bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the Onset of Gas Entrainment in Dual Discharging Oriented Branches on a Curved Wall With Stratified Flow Using Stereo PIV
Authors: Saleh Wael Fairouz , Bowden Robert C. , Hassan Ibrahim Galal , Kadem Lyes
Published: July 2010

The discharge of two-phase flow from a stratified region through single or multiple branches is an important process in many industrial applications including the pumping of fluid from storage tanks, shell-and-tube heat exchangers, and the fluid flow through header to the cooling channels, feeder’s tube, of nuclear reactors during loss-of-coolant accidents (LOCA). Knowledge of the flow phenomena involved along with the quality and mass flow rate of the discharging stream(s) is necessary to adequately predict the different phenomena associated with the process. Stereoscopic Particle Image Velocimetry (3D-PIV) was used to provide detailed measurements of the flow patterns involving distributions of mean velocity, vorticity field, and flow structure. The experimental investigation was carried out to simulate two phase discharge from a stratified region through branches located on a quarter-circular wall configuration exposed to a stratified gas-liquid environment. The quarter-circular test section is in close dimensional resemblance with that of a CANDU header-feeder system, with branches mounted at orientation angles of zero, 45° and 90° degrees from the horizontal. The experimental data for the phase development (mean velocity, flow structure, etc..) was done during dual discharge through the horizontal branch and the 45° or 90° branch from an air/water stratified region over a two selected Froude numbers in the horizontal branch while maintaining the Froude number in the other branch constant. These measurements were used to describe the effect of outlet flow conditions on phase redistribution in headers and understand the entrainment phenomena.
Effect of Entrance Position on Particle Dispersion in Bidirectional Vortex Flow
Authors: Dehghani S. R. , Saidi M. H. , Mozafari A. A. , Ghafourian A.
Published: July 2010

Particle dispersion in the vortex flow has been one of the most interesting subjects in recent years. Bidirectional vortex flow field is an industrial sample of rotating flow which is used to obtain advantages of better mixing and combustion. In this work penetration and dispersion quality of particles which are entering from various positions on the vortex engine walls have been numerically predicted. Head side, end side, and sidewall are considered as the entering positions. The particle has been assumed to be a rigid sphere. Initial velocity, diameter, and density of entering particles are assumed to be known. If the particle length scale is considered not to be comparable with the chamber length and if the particle number density is low, then influence of particle on the flow field is negligible and one-way solution is applicable. The solutions in each case are carried out for estimating particle trajectory and their affecting parameters. The governing equation includes affecting forces on the particle and consequently particle movement and velocity. The governing equation is converted to a set of nonlinear, coupled, second order of ordinary differential equation (ODE), and solved by a numerical scheme. The results present axial and radial trajectory of the particles in the vortex engine from the point of entering position to the wall. They show that a high centrifugal force pushes the particles towards the sidewall. This pushing force becomes more powerful when the particles approach the chamber centerline. The results imply that the best injection arrangement in the vortex engine is not the head side. The sidewall and the end side composition arrangement of injection can be the best.
Surface Wettability Through Asymptotic Contact Angle
Authors: Vafaei Saeid , Wen Dongsheng , Ramanath Ganapathiraman , Borca-Tasciuc Theodorian
Published: July 2010

The purpose of this investigation is to find a unique and accurate criterion to measure surface wettability. The asymptotic contact angle (droplet contact angle in no gravity condition), which is independent of droplet size, is used to identify the surface wettability in this work. The asymptotic contact angle is calculated by equating the normal component of interfacial force on an axisymmetric droplet and spherical droplet. The effect of 2.5 nm bismuth telluride nanoparticles on surface wettability is measured and evaluated by asymptotic contact angles as a sample. This paper also studies the effects of nanoparticles on solid, gas and liquid interactions at the triple line as well as the gas-liquid surface tension of aqueous solutions of 2.5 nm bismuth telluride nanoparticles functionalized with thioglycolic acid. Experimental measurements of nanofluid droplet shapes show that the contact angle strongly depends on nanoparticle concentrations. Fitting the droplet shape with predictions of the Laplace-Young equation, the nanofluid gas-liquid surface tension is determined.
A Diffuse Interface Model for the Numerical Simulation of Thermocapillary Effects
Authors: Schied Nicolas , Villedieu Philippe , Vila Jean Paul
Published: July 2010

The aim of this paper is to present a simple diffuse interface model for compressible two-phase flows with thermo-capillary effects. We mainly focus on two aspects; the continuum formulation of thermo-capillary forces, and the influence of the model used for the computation of the transport coefficients in the interfacial region. Several validation test cases of increasing complexity are considered for the assessment of the model.
Non-Isotropic Porous Medium 3D Computational Fluid Dynamics Model for a Boron Injection System
Authors: Mount Brian , Lopez de Bertodano Martin
Published: July 2010

This work is a 3D implementation of the model for a shutdown boron injection jet of a Pressurized Heavy Water Reactor [1]. The boron shutdown system injects boron into a moderator tank with an array of cylindrical coolant channels. In order to accurately model the distribution of boron inside the moderator tank, the modeling of the turbulent jet mixing is required. The distribution of boron inside the moderator tank is then used to calculate the multidimensional insertion of negative reactivity into the reactor during a fast shutdown in a PARCS/RELAP5 coupled model. A CFD code is used to calculate the boron distribution in the moderator tank. A porous medium model is used to represent the coolant channels. The porous medium model volume averages the governing equations similar to the two fluid model. Additional source terms that arise, due to the volume averaging, need to be constituted so that the problem can be solved. The additional sources terms for the present model have been related to: 1. drag over a cylinder for the momentum equation and 2. additional mixing effect of the cylinders which results in the form of source terms for both the turbulent kinetic energy and turbulent dissipation transport equations. The CFD analysis is performed on a porous, three dimensional domain. The CFD results are compared with experimental data for the boron concentration distribution obtained in a scaled facility. Though the CFD results over predict the concentration measurements, good agreement is achieved for the curvature of the jet centerline.
Experimental Study of the Fence Wake Manipulation Using Pulsating Jet
Authors: Kang In-Su , Choi Young-Ho , Park Chel-Woo , Kim Hyoung-Bum
Published: July 2010

In this study, we experimentally investigated the effect of rear-located pulsating jet to reduce the separated flow region behind the vertical fence. The separation bubble behind the fence is the representative feature of fence wake. Control of fence wake can be used for various purposes such as the reduction of drag, increasing or decreasing the mixing, etc. The vertical fence was submerged in the turbulent boundary layer in the circulating water channel. Reynolds number based on the fence height and upstream flow velocity was 3000. The parameters used for controlling the pulsating jet included the frequency, jet speed and distance between the fence and slit nozzle. In addition, we investigated the effect of continuous jet on the fence wake. Phase averaged DPIV method was applied to measure the instantaneous velocity fields around the fence. And the obtained results were compared with those of uncontrolled fence flow. The obtained results quantitatively show the decrease of reattachment region brought by the pulsating jet. And the specific jet condition which were effective to reduce the separation bubble behind the fence were found.
Effects of Channel Scale on Slip Length of Flow in Micro/Nano-Channels
Authors: Yang Xiaofan , Zheng Zhongquan C.
Published: July 2010

The concept of slip length, related to surface velocity and shear rate, is often used to analyze the slip surface property for flow in micro or nanochannels. In this study, a hybrid scheme that couples Molecular dynamics simulation (used near the solid boundary to include the surface effect) and a continuum solution (to study the fluid mechanics) is validated and used for the study of slip length behavior in the Couette flow problem. By varying the height of the channel across multiple length scales, we investigate the effect of channel scale on surface slip length. In addition, by changing the velocity of the moving-solid wall, the influence of shear rate on the slip length in a certain range of the channel height is studied. The results show that within a certain range of the channel heights, the slip length is size-dependant. This upper bound of the channel height can vary with the shear rate.
Curvature and Rotation Sensitive Variants of the K-Omega SST Turbulence Model
Authors: Dhakal Tej Prasad , Walters D. Keith
Published: July 2010

The two-equation, eddy-viscosity class of models remains the primary means of turbulence closure for most CFD applications, however these models typically are not sensitized correctly to streamline curvature or system rotation. This paper presents the development and testing of new versions of the k-omega SST turbulence model that are intended to exhibit a physically accurate response to curvature and rotation. Model development is based on a rigorous simplification of the differential Reynolds Stress Model under conditions of weak equilibrium. The new turbulence model is implemented in a commercial CFD solver and tested on several problems, including fully-developed, rotating channel flow and flow development in a U-bend. The new model performs superior to existing k-omega model forms for these cases, especially when rapid rotation or strong streamline curvature exists.
Flow Analysis of a Hydrocyclone Designed to High Oil Content Application
Authors: Raposo G. M. , Nieckele A. O.
Published: July 2010

Development of small size and weight separation equipment are crucial for the petroleum off-shore exploration. Since centrifugal fields are several times stronger than the gravity field, cyclonic separation has became very important as a unit process for compact gas-liquid, liquid-liquid and solid-liquid separation. The major difference between the various cyclones is their geometry. Cyclone optimization for different uses is, every year, less based on experiments and more based on mathematical models. In the present work, the flow field inside high oil content hydrocyclones is numerically obtained with FLUENT. The performance of two turbulence models, Reynolds Stress Model (RSM) and Large Eddy Simulation (LES), to predict the flow inside a high oil content hydrocyclone, is investigated by comparing the results with experimental data available in the literature. All models overpredicted the tangential component, especially at the reverse cone region. However, the prediction of the tangential turbulent fluctuations with LES was significant better than the RSM prediction. The influences of the inlet flow rate and hydrocyclone length in the flow were also evaluated. RSM model was able to foresee correctly, in agreement with experimental data, the correct tendency of pressure drop reduction with decreasing inlet flow rate and increasing length.
Influence of the Blade Number on Inducer Cavitating Behavior
Authors: Coutier-Delgosha O. , Caignaert G. , Bois G. , Leroux J.-B. , Olivier Patrick , Choquet Jannick
Published: July 2010

Effects of the blade number on the performance of a rocket engine turbopump inducer are investigated in the present paper. For that purpose, two inducers characterized by three blades and five blades respectively were manufactured and tested experimentally. The two inducers were designed on the basis of identical design flow rate, and identical pressure elevation at nominal flow rate. The first part of the study focuses on the steady behavior of the inducers in cavitating conditions: evolutions of performance, torque, mass flow rate, and amplitude of radial forces on the shaft according to the inlet pressure are considered. Several flow rates and rotation speeds are investigated. Significant differences between the inducers are obtained concerning the critical cavitation number, the amplitude of the radial forces, and the organization of cavitation in the machinery. Cavitation instabilities are investigated in the second part of the study. Various flow patterns are detected according to the mass flow rate and the cavitation number.
Large Eddy Simulation of Internal Flow of a Mixed-Flow Pump
Authors: Yamade Yoshinobu , Kato Chisachi , Shimizu Hayato , Nagahara Takahide
Published: July 2010

Large eddy simulation (LES) of internal flows of a mixed-flow pump is performed. The pump has 5 open impeller blades and twelve diffuser vanes. The objective of the present research is to verify the accuracy of the pump performance prediction by LES with a particular emphasis placed on the instability characteristics. The following two cases of computations are preformed for LES with different grid resolutions. In the first case, we perform LES of internal flow of the pump for a wide range of flow rate, including a flow rate from the shutoff point to the maximum flow. Secondly, we focus on internal flows at flow rates of 55%∼60%, where the instability characteristics take place, with finer computational grid compared to the first case. We use 8 million girds for the first case (the coarse LES), and 78 million girds for the second case (the fine LES). We intended to resolve the turbulent boundary layer (TBL) developed on the surfaces of impeller blades and diffuser vanes in the fine LES. We obtained a good agreement between the measured and predicted pump performance for a wide range of flow rate in the coarse LES, although the predicted total head drop at the flow rate of 55%∼60% is smaller than the measured one. In the fine LES, accuracy of pump performance prediction at 55%∼60% flow rate was improved.
Numerical Simulation of Dispersion of Fire Extinguishing Agents in Turbulent Flow in the Presence of Clutter Elements of Aircraft Engine Nacelles
Authors: Zbeeb K. , Ghenai C.
Published: July 2010

The combination of highly turbulent airflow, flammable fluids, and numerous ignition sources makes aircraft engine nacelles a difficult fire zone to protect. Better understanding of nacelle air flow and how it influences the spread of fires and fire extinguishing agents is needed to improve the efficiency of fire suppression. The principal objective of this study is to analyze the flow field and the dispersion of fire extinguishing agents in the presence of various clutter elements of aircraft engine nacelles. Three dimensional simulations of the transport of liquid droplets in highly turbulent flow past clutter elements are performed in this study. A three dimensional model with 2000 mm length, 915 mm width and 610 mm height was first created. The clutter package consists of 16 cylindrical elements; each element has an outer diameter D of 50.8 mm and assembled to form three separate arrays of 5, 6 and 5 elements. The stream wise spacing between each clutter array is set to twice the diameter (2 D). The three dimensional geometry is similar to the one used in the experimental study at Sandia National Laboratory. This will help to validate the numerical results before performing a parametric study. Water with initial droplet size of 150 to 280 μm, and flow rate of 0.285 Kg/s is used as suppressant agent. The three velocity components, turbulence intensity, and droplet concentrations and trajectories behind the clutter package are obtained in this study. The droplet X-velocity and Y-velocity and the droplet size distribution downstream the clutter elements show a good agreement with the experimental data. The effect of initial turbulence intensity, the air flow velocity at the inlet, and droplet diameter at the injection on the transport and dispersion of fire extinguishing agent in this complex geometry is presented in this paper.
Design of a Propeller Fan Using 3-D Inverse Design Method and CFD for High Efficiency and Low Aerodynamic Noise
Authors: Okamoto Hidenobu , Goto Akira , Furukawa Masato
Published: July 2010

Three-Dimensional Inverse Design Method, where the 3-D blade profile is designed for a specified blade loading distribution, has been applied for designing a propeller fan rotor with high efficiency and low noise. A variety of the blade loading distributions (pressure jump across the blade), vortex pattern (forced vortex, free vortex, and compound vortex) and the stacking conditions (sweep angles) were specified and the corresponding 3-D blade configurations were obtained. Among the 22 different designs, 14 propeller fan rotors including the reproduced baseline fan were manufactured by a rapid prototyping based on a selective laser sintering system (SLS) and tested. It was confirmed experimentally that the best design achieved about 5.7 points improvement in the peak total-to-static efficiency and the 2.6dB(A) reduction in aerodynamic noise. The flow mechanisms leading to the higher efficiency and lower aerodynamic noise were discussed based on experiments and the RANS steady flow simulations. Based on these investigations, design guidelines for the inverse design of propeller fan rotors with higher efficiency and lower aerodynamic noise were proposed.
Impact and Outcomes of a Flow Visualization Course
Authors: Hertzberg Jean , Sweetman Alex
Published: July 2010

For the past six years, a course on flow visualization has been offered to mixed teams of graduate and undergraduate engineering and fine arts photography students at the University of Colorado. The course has significant technical content on flow visualization and photographic techniques, and includes some emphasis on documentation and the interpretation of results, particularly with respect to atmospheric dynamics as revealed by clouds. What makes this course unusual is the emphasis on the production of images for aesthetic purposes: for art. While a number of art/science collaborations are growing worldwide, both in professional and academic communities, typically scientists are expected to contribute technical support while artists produce art. A particularly unusual aspect of this course is that all students are expected to demonstrate both aesthetic sensibility and scientific discipline. Another is that students are not constrained to study specific phenomena or use specific techniques; instead, creativity is required. A major outcome from this course is a series of stunning images. In addition, anecdotal evidence suggests that this course has a lasting impact on students’ perception of fluid physics, which can be contrasted to the effect of traditional introductory fluids courses. This raises the question of whether this impact is significant with respect to students’ understanding and appreciation of fluid mechanics, and if so, what aspect of the flow visualization course is most important? A survey instrument is being designed to quantify whether students’ awareness of fluid mechanics in the world around them changes when they take these courses and if students’ attitudes towards fluids is changed when they take these courses.
CFD Analysis of Drag Coefficient of a Parachute in a Steady and Turbulent Condition in Various Reynolds Numbers
Authors: Izadi Muhammad Javad , Dawoodian Mazyar
Published: July 2010

Study of parachutes is very important in aerospace industry. In this research, the effect of various Reynolds numbers on a parachute with a vent and without a vent at the top on drag coefficient in a steady and turbulent condition is studied. After a complete research on an efficient grid study, the drag coefficients are calculated numerically. The Reynolds number is varied from 78000 to 3900000 (1 m/s to 50 m/s). It is found that, for a parachute without a vent at the top, as the Reynolds number is increased from 78000 to 800000, the drag coefficient is decreased from about 2.5 to 1.4, and then as the Reynolds number is increased to 1500000, the drag coefficient increased to about 1.62 and it stayed constant for higher Reynolds number up to 3900000. As the vent ratio of the parachute is increased from zero to 5 percent of the parachute inlet diameter, the drag coefficient increased and for further increase of the vent ratio diameter, the drag coefficient decreased, but the general variation of drag coefficient was the same as of same parachute with no vent.
CFD Modeling Inside an Electrical Submersible Pump in Two-Phase Flow Condition
Authors: Barrios Lissett , Prado Mauricio Gargaglione , Kenyery Frank
Published: July 2010

Dynamic multiphase flow behavior inside a mixed flow Electrical Submersible Pump (ESP) has been studied theoretically for the first time. The main goal is to model two-phase flow behavior in an ESP. A three-dimensional CFD model has been developed to describe the operational envelope of the ESP, namely the onset of surging. The theoretical study includes CFD simulations for the prediction of the flow behavior inside the pump. The CFD modeling depends on two important variables, namely the bubble size and the bubble drag coefficient. The bubble size has been measured and a physically based correlation presented in Barrios (2007) is used. A new correlation for the drag coefficient is used (Barrios 2007) as a function of rotational speed and Reynolds number. Single-phase and two-phase flow CFD simulations were carried out to investigate liquid flow field. Results from the CFD simulations are consistent with the experimental data (Barrios 2007).
Analysis of the Diameter of Microbubbles Formed in a Cross Flow Microchannel
Authors: John T. J. , Mathew B. , Hegab H.
Published: July 2010

Two microfluidic devices for generating microbubbles are considered in the study presented in this paper. The first device consists of a liquid channel and a gas channel that is perpendicular to each other. In this device, the microbubble diameter varies inversely with the liquid flow rate (i.e. with flow velocity) but at the expense of high pressure drop. This device is modified by introducing a solid structure in front of the orifice to become the second device. This modification causes an increase in fluid velocity only in front of the orifice. In this paper a model is developed for determining the diameter of microbubbles generated in both of these devices. The model is developed by balancing the forces acting on the microbubble during growth and at the moment of detachment from the orifice. The detachment of the microbubble is assumed to happen when the sum of all detaching forces equals the net attaching force acting on the microbubble during the growth. Non-slip boundary condition is assumed on the walls of the channels in this model. Based on these assumptions a mathematical model is developed and solved numerically for different values of liquid and gas flow rate to obtain the microbubble diameter at the moment of detachment. A MATLAB® code is developed for solving the force balance equation. The superiority of the second device over the first one is validated by comparing the results obtained from the models in both cases.
Investigation of the Fluid Flow in a Rotor-Stator Cavity With Inward Through-Flow
Authors: Will Bjo¨rn-Christian , Benra Friedrich-Karl
Published: July 2010

The present paper covers fluid flow in rotor-stator cavities with inward through-flow. First, a general introduction into the physics of the cavity boundary layer flow is given. The structure of the flow is very complex and depends on different dimensionless parameters. For practical applications, simple and robust calculation procedures are crucial for design purposes. Two basic modelling approaches are compared (3 layer model of Kurokawa [14] and “one layer” approach of Mo¨hring [17]) with experimental data from the literature. The flow models are classified in context of the simplified equations of motion by emphasizing the main assumptions and simplifications in their derivation. Further on, for the one layer model, the use of the logarithmic law for the velocity distribution close to the wall is proposed instead of the classic 1/7 power law. The modified flow model is validated against experimental data for different parameter combinations, yielding better agreement for moderate inlet rotation. Finally numerical simulations have been performed in order to investigate the discrepancies between measured and calculated core rotation distributions for strong inlet swirl. It is supposed that the assumption of radial equilibrium in the core region is not necessarily appropriate for evaluation of the core rotation. Further on, it is clarified in which situations the tangential velocity component of the absolute velocity at the impeller outlet can be used as a boundary condition for the flow model.
Experimental and Numerical Investigation of a Centrifugal Pump Working as a Turbine
Authors: Ferna´ndez Joaqui´n , Barrio Rau´l , Blanco Eduardo , Parrondo Jorge , Marcos Alfonso
Published: July 2010

An experimental and numerical investigation of a conventional centrifugal pump working as a turbine is presented. The numerical simulations were performed with the code Fluent by means of unsteady flow calculations and a sliding mesh technique to account for the impeller-volute interactions. Thus, it was possible to properly simulate the effect on the local flow of the passage of the impeller blades in front of the volute tongue. The numerical results were compared with the experimentally determined performance curves and additionally with the static pressure distribution measured around the impeller periphery. Once validated, the model was used to estimate the steady and unsteady radial forces on the impeller for a number of flow rates. The steady radial force was also experimentally estimated from the static pressure measurements around the periphery of the impeller. The numerical predictions showed that, for the flow interval considered in the present investigation, the unsteady radial force varied between 24% and 54.3% of the steady magnitude, and that its maximum amplitude was reached when the trailing edge of one of the blades was located 3 deg downstream the tip of the tongue.
Laminar Entrance Length in Microtubes
Authors: Lemley Evan C. , Handy Tim A. , Papavassiliou Dimitrios V. , Neeman Henry J.
Published: July 2010

The goal of this study was to determine the entrance length — the distance from a microtube entrance to the point where flow is fully developed — for laminar liquid flow in smooth, straight, circular-microtubes and trapezoidal microchannels. Knowledge of the entrance length and pressure losses in this region for microtubes are of interest in microfluidic devices, in porous media, and in other networks of small ducts or pores. Although laminar entrance length has been studied extensively in macroscale tubes, only recently has attention been paid problem of entrance length in microtubes. Some differences do exist in macro versus micro flow, sometimes attributed to the relatively small volume to surface area ratio at the microscale. The entrance length determined in this study is intended to provide a means to analyze and design microtubes or networks of microtubes. The inlet velocity was varied to provide a Reynolds number of 10 to 2000 and the length was varied based on Reynolds number to ensure the length captured the entire entrance region. Simulations of water at standard conditions were performed using FLUENT and a custom written computer code, which automated the process of creating the flow geometries, extracting results, and determining the entrance length for each run. A grid resolution study was performed to ensure grid size was not a factor. Pressure and velocity distributions as a function of position were extracted to determine flow characteristics. Fluid velocity magnitudes from the tube centerline to 95% of the distance to the tube wall were used to determine when fully developed flow was reached by finding the point at which all velocity magnitudes did not change by more than 1% for additional distance along the tube. Results were compared to results from the literature for entrance length in macro-scale tubes and found to be qualitatively the same. The entrance length (in units of the number of diameters) for circular tubes is often expressed as C times the Reynolds number. For Reynolds numbers greater than 100, this study found C to be 0.0505, which is in general agreement with macroscale experiments and simulations, where C is reported to be between 0.05 and 0.2. For trapezoidal microchannels we found a relationship for entrance length over hydraulic diameter that is proportional (slope of 0.674) to Reynolds number for Reynolds number over 100. As Reynolds numbers get small the value of entrance length over hydraulic diameter goes to 0.674.
Direct Interaction of Fluid-to-Fluid in an Unsteady Ejector With a Zero-Degree Conning Radial Diffuser
Authors: Ababneh Amer Khalil , Garris Charles
Published: July 2010

Unsteady ejectors have been investigated as advanced technologies to classical ejectors for the purpose of energizing secondary fluids whereby the attractiveness of these devices lies in their mechanical simplicity. The primary fluid is accelerated to Mach 2 utilizing eight rectangular supersonic nozzles. The geometry of the diffuser where the primary and secondary fluids interact and hence exchanging energy is considered to be an important factor in affecting the performance. Specifically, proper design of the diffuser contributes significantly for producing quality flow; e.g., reducing the likelihood of developing shocks, and hence less of entropy generation, which is an indication for degrading the potential for energy exchange. The diffuser is chosen to be upright, or zero-degree conning, thus allowing the two fluids to smoothly come into contact. Because of their prime potential application being in thrust augmentation and refrigeration the working fluid was chosen to be water vapor, which is more suitable with the later application. A CFD package; i.e., FLUENT, was employed for the investigation.
Rheological Studies of Lubricants With Nanocarbon Additives
Authors: Kutelia E. R. , Bakhtiyarov S. I.
Published: July 2010

A comparative SEM, TEM and Auger-spectroscopic investigations of structure of friction surfaces of different objects were carried out. It was find out that the amorphous fine carbon (AFC) additives, obtained, for example, via oxidizing pyrolysis of methane during production of acetylene, improves the resistance to mechanical, chemical and abrasive scuffing and fret. It also provides increase in resistance to contact fatigue (pitting), fretting and corrosion resistance; reduces energy losses caused by external and internal friction, improves a wear-in of sliding surfaces, and the “aftereffect” is achieved.
Slurry Pump Casing Wear Prediction Using Numerical Multi-Phase Flow Simulation
Authors: Roudnev Aleksander S. , Bourgeois Ronald J. , Kosmicki Randy J.
Published: July 2010

Wet end components of centrifugal slurry pumps used in the hydraulic transport of solids are subject to substantial erosive wear. Accurate prediction of the casing wear rate and location for a particular duty is beneficial for correct pump selection and design, maintenance planning, and elimination of emergency shutdowns. CFD multi-phase simulation using the Eulerian-Eulerian approach is being used successfully to determine the velocity fields and solids concentration in the centrifugal pump allowing for accurate predictions of casing wear patterns resulting from sliding abrasive wear. Simulation results for various single domain and multi-domain multiphase simulations are discussed. Emphasis is placed on results from a 3 dimensional, multi-domain transient, multiphase simulation and comparison to field data.
Determination of Physical Properties of Isotropic Porous Materials by Impedance Tube
Authors: Sharma Sanjay , Siginer Dennis
Published: July 2010

Simulation of fluid flow in porous materials depends upon the accuracy of permeability measurement. This study details the development of an acoustical method to determine permeability of porous medium. Standardized acoustical testing for low frequency using impedance tube is carried out to determine the acoustical properties of the fibers. Physical properties of porous medium are determined by reverse calculation from the acoustical properties. The acoustical method is validated by comparing the measured acoustical properties of the porous medium by the analytical method. A variety of foams and fibers are tested using this methodology.
Utilisation of Bio-Fuels in Aviation Gas-Turbine Engines: An Experimental and Theoretical Evaluation
Authors: Cromarty Jason , Abanteriba Sylvester
Published: July 2010

An experimental and theoretical investigation was undertaken to identify and evaluate the key technical issues surrounding the ‘drop-in’ utilisation of alternative bio-fuels in aviation gas-turbine propulsion systems. Region-suitable biofuels were identified and suitability evaluated based on the following three criteria: ‘drop-in’ capability, environmental and economic sustainability and industrialisation prospects. Bio-fuel engine performance will be evaluated based on the specific fuel consumption, specific thrust, nature and quantity of emissions through theoretical modelling. This paper outlines a variety of different bio-fuel type options that were investigated. By using engineering and scientific methodology the fuels were evaluated to verify their suitability for gas-turbine aviation use. The eventual bio-fuel selected for further evaluation was a locally produced mustard seed oil derivative bio-fuel which was blended at various blend ratios with standard Jet A-1 turbine fuel. Verification testing processes for future investigation are detailed. In addition to engine performance evaluation endeavours, this paper also seeks to address and offer recommendations in the areas of bio-fuel production, transport, storage, certification and emissions.
An analytical model of the effects of pulse pileup on the energy spectrum recorded by energy resolved photon counting x‐ray detectors
Authors: Taguchi Katsuyuki , Frey Eric C. , Wang Xiaolan , Iwanczyk Jan S. , Barber William C.
Published: July 2010

Purpose:

Recently, novel CdTe photon counting x‐ray detectors (PCXDs) with energy discrimination capabilities have been developed. When such detectors are operated under a high x‐ray flux, however, coincident pulses distort the recorded energy spectrum. These distortions are called pulse pileup effects. It is essential to compensate for these effects on the recorded energy spectrum in order to take full advantage of spectral information PCXDs provide. Such compensation can be achieved by incorporating a pileup model into the image reconstruction process for computed tomography, that is, as a part of the forward imaging process, and iteratively estimating either the imaged object or the line integrals using, e.g., a maximum likelihood approach. The aim of this study was to develop a new analytical pulse pileup model for both peak and tail pileup effects for nonparalyzable detectors.

Methods:

The model takes into account the following factors: The bipolar shape of the pulse, the distribution function of time intervals between random events, and the input probability density function of photon energies. The authors used Monte Carlo simulations to evaluate the model.

Results:

The recorded spectra estimated by the model were in an excellent agreement with those obtained by Monte Carlo simulations for various levels of pulse pileup effects. The coefficients of variation (i.e., the root mean square difference divided by the mean of measurements) were 5.3%–10.0% for deadtime losses of 1%–50% with a polychromatic incident x‐ray spectrum.

Conclusions:

The proposed pulse pileup model can predict recorded spectrum with relatively good accuracy.
Stereotactic body radiation therapy: The report of AAPM Task Group 101
Authors: Benedict Stanley H. , Yenice Kamil M. , Followill David , Galvin James M. , Hinson William , Kavanagh Brian , Keall Paul , Lovelock Michael , Meeks Sanford , Papiez Lech , Purdie Thomas , Sadagopan Ramaswamy , Schell Michael C. , Salter Bill , Schlesinger David J. , Shiu Almon S. , Solberg Timothy , Song Danny Y. , Stieber Volker , Timmerman Robert , Tomé Wolfgang A. , Verellen Dirk , Wang Lu , Yin Fang‐Fang
Published: July 2010

Task Group 101 of the AAPM has prepared this report for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for the external‐beam radiation therapy technique referred to as stereotactic body radiation therapy (SBRT). The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information is provided for establishing a SBRT program, including protocols, equipment, resources, and QA procedures. Additionally, suggestions for developing consistent documentation for prescribing, reporting, and recording SBRT treatment delivery is provided.
Quantification of arterial plaque and lumen density with MDCT
Authors: Paul Narinder S. , Blobel Joerg , Kashani Hany , Rice Murray , Ursani Ali
Published: July 2010

Purpose:

This study aimed to derive a mathematical correction function in order to normalize the CT number measurements for small volume arterial plaque and small vessel mimicking objects, imaged with multidetector CT (MDCT).

Methods:

A commercially available calcium plaque phantom (QRM GmbH, Moehrendorf, Germany) and a custom built cardiovascular phantom were scanned with 320 and 64 MDCT scanners. The calcium hydroxyapatite plaque phantom contained objects 0.5–5.0 mm in diameter with known CT attenuation nominal values ranging 50–800 HU. The cardiovascular phantom contained vessel mimicking objects 1.0–5.0 mm in diameter with different contrast media. Both phantoms were scanned using clinical protocols for CT angiography and images were reconstructed with different filter kernels. The measured CT number (HU) and diameter of each object were analyzed on three clinical postprocessing workstations. From the resultant data, a mathematical formula was derived based on absorption function to demonstrate the relation between measured CT numbers and object diameters.

Results:

The percentage reduction in measured CT number (HU) for the group of selected filter kernels, apparent during CT angiography, is dependent only on the object size (plaque or vessel diameter). The derived formula of the form showed reduction in CT number for objects between 0.5 and 5 mm in diameter, with asymptote reaching background noise for small objects with diameters nearing the CT in‐plane resolution (0.35 mm). No reduction was observed for the objects with diameters equal or larger than 5 mm.

Conclusions:

A clear mathematical relationship exists between object diameter and reduction in measured CT number in HU. This function is independent of exposure parameters and inherent attenuation properties of the objects studied. Future developments include the incorporation of this mathematical model function into quantification software in order to automatically generate a true assessment of measured CT number (HU) corresponding to plaque physical density . This is a significant development for the accurate, noninvasive classification of noncalcified arterial plaque.
Local plate/rod descriptors of 3D trabecular bone micro‐CT images from medial axis topologic analysis
Authors: Peyrin Françoise , Attali Dominique , Chappard Christine , Benhamou Claude Laurent
Published: July 2010

Purpose:

Trabecular bone microarchitecture is made of a complex network of plate and rod structures evolving with age and disease. The purpose of this article is to propose a new 3D local analysis method for the quantitative assessment of parameters related to the geometry of trabecular bone microarchitecture.

Methods:

The method is based on the topologic classification of the medial axis of the 3D image into branches, rods, and plates. Thanks to the reversibility of the medial axis, the classification is next extended to the whole 3D image. Finally, the percentages of rods and plates as well as their mean thicknesses are calculated. The method was applied both to simulated test images and 3D micro‐CT images of human trabecular bone.

Results:

The classification of simulated phantoms made of plates and rods shows that the maximum error in the quantitative percentages of plate and rods is less than 6% and smaller than with the structure model index (SMI). Micro‐CT images of human femoral bone taken in osteoporosis and early or advanced osteoarthritis were analyzed. Despite the large physiological variability, the present method avoids the underestimation of rods observed with other local methods. The relative percentages of rods and plates were not significantly different between osteoarthritis and osteoporotic groups, whereas their absolute percentages were in relation to an increase of rod and plate thicknesses in advanced osteoarthritis with also higher relative and absolute number of nodes.

Conclusions:

The proposed method is model‐independent, robust to surface irregularities, and enables geometrical characterization of not only skeletal structures but entire 3D images. Its application provided more accurate results than the standard SMI on simple simulated phantoms, but the discrepancy observed on the advanced osteoarthritis group raises questions that will require further investigations. The systematic use of such a local method in the characterization of trabecular bone samples could provide new insight in bone microarchitecture changes related to bone diseases or to those induced by drugs or therapy.
Fast, low‐dose patient localization on TomoTherapy via topogram registration
Authors: Moore Kevin L. , Palaniswaamy Geethpriya , White Benjamin , Goddu S. Murty , Low Daniel A.
Published: July 2010

Purpose: To investigate a protocol which efficiently localizes TomoTherapy patients with a scout imaging (topogram) mode that can be used with or instead of 3D megavoltage computed tomography (MVCT) imaging.

Methods: The process presented here is twofold: (a) The acquisition of the topogram using the TomoTherapy MV imaging system and (b) the generation of a digitally reconstructed topogram (DRT) derived from a standard kV CT simulation data set. The unique geometric characteristics of the current TomoTherapy imaging system were explored both theoretically and by acquiring topograms of anthropomorphic phantoms and comparing these images to DRT images. The performance of the MV topogram imaging system in terms of image quality, dose incurred to the patient, and acquisition time was investigated using ionization chamber and radiographic film measurements.

Results: The time required to acquire a clinically usable topogram, limited by the maximum couch speed of , was 12.5 s for a 50 cm long field. The patient dose was less than 1% of that delivered by a helical MVCT scan. Further refinements within the current TomoTherapy system, most notably decreasing the imaging beam repetition rate during MV topogram acquisition, would further reduce the topogram dose to less than per scan without compromising image quality.

Conclusions: Topogram localization on TomoTherapy is a fast and low‐dose alternative to 3D MVCT localization. A protocol designed that exclusively utilized MV topograms would result in a 30‐fold reduction in imaging time and a 100‐fold reduction in dose from localization scans using the current TomoTherapy workflow.
On the use of a proton path probability map for proton computed tomography reconstructiona)
Authors: Wang Dongxu , Mackie T. Rockwell , Tomé Wolfgang A.
Published: July 2010

Purpose:

To describe a method to estimate the proton path in proton computed tomography (pCT) reconstruction, which is based on the probability of a proton passing through each point within an object to be imaged.

Methods:

Based on multiple Coulomb scattering and a semianalytically derived model, the conditional probability of a proton passing through each point within the object given its incoming and exit condition is calculated in a Bayesian inference framework, employing data obtained from Monte Carlo simulation usingGEANT4. The conditional probability at all of the points in the reconstruction plane forms a conditional probability map and can be used for pCT reconstruction.

Results:

From the generated conditional probability map, a most‐likely path (MLP) and a 90% probability envelope around the most‐likely path can be extracted and used for pCT reconstruction. The reconstructed pCT image using the conditional probability map yields a smooth pCT image with minor artifacts. pCT reconstructions obtained using the extracted MLP and the 90% probability envelope compare well to reconstructions employing the method of cubic spline proton path estimation.

Conclusions:

The conditional probability of a proton passing through each point in an object given its entrance and exit condition can be obtained using the proposed method. The extracted MLP and the 90% probability envelope match the proton path recorded in theGEANT4 simulation well. The generated probability map also provides a benchmark for comparing different path estimation methods.