bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Model for a Horizontal Tube Falling Film Evaporator in a Desalination Unit
Authors: Sharma Rohit , Mitra Sushanta K.
Published: March 2009

A model has been developed to predict the evaporative heat transfer coefficient in a horizontal tube falling evaporator and has been applied to evaluate overall performance of a desalination unit. Performance variation with different parameters like operation pressure, temperature, tube diameter, spatial arrangement of the tubes and the type of water distribution system has been studied. Also, variation of the mass flow rate of distilled water inside the exchanger is analyzed. The predicted transfer characteristics obtained from the simulations are compared with the experimental data. It has been observed that the model is able to predict the trends of heat transfer characteristics of the evaporator reasonably well. However, at low liquid film flow rate conditions, the model over predicts the heat transfer characteristics marginally. In order to improve the evaporative exchanger performance, it is observed that preheating of the liquid film before injection into the evaporator is desirable.
Simulation of the Critical Flashing Flow With the Transient 1D Two-Fluid Model
Authors: Gale Janez , Tiselj Iztok
Published: March 2009

The paper presents results of the 1D computer code WAHA, developed for the water hammer simulations, applied for the simulation of the critical flashing flow in the “Super Moby Dick” convergent-divergent nozzle. The mathematical model of the code is briefly introduced with special emphasis on applied dispersed flow homogeneous-relaxation model of inter-phase heat and mass transfer. The results of the simulations of the critical flashing flow are compared to the experimental data.
Analysis of Airflow Diversion in a System of Integrated Electrical Components
Authors: Montgomery Zachary , Minter Dion L. , Scott Elaine P.
Published: March 2009

The task of system-level thermal management in electrical systems has never been simple and has only become more difficult in recent years as industry pushes toward devices with higher power densities. A common practice in many power electronic devices is to use an aluminum heat sink along with at least one cooling fan. This paper presents a parametric study that was performed on a DC-DC power converter to determine the thermal response of heat dissipating components when the incoming cool air is diverted. The scenarios that are investigated include diverting the air to flow only over the top of the heat sink and diverting the air to flow only over the top of the heat sink and diverting the air to flow only through the heat sink. The analysis performed in this paper was done so using IDEAS, a three-dimensional finite element analysis (FEA) program that allows the user to simulate the affects of conduction and convection heat transfer in a forced-air cooling environment. To divert the incoming air, a plate was inserted into the model between the heat sink and the two inlet fans such that the fans were partitioned into four sections. The amount of air that each fan section produced was governed, thus diverting the air to flow in pre-specified areas. The study looked at six scenarios, each with its own unique volumetric flow setting. The scenario that involved diverting all of the air to flow through the fins of the heat sink proved to cause the lowest system-wide temperatures. This best-case scenario reduced the maximum system temperature by nearly 50% from the worst-case scenario.
Heat and Mass Transfer in a CVD Optical Fiber Coating Process
Authors: Huang Wei , Chiu Wilson K. S.
Published: March 2009

In this paper, we study the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw. Temperature is calculated by coupling radiation and convection heat transfer by the reactor walls and gas flow with a radially-lumped heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled using the Maxwell-Stefan equations. Gas-phase reaction kinetics is modeled using a 2-step chemical kinetics mechanism derived from RRKM theory with detailed kinetics data compiled from literature. Surface reaction kinetics are described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.
Mixing in Large Scale Tanks: Part IV — Cleaning Nuclear Waste From Tanks
Authors: Augeri Michael J. , Hubbard Michael , Thomas Jonathan L.
Published: March 2009

The prototypical Advanced Design Mixer Pump (ADMP) was installed in the center of a nuclear waste tank to suspend settled solids, allowing removal of the solids from the tank with a separate transfer pump. Traditional waste removal methods use multiple (up to four) long shaft vertical pumps for suspending the waste solids. A combination of Computational Fluid Dynamic (CFD) modeling, scale modeling, and equipment testing was used to predict the capability of a single mixer pump to suspend radioactive waste solids in liquid using a forty mile per hour discharge jet velocity. Modeling and testing predicted the cleaning effectiveness of the mixer pump to ensure that the majority of waste solids throughout the tank would be suspended for removal to the extent technically and economically practical. In spite of unexpected field conditions and pump phenomena that hindered performance, observation showed that the pump performed as predicted by the modeling and testing.
Analysis of Melting in a Single-Component Metal Powder Bed Subject to Constant Heat Flux Heating
Authors: Xiao Bin , Zhang Yuwen
Published: March 2009

To model Selective Laser Sintering (SLS) of single-component metal powders, melting of a subcooled powder bed with single-component metal powder is investigated analytically. Since laser processing of metal powder is a very rapid process, the liquid and solid phases of a partially molten powder particle may have different temperatures: the temperature in the liquid phase is higher than the melting point, and the temperature in the solid phase is below the melting point. Therefore, the local temperature of regions with partial molten particles is within a range of temperature adjacent to the melting point, instead of at melting point. In addition, the powder bed experiences a significant density change during melting. Therefore, melting of a metal powder bed can be modeled as a melting that occurs in a range of temperature with significant density change. The temperature distributions and locations of the various interfaces were obtained by solving the governing equations for solid, liquid and mushy zones in a one-dimensional system using an integral approximate method. The effects of porosity, sub-cooling, dimensionless thermal conductivity of gas, and dimensionless heat flux on the surface temperature and locations of the interfaces were investigated.
Development of Simple Dispersion Model for Simulation of Air Toxics in Urban Areas
Authors: Richter Donald , Lamb Brain , Westburg Hal , Vaughan Joseph , Gross Mark
Published: March 2009

The paper details the development of an air dispersion model, Simflx7, a computer model that requires a minimum amount of input data while still allowing for the use of both a ground reflection and a reflection from a confining layer above. Simflx7 is based on the classical Gaussian approach and can accommodate gridded independently varying emission sources and calculates the result of all sources emissions on multiple receptors. The project used “real world” data from the Seattle-Tacoma basin for the model demonstration and validation. A gridded inventory for an area of approximately 154 miles by 166 miles was used that has been developed jointly by the Washington State University and the Washington Department of Ecology. The receptor data used for model verification were from six receptor sites located in the greater Seattle area and 24-hour average data collected, and analyzed by Washington State University Laboratory for Atmospheric Research. These data created a unique opportunity for the validation of a model using “real world” data. Typical statistical measures were used to judge model performance against the observations.
Computational Analyses of Cavitating Control Elements in Cryogenic Environments
Authors: Ahuja V. , Hosangadi A. , Shipman J.
Published: March 2009

The safe and reliable operation of high pressure test stands for rocket engine and component testing places an increased emphasis on the performance of control valves and flow metering devices. In this paper, we present high fidelity computational analyses of cavitating venturi-type cryogenic control valves used to support rocket engine and component testing. The computational analyses are carried out with a generalized multi-phase formulation for cavitation in fluids operating in regimes where thermodynamic effects become important. The thermal effects and the accompanying property variations due to phase change are modeled rigorously. Thermal equilibrium is assumed and fluid thermodynamic properties are specified along the saturation line using the NIST-12 databank. The thermodynamic cavitation framework has been validated against experimental data of Hord [1] for hydrofoils operating in liquid nitrogen and liquid hydrogen. In this paper, we will discuss performance losses related to cryogenic control valves and provide insight into the physics of the dominant multi-phase fluid transport phenomena that are responsible for the choking like behavior of cryogenic control elements.
Yucca Mountain Project Preclosure Ventilation Heat Transfer Analysis: Solution Method and Results
Authors: Chipman Veraun , Kirstein Bruce , Case John
Published: March 2009

The thermal energy balance for emplacement drift ventilation is solved analytically by using “well-mixed” volume elements that discretize the domain down the length of a drift. The solution technique is based on the use of a lumped parameter quasi-steady-state approximation, and the principle of superposition. The lumped parameters are convective and linearized radiation heat transfer coefficients. The quasi-stead-state approximation allows the energy balance equations to be written without time derivatives and solved algebraically for a single time step. The progress of the heat transfer analysis through time is like that of integrating a function using Euler’s method. The principle of superposition is used to calculate the temperature response of the drift wall due to an arbitrary heat flux and a given set of thermophysical rock properties. The results of this calculation are used as a “multiplier” on the drift wall heat flux in the algebraic solution of the four energy balances, and eliminates the need to solve the conduction heat transfer in the rock mass at every time step. The results of the analysis are compared to a similar numerical model and include time and location dependent waste package, in-drift air, and drift wall temperatures, and ventilation efficiencies.
Optimal Regularization Methods for Inverse Heat Transfer Problems
Authors: Okamoto Kei , Li Ben Q.
Published: March 2009

The Tikhonov regularization method has been used to find the unknown heat flux distribution along the boundary when the temperature measurements are known in the interior of a sample. Mathematically, the inverse problem is ill-posed, though physically correct, and prone to instability. This paper discusses the fundamental issues concerning the selection of optimal regularization parameters for inverse heat transfer calculations. Towards this end, a finite-element-based inverse algorithm is developed. Five different methods, that is, the maximum likelihood (ML), the ordinary cross-validation (OCV), the generalized cross-validation (GCV), the L-curve method, and the discrepancy principle, are evaluated for the purpose of determining optimal regularization parameters. An assessment of these methods is made using 1-D and 2-D inverse steady heat conduction problems where analytical solutions are available. The optimal regularization method is also compared with the Levenberg-Marquardt method for inverse heat transfer calculations. Results show that in general the Tikhonov regularization method is superior over the Levenberg-Marquardt method when the input data errors are noisy. With the appropriately determined regularization parameter, the inverse algorithm is applied to estimate the heat flux of spray cooling of a 3-D microelectronic component with an embedded heating source.
Experimental Investigation of Fluid Flow and Phase Moving Interface During the Solidification of Binary Mixture in Trapezoidal Cavity
Authors: Ghenai C. , Duggirala R. K. , Lin C. X. , Ebadian M. A.
Published: March 2009

This experimental study focuses on the solidification of a ammonium chloride-water (NH4Cl-H2O) solution in a trapezoidal cavity with one and two vertical cooling walls. The effect of the initial concentration of ammonium chloride (sub-eutectic: f < 19.8% and eutectic f = 19.8%, where f is the percentage in weight) and boundary temperatures (Tcold = −30°C to −10°C) on the solidification process is examined. Particle Image Velocimetry (PIV) is used in this study to measure the velocity fields in the melt during the solidification process. The temperatures distributions at discrete locations in the solution and the boundary walls were measured by 32 thermocouples. The convection flow patterns; the ice shape and thickness; the velocity of the moving liquid/solid interface; and the temperature distribution were obtained. The convection patterns obtained for different initial concentrations showed significant differences. The results showed that the process of solidification is slower with an increase in the initial concentration levels of the binary solution. The growth rate of the frozen layer, the velocity of the moving solid-liquid interface and the temperature in the melt was significantly reduced when increasing the initial concentration of ammonium chloride.
Experimental Investigation of Condensation Heat Transfer in Annular Helicoidal Pipes at Different Orientations
Authors: Mo H. L. , Prattipati R. , Lin C. X. , Ebadian M. A.
Published: March 2009

Experimental investigations were conducted on condensation of R134a in annular helicoidal pipes with three orientations, 0°, 45° and 90°. The experimental results indicated that the refrigerant heat transfer coefficients increased with the increase of cooling water temperature, mass flow rates of refrigerant and cooling water, and decreased with the increase of saturation temperature of R134a. When the orientation increased from 0° to 90°, the refrigerant Nusselt number increased around 11% at refrigerant Reynolds number of 80, and around 16% at 200, the percentage increase of refrigerant Nusselt number from 0° to 45° accounted for more than two times of that from 45° to 90°. The performance of annular helicoidal pipe was evaluated by comparing with equivalent smooth straight pipe and identical helicoidal pipe.
Comparison of CFD Calculations With Experimental Results for the YMP Scaled Natural Convection Tests
Authors: Dunn Sandra Dalvit , Webb Stephen W. , Del Mar John , Itamura Michael T. , Francis Nicholas D.
Published: March 2009

The Yucca Mountain Project (YMP) is currently designing a geologic repository for high level nuclear waste. The design encompasses two distinct phases, the pre-closure period where temperatures within the repository will be controlled by active ventilation, and the post-closure period where the repository will be sealed. A prerequisite for designing the repository is the ability to both understand and control the heat generated from the decay of the nuclear waste. This decay heat affects the performance of both the waste packages and the emplacement drift. The ability to accurately model the complex heat transfer within the repository is critical to the understanding of the repository performance. Currently, computational fluid dynamics codes are being used to model the post-closure performance of the repository. Prior to using the codes on the project they were required to be thoroughly validated. Eight pilot-scale tests were performed at the Department of Energy North Las Vegas Atlas Facility to evaluate the processes that govern thermal transport in an environment that scales to the proposed repository environment during the post closure period. The tests were conducted at two geometric scales (25 and 44% of full scale), with and without drip shields, and under both uniform and distributed heat loads. The tests provided YMP specific data for model validation. A separate CFD model was developed for each of the four test configurations. The models included the major components of the experiment, including the waste packages (heated steel canisters), invert floor, and emplacement drift (insulated concrete pipe). The calculated model temperatures of the surfaces and fluids, and velocities, are compared with experimental data.
Modeling of Free Surface Effects Via Subgrid Scale Models
Authors: Cehreli Zeynep N. , Yavuz Ibrahim , Celik Ismail B.
Published: March 2009

In large eddy simulation, the key to the reliability of the solution with relatively large mesh size (this is unavoidable for high Re flows) is to develop effective and physically correct subgrid-scale (SGS) models. The behavior of various SGS models in large eddy simulations (LES) of free surface turbulent flows is investigated. The anisotropy of the turbulence observed near a free surface even a sub-grid scales can not be realized by a standard Smagorinsky model (SMG). The SMG model is improved with free surface modifications. This model is verified on an open channel flow benchmark and then applied to the simulation of a surface ship wake. The turbulence features are studied and compared with the results of a simulation without free surface effects. The modifications in the SGS model damps the vertical velocity fluctuations as desired. This study provides a better understanding of SGS models, when applied to the case of the wake of a turning surface ship.
Performance Assessment of Probe for Radio-Frequency Ablation
Authors: Mudaliar Ashvinikumar V. , Scott Elaine P.
Published: March 2009

Radio-frequency (RF) ablation is one of the most widely used methods for the treatment of hepatic malignancies. A finite element method (FEM) analysis was employed to determine the thermal dose delivered to the tumor/tissue region. We simulated heating within a RF probe implanted in generic tumor surrounded by healthy tissue using ANSYS. The 3-D model consists of a tumor / tissue region into which the RF probe is embedded inside the tumor. One-quarter symmetry was then invoked. The blood flow was modeled using Penne’s bio-heat transfer equation with differing perfusion rates between the healthy tissue and tumor volume based on literature values. The resulting temperature distribution throughout the region was determined over time. A program was written in Visual Basic to extract the temperature distribution data in the tumor/tissue region and calculate the thermal dose throughout the region. This was done by using a time–temperature Arrhenius relationship for chemical and physical rate process. Tissue necrosis is assumed complete when a thermal dose of one hour has been achieved at 43 °C. In the present study, the geometry of the electrode had a significant effect on the size of the volume of necrosis. It was found that the lower portion of the tumor did not receive the specified thermal dose relative to the upper portion of the tumor in single setting during the RF ablation therapy. This might be due to the Ni-Ti electrode, which protruded only from the top surface of the trocar. The effectiveness of the existing probe can be improved by having one more set of electrodes protruding out from the lower curved surface of the trocar. It was found that the modified probe significantly improved heating in the lower portion of tumor/tissue area, providing more symmetry between the upper and lower portion.
Atomistic Simulations of G-Type Phonons in Silicon Devices
Authors: Sinha Sanjiv , Schelling P. K. , Phillpot S. R. , Goodson K. E.
Published: March 2009

Heat conduction in highly compact silicon transistors is impeded due to localization of the electronically generated heat in the device drain. This work studies phonon transport from such heat sources using parallel molecular dynamics. Device Monte Carlo calculations provide an estimate of the size and energy density of the phonon source which is embedded in a one-dimensional crystal. We calculate the scattering times and decay channels for the excited phonons in the absence of thermal phonons. The hotspot is evolved in time and resulting atomic displacements are Fourier analyzed for various phonon modes. Simulations show that decay channels differ depending on the initial energy density of the hotspot. This approach provides a novel method of extracting anharmonic phonon scattering rates for non-equilibrium conditions in a transistor, where first order perturbation theory based calculations may be inaccurate.
Heat Transfer Augmentation in 3D Inner Finned Helical Tube
Authors: Li Longjian , Cui Wenzhi , Liao Quan , Xin Mingdao , Jen Tien-Chien , Chen Qinghua
Published: March 2009

Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%∼120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%∼119%.
Mechanical Degradation Effects on Turbulent Flows With Macro-Molecular Polymer Structures
Authors: Szwalek Jamison L. , Sun Chee Fore Ryan C. , Kim Kihyun , Sirviente Ana I.
Published: March 2009

Macro-molecular polymer structures due to either the entanglement of polymer molecules or the ionic character of the polymer, have been shown in the literature to enhance the drag reducing abilities of polymer solutions in internal water flows. The purpose of this study is to contrast the performance of an ionic and a non-ionic polymer as drag reduction agents with and without the presence of such macro molecular polymer structures. The endurance of such polymer structures to mechanical degradation is also assessed and documented herein. It will also be shown that special attention needs to be paid to the design of optimum polymer delivery systems since they can contribute to the formation or to further enhancing the drag reducing abilities of homogeneous polymer solutions.
Modeling of Stokes Flow in Axisymmetrical Fields Due to Various Boundary Velocity Distributions
Authors: Gadalla Mohamed A.
Published: March 2009

This paper aims at investigating the effect of various boundary velocity distributions on the flow field in Stokes flow of incompressible fluids flow with axisymmetry. It was reported in literature that if the velocity variation at a plane boundary is suitably prescribed, the whole field of Stokes flow in a half-plane can be identified immediately by the artifice of Laplace transform. Similarly, it can be shown that if the boundary velocity distribution is represented for an axisymmetrical half-space, the whole field of Stokes flow can be described by the use of Hankel transform. With suitable given boundary velocity variations, the exact solution can be obtained through the integration of the resulting inverse transform. In this paper several realistic, continuous and discontinuous boundary velocity variations are analyzed following an intuitive derivative of the exact solution in cylindrical coordinates. The variations of the velocities and the pressure in the fluid are obtained for several examples of particular velocity variations at the plane boundary.
Dynamic Structure SGS Models for Large Eddy Simulations
Authors: Chumakov Sergei , Rutland Christopher J.
Published: March 2009

Large Eddy Simulation (LES) is based on separation of variable of interest into two parts — resolved and unresolved, where resolved parts are obtained numerically using transport equations, and the effect of unresolved parts on resolved is modeled using subgrid-scale (SGS) models. This technique has been successfully applied to variety of problems including simulation of internal combustion engines. In this paper we present and discuss three new LES sub-grid scale (SGS) models for: • SGS scalar flux; • SGS scalar dissipation; • SGS energy dissipation. The proposed models belong to a new family of SGS models — Dynamic Structure (DS) models. The DS models take the structure of the model term from the corresponding Leonard-type term, and a particular form of a scaling factor is then used. The models are evaluated a priori using available DNS data for a non-reacting mixing layer and decaying isotropic turbulence. The evaluation results compare well with viscosity and similarity models. During the a priori tests, the DS models were found do be robust and perform better than dynamic viscosity and similarity models under variety of conditions including different test-to-base filter size ratios and non-symmetric filters. To evaluate the models a posteriori, they are implemented into a high-order finite-difference code and two LES simulations are conducted: an LES of decaying isotropic turbulence and an LES non-reacting incompressible mixing layer. The results from both runs are compared with data available from the literature and DNS simulations.
Heat Transfer and Fluid Flow in a Furnace Using the Non-Boussinesq Approximation
Authors: Kamel John K. , Paolucci Samuel
Published: March 2009

Heat transfer and flow field distributions inside a furnace used for manufacturing carbon aircraft brakes are investigated by using non-Boussinesq equations. These equations, unlike their Boussinesq counterpart, enable us to account properly for the large variation of properties with temperature. Radiation between the furnace wall and the porous brake substrates is modelled by taking these surfaces as gray and diffuse, while the gas is considered to be a non-participating medium. A non-Darcian model is used for the flow in the porous brakes. We have implemented the equations within FIDAP, a commercial finite element code. The accuracy of the solution is validated by using well-established numerical solutions for laminar flows.
Droplet Manipulation Over a Hydrophobic Surface With Roughness Patterns
Authors: Chen Jia-Hui , Yang Jing-Tang , Huang Ker-Jer , Yu Chih-Sheng , Hu Joseph Yih-Chiuen
Published: March 2009

A novel concept is proposed to manipulate droplets without external power sources in this study. The proposed device is a hydrophobic surface containing specific roughness gradients, which is composed of several textured regions with gradually increased structural roughness. Four types of hydrophobic materials, AZ6112, Teflon, Parylene C, and plasma polymerization fluorocarbon film (PPFC), are adopted to fabricate the textured surfaces and tested. Actuating forces come from the different Laplace pressures exerting on a droplet across different hydrophobic surfaces, whereas dragging forces come from the contact angle hysteresis. Two patterns of devices are shown in this article, the chain-shaped and the concentric circular. The former functions as a droplet transporting route and the latter provides both transporting and orientation functions. Theoretical estimation and experimental verification of the droplet motion, including actuation and drag forces, on the device are conducted. Optimal design will be achieved based on accurate estimations of the acting forces. The proposed device provides a simpler fabrication process and shows better biocompatibility for droplet manipulation in microfluidic systems.
Numerically Efficient Solution Techniques for Computational Fluid Dynamics and Heat Transfer Problems
Authors: Garbey Marc , Shyy Wei , Hadri Bilel , Rougetet Edouard
Published: March 2009

We present a numerical software interface that can be integrated easily in a CFD or Heat transfer code and allows the systematic investigation of the efficiency of a broad class of solvers to optimize the code. We consider three classes of solvers that are respectively direct solver with LU decomposition, Krylov method with incomplete LU preconditionner and algebraic multigrid that have been implemented in Lapack, Sparskit, and Hypre. We systematically investigate the performance of these solvers with four test cases in ground flow, multiphase flow, bioheat transfer, and pressure solve in an Incompressible Navier Stokes code for flow in pipe with overset composite meshes. We show for each test case that the choice of the best solver may depend critically on the grid size, the aspect ratio of the grid, and further the physical parameters of the problem and the architecture of the processor. We have constructed an interface that allows to easily include in an existing CFD or heat transfer code any of the elliptic solvers available in Lapack, Sparskit and Hypre. This interface has the simplicity of Matlab command but keeps the efficiency of the original Fortran or C library. This interface can help us to investigate what would be the best solver as a preprocessing procedure. This work is a first step to construct intelligent software that will optimize an existing code automatically using the best algorithm for the application.
Development of a 2-D Model for Shallow Water Flow Using Godunov’s Finite Volume Method
Authors: Guillot Martin J. , Bai Leding
Published: March 2009

In this effort we develop a hydrodynamic model for the 2-D shallow water equations (SWE) using a first order Godunov method. The method is formulated as a discontinuous Galerkin finite element method using constant approximating polynomials. We validate the basic implementation of the computer code using quarter annular tests where analytical solutions are available. We investigate the convergence and stability properties of the method by computing the convergence in the L2 norm and verifying the stability requirement in terms of Courant number. We then apply the method to Lake Pontchartrain to provide a more realistic test of the method. We draw conclusions as to the accuracy requirements of the method and discuss extending the developed computer code to include additional physical models, as well as implementing higher degree approximating polynomials.
Study on Particle Response to Local Fluid Velocity in a Gas Particle Turbulent Flow
Authors: Wang Bing , Zhang Hui-Qiang , Wang Xi-Lin
Published: March 2009

Solid particle response to local gas velocity was discussed based on the simulation results of instantaneous velocities of three-dimensional backward-facing step gas particle turbulent flow. Gas flow was simulated by the method of large eddy simulation and particle motion was calculated by the Lagrangian particle tracking model. Instantaneous particle response to gas velocity in two different typical flow regions was discussed. Some factors, such as the waveform similarity function and time-averaged method were used for quantitatively studying particle response regularity based on the relationship between the gas velocity and particle velocity for different size particles. It is shown that the smaller the particle is, the smaller the waveform similarity function value is. The extent that particle velocities make response to gas flow velocities in different flow regions is also distinct. Moreover, for time-averaged results, the quantitative results that particle velocities depend on gas velocities are obviously different in the main flow region. These studies also provide some reference for researches of improving particle stochastic separated flow models for turbulent two-phase flow and for studies of two-way coupling problem for two-phase flow.
Investigation of a Capillary Assisted Thermosyphon (CAT) for Shipboard Electronics Cooling
Authors: Larsen E. H. , Cerza M. , Smith A. N. , Conroy C. Thomas
Published: March 2009

As microprocessors shrink in size and increase in power dissipation levels, the current need for advanced electronics cooling techniques is paramount since power dissipation levels are rapidly exceeding the capabilities of forced air convection cooling. This paper reports an investigation of using a capillary assisted thermosyphon for the shipboard cooling of electronics components. The capillary assisted thermosyphon differs from the capillary pumped loop or loop heat pipe system in that the basic cooling loop is based on a thermosyphon. The capillary assist comes from the fact that there is a wicking structure in the flat evaporator plate, however, the wicking structure is there to spread the working fluid across the flat plate evaporator in the areas under the heat sources. This differs from a capillary pumped loop in that the wick structure does not produce a capillary pumping head from the liquid return to the vapor outlet side of the evaporator. In fact, the liquid return and vapor outlet are almost at the same pressure. The forced circulation in the thermosyphon is caused by a gravity head between the condenser cold plate and the flat plate evaporator. An experimental facility for conducting research on capillary assisted thermosyphon was developed. In order to simulate the shipboard cooling water encountered at various locations of the ocean, the heat sink temperature of the facility could be varied. A vertical flat plate, CAT evaporator was designed and tested under thermal sink temperatures of 4, 21 and 37°C. The condenser cold plate cooling water flow rate varied from 0.38 to 3 GPM. The heat input varied from 250 to 1500 W evenly spread over the area of the evaporator. The CAT flat plate evaporator performed very well under this range of heat inputs, sink temperatures, and cold plate flow rates. The main result obtained showed that as heat input increased the amount of subcooling between the evaporator vapor outlet line and liquid return line increased. This subcooling did not hinder thermal performance as measured by the internal operating temperature.
Experiment Research of the Regenerative Heat Exchanger of Packed Bed
Authors: Li Chaoxiang , Yuan Yinmei , Cai Jiuju
Published: March 2009

Through the test of regenerative heat exchanger, the switch time and the flow velocity of liquid passed through the heat exchanger are found to be the two important factors influencing the efficiency of heat exchanger, and the qualitative relation between the two factors is found. The test result gives a reference to the research, design and operation of the regenerative heat exchanger.
Detached-Eddy Simulation of High Reynolds Number Beveled-Trailing-Edge Flows and Wakes
Authors: Paterson Eric G. , Peltier Leonard J.
Published: March 2009

Flow over three different trailing-edge geometries is studied using incompressible detached-eddy simulation and unsteady Reynolds-averaged Navier Stokes CFD methods. Of interest is the ability of DES, coupled with localized overset–grid refinement, to resolve the proper physics of separated flows from trailing edges—trailing-edge turbulence and vortex shedding, in particular. The DES model is shown to provide a good qualitative description of the trailing-edge flow. However, the modeled separations are overly energetic due to premature separation related to artificially low turbulence levels from upstream. The transition from RANS to DES is isolated as an issue. The simulated physics of the wake are shown to be in agreement with other LES studies: the model produces the “rib/roller” structures representing the first instability modes, horseshoe vortices are observed, and in regions of high resolution, small scales are formed, as expected. The turbulence statistics are qualitatively similar to benchmark data near the trailing edge and in the near wake, however, quantitative comparisons of urms show an over prediction in magnitude of 50–100%. Despite this, the results are promising, and future modeling efforts have been motivated and identified.
Vertical Buoyant Jet Analysis in an Enclosure Using ITM and LES
Authors: Badeau Allen E. , Celik Ismail B.
Published: March 2009

The objective of this study is to investigate vertical buoyant jets in an enclosure using Large Eddy Simulation (LES) methods with no sub-grid scale model. This type of methodology is called Implicit Turbulent Modeling (ITM). Two different boundary conditions are applied at the inlet, being a uniform and periodic forcing velocity distribution. To accomplish this goal, a numerical solver was written, named DREAM®, which is capable of solving three dimensional, transient flows using an accurate monotonic upwinding scheme. The three-dimensional Navier-Stokes equations are solved in Cartesian coordinates, with the control volume approach being implemented on a staggered grid. The numerical scheme uses a fractional time step method, Crank-Nicolson, with the overall spatial and temporal accuracy being second order. In ITM simulations, there is no explicit subgrid-scale model (SGS) used for the modeling of the small scale vortical structures. ITM simulations assume that through strict conservation of the fluxing quantities in and out of the cell, the grid resolution is fully capable of capturing the important scales of the flow. The control volume averaging techniques used in the ITM methods acts as an implicit subgrid-scale model, and the resolvable scales of the flow are only dependent on the grid resolution within the domain. The available experimental data, as well as simulations that used SGS models, compare favorably to the ITM simulations from DREAM® in most cases as long as an “adequate” grid resolution is maintained. Results show that the density stratification tends to accelerate the jet and increase the amount of turbulence present within the flow. Perturbation of the inlet boundary condition ensures a sooner onset of turbulence, which is faster than the non-perturbed inlet boundary condition. A similarity solution is achieved at approximately 8 and 13 inlet diameters downstream of the inlet for the perturbed and uniform inlet boundary condition. Comparison between the vertical buoyant jet simulations to the available experimental data shows good agreement for the jet width and buoyant path centerline locations based on the internal densimetric Froude number. The application of these methods to immiscible fluids shows a new dimension to ITM and allows for a high resolution of the resulting flow field without the need for an explicit SGS model.
Mitigation of the Large-Scale Oscillation Self-Sustained by Shallow Cavities With a Perforated Lid
Authors: Jordan Stephen A.
Published: March 2009

Flow past cavities covered by perforated lids pose a challenging problem for design engineers. Kelvin-Helmholtz waves appear early in the separated shear layers above the perforations that quickly mature into large-scale coherent structures far downstream. This evolution is sustained by a hydrodynamic feedback mechanism within the cavity even when its aft wall is far removed from the lid. Herein, the results from large-eddy simulations show analogous fundamental characteristics between open and perforated-cover cavities. Both adequately scale the fundamental frequency of the large-scale disturbance using the freestream velocity and the cavity width (or lid length). Moreover, the dimensionless frequencies jump to higher modes at equivalent length scales. Unlike the open cavity, one can invoke certain conditions that instigate the instability above the perforations but not a simultaneous long-term feedback mechanism necessary to fully sustain the periodic oscillation. The lid itself offers options for mitigating (or even eliminating) the instability. Results (for laminar separation) show the perforation spacing as the key factor. While maintaining the same fundamental frequency, one can easily dampen its spectral peak to complete disappearance by extending the perforation spacing.
3D Measurements of Deterministic Stresses Within a Rotor-Stator Gap at Mid-Span and Tip Regions
Authors: Uzol Oguz , Chow Yi-Chih , Soranna Francesco , Katz Joseph , Meneveau Charles
Published: March 2009

Stereoscopic Particle Image Velocimetry is used for measuring the distributions of the deterministic stresses, in the tip and mid-span regions, within the second stage rotor-stator gap of a two-stage axial turbomachine. This effort extends our previous two-dimensional measurements to study the dynamics of deterministic stresses in a multistage turbomachine using experimental data. All three components of the velocity vector, and all six components of both the turbulent and deterministic stress tensors are obtained at a Reynolds number of 370,000 based on the tip speed and the rotor blade chord, and in an optically unobstructed facility that uses blades and fluid with matched optical indices of refraction. Results at 50% show that although the radial velocity levels are about an order of magnitude smaller than the axial and lateral velocity levels, the flow is not exactly two-dimensional. The wake kinking phenomenon and the presence of chopped-off stator wake segments introduce three-dimensionality to the flow. The radial velocity fluctuations are high around the kink region, and get even higher when the potential field of the stator blade starts to interact with the kink zone. In general, the turbulent normal stresses are higher than the deterministic normal stresses while the turbulent and deterministic shear stress levels are in the same order of magnitude. The flow at 90% span is dominated by the tip vortices, which create high levels of non-uniformities in the distributions of all three velocity components. The tip vortex loses its structure when it gets close to the pressure side of the following rotor blade and undergoes a possible spiral-type vortex breakdown. The meandering and convection of the tip vortices contribute to the elevated levels of average-passage turbulence and deterministic stresses along the tip vortex transport direction. The deterministic axial normal stress is higher than the turbulent axial normal stress; the deterministic lateral normal stress is initially higher, but it quickly drops down to turbulent lateral normal stress levels; and the deterministic radial normal stress is initially close to turbulent radial normal stress levels, but it decays relatively quickly and becomes less than the turbulent radial normal stress levels further downstream. The deterministic shear stress components are 5 to 10 times higher than the turbulent shear stress components.
Correlation of Surface and Interfacial Energies on Enhanced Pool Boiling Heat Transfer
Authors: Mele´ndez Elva , Reyes Rene´
Published: March 2009

The surface energy of the material used in the construction of capillary covers is an important element to increase the boiling heat transfer on the coverings. There are a variety of methodologies for measuring the surface energy of solids, but few could be used with the construction materials tested. The sessile drop methodology allows the evaluation of either the surface energy of solids or the interfacial energy of liquids. The methodology uses an image digitalization system for measuring the contact angle of liquids on the solid’s surface. The contact angles thus measured are used to calculate the superficial and interfacial energies. This methodology was tested with an experimental set up built for this study. The accuracy of the set up was obtained with clean and greased surfaces of high heat conductivity metals. The surface energies calculated were in accordance with previous experimental results. The surface energies of metal foils used for construction of capillary coverings were similar to the values calculated for the parental solid metal. The surfaces with different grease thickness get values of surface energy close to the value for the adhered hydrocarbons. The same methodology is used for measuring interfacial energies of pure and mixtures of liquids. The liquids studied include those used for increasing boiling heat transfer. Ethanol-water mixtures were analyzed. The mixture with 16% ethanol by weight had the lowest contact angle (associated to the lowest interfacial energy) and produced the highest convective heat transfer coefficient, h. A minimum in the value of the contact angle around the 16% weight ethanol mixtures follows the maximum in the value of h around this composition, and a maximum in the wettability. Similarly, the surfactant sodium-lauryl-sulfate (SLS) produced an increment of the wettability of the mixture on the solid surface. The reduction of the contact angle is obtained with the addition of 100 ppm of SLS or less, depending on the base metal, but above this concentration, the surfactant does not modify the value of the contact angle. The h values increased with the addition of surfactant up to 100 ppm but do not change if the concentration of surfactant is higher than that value.
Experimental Cold Flow Water Model of a Blast Furnace Hearth: Part I
Authors: Nnanna A. G. Agwu , Mehok T. J. , Stella D. , Ahmed Uludogan , Roldan David , Zhou C. Q. , Chuabal P.
Published: March 2009

An experimental investigation of the cold flow water model of the blast furnace hearth has been performed to examine the influence of dead man porosity and taphole height on the flow patterns in the hearth. The model is 1/10th-scale of Ispat blast furnace No. 7. This model satisfied both the geometrical and Froude number similarities of the prototype. Experimental simulations were performed for dead man structure with porosity of zero and 0.3, and for various taphole heights. Results show that there is a considerable influence of the porosity of the dead man structure and the taphole height on the flow contours within the coke free zone of the hearth. Furthermore, experimental evidence shows that the maximum fluid velocity occurred in the vicinity of the taphole, which is possibly the region of high refractory wear in the prototype. This information is useful to design engineers in the redesign and reline of a blast furnace to reduce refractory erosion and increase campaign life. A comparison between experimentally and CFD predicted flow patterns shows good agreement qualitatively without agreeing quantitatively. In the absence of measured flow data for blast furnace hearth, an experimental model is needed to validate either numerically or analytically predicted flow patterns.