bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid-Acoustics Interaction in Self-Sustained Oscillations Over a Cavity in a Turbulent Boundary Layer
Authors: Yokoyama H. , Kato C.
Published: July 2009

Self-sustained oscillations with fluid-acoustics interaction over a cavity can radiate intense tonal sound and fatigue nearby components of industrial products. The prediction and the suppression of these oscillations are very important for many practical applications. However, the fluid-acoustics interaction has not been thoroughly clarified in particular for the oscillations in turbulent flows. We investigate the mechanism of the oscillations over a rectangular cavity with a length-to-depth ratio of 2:1 by directly solving the compressible Navier-Stokes equations. The boundary layer over the cavity is turbulent and the freestream Mach numbers are M = 0.4 and 0.7. The results clarify that the self-sustained oscillations occur in the shear layer of the cavity and the oscillations are reinforced by the streamwise acoustic mode in the cavity for both Mach numbers. The shear layer of the cavity undulates. This undulation causes the deformation of fine vortices in the shear layer and radiates acoustic waves from the downstream edge of the cavity. Also, we clarify by the conditional identification of longitudinal vortices that the acoustic waves cause the undulation of the shear layer and a feedback loop is formed. Moreover, the comparison of the flow field over the cavity with that over a simple backstep shows that the shear layer in the cavity becomes two-dimensional by the acoustic feedback. Finally, we show that the oscillations become weaker particularly at M = 0.4 and the frequencies of the oscillations become lower as the boundary layer thickness at the upstream edge of the cavity increases. Considering this effect of the boundary layer thickness, the peak frequencies predicted by our computations are in good agreement with those measured in a past experiment.
Active Flow Control of Separated Turbulent Flow Over a Hump Using RANS, DES, and LES
Authors: Gan Subhadeep , Ghia Urmila , Ghia Karman
Published: July 2009

Most practical flows in engineering applications are turbulent, and exhibit separation. Losses due to separation are undesirable because they generally have adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. It is of utmost importance to understand the complex flow dynamics that leads to flow separation and come up with methods of flow control. In the past, passive flow-control was mostly implemented that does not require any additional energy source to reduce separation losses but it leads to increasing viscous losses at higher Reynolds number. More recent work has been focused primarily on active flow-control techniques that can be turned on and off depending on the requirement of flow-control. The present work is focused on implementing flow control using steady suction in the region of flow separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. The flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by Gan et al., 2007. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65% C by using steady suction. Solutions are presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. Second-order accurate time derivatives are used for all implicit unsteady simulation cases. Mean-velocity contours and turbulent kinetic energy contours are examined at different streamwise locations. Detailed comparisons are made of mean and turbulence statistics such as the pressure coefficient, skinfriction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow causes a reduction in the reattachment length, compared with the uncontrolled case. The effects of steady suction on flow separation and reattachment are discussed.
Rotating Stall Behavior in a Diffuser of Mixed Flow Pump and Its Suppression
Authors: Miyabe Masahiro , Furukawa Akinori , Maeda Hideaki , Umeki Isamu
Published: July 2009

The relationship between pump characteristic instability and internal flow was investigated on a mixed flow pump with specific speed ωs = 1.72 (dimensionless) or 700 (m3/min, m, min−1) by using a commercial CFD code and a dynamic PIV (DPIV) measurement. As a result, it was clarified that the diffuser rotating stalls causes the positive slope of a head-flow characteristic and the backflow at hub-side of the vaned diffuser plays an important role on the onset of the diffuser rotating stall. The complex behaviors of diffuser rotating stall were visualized by the DPIV measurements and CFD simulation. Moreover, the internal flow was investigated in detail and the inception of characteristic instability was presumed as follows: At the partial flow rate, low energy fluids are accumulated in the corner between the hub surface and the suction surface of the diffuser vane. As the flow rate is further decreased, the low energy fluids region at the corner axi-symmetrically expands along the hub and become unstable due to adverse pressure gradient. Then, strong backflow occurs and impinges against passage flow from the impeller at the inlet of the vaned diffuser. In addition, the backflow blocks the passage flow from impeller and the inlet flow angle at the leading edge of adjacent diffuser vane is reduced. Therefore, flow separation occurs near the inlet of suction surface of the vaned diffuser, and a strong vortex is generated there. After that, the vortex develops and becomes a stall core. Based on above considerations, pump design parameter studies were numerically carried out and diffuser rotating stall was suppressed and pump characteristic instability was controlled by enlarging the inlet diameter of diffuser hub.
U-RANS Simulation of Mixed-Convection Around a Finite Wall-Mounted Heated Cylinder Cooled by Cross-Flow
Authors: Lecocq Y. , Bournaud S. , Manceau R. , Duret B. , Brizzi L.
Published: July 2009

VALIDA experiments [1] were carried out within the framework of radioactive waste management to improve the understanding of mixed-convection flow and more particularly the interaction between a global cross-flow circulation and local natural convection effects around a vertical heated cylinder. The VALIDA loop implements a cylinder of 3.1 height to diameter ratio, mounted vertically in an insulated tunnel and cooled by a cross-flow air circulation. The air flow and the temperature fields on the cylinder and in the plume behind it have been numerically studied using Unsteady Reynolds Average Navier Stokes simulation (U-RANS) and compared to experimental data. The purpose of this paper is to present the results of a k-ω SST model on several test cases. The numerical tools used herein are Code_Saturne, EDF finite volume CFD code [2], and Syrthes, EDF finite element code for solid temperatures [9]. For the studied test-cases, Reynolds and Grashof numbers are characteristic of a sub-critical flow regime with laminar boundary layers around the cylinder and a turbulent wake. From the transient downstream air calculations, the plume behind the cylinder and its wall temperatures are analysed and compared to experimental data. The flow pattern strongly depends on the ratio of the buoyancy to the inertia force. Results show satisfactory qualitative and quantitative behaviour.
Transferring Methods of Efficiency for Hydraulic Machines Using Model Based on Smooth-Pipes Flow
Authors: Long Li , Wang Ze , Yang Xuelin , Li Dan
Published: July 2009

The scope of Reynolds number in the model experiment and the serviceability on Blasius friction factor equation were analyzed. The exponent of prototype–model scale and the proper distribution of the friction and vortex head loss in Moody’s formula were studied. It was consider that the friction head loss could not be reduced with the accession of vortex head loss. New conversion method of hydraulic efficiency for prototype pump performance using model based on Prandtl-Colebrook formula with a wide Reynolds number range and Nikuradse’s experiments to be consistent with was proposed The conversion results was compared with IEC 60995:1991, JIS B 8327:2002 methods. It is indicated that Prandtl-Colebrook formula has advantage of the strongly theoretical elements, the simply computational method and the high computation precision. It can be becoming to confirm of the prototype hydraulic efficiency from model acceptance tests of hydraulic machines with consideration of scale effects.
Effect of Inlet Curvature on the Discharge Coefficients of Critical-Flow Venturi Nozzle With a Toroidal Throat in the Laminar-Turbulent Transition
Authors: Funaki Tatsuya , Ishibashi Masahiro
Published: July 2009

Studies have been made to predict the discharge coefficient of critical flow Venturi nozzle theoretically and experimentally. However, the studies about the influence of the inlet curvature to the discharge coefficient in the laminar–turbulent transition boundary layer region are very difficult because of the lack the accuracy of the critical flow Venturi nozzle shape. To solve these problems, our group suggested the technique with High-Precision Nozzle and already confirmed the effectiveness. In this research, we clarify that the effect of the inlet curvature R on the discharge coefficient Cd of critical-flow Venturi nozzle with a toroidal throat is investigated in the laminar boundary layer region, the laminar-turbulent transition in the boundary layer and turbulent boundary layer region. R ranged from 2.0D to 1.0D, which were obtained by shaving the inlet of a high precision nozzle that was originally complying with ISO 9300. At first, we measure the discharge coefficient of critical flow Venturi nozzle experimentally and discuss the phenomena of the laminar-turbulent transition by the inlet diameter. Here, the calibrations were performed by a constant volume tank system developed for the primary standard in Japan. Moreover, we try to propose and discuss the hyperbolic tangent equation as the revised Universal Curve to combine the Cd’s for the laminar and turbulent boundary layers.
Robust Gradient Estimation Schemes Using Radial Basis Functions
Authors: Karri Satyaprakash , Charonko John , Vlachos Pavlos
Published: July 2009

Utilization of Radial Basis Functions (RBFs) for gradient estimation is tested over various noisy flow fields. A novel mathematical formulation which minimizes the energy functional associated with the analytical surface fit for Gaussian (GA) and Generalized Multiquadratic (GMQ) RBFs is presented. Error analysis of the wall gradient estimation was performed at various resolutions, interpolation grid sizes, and noise levels in synthetically generated Poiseuille and Womersley flow fields for RBFs along with standard finite difference schemes. To test the effectiveness of the methods with DPIV (Digital Particle Image Velocimetry) data, the methods were compared using the velocities obtained by processing images generated from DNS data of an open turbulent channel. Random, bias and total error were computed in all cases. In the absence of noise all tested methods perform well, with error contained under 10% at all resolutions. In the presence of noise the RBFs perform robustly with a total error that can be contained under 10–15% even with 10% noise using various interpolation grid sizes, For turbulent flow data, although the total error is approximately 5% for finite difference schemes in the absence of noise, the error can go as high as 150% in the presence of as little as 1% noise. With DPIV processed data the error is 25–40% for TPS and MQ methods optimization of the fitting parameters that minimize the energy functional associated with the analytical surface using RBFs results in robust gradient estimators are obtained that are applicable to steady, unsteady and turbulent flow fields.
Study of Mixing Characteristics of Rectangular Turbulent Jets
Authors: Abdel-Salam Tarek , Micklow Gerald
Published: July 2009

This paper reports a numerical study to investigate the effect of various parameters on the mixing characteristics of two-dimensional turbulent co-flowing jets. The paper is a part of an ongoing research to simulate and investigate the mixing and combustion processes of subsonic jets. Results are obtained with a finite volume CFD code. Turbulence is treated with a two equation k-ε model. The effects of nozzle width (H/W), and nozzle exit velocity (U) on the merging and the combined points are also studied. Different initial jet velocities have been examined corresponding to Reynolds number of 2,000 to 35,000 moreover, three values of the nozzle width ratio H/W = 1.5, 2.0, and 2.5 are used. The results provide acceptable agreement in comparison with the experimental results in prior literature. Results show that the initial velocity of the inner jet has a significant effect on the location of the merging and combining points from the jet exit plane. Also, the increase of the initial jet velocity of the outer jets increases the mixing rate of the jets.
Simulation of Flow Field on a Large Scale Wind Turbine
Authors: Janajreh I. , Ghenai C.
Published: July 2009

Large scale wind turbines and wind farms continue to evolve mounting 94.1GW of the electrical grid capacity in 2007 and expected to reach 160.0GW in 2010 according to World Wind Energy Association. They commence to play a vital role in the quest for renewable and sustainable energy. They are impressive structures of human responsiveness to, and awareness of, the depleting fossil fuel resources. Early generation wind turbines (windmills) were used as kinetic energy transformers and today generate 1/5 of the Denmark’s electricity and planned to double the current German grid capacity by reaching 12.5% by year 2010. Wind energy is plentiful (72 TW is estimated to be commercially viable) and clean while their intensive capital costs and maintenance fees still bar their widespread deployment in the developing world. Additionally, there are technological challenges in the rotor operating characteristics, fatigue load, and noise in meeting reliability and safety standards. Newer inventions, e.g., downstream wind turbines and flapping rotor blades, are sought to absorb a larger portion of the cost attributable to unrestrained lower cost yaw mechanisms, reduction in the moving parts, and noise reduction thereby reducing maintenance. In this work, numerical analysis of the downstream wind turbine blade is conducted. In particular, the interaction between the tower and the rotor passage is investigated. Circular cross sectional tower and aerofoil shapes are considered in a staggered configuration and under cross-stream motion. The resulting blade static pressure and aerodynamic forces are investigated at different incident wind angles and wind speeds. Comparison of the flow field results against the conventional upstream wind turbine is also conducted. The wind flow is considered to be transient, incompressible, viscous Navier-Stokes and turbulent. The k-ε model is utilized as the turbulence closure. The passage of the rotor blade is governed by ALE and is represented numerically as a sliding mesh against the upstream fixed tower domain. Both the blade and tower cross sections are padded with a boundary layer mesh to accurately capture the viscous forces while several levels of refinement were implemented throughout the domain to assess and avoid the mesh dependence.
A Study of Grazing Behavior of Copepods Using Digital Holographic Cinematography
Authors: Talapatra Siddharth , Hong Jiarong , Sheng Jian , Waggett Becky , Tester Pat , Katz Joseph
Published: July 2009

Generating proper feeding currents for entraining prey is one of the important features in the grazing behavior of (∼1mm) copepods. These feeding currents vary with the copepod species, as well as with the species or strains and concentration of prey (∼10 μm) dinoflagellates. Calanoid copepods also hover for a while, while slowly sinking, and then intermittently jump to a different location. In our study, we employed high speed digital holographic cinematography to measure elements of the flow field around copepods in an environment seeded with dinoflagellates. In most cases, the flow field and feeding currents were characterized based on the trajectories of the dinoflagellates. However, in some of the tests we also added neutrally buoyant 20 μm particles as independent flow tracers. At low magnifications, we simultaneously recorded two perpendicular views to obtain the same spatial resolution in all directions. Data were recorded at varying magnifications and frame rates. In recent experiments, we exposed the copepods to different strains of the same dinoflagellate species that have varying levels of toxicity, and measured the resulting changes to the grazing behavior of the copepods. Here we present results from two of these experimental setups: Acartia tonsa with Karlodinium veneficum (non toxic strain) and Acartia tonsa in particle seeded flow. Issues such as swimming characteristics, feeding classification (raptorial vs. filter feeding approaches) and copepod response to different environmental settings were addressed.
Near-Wall Stereo PIV Investigation of the Turbulent Channel Flow Over Rough-Walls
Authors: Hong Jiarong , Katz Joseph , Schultz Michael
Published: July 2009

The near-wall turbulent flow in the rough-wall channel is of great significance in engineering applications, but remains a challenge for both experimental measurement and numerical modeling due to the complexity of the roughness geometry. For optical measurement techniques, e.g. PIV, obstruction by the roughness elements and reflection from the surface adversely affect the quality of near wall data. Our present study utilizes a facility containing a fluid with the same refractive index as the rough acrylic wall, making the interface almost invisible, and employs Stereo PIV to obtain the three-dimensional flow field in the vicinity of the roughness elements. The roughness shape is a uniformly distributed and closely packed, 0.5 mm high pyramid, corresponding to 95 wall units, with a pitch angle of 22.5 degrees. The length of the rough surface is sufficiently long to obtain self-similar roughness boundary layer, turbulent channel flow at a mean velocity of 3.8 m/s, with a clearly defined log layer. Results will include sample data of the complete flow, both around and above the roughness elements. Issues related to implementation of Stereo PIV in an index-matched facility will be discussed.
Validations of Some Slip Factor Models for Mixed-Flow Impellers
Authors: Huang Shengqin , Liu Zhenxia , Lu Yaguo , Yan Yan , Lian Xiaochun
Published: July 2009

Accurate modeling of the slip factor is essential for correct prediction of the mixed-flow impeller performance, but the slip factor model well-known for mixed-flow impeller is relatively rare. Two ways for calculating mixed-flow impeller slip factor are present in this paper: (1) Using impeller exit inclination angle correction to transform the slip factor for centrifugal impeller to mixed-flow machine. (2) Setting up model that can be used to mixed-flow machine directly. Based on these two ways, there are six slip factor models chosen for mixed-flow impeller, including models of Wiesner, Stodola, Staniz, Paeng, Backstrom and Qiu. And they are need to be validated by experiments data to find a proper method for mixed-flow machine. The test data are reproduced from Wiesner’s work and nine mixed-flow impellers are included. Experiment and simulation (including six slip factors) have been conducted and the results show that: (1) slip factor models of centrifugal impeller can be used to mixed-flow impeller while no proper mixed-flow slip factor models exist. If the impeller discharge inclination angle is greater than 45 degree, then these models can be used for mixed-flow impellers directly without transformation. (2) Equivalent blade number exists in mixed-flow impeller and it may have critical value. There are only little differences between results calculated by various slip factor models in the condition of equivalent blade number beyond the critical value. Otherwise it has to choose proper slip factor models as different situations while the equivalent blade number is less than the critical value. (3) Blade number, impeller exit inclination angle and exit blade angle of mixed-flow impeller are dominated over slip factor, but blade turning rate and flow coefficient have to be taken into account for more exact solution.
Performance Improvement of a Vacuum Cleaner by Analysis of the Flow Around Motor
Authors: Park J. W. , Hwang D. Y. , Park H. K.
Published: July 2009

A cleaner has trouble with too much noise and power consumption. To solve these problems, the investigation for motors, which are the main component of vacuum cleaner, is required. However, it is difficult to analyze the flow by the experimental means because of the high speed of the fan rotation ranging from 30,000 rpm to 50,000 rpm. Moreover it takes much time to perform the numerical simulation for the flow. In this research, it is aimed to analyze the flow through the centrifugal fan which is believed to be a main noise source, by the computational method. The efficiency of the centrifugal fan is affected by friction loss, impact loss and so on. Those losses depend on factors like the velocity of impeller, blade shape and etc. The influence of the shape of impeller on the flow is investigated in this study. The computational analysis was done by changing impeller shapes. The flow around the centrifugal fan is simulated by applying the moving mesh. To verify the validity of the computation results, the air flow rate and the pressure field to the cleaner is compared with the experimental data. All simulations are performed by using commercial code SC/Tetra. The calculated results show good agreement with the experimental ones qualitatively and it is believed to be promising to use computational simulation in the improvement of the vacuum cleaner performance.
Experimental and Numerical Analysis of Pressure Pulsation in Francis Turbine
Authors: Xiao Yexiang , Wang Zhengwei , Yan Zongguo , Luo Yongyao , Xiao Ruofu , Peng Guangjie , Xue Peng
Published: July 2009

The pressure fluctuation taking place at the whole passage of a prototype Francis hydraulic turbine is studied by carrying out both experimental and numerical simulation. Unsteady wall pressure measurements at six different typical operating conditions are performs to thoroughly investigate pressure fields in the spiral case and straight draft tube dynamically. 3-D unsteady turbulent simulations are performed and compared to the experimental data. The computed flow domain includes the spiral case, stay vanes, guide vanes, rotating runner and the draft tube. The characteristic of unsteady flow and the pressure pulsation as well as their relationships are discussed in this paper, which also analyzed the correlation between the unsteady flow pattern and the pressure fluctuation at different parts of the turbine. In order to optimize the internal flow distribution in Francis turbines at partial loads, this paper presents some preliminary methods to control the unsteady flow pattern.
Computation of Static and Dynamic Stresses of a Bulb Tubular Turbine
Authors: Luo Yongyao , Wang Zhengwei , Zhou Lingjiu , Peng Guangjie , Sun Guangwei
Published: July 2009

The static and dynamic stresses of a bulb tubular turbine unit were analyzed through Ansys. The 3D unsteady flow through the bulb tubular turbine was simulated by CFX to predict the hydraulic pressure on the key parts. The stresses in the key parts under typical work conditions were calculated. The results showed that the dynamic stresses in the runner and guide vane mainly relate to RSI effects. The dynamic stresses showed that the bulb tubular turbine unit was designed safely, and the results presented a reference to the unit during designed stage.
Study on Field Test and Simulating Calculation Following Load Rejections of Tongbai Pumped Storage Power Station
Authors: Zhang Jian , Wang Delou , Hu Jianyong , Zhou Jie , Fang Jie
Published: July 2009

Tongbai pumped storage plant of China have four sets of pump-turbines with single unit capacity 300MW, and the whole length of conveyance system about 1120m in which the lengths of diversion system and tailrace are about 748m and 347m respectively, rated head and discharge 244.0m and 143.5m3/s, separately. The plant would have the field test before the units were put into operating to ensure safety in future, and the parameters of pump turbines and water conveyance pipe system of pumped storage power station are rectified according to field test datum. Numerical calculation and field test indicate that water hammer in pumped storage plant water conveyance system caused by wicket gate closing together with rotation speed-rise. Compared with field test data following load rejection of two sets of pump turbines on June 30th, 2006, simulating calculation has identical result, which would ensure Tongbai pumped storage power station safety.
Numerical Study of Smoke Propagation in a Simulated Fire in a Wagon Within a Subway Tunnel
Authors: Vittori Felipe , Rojas-Solo´rzano Luis , Blanco Armando J. , Urbina Rafael
Published: July 2009

This work deals with the numerical (CFD) analysis of the smoke propagation during fires within closed environments. It is evaluated the capacity of the emergency ventilation system in controlling the smoke propagation and minimizing the deadly impact of an eventual fire in a wagon within the Metro de Caracas subway tunnel on the passengers safety. For the study, it was chosen the tunnel section between Teatros and Nuevo Circo subway stations, which consists of two parallel independent twin tunnels, connected through a transverse passage. The tunnels are provided by a longitudinal ventilation system, integrated by a set of reversible fans located at both ends of the tunnels. Three stages were considered in the study: (a) Model set up; (b) Mesh sensitivity analysis; (c) Validation of the physical-numerical parameters to be used in the numerical model; and (d) Simulation of fire scenarios in Metro de Caracas subway stations. Stages (b)–(c), aimed to testing and calibrating the CFD tool (ANSYS-CFX10™), focused on reproducing experimental data from Vauquelin and Me´gret [1], who studied the smoke propagation in a fire within a 1:20 scale road tunnel. Stage (d) critical scenarios were established via a preliminary discussion with safety experts from Metro de Caracas, in order to reduce the computer memory and the number of simulations to be performed. The analyses assessed the reliability of escape routes and alternative paths for the evacuation of passengers. Additionally, the smoke front movement was particularly computed, as a function of time, in order to determine the possible presence of the “backlayering” phenomenon [5]. Results demonstrate the strengths and weaknesses of the current ventilation system in the event of a fire in the subway tunnel, and suggest new strategies to address this potentially lethal event to minimize the risks for passengers.
The Probability Distribution of the Relative Highest Water Level in Surge Tank of Waterpower Station
Authors: Zhu Yongzhong , Zhang Jian , Yuan Yongsheng , Chen Jieren , Zheng Yuan
Published: July 2009

In the operation of waterpower station, the randomness of numerous factors in water conveyance system including parameter of pipeline, boundary conditions and initial conditions determines that surge in the tank of water conveyance system is random in nature. To make a clear analysis of the working process of surge in tank, the stochastic model has to be set up to deal with the randomness of them. The stochastic model with both stochastically initial conditions and stochastically coefficients is established in the paper, and the stochastic analysis of surge in tank made. Besides, with pipe roughness and original load taken as random variables, probability density function of hydraulic head-loss and probability density function of maximum value of relative surge level are rigidly deduced and the results of the examples concerned agree completely with those from the Monte-Carlo method.
Large Eddy Simulation of Particle Deposition in a Turbulent Channel Flow
Authors: Rahnama Mohammad , Salmanzadeh Mazyar , Ahmadi Goodarz
Published: July 2009

Particle transport and deposition in a turbulent channel flow simulated by the Large Eddy simulations (LES) were studied. Particular attention was paid to the effect of subgrid scales (SGS) turbulence fluctuation on particle motion. Finite volume method was used for finding instantaneous filtered fluid velocity fields of LES of the continuous phase in the channel. Selective structure function model was used to account for the subgrid-scale Reynolds stresses. It was shown that the LES was capable of capturing the turbulence near wall coherent eddy structures. Particle motions were investigated using a Lagrangian particle tracking approach with inclusion of the Stokes drag, lift, Brownian and gravity forces. Effects of SGS of turbulence fluctuations on deposition rate of different size particles were studied. It was shown that the inclusion of the SGS turbulence fluctuations improves the model predictions for particle deposition rate especially for small particles.
Fundamental Investigations of Driving Force of a Neutrophile in Liquid Using Concentration Marangoni Effect for Developing Microcapsules in Drug Delivery Systems
Authors: Tamagawa Masaaki
Published: July 2009

This paper describes the effects of gradient of cytokine concentration on chemotaxis of neutrophile by observing the motion in liquid with adding cytokine concentration. The aim of this investigation is to control of neutrophile motion in liquid by concentration gradient for drug delivery systems.
Correlations of the Droplet Size-Velocity of the Two-Phase, Air/Liquid Spray Using a Particle-Dynamic-Analyzer
Authors: Rahman Mohammad A. , Gomez Johana , Heidrick Ted , Fleck Brian A. , McMillan Jennifer
Published: July 2009

In the heavy oil process industry preheated bitumen and steam are mixed upstream of the feed nozzle and subsequently injected into fluid bed coker reactors via feed nozzles. To achieve high liquid product yields, the bitumen should contact a large number of fluidized coke particles quickly and uniformly. One of the drawbacks of the spray issuing from the nozzle is the potential pulsation within the spray and in the feeding conduit, which is highly undesirable to yield high productivity. These pulsations result in poor atomization and in most instances, a slug of liquid is ejected out of the nozzle. It would be valuable to investigate under which two-phase fluid conditions this pulsation aggravates. It would also be beneficial to examine the detailed spray map with changing air-to-liquid ratio (ALR) by mass and void fraction (α). The average void fraction in the feeding conduit was measured by a pneumatic controlled quick-closing-valve (QCV). The length and diameter of the feeding conduit was 36.8 cm and 6.35 mm, respectively. The experiments were performed using mixtures of air with water at water flow rates of 1.50 to 7.50 kg / min and air-to-liquid (ALR) mass ratios of 0.30 to 9.3%. This study indicates that there exists a strong positive correlation between the droplet diameter and axial velocity at the center of the spray. A positive correlation also exists in between the spray center and periphery. However, a strong negative correlation exists at the periphery of the spray. Knowledge from this study would help the heavy oil process industry to upgrade their heavy oil upgrading process and increase the product yield.
A Numerical Method for Damping Computation of Rigid Cylindrical Containers
Authors: Yang Wei , Liu Shuhong , Wu Yulin
Published: July 2009

It is known that the viscous damping at the free surface is an important part of the whole damping in partly filled liquid container. In order to compute the damping in partly filled rigid circular cylinder more reliably, a VOF (Volume of Fluid) method basing on FVM (Finite Volume Method) with adhesion wall boundary condition is used. Damping of viscous liquid sloshing is very difficult to compute precisely through numerical computation basing on Stokes equations with such two kinds of wall boundary conditions: One is to keep no-slip condition at tank bottom and slip condition at side walls. The other is to keep no-slip condition at side walls and slip at tank bottom. The damping computation discrepancy of these two conditions depends on the liquid height ratio h/R, where h is the liquid height and R is the radius of the cylindrical container. The method used in the present paper maintains all the wall boundary conditions, both side walls and bottom, with no slip conditions and can give an exact damping value instead of computing an estimation range. The simulation damping results show a better agreement with the published experimental measurements especially for liquid height ratio h/R < 1.
Thermal Conductivity Measurements of Si-SiO2-Si Sandwich Structures for Micro/Nano Electronics
Authors: Royce Christina , Arik Mehmet , Weaver Stanton , Bray J. W. , Ovsyuk Victor , Klimenko Anatoly , Yartsev Andrey
Published: July 2009

There are many applications that use SiO2 in microelectronics systems for electrical and thermal isolation. A recent nano-electronic development necessitated understanding of the thermal performance of Si-SiO2-Si sandwich structures so that system level performance can be achieved. Based on a literature search, there have been numerous papers on Si-SiO2 structures, but none that dealt with a complete sandwich. Therefore our research designed, built and tested these sandwich devices to understand the thermal conductivity of the bonding layer. In this paper the transverse thermal conductivity through a Si-SiO2-Si sandwich, where the two layers of Silicon are heavily doped, is measured and used to calculate the thermal conductivity through the thin oxide film. Test samples have been manufactured in a class-1000 clean room with Silicon microfabrication techniques to deposit the thin films. Control of the interfaces depends on the chermical bond due to thin film deposition, so no additional thermal interface materials were used in the actual samples. While in the literature various techniques such as thermal reflectance, 3-Omega, and micro thermocouples have been widely used to determine the thermal conductivity of thin oxide films, in this study we explored two techniques based on a transient and a steady state measurement. First, a laser flash technique was utilized to measure the thermal diffusivity to obtain the thermal conductivity. A MicroFlash meter equipped with a custom-made holder was employed. Four different thickness square samples (5×5 mm) with oxide thicknesses of 56, 210, 1011 and 2136 nm were tested. Second, the same samples were tested via steady state measurements employing micro thermocouples. Results show that thin film oxide thermal conductivity follows the bulk oxide thermal conductivity, published as 1.4 W/m-K at room temperature, but then falls as oxide thickness decreases. A further study has been performed to better understand the uncertainty in the experimental measurements. It is found that uncertainty in the oxide thermal conductivity is on average 122%, 78%, 21% and 19% (higher uncertainties for the lower oxide thicknesses) within 95% confidence level for laser flash measurements. The effect of noise parameters such as settling time, nitrogen level and sample preparation have also been studied during the laser flash measurements.
A Dynamic Heat Transfer Analysis of a Three Sided Pyramidal Fin of Scalene Triangular Cross-Sectional Area
Authors: Carranza Richard G.
Published: July 2009

A dynamic analysis is performed on a three sided pyramidal fin of scalene triangular cross-sectional area (from here on referred to as a TSPSCA). Finite differences are used to solve the governing equation and produce a temperature profile throughout the TSPSCA as a function of time. Dimensionless variables are used. The characteristics of the temperature profile throughout the TSPSCA as a function of time are dependent upon a dimensionless parameter: the thermal conductance due to convection per the thermal conductance due to conduction. It is assumed that the temperature of the fin is homogenous and equal to the temperature of the convecting fluid at time equal zero. The results show that when the conductance ratio is high, the fin temperature profile reaches steady-state quickly; and that the temperatures through the fin deviate greatly from the fin base. Conversely, as this ratio falls in magnitude, the temperature throughout the fin at steady-state approaches the temperature of the fin base; and is slower to reach steady-state.
Two-Phase Friction Factor Obtained From Various Void Fraction Models During Condensation of R134A in Vertical Downward Flow at High Mass Flux
Authors: Dalkilic Ahmet Selim , Laohalertdecha Suriyan , Wongwises Somchai
Published: July 2009

Void fractions are determined in vertical downward annular two-phase flow of R134a inside 8.1 mm i.d. smooth tube. The experiments are done at average saturated condensing temperatures of 40 and 50°C. The average qualities are between 0.84–0.94. The mass fluxes are around 515 kg m−2s−1. The experimental setup is explained elaborately. Comparisons between the void fraction determined from 35 void fraction correlations are done. According to the use of various horizontal and vertical annular flow void fraction models together with the present experimental condensation heat transfer data, similar void fraction results were obtained mostly for the smooth tube. The experimental friction factors obtained from void fraction correlations are compared with the friction factors determined from graphical information provided by Bergelin et. al. Effect of void fraction alteration on the momentum pressure drop is also presented.
Buoyant Convection in Superposed Metal Foam and Water Layers
Authors: Kathare V. , Kulacki F. A. , Davidson Jane H.
Published: July 2009

Experiments on natural convection in superposed metal foam and water layers are reported. The heat transfer system comprises a vertical cavity heated from below and held at constant temperature at the top. Two systems are considered: a water-filled cavity with a foam layer on the heated surface and a water-filled cavity with foam layers on the upper and lower surfaces. The present experiments use open cell copper foams with a nominal porosity of 92%, and the relative thicknesses of the water and foam layers are varied. Steady state Nusselt numbers show the presence of foam on the boundaries enhances overall heat transfer coefficients over that for the water-only layer. Enhancement of overall Nusselt numbers varies from 12 to 60% depending on Rayleigh number. Sub-layer configurations with foam on both heat transfer surfaces are more effective for enhancement than a configuration with foam only on the heated surface.
Molecular Dynamics Simulations of Translational Thermal Accommodation Coefficients for Time-Resolved LII
Authors: Daun K. J. , Liu F. , Smallwood G. J.
Published: July 2009

Time-resolved laser-induced incandescence demands precise knowledge of the thermal accommodation coefficient, but little is known about the gas-surface scattering physics underlying this parameter. This paper presents a molecular dynamics simulation that shows how the thermal accommodation coefficient is influenced by gas molecular mass and the gas temperature. The MD results also define scattering kernels that form boundary conditions in DSMC simulations of heat and momentum transfer between soot aggregates and surrounding gas molecules.
Experimental Study of Natural Convection Heat Transfer in a Vertical Pipe With Stationary Inserts
Authors: Tanbour Emad Y. , Rahmani Ramin K.
Published: July 2009

Enhancement of natural and forced convectional heat transfer rate has been the subject of several academic and industrial studies. Air blenders, mechanical agitators, and static mixers have been developed to increase the forced convectional heat transfer rate in compressible and incompressible flows. Stationary devices can be efficiently employed as heat transfer enhancement tool in the natural convection systems with compressible flow. Generally, a stationary heat transfer enhancement insert consists of a number of equal motionless units, placed on the inside of a pipe or channel in order to control flowing fluid streams. These devices have low maintenance and operating costs, low space requirements and no moving parts. A range of designs exist for a wide range of specific applications. The shape of the elements determines the character of the fluid motion and thus determines thermal effectiveness of the heat transfer enhancement insert. There are several key parameters that may be considered in the design procedure of a heat transfer enhancement insert, which lead to significant differences in the performance of various designs. An ideal heat transfer enhancement insert for natural conventional heat transfer of compressible flow applications provides a higher rate of heat transfer and a thermally homogenous fluid with minimized pressure drop and required space. This paper presents the outcomes of the experimental studies by the authors on two industrial stationary inserts and illustrates how a heat transfer enhancement insert can improve the heat transfer in a buoyancy driven compressible flow. Using different measuring tools, the global performance of the inserts are studied in order to choose the most effective design.
CFD Modeling Analysis of Mechanical Draft Cooling Tower
Authors: Lee Si Y. , Bollinger James S. , Garrett Alfred J. , Koffman Larry D.
Published: July 2009

Industrial processes use mechanical draft cooling towers (MDCT’s) to dissipate waste heat by transferring heat from water to air via evaporative cooling, which causes air humidification. The Savannah River Site (SRS) has a MDCT consisting of four independent compartments called cells. Each cell has its own fan to help maximize heat transfer between ambient air and circulated water. The primary objective of the work is to conduct a parametric study for cooling tower performance under different fan speeds and ambient air conditions. The Savannah River National Laboratory (SRNL) developed a computational fluid dynamics (CFD) model to achieve the objective. The model uses three-dimensional momentum, energy, continuity equations, air-vapor species balance equation, and two-equation turbulence as the basic governing equations. It was assumed that vapor phase is always transported by the continuous air phase with no slip velocity. In this case, water droplet component was considered as discrete phase for the interfacial heat and mass transfer via Lagrangian approach. Thus, the air-vapor mixture model with discrete water droplet phase is used for the analysis. A series of the modeling calculations was performed to investigate the impact of ambient and operating conditions on the thermal performance of the cooling tower when fans were operating and when they were turned off. The model was benchmarked against the literature data and the SRS test results for key parameters such as air temperature and humidity at the tower exit and water temperature for given ambient conditions. Detailed modeling and test results will be presented here.
A Study on the Optimal Design of Heating Chamber in Sputtering Process for Large-Sized LCD Panel Manufacturing
Authors: Hu Bin , Kim Kwang-Sun , Im Ik-Tae , Yun Byung-Han
Published: July 2009

A thermal model was constructed to simulate the combined heat transfer phenomena, including thermal radiation in the heating chamber, during the sputtering process. The changes in thermal characteristics when thermal radiation occurred within the chamber system were analyzed using CFD (Computational Fluid Dynamics) method. The research emphasis in this paper was to explore the temperature distribution on the large glass panel. In order to achieve the temperature uniformity criterion (±15°C), the chamber design was improved to prevent a significant difference between temperature distributions. Several design factors were made to observe the effect on temperature distribution. After optimizing the chamber structure, the IR heater settings were in the end determined to meet the standards of three different sputtering circumstances.
Characteristics of Two-Component Two-Phase Flow and Heat Transfer in a Flat Microchannel
Authors: Roesle Matthew L. , Kulacki F. A.
Published: July 2009

Experiments are reported on heat transfer and flow characteristics of two-component, two-phase flow in a flat microchannel with cross-section 0.1 × 30 mm. The channel is heated at nearly constant wall temperature on one side for a length of 30 mm. Water and FC-72 ® are the working fluids, and local temperature data and high-speed video of the two-phase flows are reported. Total mass flux ranges from 40 and 467 kg/m2s, with mass fraction of FC-72 between 0.04 and 0.69. All flows are sub-cooled up to 32 °C below the saturation temperature of FC-72 and wall heat flux is controlled so that boiling of the FC-72 component occurs. The rate of FC-72 flow through the channel is unsteady due to conditions upstream of the microchannel, which cause temperature fluctuations in the channel. The components remain distinct within the microchannel, as predicted by the low Weber numbers of the flows, and the fraction of the channel cross-section occupied by FC-72 varies inversely with water flow rate. At high water flow rates waviness develops in the interface between the FC-72 and water streams and some droplets of FC-72 leave the main body of the flow. Under some conditions pressure drop oscillation in the boiling FC-72 stream is observed. Estimates of the average heat transfer coefficient are obtained based on average wall temperatures. Large mass fractions of FC-72 reduce overall heat transfer coefficients, indicating that only small mass fractions of FC-72 are needed to produce heat transfer enhancement. Upstream mixing of the two components is seen as key step in fluid management to assure improved heat transfer.