bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Evaluation of a Regenerative Pump of Small Size
Authors: Kang Shin-Hyoung , Lim Hyung-Soo , Ryu Su-Hyun
Published: March 2009

Performance of a regenerative pump for automobile was tested and carefully corrected to obtain performance of the pump. Flow calculations are also performed in one vane to vane region of the impeller and side channel. Corrections of leakage loss and performance reduction in the transient regions at the inlet and outlet are discussed in the study. The calculated values are good coincident with the measured and corrected values near the design and high flow rates. The flow is very complex three dimensional with a strong radial vortex due to centrifugal force and an axial vortex due to re-circulating flow between the impeller and the side channel. Momentum exchange on the plane between the impeller and the side channel are evaluated to estimate viscous losses in the pump. The present study contributes to showing the capability of flow simulation of complex flow in the regenerative pump by comparing the calculated performance with the measured value.
Study of Particulate Flow in the Impeller of a Slurry Pump Using PIV
Authors: Mehta M. , Kadambi J. R. , Sastry S. , Sankovic J. , Wernet M. , Addie G. , Visintainer R.
Published: March 2009

Particle Image Velocimetry (PIV) technique in conjunction with refractive index matching was successfully utilized to investigate the velocities of the slurry particles in the impeller of a centrifugal slurry pump. Tests were performed in an optically clear centrifugal slurry pump at speeds of 725 rpm and 1000 rpm using a slurry made up of sodium iodide solution as the working fluid and glass beads (500μm mean diameter) as solid particles at volumetric concentrations of 1%,2%, and 3%. In the intra blade region of the impeller, the highest particle velocities were obtained on the suction side of the blade and in the blade trailing edge region as the blade sweeps through and velocity magnitude increases with the pump speed. But this magnitude was less than that of circumferential velocity of the blade tip. Relative velocity plots show that flow separation takes place on the suction side of the blade in the region below the blade tip for clear fluid flow conditions. This was expected as the pump is made to operate with a slurry and not a single-phase liquid. At higher pump speeds and particle volumetric concentrations, a marked improvement in the slurry flow in the impeller is observed i.e., the recirculation zone decreases. This results from the centrifugal forces on the particles and its inertia at that speed. Also the slurry particles are pushed on the pressure side of the blade and slide along it which can result in frictional wear. These results are discussed in this paper.
Radiation Heat Transfer and Soot Thermophoresis in Laminar Tube Flow
Authors: Akbar M. K. , Ghiaasiaan S. M.
Published: March 2009

The transport of soot particles suspended in laminar hot gas, flowing in a tube, was numerically modeled and parametrically studied. The objective was to assess the coupled effects of radiation heat transfer and thermophoresis on the soot particle transport in hot-walled tubes. The wall material was assumed to be transparent to radiation for wavelengths shorter than a threshold wavelength at high temperatures, an essential property of high temperature resistive materials. The results indicated that, as a consequence of strongly-coupled thermal radiation transport and thermophoresis, a radially-nonuniform temperature profile develops as the distance from the tube inlet is increased. Furthermore, the soot particles move towards the tube centerline due to thermophoresis, leading to the development of a sharp radial soot concentration profile. The pace of the development of the nonuniform radial temperature and soot concentration profiles is sensitive to several parameters. Reduction in soot particle size, higher average soot concentration, and higher tube wall temperature all promote the development of sharp radial profiles.
Analysis of Equivalent Pipe Flow System for K-10-8G Combustor
Authors: Ganesan Sivasankar , Subramanian Vijay
Published: March 2009

The pressure loss in the K-10-8G combustor has been quantified by constructing an equivalent pipe flow circuit where, the obstructions and branching are analogous to the flow pattern in the combustor. The adoption of skin friction coefficients and Hardy-Cross method cannot be employed due to the combustor’s short length (550 mm). For the evaluation of pressure loss, three flow systems have been constructed. In the first two systems, the fluid volume flowing through the core divides equally at the corresponding branching points, mixes with the flow from the outer annulus and combines back again. The third system is similar to the first except that the volumes combining after mixing are equal. The initial flow distributions in the core, outer and inner annuli were obtained from flow visualization. These systems can be used for corroborating the pressure loss produced, around 4.12%, which is in good agreement to that found from flow visualization (4.14%). The equivalent system was found to be similar to the combustor.
Torque Transient of Magnetically Driven Flow for Viscosity Measurement
Authors: Ban Heng , Lin Bochuan , Li Chao , Scripa Rosalia N. , Su Ching-Hua , Lehoczky Sandor L.
Published: March 2009

Viscosity is a good indicator of structural changes for complex liquids, such as semiconductor melts with chain or ring structures. This paper discusses the theoretical and experimental results of the transient torque technique for non-intrusive viscosity measurement. Such a technique is essential for the high temperature viscosity measurement of high pressure and toxic semiconductor melts. In this paper, our previous work on oscillating cup technique was expanded to the transient process of a magnetically driven melt flow in a damped oscillation system. Based on the analytical solution for the fluid flow and cup oscillation, a semi-empirical model was established to extract the fluid viscosity. The analytical and experimental results indicated that such a technique has the advantage of short measurement time and straight forward data analysis procedures.
Ion Transport in Nanochannels
Authors: Li Deyu , Yue Min , Karnik Rohit , Majumdar Arun , Fan Rong , Yang Peidong
Published: March 2009

Two kinds of nanochannels have been fabricated and ion transport in these nanochannels has been measured. Silica nanotube arrays have been fabricated from Si nanowire templates. The silica nanotubes can be more than 20 μm long with an inner diameter from 10 to 200 nm. A nanofluidic device based on individual silica nanotubes has been fabricated by placing the nanotube on a glass substrate and patterning with respect to individual nanotubes. A similar nanofluidic device with SiNx as the channel wall material has also been fabricated. The cross-section of the SiNx nanochannel is 40 nm high and 1 μm wide, while the channel length extends up to more than 24 μm. Ion transport though these nanochannels has been studied with different concentration KCl solutions to investigate the effects of electric double layer thickness on ion transport. Results show that for high concentration solutions, the measured current fit the theoretical prediction based on the bulk concentration. However, for low concentration solutions, the measured current was larger than that calculated with the bulk concentration, indicating that for low concentration solutions, the ion concentration within the channel was decided not only by the bulk solutions, but also by the surface charge density.
Direct Power Generation Using Tunneling and Thermionic Emission
Authors: Zeng Taofang
Published: March 2009

Thermionic emission in vacuum could be a highly efficient cooler or power generator if the work function, the minimum work for electrons to go into vacuum, is around 0.3–0.4 eV for heat source at a temperature below 500C [Mahan, 1994]. Unfortunately, the work function of existing materials is currently above 1 eV. Theoretical and experimental studies have shown that the work function can be reduced to 0.3–0.4 eV if the distance between the two electrodes (cathode and anode) of the thermionic emission cooler/power generator is below 10 nm [Hishinuma, et al, 2001, 2003]. At this nanometer scale, electron transport between the two electrodes takes two paths: electron tunneling and thermionic emission. The combined physical processes result in a desired work function. However, maintaining a nanometer gap for two parallel plates within an area larger than 1 cm2 is a daunting task, if not impossible, especially if the power generator is mounted on a moving or vibrating device. Even a slight vibration or thermal expansion of the two plates (electrodes) could cause direct contact between the two plates (electrodes), and thus shorten the circuits. Thus vacuum thermionic power generator based on difficult to make and to operate [Tavkhelidze, et al., 2002]. In this study, we propose to use a solid insulating spacer for preventing the shortening and for feasibility of manufacturing. The spacer is less than 5nm, and electron transport as thermionic emission and tunneling concurrently. In this study, we first investigate electron and phonon transport in single-layer (spacer) double heterostructures by including the tunneling effects. It is found that single-layer generator can have a high efficiency, but small power intensity due to the small temperature difference between the two electrodes. We then investigate the efficiency of multilayer-layer power generator. Calculations show that the solid power generator operating at a temperature below 500°C, can have an efficiency of larger than 40% of the Carnot efficiency.
Evaluation of the Parallel Parent and Daughter Classes Technique (PPDC) for Solving Population Balance Equations by Discretization: Aggregation and Breakage
Authors: Bove Stefano , Solberg Tron , Hjertager Bjo̸rn H.
Published: March 2009

An evaluation of the parallel parent and daughter classes (PPDC) algorithm for solving population balance equations (PBEs) by discretization is presented. By using this technique, the discretized form of the PBE, accounting for breakage and agglomeration, can easily be split into aggregation and breakage part. Numerical solutions of the PBE on simultaneous aggregation and breakage processes with different kernels, obtained by using the PPDC technique, show good agreement with solutions obtained by standard method of classes, on a linear grid, and by the quadrature method of moments (QMOM). Numerical investigations have shown the ability of the PPDC technique to predict the moments with high accuracy by using only a few classes (2–4 classes). The PPDC technique is then one of the best candidates for CFD applications involving PBEs as polymerization and de-polymerization processes, aerosol dynamics, bubbly flows etc.
Numerical Analysis of Response Time for Thin Film Temperature Sensors in Lubricated Contact
Authors: Jia Yi , Araya Juan Guillermo , Gutie´rrez Gustavo
Published: March 2009

Thin film temperature sensors integrated onto mechanical component surface are promising for real-time machine condition monitoring. In this paper one-dimensional heat conduction model has been developed to study the response time of the thin film sensors designed for monitoring of temperature distribution in elastohydrodynamic lubrication contact. A control volume approach was used to numerically analyze the effects of film thickness (from 0.1 μm to 100 μm), sensing materials, and substrate materials on the transient time response of the thin film sensor. Validation of the numerical model was compared to an analytical solution in a semi infinite domain. The time constants are obtained based on a constant heat load and sensor sensibility is studied when a typical dynamic pressure in lubricated contact is applied. The faster response time and the short time delay for a thin film sensor are expected in lower conductivity of substrate. It is also clear that the response time decreases with increasing film thickness and the conductivity of the substrate. Results show that when thickness of the sensor is less than 1 μm, the sensor is feasible to capture the transient temperature profile in real-time for machine health monitoring under various operating condition.
Laminar Combined Free and Forced Convection Heat Transfer in the Entry Length of a Horizontal Pipe
Authors: Al Araby Mahmoud Ahmed , Shaban Mohamed Khamis , Sarhan Salem Abd El Azez , Mahmoud Mamdouh M.
Published: March 2009

The present research work was carried to represent a numerical study and experimental investigation of laminar combined free - and - forced convection in the entry region of a horizontal constant wall temperature with simultaneous development of fluid velocity and temperature. The analytical study employed a sample case with Re = 100, Pr = 0.7 and Gr = 5000, 10000 and 100000 to demonstrate the results which are temperature, axial, radial and angular velocities. The experimental investigation presents temperatures profiles for Gr = 100000 at Re = 200 to 1000. The aim of the present study is to investigate the characteristics of laminar combined free - and - forced convection in the entrance region of a horizontal pipe of constant surface temperature with simultaneous development of fluid velocity and temperature.
Microscale Desorption Based on Membrane Separation
Authors: Thorud Jonathan D. , Siekas Jeremy J. , Liburdy James A. , Pence Deborah V.
Published: March 2009

A scheme to achieve high desportion rates in a microscale system has been conceived based on the use of a hydrophobic porous membrane forming one wall of a high aspect ratio channel. To accomplish desorption, vapor is drawn through the membrane, during the addition of heat, as the binary mixture flows along the channel. The channel geometry is designed to achieve a thin film of binary mixture (lithium bromide and water) that is approximately 350 microns thick, while achieving a high membrane surface area which is approximately 3 cm × 6 cm. Vapor is drawn from the channel by creating a pressure differential across the membrane. Experiments were run varying the inlet mass flow rate, heat input, and pressure difference across the membrane, for an inlet mass fraction of 0.41. Mass fraction increases through the channel were up to 0.05. It is shown that the mass flux of vapor per mass flow rate into the channel decreases as the inlet flow rate increases, for a given heat flux. Also, the mass flux of vapor is linearly dependent on the heat input rate and not a function of inlet flow rate or pressure differential for the range of conditions studied. Images within the channel show bubble formation and desorption through the membrane under high heat flux and low inlet flow conditions.
A Model for Turbulent Kinetic Energy Distribution Across the Interface Between a Porous Medium and an Unobstructed Region
Authors: de Lemos Marcelo J. S.
Published: March 2009

The study of important environmental and engineering flows can benefit from more realistic modeling. Accordingly, grain storage and drying as well as flows over layers of vegetation can be characterized by some sort of porous structure through which a fluid permeates. For such hybrid media, involving both a porous structure and a clear flow region, difficulties arise due to the proper mathematical treatment given at the macroscopic interface. The literature proposes a jump condition in which shear stresses on both sides of the interface are not of the same value. This paper presents numerical solutions for such hybrid medium, considering here a channel partially filled with a porous layer through which fluid flows in turbulent regime. Here, diffusion fluxes of both momentum and turbulent kinetic energy across the interface present a discontinuity in their values, which is based on a certain jump coefficient. Effects of such jump parameter on mean and turbulence fields around the interface regions are numerically investigated. Results indicate that depending on the value of the stress jump parameter, a substantially different structure for the turbulent field is obtained.
Micro Fluidic Jets for Thermal Management of Electronics
Authors: Garg Jivtesh , Arik Mehmet , Weaver Stanton , Saddoughi Seyed
Published: March 2009

Micro fluidics devices are conventionally used for boundary layer control in many aerospace applications. Synthetic Jets are intense small scale turbulent jets formed from entrainment and expulsion of the fluid in which they are embedded. The idea of using synthetic jets in confined electronic cooling applications started in late 1990s. These micro fluidic devices offer very efficient, high magnitude direct air-cooling on the heated surface. A proprietary synthetic jet designed in General Electric Company was able to provide a maximum air velocity of 90 m/s from a 1.2 mm hydraulic diameter rectangular orifice. An experimental study for determining the thermal performance of a meso scale synthetic jet was carried out. The synthetic jets are driven by a time harmonic signal. During the experiments, the operating frequency for jets was set between 3 and 4.5 kHz. The resonance frequency for a particular jet was determined through the effect on the exit velocity magnitude. An infrared thermal imaging technique was used to acquire fine scale temperature measurements. A square heater with a surface area of 156 mm2 was used to mimic the hot component and extensive temperature maps were obtained. The parameters varied during the experiments were jet location, driving jet voltage, driving jet frequency and heater power. The output parameters were point wise temperatures (pixel size = 30 μm), and heat transfer enhancement over natural convection. A maximum of approximately 8 times enhancement over natural convection heat transfer was measured. The maximum coefficient of cooling performance obtained was approximately 6.6 due to the low power consumption of the synthetic jets.
Evaluation of Human Thermal Comfort in Offices in Kuwait and Assessment of the Applicability of the Standard PMV Model
Authors: Al-Mutawa Nawaf , Chakroun Walid , Hosni Mohammad H.
Published: March 2009

It has been known that the human thermal comfort is not exclusively a function of air temperature but also a function of six additional parameters, namely, mean radiant temperature, air velocity, turbulence intensity, humidity, activity level, and clothing insulation. The combined physical and psychological impact of these parameters on thermal comfort is mathematically described in various comfort models. The current comfort models, while use extensive human comfort data, may not be applicable in all world regions due to environmental conditions and people’s expectations. The State of Kuwait has a population of 2.5 million inhabitants with majority of people living in a few populated cities with heavy vehicle traffic, office buildings, factories, petroleum operations, and shopping centers. During the summer months (especially in July and August) the temperature reaches 48 °C in the afternoon, and can sometimes exceed 55 °C requiring extensive use of air conditioning. The traditional clothing (Disdasha) is made of lightweight, white, fabric material to provide some level of comfort. To better understand the regional preferences and assess the applicability of the standard comfort models in Kuwait, important parameters influencing human thermal comfort were measured in ten different government offices and the corresponding PMV indices were calculated. The results were compared with other comfort indices to obtain the most viable comfort index and the appropriate temperature range for local comfort for Kuwait offices. This study is not only important for comfort evaluations but also for evaluation of energy consumption in office buildings.
Exploratory Experiments to Determine Flow and Structure Borne Noise of Erosive Cavity Implosions
Authors: Foeth Evert-Jan , Kuiper Gert
Published: March 2009

In two exploratory setups, a high-frequency pressure transducer has been used to determine both the flow and the structure borne noise above 200 kHz. In the first set of tests the impact noise due to a single bubble is investigated in order to gain insight in the acoustic signals emitted by an imploding bubble. A quantitative analysis of the signals indicates a short and clear acoustic signal in the fluid and a long chiming signal in the structure. In the second set of tests the noise signal emitted by sheet cavitation implosion on a hydrofoil is acquired. The convoluted signals of individual bubbles can be identified both in the fluid and in the structure. Analyses of the signals by examining the peak distribution for sheet cavitation indicates a relation with the cavitation index and suggest that fluid and structure borne noise are not per se linked. Acoustic signals correlate well with visual observation.
An Uncertainty Analysis of a NIST Hydrocarbon Liquid Flow Calibration Facility
Authors: Yeh T. T. , Espina P. I. , Mattingly G. E. , Briggs N. R. , Aguilera Jesu´s
Published: March 2009

This paper presents the uncertainty characterization of NIST’s new hydrocarbon liquid flow calibrator (HLFC). This facility uses a passive piston prover technique where fluid is driven by pumps while the measuring piston is passively stroked through the calibration interval. This facility is typically operated using MIL-C-7024C fluid (also known as Stoddard solvent – a surrogate liquid for JP-4 and JP-5 jet fuels), but using a variety of other fluids offers a wider range of measurements. The range of flows for this facility is 0.19 to 5.7 liters per minute – lpm (0.05 to 1.5 gallons per minute – gpm). Over this range, the expanded uncertainty claim for this facility is ±0.01%, at 95% confidence level. The uncertainty of a dual-turbine meter tested in the system is also reported. In addition, NIST is working to incorporate additional piston provers so that the flow for hydrocarbon liquids calibration service will reach 760 lpm (200 gpm).
Unsteady Flow in Multistage Centrifugal Fans
Authors: Khelladi Sofiane , Kouidri Smai¨ne , Bakir Farid , Rey Robert
Published: March 2009

In order to improve the design of the multistage centrifugal fans, theoretical and experimental works were carried out in the optimization field of the unsteady 3D flows. Particular attention is given to the flows located at the rotor-stator interface. This zone is the seat of strong interactions between the moving part and the fixed part. This phenomenon has as consequences: strongly unsteady flow, fluctuating efforts on the stator bladings and an efficiency decrease. The analysis of the fluid behavior in this zone allowed the judicious choice of the fan geometry, the aim is to improve the flow organization and consequently the aeroacoustic performances. A numerical simulation tool was used in order to determine the kinematics and the dynamics of these flows. The measurements of the steady and unsteady flow characteristics allowed the comparison of the theoretical and experimental results.
Heat Transfer Studies on Freeze Concentration of Salt Brines in a Liquid Solid Fluidized Bed Heat Exchanger
Authors: Habib B. A. , Farid M. M.
Published: March 2009

Fluidized bed freeze concentration is a technology in which liquid solutions can be concentrated within a fluidized bed heat exchanger by preferential freezing of water out of the solution. Water forms an ice layer on the heat exchanger wall from where it is removed by the action of the fluidized bed on it. A double pipe fluidized bed heat exchanger was constructed which included a bed of 4×4 mm 304 stainless steel solid cylinders. Salt solutions (0–9.4 wt%) were used in the process to form ice, which could successfully be removed by the particles with bed porosity of 0.81–0.83. Freeze concentration effects were observed with continuous freezing point depression in these experiments. Coolants used in experiments were 34% ethylene glycol solution and a potassium formate solution. The respective overall heat transfer coefficients were ∼600 W/m2K with ethylene glycol and ∼1000 W/m2K with potassium formate solution (Tyfoxit).
Dynamic Modeling of Thermal Processes in Rotational Molding
Authors: Ghosh Kalyanjit , Garimella Srinivas
Published: March 2009

Transient heat transfer phenomena in the rotational molding of plastic parts are modeled in this study. Natural convection and radiation from the furnace and flue gases to the mold housing are analyzed. Other models include transient heat transfer through the mold, single-phase conduction through the particulate plastic material prior to phase change, melting of the plastic, and heating of the liquid pool. Subsequent staged cooling and solidification of the mold and plastic using a combination of free and forced convection and radiation is also modeled. Information about the properties of the plastic in powder, liquid and solid forms is obtained from the literature. Assumptions about the behavior of the plastic powder and the molten plastic during the rotational operations are also made in accordance with the available literature. The mold wall, melt and solidified plastic regions are divided into a number of finite segments to track the temperature variation with time during the molding process. The corresponding variations in masses and thicknesses of the melt and solidified plastic regions are also estimated. Consequently, the energy consumption rates in the process are estimated. The model is applied to a specific molding process in a commercial rotational molding plant. Parametric studies of the effect of heating and cooling durations on the plastic temperatures and the energy consumption rates are also conducted. These analyses provide insights about opportunities for optimization of the heating and cooling schedules to reduce overall energy consumption and also improve throughput.
Cavitation Detection Using Wavelet Denoising
Authors: Welz Joseph P. , Iannacci Matthew P. , Jenkins David M.
Published: March 2009

Cavitation in turbomachinery provides a source of damage to the hydrodynamic surfaces. Detection of cavitation at the earliest possible time after inception is desirable from a damage prevention standpoint. In order to detect cavitation in real time, acoustic sensing of the cavitation events has long been an accepted practice. A problem with this measurement technique is the potential contamination from electrical and acoustic background noise sources. This work employs an algorithm based on wavelet denoising. The wavelet denoising algorithm depends on a measurement of the acoustic background noise in the absence of cavitation. Cavitation measurements of a stationary object are evaluated with and without the application of the denoising process. The results of this comparison indicate that the wavelet denoising procedure allows an increased number of cavitation events to be detected at a given static pressure, and cavitation is detected at higher pressures than previous techniques.
pRTA (Probe Recovery Temperature Anemometry)
Authors: Ishibashi Masahiro
Published: March 2009

It is shown that the recovery temperature measured by a thin thermocouple wire inserted in airflow does not depend on the angle of incidence of the flow onto the wire and agrees very well with the theoretical value assuming the recovery factor of the square root of the Prandtl number. This fact allows RTA (Recovery Temperature Anemometry) employing a sensor of various structures; pRTA (probe RTA) is one of the examples where the thermocouple wire is bent at its contact point forming the probe apex. The paper demonstrates that pRTA measures the same flow velocity distributions in a critical nozzle as those by sRTA (streamwise RTA) where a thermocouple wire is settled parallel to the axis of symmetry of the nozzle.
Schlieren Measurements of Buoyancy Effects on Flow Transition in Low-Density Gas Jets
Authors: Pasumarthi Kasyap S. , Agrawal Ajay K.
Published: March 2009

The transition from laminar to turbulent flow in helium jets discharged into air was studied using Rainbow Schlieren Deflectometry technique. In particular, the effects of buoyancy on jet oscillations and flow transition length were considered. Experiments to simulate microgravity were conducted in the 2.2s drop tower at NASA Glenn Research Center. The jet Reynolds numbers varied from 800 to 1200 and the jet Richardson numbers ranged between 0.01 and 0.004. Schlieren images revealed substantial variations in the flow structure during the drop. Fast Fourier Transform (FFT) analysis of the data obtained in Earth gravity experiments revealed the existence of a discrete oscillating frequency in the transition region, which matched the frequency in the upstream laminar regime. In microgravity, the transition occurred farther downstream indicating laminarization of the jet in the absence of buoyancy. The amplitude of jet oscillations was reduced by up to an order of magnitude in microgravity. Results suggest that jet oscillations were buoyancy induced and that the brief microgravity period may not be sufficient for the oscillations to completely subside.
Numerical Analysis of Flow Evolution in a Helium Jet Injected Into Ambient Air
Authors: Satti Rajani P. , Agrawal Ajay K.
Published: March 2009

A computational model to study the stability characteristics of an evolving buoyant helium gas jet in ambient air environment is presented. Numerical formulation incorporates a segregated approach to solve for the transport equations of helium mass fraction coupled with the conservation equations of mixture mass and momentum using a staggered grid method. The operating parameters correspond to the Reynolds number varying from 30 to 300 to demarcate the flow dynamics in oscillating and non-oscillating regimes. Computed velocity and concentration fields were used to analyze the flow structure in the evolving jet. For Re = 300 case, results showed that an instability mode that sets in during the evolution process in Earth gravity is absent in zero gravity, signifying the importance of buoyancy. Though buoyancy initiates the instability, below a certain jet exit velocity, diffusion dominates the entrainment process to make the jet non-oscillatory as observed for the Re = 30 case. Initiation of the instability was found to be dependent on the interaction of buoyancy and momentum forces along the jet shear layer.
An Assessment of Five Turbulence Models in Predicting Turbulent Separation
Authors: Spall Robert E. , Phillips Warren F. , Alley Nick
Published: March 2009

Four different turbulence models were employed to predict the flow over a wall-mounted Glauert-Goldschmied body. The models evaluated include: 1) two-layer k–ε, 2) shear stress transport, 3) low-Reynolds number k–ω, 4) Spalart-Allmaras, and 5) v2−f. Calculations were performed for both an uncontrolled case, and a controlled-flow case which used steady suction through a slot located at the 65% chord station. The flow conditions include a freestream Mach number of approximately 0.1, and a chord Reynolds number of just under 1 million. For each model, the numerical results over predicted the experimentally determined re-attachment length. An examination of streamwise velocity profiles at several stations downstream of the trailing edge revealed considerable variation in the predictions of the five turbulence models.
Optimal Allocation of Heat Transfer Surface of a Two-Stage Refrigeration System
Authors: Morales M. J. , Sherif S. A.
Published: March 2009

The purpose of this study is to investigate how the heat exchanger inventory allocation plays a role in maximizing the thermal performance of a two-stage refrigeration system with two evaporators. First, the system is modeled as a Carnot refrigerator and a particular heat transfer parameter is kept constant as the heat exchanger allocation parameter is allowed to vary. The value of the heat exchanger allocation parameter corresponding to the maximum coefficient of performance (COP) is noted. The results are compared to those of a non-Carnot refrigerator with isentropic and non-isentropic compression. It is found that the Carnot refrigerator can be used to predict the value of the heat exchanger allocation parameter where the maximum COP occurs for a non-Carnot refrigerator. In order to improve the accuracy of that prediction, the predicted value of the heat exchanger allocation parameter has to be inputted into the set of equations used for the non-Carnot refrigerator. This study is useful in designing a low cost, high-performance refrigeration system.
Gravimetric Calibration of Critical Flow Venturi Nozzles
Authors: Morrow Thomas B.
Published: March 2009

The Metering Research Facility (MRF) was commissioned in 1995/1996 at Southwest Research Institute for research on, and calibration of natural gas flow meters. A key commissioning activity was the calibration of critical flow Venturi (sonic) nozzles by a gravimetric proving process flowing nitrogen or natural gas at different pressures. This paper concerns the calibration of the four sonic nozzles installed in the MRF Low Pressure Loop (LPL). Recently, a new project prompted a review of the relations used to calculate sonic nozzle discharge coefficient in the LPL data acquisition computer code. New calibrations of the LPL sonic nozzles were performed flowing natural gas over a lower range of pressure than used in the original commissioning tests. The combination of new and old gravimetric calibration data are shown to agree well with correlations published by Arnberg and Ishibashi (2001) and by Ishibashi and Takamoto (2001) for laminar, transitional and turbulent boundary layer flow in critical flow Venturi nozzles.
Orifice Meter Expansion Factor Experiments
Authors: Morrow Thomas B.
Published: March 2009

This paper presents new experimental data for orifice meter expansion factor and compares the results with previous data and accepted expansion factor correlations. The tests were performed in the Low Pressure Loop (LPL) of the Metering Research Facility (MRF) at Southwest Research Institute (SwRI) flowing natural gas through 100 mm (4-inch) and 150 mm (6-inch) diameter orifice meter tubes for values of the orifice diameter ratio (β) between 0.25 and 0.60. The results for expansion factor, within the β range of the tests, are in good agreement with previous data reported by Murdock and Foltz (1953) flowing steam in a 100 mm meter tube and by Seidl (1995) flowing air in a 50 mm (2-inch) diameter meter tube.
Parabolized Stability Equation Based Analysis of Noise From an Axisymmetric Hot Jet
Authors: Lin Ray-Sing , Reba Ramons A. , Narayanan Satish , Hariharan Nathan S. , Bertolotti Fabio P.
Published: March 2009

Noise generated from large-scale wave-like eddies in a Mach 0.9 hot axisymmetric jet is studied. The mean jet flow is computed using a Reynolds-Averaged Navier-Stokes solver with the k-ω turbulence model. Spatial development of near-field pressure perturbations is computed using a 3D Parabolized Stability Equation (PSE) method, and the far-field noise radiated from these convective instabilities is obtained by solving the wave equation. The 3D PSE method developed here allows the effects of strong azimuthal mean-flow variations to be captured and analyzed. Results show that large-scale wave-like eddies, or instability waves, travel slightly above sonic speed for the first few jet diameters, and that the dominant noise sources are concentrated near the edge of the time-averaged potential core. Good agreement between computed results and experiment are found for relative sound pressure levels and directivity. Also, at the low frequencies considered, the sound field associated with azimuthal wave-number m = 0 shows better agreement with experimental data than with (the most amplified) m = 1.
Aeroacoustic Characteristics of Efficient Automotive Engine Cooling Fan Systems
Authors: Moreau S. , Bakir F.
Published: March 2009

Recent studies on automotive engine cooling fan systems carried out in partnership between LEMFI and Valeo have led to the definition of a range of efficient stator designs. It was shown that an adequate rotor-stator coupling could yield significant efficiency gains over the whole range of Valeo fans with diameters ranging from 280 mm to 460 mm. Efficiency gains ranging from 12 percentage points for the 350 mm fan diameter to 2 points for the 460 mm were estimated by using a simplified radial equilibrium design (SRE). These predictions have been verified experimentally by recent designs for various fan system diameters. The present study then describes a newly developed aeroacoustic test facility dedicated to automotive fan systems. The influence of the rotor-stator coupling is then shown by comparing the rotor alone and rotor-stator configurations, not only on the overall performances and velocity fields at the system outlet measured by a 5-hole probe, but also on the noise generated by the fan systems for various flow conditions. At the nominal flow rate, the efficient stators are shown to bring little or no extra noise if the number of stators and the rotor-distance are carefully chosen. At other flow rates, additional noise might be expected.
An Experimental Study of Synthetic Jets From Rectangular Orifices
Authors: Milanovic Ivana M. , Zaman Khairul B. M. Q.
Published: March 2009

Results of an experimental investigation on isolated synthetic jets in crossflow from rectangular orifices of different aspect ratio and orientation are presented. Three aspect ratios, AR = 4, 8, and 16, with pitch α = 90°, were investigated. Additionally, the AR = 8 case was pitched at 20°. The yaw angle, β, was varied through 0°, 10°, 45° and 90°. All orifices had same exit area and the data were compared with synthetic as well as steady jet from a circular orifice of same area. Hotwire measurements were performed to obtain all three components of mean velocity and turbulent stresses. Data were acquired for momentum-flux ratio up to J = 50. Distributions of time- and phase-averaged data were obtained on the cross sectional plane at x/D = 0.5, 5 and 10, as well as on the axial plane of the symmetry. Qualitative flowfield similarity between synthetic and steady jets is observed. However, high-momentum ‘cap’ above the low-momentum ‘dome’, characteristic of steady jets, does not necessarily appear in the synthetic jet. The position and shape of the high-momentum region depend on the distance from the orifice, pitch, yaw as well as momentum-flux ratio. Consequently, the location of the minimum velocity in the ‘dome’ measured at the plane of symmetry, ymin, is adopted as a reference for penetration estimate and trajectory comparison. For AR = 16, the dome is the largest in area with maximum velocity deficit. However, the penetration is somewhat higher for AR = 4. Increase in yaw reduces the spatial extent of the dome and the penetration height but augments the velocity deficit. At low J the dome is connected to the boundary layer and traces of the cap of high momentum fluid are visible above it. Increase in J lifts the dome and reorganizes the high-momentum fluid around its perimeter, eventually bringing it underneath. Phase-averaged data document dynamic topological changes within the cycle. Phase-averaged streamwise velocity contours on the cross-sectional plane exhibit behavior commensurate with that seen in time-averaged data at various J.
Towards Conjugate Heat Transfer in Complex Geometries With an Immersed Boundaries Cartesian Solver
Authors: Moreau S. , Iaccarino G. , Kalitzin G.
Published: March 2009

The Cartesian incompressible RANS solver with Immersed Boundaries, IBRANS, recently developed at Stanford, has been extended to include conjugate heat transfer modeling and used for the simulation of the electrical motor of an automotive engine cooling fan system. Such applications are particularly challenging as they involve very complex geometries with tight tolerances and rotating parts. The new conjugate heat transfer capability of IBRANS has been validated on heated cylinder flows. Results are presented for a range of Reynolds numbers covering flow regimes ranging for a steady laminar flow to unsteady turbulent flows. Excellent agreement is achieved with similar simulations run with a “conventional” body fitted solver (Fluent) and equivalent turbulent models. Preliminary 3D simulations of the flow and heat transfer within the complete electrical motor are presented. The numerical predictions of the pressure drop through the motor as a function of flow rate agree very well with the measured data over the complete operating range.
The Use of Active Ionic Polymers in Dynamic Skin Friction Measurements
Authors: Etebari Ali , Akle Barbar , Farinholt Kevin , Bennet Matthew , Leo Donald J. , Vlachos Pavlos P.
Published: March 2009

A class of wall shear stress sensors has been developed. The potential of ionic polymer membrane transducers for measuring skin friction in liquid flows is demonstrated. Ionic polymer transducers are thin polymer membranes that exhibit high sensitivity to mechanical strain, and have been shown to demonstrate sensitivities two orders of magnitude higher in charge-sensing mode than piezoelectric polymers such as PVDF. Thus, they are as sensitive to mechanical strain as piezoelectric ceramics (i.e. PZT) but have the high compliance and durability of a polymer. The application of active ionic polymers in delivering easy to implement, accurate, dynamic measurements of skin friction in harsh environments promises significant advantages over current technologies. In particular, a robust technique for measuring wall shear stress is needed to assess the effectiveness of new friction-reducing techniques, including the use of lubricants and micro-bubble injection within the viscous sublayer. Conventional technologies have been unable to provide sufficiently accurate measurements over a large range of fluid velocity fluctuation scales. Moreover, their implementation can be complicated in the case of non-flush mounting sensors, and their applicability is often limited to forgiving environments. An initial feasibility test was designed with the objective of replicating classic theoretical and experimental skin friction coefficient results for a sharp edge flat plate boundary layer. An ionic polymer and a piezoelectric film (PVDF) were evaluated for Reynolds numbers ranging from the laminar flow regime to fully turbulent flow. The PVDF sensor displayed no discernable response to wall shear. The ionic polymer sensor, however, showed significant response to wall shear and strong correlation with the Reynolds number. In addition, a Stokes oscillating plate apparatus was designed for calibration and testing of the ionic polymer sensor.
Turbulent Multi-Phase Flow Interactions Through Grid Turbulence Measured by Particle Image Velocimetry
Authors: Brady Michael R. , Vlachos Pavlos P. , Telionis D.
Published: March 2009

Industrial processes involving multi-phase flows such as flotation require an understanding of the relationships between bubbles, solid particles and the flow. For decades engineers and researchers based their calculations on algebraic formulas that model these interactions. These formulas were derived either from simple models, or from experimental data. Modern experimental tools are employed in this effort to measure with great accuracy the basic features of the motion of all three phases in turbulent flow. We employed a unique Digital Particle Image Velocimeter (DPIV) that can record with great accuracy and kHz temporal resolution, velocity vectors of all three phases, namely the fluid, the solid particles and the air bubbles. The interaction of these three phases was studied in grid turbulence. Flow was directed through a rectangular grid of circular rods and the resulting homogeneous isotropic turbulence was documented. Particles and bubbles were released and the motion of the three phases was monitored. The particle RMS was in good agreement with a model proposed by Shubert, having an average RMS velocity of about 13% of the free stream velocity in the fully developed region. A theoretical model, derived first by Levins and Glastonbury was found to underpredict the particle RMS. The bubble RMS was about 26% of the free stream in the homogeneous isotropic region, 100% greater than the particle RMS and not consistent with the model predictions.
A Study of the Efficiency of Plate Freezing vs. Blast Freezing of Boxed Boneless Meat in an Abattoir
Authors: Hessami Mir-Akbar
Published: March 2009

Meat export is a major industry in Australia, and meat packaging and freezing is an energy intensive activity, requiring an objective technical investigation. This study was undertaken in order to assess the relative merits of plate and air blast freezing methods used in industry. To describe the efficiency and the technical superiority of one method over the other, in this paper, the details of an experimental study involving time-temperature measurement of meat boxes inside a plate freezer and a blast freezer under normal working conditions are provided. For the configurations used in this study, it is shown that the freezing time is much shorter for plate freezing, and also there is a much smaller variation in freezing time of various boxes compared to those for blast freezing. The smaller variation in freezing time of various boxes in each batch would help preserve the quality of meat being frozen. Also, it is explained that despite the initial higher capital cost of plate freezing, the total cost over the life of the equipment is much smaller for plate freezing compared to blast freezing.
Numerical Calculation of Wall Pressure Fluctuations in a Centrifugal Fan
Authors: Velarde-Sua´rez Sandra , Ballesteros-Tajadura Rafael , Hurtado-Cruz Juan Pablo , Santolaria-Morros Carlos
Published: March 2009

In this work, a numerical code has been applied in order to obtain the wall pressure fluctuations at the volute of an industrial centrifugal fan. The numerical results have been contrasted using previous experimental investigations carried out in the same machine. A three-dimensional numerical simulation of the complete unsteady flow on the whole impeller-volute configuration has been carried out using the computational fluid dynamics code FLUENT®. This code has been employed to calculate the time-dependent pressure both in the impeller and in the volute. In this way, the pressure fluctuations in some locations over the volute wall have been obtained. The power spectra of these fluctuations have been calculated, showing an important peak at the blade passing frequency. The amplitude of this peak presents the highest values near the volute tongue, but the spatial pattern over the volute extension is different depending on the operating conditions. The code has successfully simulated the volute pressure fluctuations due to the aerodynamic field, capturing the main flow phenomena such as the jet-wake effects and the impeller-volute interaction.