, ul of CO2 diluted flames were slightly smaller than those of N2 diluted flames. The ratios, utn(30mm) / ul of CO2 diluted flames were larger than those of N2 diluted flames. Increase in the turbulence Karlovitz number and decrease in the Markstein number by the CO2 dilution might cause the increase in utn(30mm) / ul of CO2 diluted flames in both conditions.
Nucleate Boiling Bubble Dynamics in a PDMS Microchannel With a Single Nucleation Site
Authors: Wang Haojie , Lin Xipeng , Christopher David M.
Published: March 2011

The bubble dynamics for flow boiling in a single microchannel was experimentally studied in the present work. A platinum heater was used as the nucleation site in a 0.1 mm hydraulic diameter PDMS (Polydimethylsiloxane) microchannel with FC72 as the working fluid. A high speed camera was used to visualize the bubble dynamics. The results show that the bubbles grow much slower than predicted by standard correlations due to the very large convective heat transfer to the liquid flowing around the bubble in the microchannel. The results also show that the bubble departure frequency, heat flux and bubble departure diameter are well correlated by two dimensionless parameters that also include the effect of the properties. Finally, the results suggest very high speed dryout and rewetting of the heater surface during the bubble growth with a very short period of more complete rewetting of the heater surface when a bubble separates from the main vapor stem.
Measurements of the Thermal Conductivity of Individual α-Tetragonal Boron Nanoribbons
Authors: Yang Juekuan , Waltermire Scott W. , Yang Yang , Li Deyu , Wu Xiaoxia , Xu Terry
Published: March 2011

Boron-based materials (i.e., boron and its borides) are mostly semiconductors with complex structures. These structures are characterized by an arrangement of an icosahedral cluster of B12 atoms [1]. The complexity of the crystal structure gives boron-based material a high melting point and low thermal conductivity at high temperature. On the other hand, the Seebeck coefficients and electrical conductivities of most bulk boron-based materials increase as temperature increases. Therefore, bulk boron-based materials are good candidates for high-temperature thermoelectric applications [2]. Due to the unique properties of bulk boron-based materials, one-dimensional nanostructures of boron-based materials have also attracted much attention, and various boron-based nanostructures have been synthesized recently [3]. These boron-based nanostructures are projected to be promising materials for novel nanoelectronic and nanoelectro-mechanical devices, as well as high temperature thermoelectric materials. However, compared to the extensive studies of carbon nanotubes and silicon nanowires, little has been done on the property characterization of boron and boride nanostructures.
Observation of Micro Premixed Flames Surrounded by High Temperature Burned Gas Flow
Authors: Fuchihata Manabu , Ida Tamio , Kuwana Kazunori , Mizuno Satoru
Published: March 2011

Flame structure of micro scale methane-air premixed flames is investigated experimentally. The flame is stabilized even on the burner whose diameter is 0.3 mm when it is with pilot flame. However, shape of the flame formed on the burner whose diameter is less than 1 mm is similar to micro diffusion flame. It is supposed that the flame formed on the burner whose diameter is submillimeter is dominated by the diffusion mixing of oxygen and methane from the premixture and heat and radicals from the pilot gas flow.
Crystal Orientation Rotation of Ice During Growth in a Bended Capillary
Authors: Teraoka Yoshikazu , Fukuno Ryo , Matsumoto Koji
Published: March 2011

A control technique of crystal orientation of ice can presumably help to improve freezing processes of various industries. However, the technique without seed ice has not been established yet. The author had found that crystal orientation of ice rotated gradually during high-rate growth along a cooling wall. The purpose of this paper is to examine the crystal orientation rotation of ice during growth in several types of bended capillaries at supercooling temperature. We show that, after growing through the capillaries, c-axis of ice crystal is within a certain angle range. On the basis of the measurement the rotation of crystal orientation before and after the growth through some sections of the capillaries, we constructed an empirical model of c-axis rotating gradually during ice growth in the capillary. The calculation of the model can explain the approach process of c-axis of ice crystal growing in the bended capillary to the specified direction.
Proper Orthogonal Decomposition of HUSIR’s Temperature and Velocity Fields
Authors: Chung Kimberly H. , DiCarlo Anthony A.
Published: March 2011

Thermal distortion is a critical design consideration for the Haystack Ultrawide-band Satellite Imaging Radar (HUSIR) with respect to its performance at W-band. This design consideration is needed due to the thermal distortion effects on the surface accuracy of a parabolic reflector. For example, a tight surface tolerance of ∼100 microns root-mean-squared is required to obtain 85 percent antenna performance efficiency for the 37 meter (120 foot) diameter reflector. An understanding of the temperature and velocity fields aids compensation of these losses. Computational fluid dynamics models (CFD) are too computationally expensive to implement in a control algorithm. Therefore, this work applies proper orthogonal decomposition (POD) to simulated CFD data and creates a reduced order model of the fluid system that characterizes the dominant features of both the temperature and velocity fields. A case study of the HUSIR’s convective flow inside a dome is illustrated.
Engine Performance Characteristics Under Controlled Engine Temperature With Variable Operating Parameters
Authors: Mandloi R. K. , Rehman A.
Published: March 2011

In the present scenario, the designs of S I engine being used in automotives by various manufacturers are not properly suitable to Indian climate condition. India is among those tropical countries where the variation in the temperature is having very vast range i.e. from 0°C to 50°C in various regions of the country. Looking in to this vast varying temperature range, it is very difficult to say that which temperature is most suited for operating condition of engines and will give the best performance levels as far as SFC & BP is concerned. In this work, it has been tried to investigate the best option to run the SI engine and simultaneously to maintain the emission norms. Today research and development in the field of gasoline engines have to face double challenge; on one hand, fuel consumption has to be reduced, while on the other hand, even more stringent emission standard have to be fulfilled. The development of engines with its complexity of in-cylinder process requires modern developed tools to exploit the full potential in order to reduce fuel consumption. There are many strategies for improving fuel economy and reducing exhaust emission HC & CO. The experimental study is carried out on a three cylinders, four stroke, petrol, carbureted, water cooled engine test rig connected to eddy current type dynamometer. The objective of this work was to examine engine performance parameter i.e. specific fuel consumption (SFC), brake power (BP) and also exhaust emission on Varying Engine Temperature at 50, 60, 70, 80° C and at an engine speed of 1500, 2000, 2500 rpm with respect to engine load 6, 9, 12 kg. The results are shown by various graphs with effect of engine temperature on specific fuel consumption, brake power, engine speed, engine load and emission levels of Nox, HC, CO for gasoline and LPG to improve fuel consumption.
Molecular Dynamics Simulations and Kaptiza Conductance Prediction of Si/Au Systems Using the New Full 2NN MEAM Si/Au Cross-Potential
Authors: Abs da Cruz Carolina , Chantrenne Patrice , Kleber Xavier
Published: March 2011

Superlattices made by superposing dielectric and metal nanolayers are of great interest as their small size may increase the thermoelectric figure of merit. Thus it is essential to predict their thermal conductivity. Potentials for Au and Si are discussed and the potential of 2NN MEAM is chosen as being the best for simulating heat transfer in Si/Au systems. Full 2NN MEAM Si/Au cross-potential parametrization is developed and the results are compared with ab initio calculus to test its ability to reproduce local density approximation (LDA) calculations. NVT molecular dynamics simulations are performed to deposit Au atoms on an Si substrate by physical vapor deposition and the results of the intermixing zone are in good agreement with the Cahn and Hilliard theory. Non-equilibrium molecular dynamics simulations are performed for an average temperature of 300 K to determine the Kaptiza conductance of Si/Au systems, and the value of 188 MW/m2K obtained is in good agreement with the results of Komarov et al. for Au deposited on isotopically-pure Si-28 and natural Si, with values ranging between 133 and 182 MW/m2K.
Numerical Simulations Versus Experimental Data for a Pyroelectric Energy Converter Harvesting Waste Heat
Authors: James Brian A. , Navid Ashcon , Moreno Raylene C. , Pilon Laurent
Published: March 2011

This paper is concerned with the direct energy conversion of waste heat into electricity using pyroelectric materials. It reports detailed numerical simulations of a prototypical pyroelectric energy converter assembled experimentally and previously reported. The device consisted of a hot and cold source separated by a series of microchannels supporting pyroelectric thin films. A piston was used to vertically oscillate a working fluid back and forth between the thermal sources. The experimental device was fully instrumented with thermocouples and pressure sensor. The transient two-dimensional mass, momentum, and energy equations were solved numerically to determine the local and time-dependent temperature at various locations inside the device for operating frequency varying from 0.025 to 0.061 Hz. Excellent agreement was found between the simulated and experimentally measured local temperatures at all operating frequencies considered. These results confirm our previous numerical results and the simulation tool can now be used to design the next generation of pyroelectric energy converters.
Microscopic Fluid Temperature Measurements Using Fluorescence Polarization Method
Authors: Tatsumi Kazuya , Tozaki Akihisa , Nakabe Kazuyoshi
Published: March 2011

A fluid temperature measurement method in microscopic scale using fluorescence polarization is described in this study. The present method has the advantages in not only noncontact but also markedly reducing the influences of solution pH and quenching on the measured fluid temperature, compared to other methods including LIF (laser induced fluorescence) method. In the case of a fluid at rest, the fluorescence intensity varied with pH and linearly decreased with the elapsed time, while the polarization degree remained nearly constant. The polarization degree showed a good correlation with the fluid viscosity and temperature that corresponded to the tendency of the analytical results. The microchannel flows case also showed a good correlation between the fluid temperature and the fluorescence polarization degree was observed, which was similar to the stationary fluid case. These results affirmed the feasibility of our method using fluorescence polarization for fluid temperature measurement.
Structure of Low-Speed Streaks in Drag Reducing Flow With Polymer Solution Blown From the Channel Wall
Authors: Xu Hening , Ishitsuka Shota , Motozawa Masaaki , Iwamoto Kaoru , Ando Hirotomo , Senda Tetsuya , Yu Bo , Kawaguchi Yasuo
Published: March 2011

For the investigation of turbulent structure in drag reducing flow with polymer solution blown from the channel wall (wall blowing), instantaneous velocity field has been precisely measured in the x-z plane at different locations along the wall-normal direction via Particle Image Velocimetry (PIV). Polymer solutions with 25 ppm and 100 ppm of weight concentration were tested at a blowing ratio of 1.2×10−4 and at 20000 of Reynolds number. About 5% and 11% of drag reduction (DR) rate was obtained, respectively. As a result of this experiment, turbulent statistic data showed that the Root Mean Square (RMS) of streamwise velocity fluctuation increased and RMS of spanwise velocity fluctuation was suppressed comparing with water flow. We found that these low-speed streaks became relatively regular in the buffer layer, including an increase of both length and width, which indicated a depression of turbulence by polymer diffused in the buffer layer.
Three-Dimensional Simulations of the Flow Deflection in a Louvered Fin Heat Exchanger With Round Tubes in a Staggered Arrangement
Authors: Huisseune Henk , T’Joen Christophe , De Jaeger Peter , Ameel Bernd , De Paepe Michel
Published: March 2011

In this study three-dimensional numerical simulations were performed to investigate the flow deflection and its influence on the horseshoe vortex development in a louvered fin round tube heat exchanger with three tube rows in a staggered layout. The numerical results are validated against experimental data. It was found that the flow deflection is affected by the tubes in the same tube row and by the tubes in the upstream tube rows. The flow efficiency values obtained with two-dimensional studies are only representative for the flow behaviour in the first tube row of a staggered louvered fin heat exchanger with round tubes. The flow behaviour in the louvered elements of the subsequent tube rows differs strongly due to its three dimensional nature. Furthermore it was found that the flow deflection affects the local pressure distributions upstream the tubes of the downstream tube rows which explains the stronger horseshoe vortex system at these locations.
Time-Resolved Diffuse Optical Tomography of Human Forearm Under Exercise
Authors: Endo Yasuomi , Tanikawa Yukari , Okawa Shinpei , Masamoto Kazuto , Okada Hidetaka , Kizuka Tomohiro , Miyakawa Michio , Hoshi Yoko , Yamada Yukio
Published: March 2011

Light in the near-infrared wavelength range can penetrate deeping into biological tissues because the absorption by both water and hemoglobin is much smaller than in the other wavelength ranges. Oxygenated and deoxygenated hemoglobins have different light absorption characteristics. Therefore, by obtaining tomographic images of the absorption characteristics, it will be possible to know the hemodynamics inside deep tissues. Thus, the diffuse optical tomography (DOT) is expected as a new modality of biomedical imaging. In this study, we try to obtain DOT images of the forearms by conducting two types of exercise, and their differences caused by the muscle activity are discussed. By comparing the reconstructed DOT images with the magnetic resonance images of the forearm at the same position, the activated muscles can be identified in detail. As a result, the hemodynamics in the dominant muscles when performing flexion and extension of wrist are observed.
A Numerical Investigation of Heat Transfer From Small Horizontal Cylinders at Near-Critical Pressures
Authors: Warrier Gopinath R. , Rousselet Yohann , Dhir Vijay K.
Published: March 2011

A numerical investigation of laminar natural convection heat transfer from small horizontal wires at near-critical pressures has been carried out with carbon dioxide as the test fluid. The parameters varied are: (i) Pressure (P): 7.50–9.60 MPa, (ii) Bulk fluid temperature (Tb): 5–50°C, (iii) Wall temperature (Tw): 5.1–200°C, and (iv) Wire diameter (D): 25.4, 76.2 and 100 μm. The steady-state Navier-Stokes equations (low Mach number asymptotic form) are solved with variable properties. The results of the numerical simulations agree reasonably well with available experimental data. The dependence of heat transfer coefficient (h) on P, Tb, Tw and D were investigated. The results obtained are as follows: (i) For given P and D, h is strongly dependent on Tb and Tw. (ii) The heat transfer coefficient decreases with increasing values of P (P/Pc > 1). (i) For fixed P, Tw and Tb, the dependence of h on D varies from h ∝ D−0.47 to h ∝ D−0.29 as D increases. (iii) For a given P, the maximum heat transfer coefficient is obtained for conditions where Tb < Tpc < Tw, where Tpc denotes the pseudocritical temperature. Based on the analysis of the temperature and flow field once can qualitatively show that this peak in h when k, Cp and Pr in the fluid peak close to the heated surface.
Sensing Changes of Surface Properties of Oxygen Nano-Bubbles in Water by the Ripplon Surface Laser-Light Scattering
Authors: Ichikawa Yuma , Nishimura Yu , Nagasaka Yuji
Published: March 2011

Micro and nano-sized bubbles containing in water have been attracting increasing attention from wide variety of research fields because of their remarkable bioactive effects. Although many application studies have been conducted, the fundamental understanding such as existence and stability of especially nano-bubbles in water is still unsatisfactory. The purpose of the present study is to detect the changes of surface properties (surface tension and viscosity) of nano-bubbles in water by the newly developed ripplon surface laser-light scattering apparatus. The present measurement technique is able to detect nanometer-order-amplitude surface wave usually regarded as ripplons excited by thermal fluctuations. Because of this technique’s nanometer-order sensitivity to surface properties, the present apparatus has the potential to detect the possible presence of nano-bubbles in the vicinity of water surface. We have observed temporal change of surface tension and viscosity of ultrapure water containing oxygen nano-bubbles in a closed container by the ripplon surface laser-light scattering apparatus for 2 weeks. When the bubbles was generated for at least 90 minutes by using a micro and nano bubble generator, the apparent surface tension and viscosity of ultrapure water containing oxygen nano-bubbles was decreased up to about 23% and was increased up to about 270% relative to those of reference water, respectively. It can be speculated from the present experimental evidence that the nano-bubbles are existing in the vicinity of water surface in a closed container.
Unsteady Flow Structure Behind a Heated Cylinder Measured by Time-Resolved PIV With Thermocouple Sensing
Authors: Ohta Yuji , Mukoyama Takuya , Hishida Koichi
Published: March 2011

This paper deals with a technique for time-resolved simultaneous measurement of velocity and temperature in wake region. A measurement technique, combining a high-speed particle image velocimetry (PIV, 1000 frame per second) with thermo-couple sensing (T-type, 50μm), has been developed for acquiring time-resolved two-dimensional velocity and temperature data in thermal-fluid flow, simultaneously. To accomplish the simultaneous measurement, thermocouple time constant was compensated by solving inverse problem with experimental time-resolved velocity data. The technique was applied to a wake region behind a heated circular cylinder in steady and unsteady flow. The evolutions of vortical and thermal structures were obtained in order to examine the mechanism of the turbulent heat transfer in such turbulent flows.
Falling Water Film Evaporation on Horizontal Finned Tube Arrays at Low Pressure
Authors: Wu Xiao-Yu , Li Wei , Luo Zhong
Published: March 2011

Experimental studies have been done on falling film evaporation of water on four types of finned tubes arrays at the pressure of 1000 Pa. The Reynolds numbers are in the laminar range of about 10 to 110. Results show that the finned tubes that can distribute liquid longitudinally have the best performances in the partial dryout regime, and those with high fins could enhance heat transfer most in the fully wet regime. High heat fluxes will make more liquid evaporate, but also generate more dry patches on the tubes. Additionally, the inner enhancement of the tubes will also improve the overall heat transfer coefficients. And four heat transfer enhancement methods of falling film evaporation are summarized in the paper.
Whole-Field Temperature and Velocity Measurements for Two-Phase Flow Using PIV/LIF
Authors: Estrada-Pe´rez Carlos E. , Tan Sinchao , Hassan Yassin A.
Published: March 2011

In this study, an improved 2-D LIF/PTV technique is presented for the simultaneous measurement of temperature and velocity fields of cavity flows. 2-D Whole-Field temperature measurements are achieved by the two-color/two-dyes laser-induced fluorescence (LIF) technique, while the 2-D velocity is measured with particle tracking velocimetry (PTV) method. The improvements presented in this work is the modification of the commonly selected dyes to achieve the two-color LIF technique. Traditionally the organic dyes used to perform two-color LIF measurements are Rhodamine-B and Rhodamine-110, Rhodamine-B provides a fluorescence emission dependent on temperature while Rhodamine-110 provides an emission independent of temperature. In this work, Rhodamine-110 is replaced by Fluorescein-27, which provides a second temperature dependent dye. By using two temperature dependent dyes, the temperature sensitivity of the technique is increased. Also, in this work, a sensitivity analysis of the RHB-FL27 solution properties is presented, and its application to a natural convection two-phase flow within a cavity is explored.