bluuebunny/crossref_metadata_2025 huggingface dataset:
Process Intensification in a ‘Simulated Moving-Bed’ Heat Regenerator
Authors: Murthy D. S. , Sivakumar S. V. , Kant Keshav , Rao D. P.
Published: March 2009

The solid-gas contacting for thermal storage and thermal recovery is generally carried out in fixed-bed regenerators. Compared to a fixed bed, higher thermal recovery can be achieved in a moving bed with countercurrent flow of gas and solids. However, the moving beds have not been widely used due to difficulties in solid handling. The relative movement of the bed to the gas flow can be simulated in a fixed bed by moving the inlet and outlet ports of the gas along the length of the bed. Similar simulated moving-beds are already in use for adsorptive separation of liquid mixtures in chemical industries. A Novel Moving-Port system is proposed to achieve simulated moving-bed operation in a fixed bed. We have carried out studies to evaluate the relative performance of the fixed and the simulated moving bed heat regenerators. We have examined the feasibility of replacing a set of three blast furnaces and thermal regeneration of an adsorption bed with the simulated moving-bed regenerator. It is found that high heat transfer intensification can be achieved. The results indicate that the volume of the Simulated Moving-Bed regenerator required is about 100 times smaller than the blast-furnace stoves. The heat transfer intensification is high enough to carry out thermal regeneration of the adsorption beds in a cycle time that is in the range of the pressure swing adsorption, which is favored for its faster rate of regeneration.
Analysis of Flow and Temperature Distribution During Friction Stir Welding
Authors: Hirasawa Shigeki , Haneda Mitsuaki , Hirano Satoshi , Tomimura Toshio
Published: March 2009

Friction Stir Welding (FSW) is a new metal-joining process and the temperature distribution during the FSW process was numerically investigated by changing such parameters as rotation speed, the thermal conductivity of the materials to be joined, the location of the tool, and the generating heat. Results indicate that the temperature on the advancing side is higher than that on retreating side. This can be reduced by heating the upstream portion of the retreating side. The mixing of materials was investigated numerically by assuming materials to be many particles connected with springs. The particles near the pin and the shoulder on the advancing side are mixed well. When the temperature is low in the plastic flow region and plastic deformation force is strong, void defects are found behind the advancing side. These results agree with experimental results.
Study of the Local Convective Heat Transfer Downstream a Backward Facing Step for Various Upstream Airflow Conditions and Enlargement Factors
Authors: Saury Didier , Harmand Souad
Published: March 2009

This paper presents an analyse of the heat transfer coefficient downstream a backward facing step with various upstream airflow conditions: uniform flow outside a laminar boundary layer, uniform flow outside a turbulent boundary layer, and a fully developed flow. The local heat fluxes are obtained from temperature determination by infrared thermography on an assumed thermally thick wall used as boundary conditions of a numerical model. In this article we mainly focus on the maximum heat flux point position determined experimentally and numerically, and also on the influence of the expansion ration on the value of the maximum Nusselt number.
Application of a Multi Level CFD-Technique for the Design Optimisation of Hydraulic Machinery Bladings
Authors: Mu¨ller N. , Einzinger J. , Lepach T. , Kra¨mer S. , Thum S. , Schilling R.
Published: March 2009

To achieve maximum hydraulic efficiency at a wide range of operation, efficient numerical tools are inevitable for the shape optimisation of hydraulic machinery, e.g. rotodynamic pumps and water turbines. A suitable geometry representation by means of B-Spline techniques for the three-dimensionally (3D) curved bladings is necessary as well as a powerful CFD technique in order to evaluate and analyze the hydraulic properties of the design. Both of these modules are integrated in one program system so as to allow the design engineer to achieve maximum performance. There is a natural contradiction between the numerical effort to describe a complex geometry and to compute the flow field as exactly as necessary for an accurate evaluation, and the industrial need to lower the costs and the duration of development of a new design. The 3D curved bladings of rotodynamic pumps and water turbines are characterized by a big number of parameters. Thus, the shape optimisation of this type of blades is still a problem to be solved by an efficient approach. To simplify this complexity, the blade profiles are defined by a reduced set of B-Spline describers on a number of stream surfaces in the conformal mapping representation. This provides an efficient and quick method for modifying the blade shape. To reduce the numerical effort in an iterative optimisation process, a new idea of using the Multi Level CFD-Technique (MLCFD) is described more detailed. The CFD tools used in this process, can be chosen by different criterions such as accuracy on the one hand and computation time on the other hand: There are quasi-3D and full-3D Euler codes as well as quasi-3D and full-3D Navier-Stokes codes for the flow computation and analysis. Starting from an initial design which may come from an artificial neural network having been trained from an existing database, a rough estimation of the quality of a geometry modification can be performed by a quick quasi-3D Euler computation, whereas the final evaluation of the optimum design should be carried out by an accurate 3D Navier-Stokes code. The MLCFD-technique is applied to optimize the blade shape of a centrifugal pump impeller with a specific speed nq = 39 l/min. The numerical results show that significant improvements of the local and integral flow quantities as well as a remarkable reduction of the numerical effort may be reached by using this new approach.
A Boundary Element Method for Three-Dimensional Steady Convective Heat Diffusion
Authors: Grigoriev M. M. , Dargush G. F.
Published: March 2009

Higher-order boundary element methods (BEM) are presented for three-dimensional steady convective heat diffusion at high Peclet numbers. An accurate and efficient boundary element formulation is facilitated by the definition of an influence domain due to convective kernels. This approach essentially localizes the surface integrations only within the domain of influence which becomes more narrowly focused as the Peclet number increases. The outcome of this phenomenon is an increased sparsity and improved conditioning of the global matrix. Therefore, iterative solvers for sparse matrices become a very efficient and robust tool for the corresponding boundary element matrices. In this paper, we consider an example problem with an exact solution and investigate the accuracy and efficiency of the higher-order BEM formulations for high Peclet numbers in the range from 1,000 to 100,000. The bi-quartic boundary elements included in this study are shown to provide very efficient and extremely accurate solutions, even on a single engineering workstation.
Investigation of the Large-Scale Flow Structures in the Cooling Jets Used in the Blown Film Manufacturing Process
Authors: Gao Nan , Ewing Dan
Published: March 2009

The development of the flow field produced by concentric jets used in the blown-film manufacturing process was studied experimentally using hot wire anemometry. It was found that the inner jet was entrained into the outer jet before the outer jet attached to the wall. The inner shear layer of the outer jet attached to the surface 3H to 5H downstream of the jet exit, and the outside shear layer of the outer jet attaches to the surface approximately 12H downstream of the jet exit. The distribution and the spectra of the fluctuating wall pressure was measured using microphones. Measurements of two-point two-time correlation of the fluctuating pressure were used to characterize the development of the large-scale structures. It was found that the structures were convected along the surface at 0.45 to 0.7 of the outer jet velocity for different ratios between inner and outer jet velocities. It was also found that the convection velocity of the large scale structures in the region farther than 10H down stream of the jet exit was determined by the upper jet velocity.
Non-Boundary Conforming Methods for Large-Eddy Simulations of Biological Flows
Authors: Balaras Elias , Yang Jianming
Published: March 2009

In the present paper a computational algorithm suitable for large-eddy simulations of fluid/structure problems that are commonly encountered in biological flows is presented. It is based on a mixed Eurelian-Lagrangian formulation, where the governing equations are solved on a fixed grid, which is not aligned with the body surface, and the non-slip conditions are enforced via local reconstructions of the solution near the solid interface. With this strategy we can compute the flow around complex stationary/moving boundaries and at the same time maintain the efficiency and optimal conservation properties of the underlying Cartesian solver. A variety of examples, that establish the accuracy and range of applicability of the method are included.
Design of the Inlet for an Open Circuit Wind Tunnel for Testing Full Scale Class Eight Trucks
Authors: Bhatnagar Bhaskar , Recktenwald Gerald
Published: March 2009

A commercial CFD program and boundary layer analysis are used to design the inlet of an open circuit wind tunnel for aerodynamic testing of full scale, class eight trucks. The goal of the study is to obtain the combination of wall shape, contraction length, and setting screens that provide a uniform velocity profile upstream of the vehicle under test. Thwaites method is used to verify that the boundary layer does not separate. Velocity field predictions upstream of the vehicle under test are presented for different design configurations of the inlet. A variation in the velocity magnitude of less than one percent outside of the boundary layer is achievable. The contraction introduces a weak secondary flow in the corners of the wind tunnel, but the cross stream components do not lead to significant distortion of the axial profile.
Experimental and Numerical Analysis of Temperature Distribution in Layered Tissue Media Due to Short Pulse Laser Irradiation
Authors: Trivedi Ashish , Basu Soumyadipta , Mitra Kunal , Kumar Sunil
Published: March 2009

Use of short pulse laser for minimally invasive therapeutic treatment has become an indispensable tool in the technological arsenal of modern medicine and biomedical engineering. The objective of this paper is to analyze both numerically and experimentally the heat affected zone in tissue phantoms irradiated with a mode-locked short pulse laser source. It is only by being able to predict reliably the resultant temperature field that necessary dose for desired therapeutic outcomes can be ensured. A multi layer model of the skin consisting of the outer skin layer (epidermis), the lower layer (dermis) and fatty tissue underneath is considered in this study. Each layer of tissue has different optical properties. The experimentally measured temperature profiles for layered phantoms are compared with the homogenous phantoms using the non-Fourier hyperbolic and Fourier parabolic heat conduction model.
A New Unsteady-Based Turbulence Model to Predict Shear Layer Rollup and Breakdown
Authors: Holloway D. Scott , Leylek James H.
Published: March 2009

This paper documents the computational investigation of the unsteady rollup and breakdown of a turbulent separated shear layer. This complex phenomenon plays a key role in many applications, such as separated flow at the leading edge of an airfoil at off-design conditions; flow through the tip clearance of a rotor in a gas turbine; flow over the front of an automobile or aircraft carrier; and flow through turbulated passages that are used to cool turbine blades. Computationally, this problem poses a significant challenge in the use of traditional RANS-based turbulence models for the prediction of unsteady flows. To demonstrate this point, a series of 2-D and 3-D unsteady simulations have been performed using a variety of well-known turbulence models, including the “realizable” k-ε model, a differential Reynolds stress model, and a new model developed by the present authors that contains physics that account for the effects of local unsteadiness on turbulence. All simulations are fully converged and grid independent in the unsteady framework. A proven computational methodology is used that takes care of several important aspects, including high-quality meshes (2.5 million finite volumes for 3-D simulations) and a discretization scheme that will minimize the effects of numerical diffusion. To isolate the shear layer breakdown phenomenon, the well-studied flow over a blunt leading edge (Reynolds number based on plate half-thickness of 26,000) is used for validation. Surprisingly, none of the traditional eddy-viscosity or Reynolds stress models are able to predict an unsteady behavior even with modifications in the near-wall treatment, repeated adaption of the mesh, or by adding small random perturbations to the flow field. The newly developed unsteady-based turbulence model is shown to predict some important features of the shear layer rollup and breakdown.
Modelling From Particle In-Flight to Coating Build-Up for Thermal Spray Processes
Authors: Wei G. , Xiong H. , Zheng L. , Zhang H.
Published: March 2009

To obtain good quality coatings, spray parameters must be carefully selected. Due to the large variety in process parameters, it is difficult to optimize the process for each specific coating and substrate combination. In this paper, the process of particle in-flight, coating growth and pore formation has been analyzed by numerical simulation. Three sub-models, plasma-particle, splat formation and coating buildup, have been developed. A comprehensive three-dimensional computational code (LAVA3D-P) is used to predict the plasma flame formation, flame-particle interaction, and particle state and trajectory. Assuming each splat is disk-like shape and the flattening ratio, a ratio between the splat diameter and droplet diameter, can be calculated based on the interplay among particle kinetic energy, dissipation energy and solidification. A set of rules of coating buildup are proposed to predict the coating deposition and pore formation, considering the influences of particle size, velocity, temperature and location related to the substrate. Using this model we can obtain the porosity, surface roughness and thickness of the coating considering splat adhesion and quenching stresses. Although the current model has severe restrictions which attributes to many assumptions, it however, forms a foundation for further improvement of an advanced ceramic coating buildup model.
Modeling an RF Cold Crucible Induction Heated Melter With Subsidence
Authors: Hawkes Grant
Published: March 2009

A method to reduce radioactive waste volume that includes melting glass in a cold crucible radio frequency induction heated melter has been investigated numerically. The purpose of the study is to correlate the numerical investigation with an experimental apparatus that melts glass in the above mentioned melter. Unique to this model is the subsidence of the glass as it changes from a powder to molten glass and drastically changes density. A model has been created that couples the magnetic vector potential (real and imaginary) to a transient startup of the melting process. This magnetic field is coupled to the mass, momentum, and energy equations that vary with time and position as the melt grows. The coupling occurs with the electrical conductivity of the glass as it rises above the melt temperature of the glass and heat is generated. Natural convection within the molten glass helps determine the shape of the melt as it progresses in time. An electromagnetic force is also implemented that is dependent on the electrical properties and frequency of the coil. This study shows the progression of the melt shape with time along with temperatures, power input, velocities, and magnetic vector potential. Coupled to all of this is a generator that will be used for this lab sized experiment. The coupling with the 60 kW generator occurs with the impedance of the melt as it progresses and changes with time. A power controller has been implemented that controls the primary coil current depending on the power that is induced into the molten glass region.
Simulation of Contaminant Dispersal in an Apartment Building
Authors: Soni Sankalp , Farouk Bakhtier , Haas Charles N.
Published: March 2009

Bio-terrorism events (like the 2001 anthrax attacks) accentuate the importance of countering these incidents. In order to develop reliable countermeasures for these events, it is essential to understand the associated transport processes. The transport processes involved pose challenges as they occur over wide ranges of spatial and temporal scales. CONTAMW, a multi zone indoor air quality and ventilation analysis program is used to predict the contaminant dispersal in an apartment building. Detailed simulation results and analysis of controlled release of propylene within a generic apartment building is presented. A zonal analysis is carried out for the entire apartment building (using CONTAMW) to obtain time histories of propylene concentration in different zones. The simulations provide the dispersion, transport and contaminant concentration within each zone of the apartment. This study also considers the effect of flow obstructions and ventilation rates on contaminant dispersal. The results are validated with the experimental results reported in Cybyk et al. (1999). We have also simulated propylene transport in the apartment with FDS, a large eddy simulation model.
A Discontinuous Finite Element Analysis of Transient Temperature Response in Semi-Transparent Media Induced by Pulsing Lasers
Authors: Ai X. , Cui X. , Li B. Q.
Published: March 2009

A discontinuous Galerkin finite element formulation is presented for the simulation of the transient temperature distribution in a semi-transparent medium heated by an extra-fast pulsing laser. For this problem, the classic Fourier law breaks down and the thermal effects are described by a hyperbolic heat conduction equation coupled with internal radiative heat transfer. These coupled equations are solved using the discontinuous finite element method, which is particularly suited for problems of the hyperbolic type. In the paper, the discontinuous finite element formulation is presented and numerical fluxes are determined by enforcing the stability of the numerical method. Numerical analysis of the transient temperature response induced by a laser pulse is conducted for a one-dimensional semi-transparent slab with black boundaries. The numerical simulation demonstrates the non-Fourier characteristic of thermal wave behaviors in the slab, and the results from radiation-conduction coupling calculations show that the internal radiation helps to reduce the non-Fourier effects in the media.
Eulerian-Eulerian Modeling of Disperse Two-Phase Flow in a Gas-Liquid Cylindrical Cyclone
Authors: Reyes-Gutie´rrez Miguel A. , Rojas-Solo´rzano Luis R. , Colmenares Jose´ , Mari´n-Moreno Juan C. , Mele´ndez-Rami´rez Antonio J.
Published: March 2009

This work presents a three-dimensional CFD study of a two-phase flow field in a Gas-Liquid Cylindrical Cyclone (GLCC) using CFX4.3™, a commercial code based on the finite volume method. The numerical analysis was made for air-water mixtures at near atmospheric conditions, while both liquid and gas flow rates were changed. The two-phase flow behavior is modeled using an Eulerian-Eulerian approach, considering both phases as an interpenetrating continuum. This method computed the inter-phase phenomena by including a source term in the momentum equation to consider the drag between the liquid and gas phases. The gas phase is modeled as a bimodal bubble size distribution to allow for the presence of free- and entrapment gas, simultaneously. The results (free surface shape and liquid angular velocity) show a reasonable match with experimental data. The CFD technique here proposed, demonstrates to satisfactorily reproduce angular velocities of the phases and their spatial distribution inside the GLCC. Computed results also proved to be useful in forecasting bubble and droplet trajectories, from which gas carry under (GCU) and liquid carry over (LCO) might be estimated. Nevertheless, moderate differences found between the computed GCU and experimental measurements, suggests that new adjustments may be done to the numerical model to improve its accuracy.
Correlation of HSP70 Expression and Cell Viability Following Thermal Stimulation of Aortic Endothelial Cells
Authors: Rylander M. Nichole , Diller Kenneth R. , Wang Sihong , Aggarwal Shanti J.
Published: March 2009

The goal of this study was to determine the kinetics of HSP70 expression and variations in cell viability resulting from thermal preconditioning of the heart. Experiments were conducted to determine combinations of elevated temperatures and brief heating durations that could produce enhanced HSP70 levels while maintaining high cell viability. Bovine aortic endothelial cells were heated with a water bath at temperatures ranging from 44–50°C and periods of 1–30 min consistent with anticipated protocols for cardiac preconditioning prior to surgery. Western blot and cell adhesion analysis in culture following heating were employed to determine HSP70 level and cell viability respectively. The results demonstrate that HSP70 expression and cell viability are not maximized simultaneously. To ensure cell viability greater than 90% required a heating protocol for which HSP70 expression was less than its maximum level. HSP70 expression increments from 2.3 to 3.6 times the value of the control can be achieved for thermal stimulation protocols varying from T = 46°C for 10 min to T = 50°C for 1 min while maintaining a cell viability of 90% or greater. An Arrhenius injury model was fit to the cell damage data yielding values for scaling and activation energy terms of A = 1.4×1066 s−1 and Ea = 4.1×105 J/mole.
Drag Reduction Through Changes in Cabin Geometry and Trailer Gap of Heavy-Duty Trucks
Authors: Lakshman M. , Aung K.
Published: March 2009

Reduction of aerodynamic drag of heavy-duty trucks can significantly save fuel costs and US dependence on the imported oil. Reduction of aerodynamic drag by 30% can result in fuel cost savings in billions of dollars every year. Aerodynamic drag of truck depends on the frontal cross-sectional area and the speed of the vehicle. In addition, the gap between the cabin and the trailer significantly affect the drag of the truck. This paper investigates how changes in the cabin geometry and the trailer gap can reduce the aerodynamic drag using numerical simulations. The numerical simulations were carried out using Computational Fluid Dynamics (CFD) software, CFX-5.5, from AEA Technologies (now owned by ANSYS). Effects of vehicle speed, cabin geometry, and trailer gap on the aerodynamic drag were investigated.
Infrared Micro-Particle Image Velocimetry of Fluid Flow in Silicon-Based Microdevices
Authors: Liu Dong , Garimella Suresh V. , Wereley Steve T.
Published: March 2009

A non-intrusive diagnostic technique, infrared micro-particle image velocimetry (IR-PIV), is developed for measuring flow fields within MEMS devices with micron-scale resolution. This technique capitalizes on the transparency of silicon in the infrared region, and overcomes the limitation posed by the lack of optical access with visible light to sub-surface flow in silicon-based micro-structures. Experiments with laminar flow of water in a circular micro-capillary tube of hydraulic diameter 255 μm demonstrate the efficacy of this technique. The experimental measurements agree very well with velocity profiles predicted from laminar theory. Cross-correlation and auto-correlation algorithms are employed to measure very-low and moderate-to-high velocities, respectively; the former approach is suitable for biomedical applications while the latter would be needed for measurements in electronics cooling. The results indicate that the IR-PIV technique effectively extends the application of regular micro-PIV techniques, and has great potential for flow measurements in silicon-based microdevices.
Yucca Mountain Project Preclosure Ventilation Heat Transfer Analysis: Sensitivity of the Ventilation Efficiency to Uncertainties in Key Inputs and Design Parameters
Authors: Chipman Veraun , Case John
Published: March 2009

Preclosure ventilation is a key design feature of the repository to store high-level nuclear waste at Yucca Mountain. The efficiency of the ventilation to remove heat generated by radionuclide decay from the repository is predicted using a lumped parameter heat transfer analysis that considers thermal radiation, convection, and conduction in the drift and the surrounding rock mass. The sensitivity of the ventilation efficiency to uncertainties in key inputs and design parameters is investigated using a statistical approach known as the Delta Method. The standard deviation (normally distributed) of the ventilation efficiency about the mean of 88.0% is 2.6% for a 600-meter long drift. In addition, the influence of each of the standard deviations of the inputs and design parameters on the mean ventilation efficiency and standard deviation is determined. The results show that the most significant variables in the ventilation heat transfer analysis are the inlet air temperature, the air flow rate, the host rock thermal conductivity (as a function of matrix saturation and specific heat), and the convection heat transfer coefficients.
Particle Velocity Measurements to Improve Erosion Prediction
Authors: Sampson Matthew J. , Shirazi Siamack A. , McLaury Brenton S.
Published: March 2009

Previous work on Computational Fluid Dynamics (CFD) based erosion modeling indicated a strong influence of particle impact velocity on erosion. Equations to predict erosion are based on particle impacting velocity, material properties and particle characteristics such as particle shape and size. Previous studies did not measure particle velocity directly but used rotating disks or simplified computer models to determine the particle velocity. In the present work, a series of experiments have been conducted to measure the velocity of small particles (sand and aluminum) as they approach a target. A laser Doppler velocimetry system was used to measure particle velocities in a jet of air as the jet impinges a target. The angle between the target and the incoming jet is varied. Particle concentration is also controlled, allowing the effects of particle to particle interaction on average particle impact velocity to be observed. These findings are expected to improve the results of erosion testing and provide new data for improving erosion models.
A Finite Element-Boundary Integral Method for 3-D Electromagnetic Heating Analysis
Authors: Huo Y. , Li B. Q. , Akarapu R.
Published: March 2009

A three-dimensional finite element-boundary integral formulation is presented for the analysis of the electric and magnetic field distribution, power absorption and the temperature distribution in electrically conduction and dielectric materials. For large-scale electromagnetic-thermal materials processing system analyses, the hybrid finite/boundary method represents an optimal approach. To further improve the efficiency, the present formulation also incorporates various efficient solvers designed specifically for the solution of large sparse systems of linear algebraic equations. The resulting algorithm with a compressed storage scheme is considered effective and efficient to meet the demand of 3-D large scale electromagnetic/thermal simulations required for processing industries. Examples of 3-D electromagnetic and thermal analysis are presented for induction and microwave heating systems. Numerical performance of the computer code is assessed for these systems. Computed results are presented for the electric field distribution, power absorption and temperature distribution in a food load thermally treated in an industrial pilot scale microwave oven designed for food sterilization.
Modeling of Multi-Species Transfer During Aluminum Nitride Vapor Growth
Authors: Cai D. , Zheng L. L. , Zhang H.
Published: March 2009

AlN has attracted much attention in the past few years as a highly promising material for electronic and opto-electronic device applications. A halide vapor phase epitaxy (HVPE) system has been designed to grow high quality aluminum nitride layers at the growth rate up to 60 μm/h with the deposition temperature of 1000–1100°C and the pressure ranging of 5.5–760 Torr [1]. A 3-D numerical model that is capable of describing multi-component fluid flow, surface chemistry, conjugate heat transfer, and species transport has been developed to help in design and optimization of the epitaxy growth system. The effects of reactor pressure on heat transfer and reactive mixing process are studied. The effects of carrier gas (N2+H2) and reacting gas (AlCl3+NH3) flow rates on species mixing process and deposition uniformity have also been investigated. To achieve a uniform reactive species distribution above the substrate under a high carrier and reacting gases flow rate, a baffle is added in between the adduct boat and the substrate. Different baffle sizes, shapes and locations are tested to examine the optional conditions for the best uniformity.
A Correlation Mapping Method to Eliminate the Peak-Locking Effect in PIV Analysis
Authors: Chen Jun , Katz Joseph
Published: March 2009

“Peak-locking” causes deterministic mean measurement bias in most of the existing cross-correlation based algorithms for PIV data analysis. This phenomenon is inherent to the typical smooth curve-fitting through discrete correlation values which are used to obtain the sub-pixel accuracy in velocity. In this paper we introduce a new algorithm/method for obtaining the sub-pixel accuracy, which eliminates the peak-locking effect. We refer to this procedure as “correlation mapping method”. In an ideal case, the second exposure (image 2) in a PIV measurement can be regarded as a mapping of the first exposure (image 1) where the mapping rules are affected by displacement, deformation, out of plane motion, etc. The correlation mapping method is based on shifting of image 1 by certain sub-pixel value, thus generating a virtual image (2′), whose gray level can be expressed in terms of the original image and the sub-pixel displacement. Thus, the correlation map of images 1 and 2′ is also a function of the intensity distribution in image 1 and the displacement. This correlation map is matched with the measured correlation map of images 1 and 2, providing a system of equations, one for discrete point in the correlation map with the sub-pixel values as unknowns. Solving these equations for each point in the vicinity of the correlation peak generates a series of sub-pixel displacements. Least square fitting is then used to determine the sub-pixel displacement with minimal difference between the real and virtual correlation values. This method is applied to several experimental and synthetic flow image pairs. In most cases the results show substantial improvements in sub-pixel accuracy in comparison to other algorithms and it eliminates the peak locking bias.
Simulations of Flow and Temperature Fields in a Two Heater PCR Device
Authors: Mautner Tom
Published: March 2009

One module in a bioagent detector currently under development involves a new two-heater, flow-through polymerase chain reaction (PCR) module which is being designed to save space and power and to reduce the amplification time. As in all PCR devices, thermal cycling requires three temperatures and residence times. These are 90–95°C for DNA denaturation, 50–65°C for hybridization and 72–77°C for replication with a time ratio of 4:9:4. The current design uses two heaters with heat conduction in the substrate providing the hybridization temperature. Typically, the flow and temperature fields in microfluidic devices have three-dimensional complexity, thus numerical simulations were performed to provide design guidelines in the development of the two-heater PCR device. The lattice Boltzmann (LB) method was used to perform low Reynolds number (typically Re = 0.10) simulations for two and three dimensional channel geometries having various wall temperature distributions. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Initial computations using two- and three-heater configurations in two dimensions demonstrated excellent comparisons with published data provided that both the top and bottom walls were heated. If only one wall was heated, large vertical thermal gradients occurred resulting in non-uniform temperature fields. However, when the same conditions were applied to three dimensional channels, lower temperatures were observed in the center of the channel regardless of the wall temperatures or channel aspect ratio. Parametric studies were performed to evaluate the effects of thermal coupling, thermal diffusion coefficients, entrance temperatures, wall temperature configurations and channel geometry. If was found that moderate variation of the thermal diffusion coefficient produced only minor differences in the temperature field, and large changes in the thermal coupling magnitude demonstrated transition from natural to forced convection flows. The simulations also indicate that the largest effect on flow and temperature uniformity arises from the applied wall temperature distribution (various thickness channel walls). It was found, in 2D, that if the channel wall starts from ambient temperature, the applied heating, on the outer surfaces only, may not result in the desired wall or fluid temperatures. However, once the channel walls are heated to a uniform temperature, excellent temperature distributions are obtained for both thick and thin channel walls. These results indicate that the two-heater design has potential in providing a new flow-through PCR device. However, careful attention must be paid to the wall heater design to provide the required sample temperatures.
Study of Scale-Interactions in Strained and Destrained Turbulence
Authors: Chen Jun , Katz Joseph , Meneveau Charles
Published: March 2009

This paper examines the interactions among different length-scales of turbulence during straining and de-straining of the flow. Understanding scale-interactions is a crucial ingredient in formulating improved subgrid models for Large Eddy Simulations. In this experimental study, planar Particle Image Velocimetry (PIV) measurements are performed in a water tank, in which high Reynolds number turbulence with very low mean velocity is generated by an array of spinning grids. Planar straining and de-straining are applied by pushing or pulling rectangular piston whose width is equal to that of the a rectangular tank towards and away from the bottom. The velocity of the piston is computer controlled and synchronized with the PIV system. The initial background turbulence, characterized by the distributions of rms values and energy spectra, confirms that that the turbulence is nearly isotropic and homogeneous. The applied straining is characterized using high-speed photography of the piston and by PIV measurements of the mean flow. The results consist of the time evolution of several turbulence parameters subjected to a sequence of straining and destraining motions, with particular emphasis on the Reynolds stresses, Sub-grid scale (SGS) stresses, SGS anisotropy and SGS dissipation. The paper also examines the scale dependence of the SGS stress and dissipation, and compares the energy flux between different scales during the straining and destraining parts of the deformation.
Effect of Fluid Loading on the Performance of Wicked Heat Pipes
Authors: Kempers R. , Robinson A. , Ching C. , Ewing D.
Published: March 2009

A study was performed to experimentally characterize the effect of fluid loading on the heat transport performance of wicked heat pipes. In particular, experiments were performed to characterize the performance of heat pipes with insufficient fluid to saturate the wick and excess fluid for a variety of orientations. It was found that excess working fluid in the heat pipe increased the thermal resistance of the heat pipe, but increased maximum heat flux through the pipe in a horizontal orientation. The thermal performance of the heat pipe was reduced when the amount of working fluid was less than required to saturate the wick, but the maximum heat flux through the heat pipe was significantly reduced at all orientations. It was also found in this case the performance of this heat pipe deteriorated once dry-out occurred.
Temperature Distribution in a Diode End-Pumped Solid State Laser Slab Subject to Two-Phase Spray Cooling
Authors: Tews Brian E. , Cole Gregory S. , Roth R. Paul , Mitra Kunal
Published: March 2009

As diode pumped solid-state lasers become more powerful, improved thermal management techniques are required. Minimizing thermal gradients in the laser increases performance and reduces thermal stress, which can cause failure by fracturing. Two-phase sprays provide an isothermal cooling method capable of dissipating high heat fluxes produced by the laser. A three-dimensional model of a spray-cooled, end-pumped solid-state laser has been developed to examine the temperature distribution within the laser slab. The model includes variable multi-nozzle arrangements, spatial distribution of two-phase heat transfer coefficients within each spray pattern, and non-uniform heat generation. A study has been conducted to minimize the range of surface temperatures across the slab by varying nozzle spacing. Two-dimensional temperature profiles at the sprayed surface and at the slab mid-plane have been generated. Results indicate that two-phase spray cooling can remove large heat fluxes and maintain temperature variations within acceptable limits. A new technique for designing and analyzing two-phase thermal management systems for solid-state lasers has been developed.
Yucca Mountain Project Preclosure Ventilation Heat Transfer Analysis: Determining the Mixed Convection Heat Transfer Coefficients
Authors: Dunn Sandra Dalvit , Webb Stephen W. , Walsh Robert , Chipman Veraun
Published: March 2009

Mixed convection is an important heat and mass transfer mechanism in the YMP drifts prior to the repository closure. There is little information in the literature on mixed turbulent convection for a similar horizontal annulus configuration. A model was developed using the Morgan approach, combining forced and natural convection models. A rigorous uncertainty analysis was performed. Comparisons between the mixed convection model and experimental values showed agreement for the inner cylinder. The model consistently under-predicted heat transfer from the outer cylinder. The methodology was later employed in the analysis to predict the heat transfer associated with a full scale ventilated emplacement drift.
Measured Performance of a Micro Thermoelectric Cooler
Authors: da Silva Luciana W. , Kaviany Massoud , Asheghi Mehdi
Published: March 2009

The measured performance of a column-type micro thermoelectric cooler, fabricated using vapor deposited thermoelectric films and patterned using photolithography processes, is reported. The columns, made of p-type Sb2Te3 and n-type Bi2Te3 with an average thickness of 4.5 μm, are connected using Cr/Au/Ti/Pt layers at the hot junctions, and Cr/Au layers at the cold junctions. The measured Seebeck coefficient and electrical resistivity of the thermoelectric films, which were deposited with a substrate temperature of 130°C, are −74 μV/K and 3.6×10−5Ω-m (n-type), and 97 μV/K and 3.1×10−5Ω-m (p-type). The cooling performance of devices with 60 thermoelectric pairs and a column width of 40 μm is evaluated under a minimal cooling load (thermobuoyant surface convection and surface radiation). The temperatures of the cold and hot surfaces are obtained with an infrared camera. The average cooling achieved is about 1 K. The measured overall electrical resistance ranges from 51 to 58 Ω. Current challenges include the reduction of the column width, implementation of higher substrate temperatures for optimum thermoelectric properties, and improvements of the top connector fabrication.
A Transient Simulation of Heated Soil Vapor Extraction System
Authors: Roy T. , Amano R. S. , Jatkar J.
Published: March 2009

Soil remediation process by heated soil vapor extraction system has drawn considerably attention for the last few years. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. Our present study is concentrated on modeling one transient Heated Soil Vapor Extraction System and predicting the time required for effective remediation. The process developed by Advanced Remedial Technology, consists of a heating source pipe and the extraction well embedded in the soil. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. A three-dimensional meshed geometry was developed using gambit. Different boundary conditions were used for heating and suction well and for other boundaries. Concentrations of different chemicals were collected from the actual site and this data was used as an initial condition. The analysis uses the species transport and discrete phase modeling to predict the time required to clean the soil under specific conditions. This analysis could be used for predicting the changes of chemical concentrations in the soil during the remediation process. This will give us more insight to the physical phenomena and serve as a numerical predictive tool for more efficient process.
Optimal Control of Thermal Damage to Targetted Regions in a Biological Material
Authors: Gayzik F. Scott , Scott Elaine P. , Loulou Tahar
Published: March 2009

A numerical technique with potential applications in hyperthermia treatment planning is presented. The treatment is simulated using a 2D transient computational model of the Pennes bioheat equation within an optimization algorithm. The algorithm recovers the heating protocol which will lead to a desired damage field. The relationship between temperature, time and thermal damage is expressed as a first order rate process using the Arrhenius equation. The objective function of the control problem is based on this thermal damage model. The adjoint method in conjunction with the conjugate gradient algorithm is used to minimize the objective function. The results from a numerical simulation show good agreement between the optimal damage field and the damage field recovered by the algorithm. A comparison between the recovered damage field and the commonly used thermal dose is also made.
The Effect of Capillary Dimension on Gas Transport in Alveolar Region of the Lungs
Authors: Merrikh Ali A. , Lage Jose´ L.
Published: March 2009

Convection in blood capillary gas transport has been considered negligible for many years. For instance, blood flow effect on gas transport in capillaries was neglected in the recent work of Hsia et al. (1995) based on the seminal work by Aroesty and Gross (1970) who studied steady-state gas transfer in a straight muscle capillary including convection effects by assuming an axisymmetric (cylindrical capillary) model with cylindrical RBCs. The goal of the current study is to demonstrate the effects of red blood cell (RBC) shape and channel dimension on convective gas transport in an alveolar capillary. This report presents numerical simulations of carbon monoxide diffusion onto the alveolar region with capillary blood flow. The alveolar region involves three basic constituents namely the tissue (a region including the alveolar and capillary membranes and the interstitial fluid), the blood plasma (a liquid region), and the RBCs as shown in Figure 1. Simulations of a single, straight capillary with one parachute-shaped RBC is considered in this preliminary study.
Effects of Ambient Temperature and Oxygen Concentration on Soot Evolution in Diesel Spray Combustion
Authors: Xu Yi , Lee Chia-Fon F.
Published: March 2009

A newly developed Forward Illumination Light Extinction (FILE) soot measurement technique was applied in a constant volume spray chamber to study the effects of ambient temperature and oxygen concentration on soot evolution in diesel combustion. The FILE technique with the capability of two-dimensional time-resolved quantitative soot measurement provides the much-needed information to investigate the soot formation mechanism. The ambient temperatures of 1200K, 1000K and 800K were tested to study the temperature effects on soot formation. A decrease of ambient temperature results in a longer ignition delay, which promotes a larger premixed combustion zone combining with higher heat release rates. The change of ambient temperature from 1200K to 800K increases the fuel portion burnt in the premixed combustion period. At 800K, combustion is dominated by the premixed combustion and much less soot is formed. Diesel combustion with 21% and 15% ambient oxygen concentration was also studied. With lower ambient oxygen concentration, the combustion process is basically not changed, but expands into a longer time span with a lower heat release rate. The lower heat release rate results in a lower flame temperature, which benefits the NOx emission control. However, with about the same amount of soot within the flame, and much longer soot life, soot has more chance to escape to the exhaust.
Detailed Characterization of Two-Phase Annular Flow in a Horizontal Tube
Authors: Schubring DuWayne , Shedd Timothy A.
Published: March 2009

In this study, non-intrusive pressure drop, liquid film thickness distribution and wave behavior measurements have been obtained for 140 and 220 two-phase flow conditions in horizontal 8.8 mm I.D and 15.1 mm I.D. tubes, respectively. Horizontal flow regimes ranging from stratified-wavy to annular were studied in long clear test sections. Pressure drop data appeared to show different trends for the wavy, wavy-annular and annular flow regimes, suggesting that a unique model may be required for each. In addition, wave frequency showed clearly different behavior for these regimes, with only minor liquid flow dependence in the wavy and wavy-annular flows and strong liquid flow dependence in annular flow. Interestingly, disturbance wave velocity could be correlated to within 10% by the gas friction velocity in the annular regime and within 20% in the wavy-annular regime, leading to a simple correlation between pressure drop and wave velocity. Base film thickness data (between waves) show that the film is relatively insensitive to gas flow at the side and top of the tube and that the film thickness around the tube becomes nearly independent of liquid flow rate at high gas flows. Empirical correlations of the various data sets are presented with the goal of aiding general horizontal two-phase flow modeling efforts.