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1
Lee, Seong W., Hu J. Cui e Yan H. Huang. "Particle Characteristics and Analysis Using the Laser-Based Phase Doppler Particle Analyzer (PDPA) and Statistical Method". Particulate Science and Technology 27, n. 3 (26 maggio 2009): 263–70. http://dx.doi.org/10.1080/02726350902922002.
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Lee, Seong W., Hu J. Cui e Yan H. Huang. "Particle Characteristics and Analysis Using a Laser-Based Phase Doppler Particle Analyzer (PDPA) and Statistical Method". Particulate Science and Technology 27, n. 6 (20 novembre 2009): 553–61. http://dx.doi.org/10.1080/02726350903328845.
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Tolpadi, A. K., D. L. Burrus e R. J. Lawson. "Numerical Computation and Validation of Two-Phase Flow Downstream of a Gas Turbine Combustor Dome Swirl Cup". Journal of Engineering for Gas Turbines and Power 117, n. 4 (1 ottobre 1995): 704–12. http://dx.doi.org/10.1115/1.2815456.
Testo completoAbstract (sommario):
The two-phase axisymmetric flow field downstream of the swirl cup of an advanced gas turbine combustor is studied numerically and validated against experimental Phase-Doppler Particle Analyzer (PDPA) data. The swirl cup analyzed is that of a single annular GE/SNECMA CFM56 turbofan engine that is comprised of a pair of coaxial counterswirling air streams together with a fuel atomizer. The atomized fuel mixes with the swirling air stream, resulting in the establishment of a complex two-phase flow field within the swirl chamber. The analysis procedure involves the solution of the gas phase equations in an Eulerian frame of reference using the code CONCERT. CONCERT has been developed and used extensively in the past and represents a fully elliptic body-fitted computational fluid dynamics code to predict flow fields in practical full-scale combustors. The flow in this study is assumed to be nonreacting and isothermal. The liquid phase is simulated by using a droplet spray model and by treating the motion of the fuel droplets in a Lagrangian frame of reference. Extensive PDPA data for the CFM56 engine swirl cup have been obtained at atmospheric pressure by using water as the fuel (Wang et al., 1992a). The PDPA system makes pointwise measurements that are fundamentally Eulerian. Measurements have been made of the continuous gas phase velocity together with discrete phase attributes such as droplet size, droplet number count, and droplet velocity distribution at various axial stations downstream of the injector. Numerical calculations were performed under the exact inlet and boundary conditions as the experimental measurements. The computed gas phase velocity field showed good agreement with the test data. The agreement was found to be best at the stations close to the primary venturi of the swirler and to be reasonable at later stations. The unique contribution of this work is the formulation of a numerical PDPA scheme for comparing droplet data. The numerical PDPA scheme essentially converts the Lagrangian droplet phase data to the format of the experimental PDPA. Several sampling volumes (bins) were selected within the computational domain. The trajectories of various droplets passing through these volumes were monitored and appropriately integrated to obtain the distribution of the droplet characteristics in space. The calculated droplet count and mean droplet velocity distributions were compared with the measurements and showed very good agreement in the case of larger size droplets and fair agreement for smaller size droplets.
4
Privitera, Salvatore, Emanuele Cerruto, Giuseppe Manetto, Sebastian Lupica, David Nuyttens, Donald Dekeyser, Ingrid Zwertvaegher, Marconi Ribeiro Furtado Júnior e Beatriz Costalonga Vargas. "Comparison between Liquid Immersion, Laser Diffraction, PDPA, and Shadowgraphy in Assessing Droplet Size from Agricultural Nozzles". Agriculture 14, n. 7 (19 luglio 2024): 1191. http://dx.doi.org/10.3390/agriculture14071191.
Testo completoAbstract (sommario):
Spray droplet diameters play a key role in the field of liquid plant protection product (PPP) application technology. However, the availability of various measurement techniques, each with its unique operating principles for evaluating droplet size spectra, can lead to different interpretations of spray characteristics. Therefore, in this study, four measurement techniques—Liquid Immersion (LI), Laser Diffraction (LD), Phase Doppler Particle Analysis (PDPA), and Shadowgraphy (SG)—were utilized to evaluate the droplet size distribution of agricultural spray nozzles. Additionally, PDPA and SG were used to assess the average velocity of spray droplets. Experiments were conducted in three different laboratories with the main aim of comparing results obtained with various types of equipment utilized under ordinary practical conditions. Spraying tests were carried out using three flat fan nozzles and an air-induction flat fan nozzle. As a general trend, the lowest values for droplet diameters were measured using the Laser Diffraction technique, followed by Shadowgraphy. The PDPA technique provided the highest values for mean diameters (D10, D20, and D30) and the numeric median diameter (Dn0.5), whereas the Liquid Immersion method yielded the highest values for the Sauter mean diameter (D32) and volumetric diameters (Dv0.1, Dv0.5, and Dv0.9). Importantly, all measurement techniques were able to discriminate the four nozzles based on their Dv0.5 diameter. Average droplet velocities showed a similar pattern across the four nozzles with the PDPA and the SG measurement techniques. The differences in diameter values observed with the four measurement techniques underline the necessity of always including reference nozzles in spray quality assessments to base classifications on relative rather than absolute values.
5
Shum, Sam C. K., Steve K. Johnson, Ho-Ming Pang e R. S. Houk. "Spatially Resolved Measurements of Size and Velocity Distributions of Aerosol Droplets from a Direct Injection Nebulizer". Applied Spectroscopy 47, n. 5 (maggio 1993): 575–83. http://dx.doi.org/10.1366/0003702934067108.
Testo completoAbstract (sommario):
Aerosol droplet sizes and velocities from a direct injection nebulizer (DIN) are measured with radial and axial spatial resolution by phase Doppler particle analysis (PDPA). The droplets on the central axis of the spray become finer and their size becomes more uniform when ≍ 20% methanol is added to the usual aqueous solvent. This could explain why the analyte signal is a maximum at this solvent composition when the DIN is used for inductively coupled plasma-mass spectrometry (ICP-MS). Mean droplet velocities are 12 to 22 ms−1 with standard deviations of ±4 to ±7 ms−1. The outer fringes of the aerosol plume tend to be enriched in large droplets. The Sauter mean diameter ( D3,2) and velocity of the droplets also vary substantially with axial position in the aerosol plume.
6
Glahn, A., M. Kurreck, M. Willmann e S. Wittig. "Feasibility Study on Oil Droplet Flow Investigations Inside Aero Engine Bearing Chambers—PDPA Techniques in Combination With Numerical Approaches". Journal of Engineering for Gas Turbines and Power 118, n. 4 (1 ottobre 1996): 749–55. http://dx.doi.org/10.1115/1.2816990.
Testo completoAbstract (sommario):
The present paper deals with oil droplet flow phenomena in aero engine bearing chambers. An experimental investigation of droplet sizes and velocities utilizing a Phase Doppler Particle Analyzer (PDPA) has been performed for the first time in bearing chamber atmospheres under real engine conditions. Influences of high rotational speeds are discussed for individual droplet size classes. Although this is an important contribution to a better understanding of the droplet flow impact on secondary air/oil system performance, an analysis of the droplet flow behavior requires an incorporation of numerical methods because detailed measurements as performed here suffer from both strong spatial limitations with respect to the optical accessibility in real engine applications and constraints due to the extremely time-consuming nature of an experimental flow field analysis. Therefore, further analysis is based on numerical methods. Droplets characterized within the experiments are exposed to the flow field of the gaseous phase predicted by use of our well-known CFD code EPOS. The droplet trajectories and velocities are calculated within a Lagrangian frame of reference by forward numerical integration of the particle momentum equation. This paper has been initiated rather to show a successful method of bearing chamber droplet flow analysis by a combination of droplet sizing techniques and numerical approaches than to present field values as a function of all operating parameters. However, a first insight into the complex droplet flow phenomena is given and specific problems in bearing chamber heat transfer are related to the droplet flow.
7
Zheng, Lei, Haizhou Xu, Hao Fu, Hua Chen e Wenlong Cheng. "Experiment and simulation study on the characteristics of pressure swirl nozzle flash spray under the influence of superheat". Journal of Physics: Conference Series 2683, n. 1 (1 gennaio 2024): 012036. http://dx.doi.org/10.1088/1742-6596/2683/1/012036.
Testo completoAbstract (sommario):
Abstract The good atomization performance of the pressure swirl nozzle makes it widely used in the fuel injection device of the internal combustion engine. Flash spray caused by fuel inlet superheat can affect spray and combustion characteristics. In this paper, a spray parameter measurement system is set up, combined with phase Doppler particle analysis (PDPA) technology to research the effect of superheat on spray velocity and droplet diameter distribution. To improve the safety of the experiment, Methyl Nonafluorobutyl Ether (HFE7100) with a boiling point of 61°C was used as the spray fluid. The cavitation model and VOF model are used to simulate the pressure swirl nozzle flash spray. The results show that when the temperature changes from 40°C to 60°C, the velocity of spray droplets increases and the particle size decreases under the action of weak evaporation; When the temperature changes from 60°C to 70°C, the evaporation mode is dominated by flash, making the droplet velocity at the spray center greatly increase and the velocity distribution change from saddle-shaped distribution to unimodal distribution. The droplet diameter increases, which may be due to the expansion of the droplet caused by the formation of bubbles inside the droplet under the action of flash.
8
Xu, Li. "Experimental Investigation on Atomization Characteristics of a Certain Type of Aero Engine Fuel Nozzle". Advanced Materials Research 354-355 (ottobre 2011): 468–71. http://dx.doi.org/10.4028/www.scientific.net/amr.354-355.468.
Testo completoAbstract (sommario):
The atomization characteristics of a certain type of aero engine fuel nozzle are discussed in this paper. The nozzle atomization characteristics have great influence on the combustion efficiency, ignition, outlet temperature field and pollution emissions. The flow characteristics, atomization particle size and distribution under different working conditions are obtained in this paper through the Phase Doppler particle analyzer and laser Doppler velocity system (PDPA / LDV). The test results show that to the dual pressure atomization nozzle, the flow rate range is wide and droplets size decreases with the increasing oil pressure, and tends to stabilize. The test data provide a reliable basis for the pressure atomizing nozzle design and modified.
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Wei, Xianggeng, Yiming Feng, Jinying Ye, Na Li e Oskar J. Haidn. "Influence of Mass Flow Rate on the Atomization Characteristics of Screw Conveyor Swirl Injectors". Aerospace 9, n. 6 (27 maggio 2022): 293. http://dx.doi.org/10.3390/aerospace9060293.
Testo completoAbstract (sommario):
This study conducted cold flow experimental research on the influence of mass flow rate on the atomization characteristics of screw conveyer swirl injectors in an opening environment. The Phase Doppler Particle Analyzer (PDPA) and high-speed photography were utilized to obtain experimental data. The results showed that the mass flow rate greatly influenced the atomization establishment and working characteristics of the injectors. The design point selection of the injectors exerted significant influence on the flow range and the performances of the injectors in a steady-state operation. The Sauter mean diameter of the atomization field continued to decrease with the increase in the mass flow rate. As the distance to the injector exit increased, the Sauter mean diameter continued to decrease, and finally tended to be stable. The average particle diameter obtained by the current image-processing method was greater than that by PDPA; therefore, the image-processing method needs improvement.
10
Bae, Ho Seuk, Won-Ki Kim, Su-Uk Son, Woo-Shik Kim e Joung-Soo Park. "An Estimation of the Backscattering Strength of Artificial Bubbles Using an Acoustic Doppler Current Profiler". Sensors 22, n. 5 (25 febbraio 2022): 1812. http://dx.doi.org/10.3390/s22051812.
Testo completoAbstract (sommario):
Acoustic Doppler current profilers (ADCPs) were developed to acquire water current velocities, as well as depth-dependent echo intensities. As the backscattering strength of an underwater object can be estimated from the measured echo intensity, the ADCP can be used to estimate plankton populations and distributions. In this study, the backscattering strength of bubble clusters in a water tank was estimated using the commercial ADCP as a proof-of-concept. Specifically, the temporal variations in the backscattering strength and the duration of bubble existence were quantitatively evaluated. Additionally, the PDSL (population density spectrum level) and VF (void fraction) of the artificial bubbles were characterized based on the obtained distribution characteristics using a PDPA (phase Doppler particle analyzer).
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Tamhane, T. V., J. B. Joshi, Kamachi Mudali, R. Natarajan e R. N. Patil. "Measurement of drop size characteristics in annular centrifugal extractors using phase Doppler particle analyzer (PDPA)". Chemical Engineering Research and Design 90, n. 8 (agosto 2012): 985–97. http://dx.doi.org/10.1016/j.cherd.2011.11.007.
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Wang, Junpeng, Cuicui Xu, Gang Zhou e Yansong Zhang. "Spray Structure and Characteristics of a Pressure-Swirl Dust Suppression Nozzle Using a Phase Doppler Particle Analyze". Processes 8, n. 9 (10 settembre 2020): 1127. http://dx.doi.org/10.3390/pr8091127.
Testo completoAbstract (sommario):
In order to understand the characteristics of the spray field of a dust suppression nozzle and provide a reference for dust nozzle selection according to dust characteristics, a three-dimensional phase Doppler particle analyzer (PDPA) spray measurement system is used to analyze the droplet size and velocity characteristics in a spray field, particularly the joint particle size–velocity distribution. According to the results, after the ejection of the jet from the nozzle, the droplets initially maintained some velocity; however, the distribution of particles with different sizes was not uniform. As the spray distance increased, the droplet velocity decreased significantly, and the particle size distribution changed very little. As the distance increased further, the large droplets separated into smaller droplets, and their velocity decreased rapidly. The distributions of the particle size and velocity of the droplets then became stable. Based on the particle size-velocity distribution characteristics, the spray structure of pressure-swirl nozzles can be divided into five regions, i.e., the mixing, expansion, stabilization, decay, and rarefied regions. The expansion, stabilization, and decay regions are the effective dust fall areas. In addition, the droplet size in the stabilization region is the most uniform, indicating that this region is the best dust fall region. The conclusions can provide abundant calibration data for spray dust fall nozzles.
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Zhang, Qing, Bo Yu e Yu Liu. "Experimental Study on the Separation Performance of Combined Gas-Liquid Separator". Applied Mechanics and Materials 685 (ottobre 2014): 127–32. http://dx.doi.org/10.4028/www.scientific.net/amm.685.127.
Testo completoAbstract (sommario):
In order to evaluate the separation efficiency of each module in this type of novel combined separator, by PDPA(Phase Doppler Particle Analyzer) we find that under different conditions in 6 combinations, combination 6 (including cyclone + stabilizer + blade+ baffler) has the highest separation efficiency, and there are relatively efficiency valley region in all the 6 combinations. Under the same conditions, the average separation efficiency of the baffler is higher than the blade, and then the blade and baffler have their own advantages in different flowrate. To use stabilizer can effectively improve the flow field inside the separator, restrain and reduce vortex and backmixing, more conductive to the gas-liquid separation.
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Mallik, Arnab Kumar, Tushar Pratim Sarma, Aritras Roy, Mahesh V. Panchagnula e Satyanarayanan Seshadri. "PHASE DOPPLER PARTICLE ANALYSER (PDPA) CHARACTERIZATION AND MODELING OF SPRAYS FROM ORTHOGONALLY INTERACTING WATER AND AIR JETS". Journal of Flow Visualization and Image Processing 27, n. 2 (2020): 199–217. http://dx.doi.org/10.1615/jflowvisimageproc.2020031030.
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Sankar, S. V., D. H. Buermann e W. D. Bachalo. "Application of Rainbow Thermometry to the Study of Fuel Droplet Heat-Up and Evaporation Characteristics". Journal of Engineering for Gas Turbines and Power 119, n. 3 (1 luglio 1997): 573–84. http://dx.doi.org/10.1115/1.2817023.
Testo completoAbstract (sommario):
Advanced, nonintrusive, laser-based diagnostics are being developed for simultaneously measuring the size, velocity, temperature, and instantaneous regression rates of vaporizing/burning fuel droplets in polydisperse flow environments. The size and velocity of the droplets are measured using a conventional phase Doppler particle analyzer (PDPA), and the droplet temperatures are simultaneously measured with a rainbow thermometer. This integrated diagnostic has been applied to the study of fuel droplet heat-up characteristics in a swirl-stabilized kerosene spray flame. It has also been shown that a novel extension of rainbow thermometry can be used additionally to extract the instantaneous droplet vaporization rate. The feasibility of measuring the instantaneous regression rate has also been demonstrated using controlled experiments with a vaporizing/burning stream of ethanol droplets.
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Kim, Hyojin, Sakda Tongchai e Ocktacke Lim. "A Study on the Particle Size and Velocity Profile on a Gasoline Port Injector Using a Phase Doppler Particle Analyzers (PDPA)". Energy Procedia 145 (luglio 2018): 374–80. http://dx.doi.org/10.1016/j.egypro.2018.04.025.
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Sankar, S. V., K. E. Maher, D. M. Robart e W. D. Bachalo. "Rapid Characterization of Fuel Atomizers Using an Optical Patternator". Journal of Engineering for Gas Turbines and Power 121, n. 3 (1 luglio 1999): 409–14. http://dx.doi.org/10.1115/1.2818488.
Testo completoAbstract (sommario):
Planar laser scattering (PLS) and planar laser-induced fluorescence (PLIF) techniques are currently being used for rapid characterization of fuel sprays associated with gas turbine atomizers, diesel injectors, and automotive fuel injectors. These techniques can be used for qualitative, quantitative, and rapid measurement of fuel mass, spray geometry, and Sauter mean diameters in various sprays. The spatial distribution of the fuel mass can be inferred directly from the PLIF image, and the Sauter mean diameter can be measured by simultaneously recording the PLIF and PLS images and then ratioing the two. A spray characterization system incorporating the PLS and/or PLIF techniques has been loosely termed an optical patternator, and in this study, it has been used to characterize both steady and pulsed sprays. The results obtained with the optical patternator have been directly validated using a phase Doppler particle analyzer (PDPA).
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Wang, M. R., D. Y. Huang e Y. C. Liu. "Droplet Dynamics Near the Wall in a Vertical Rectangular Duct". Journal of Fluids Engineering 116, n. 2 (1 giugno 1994): 349–53. http://dx.doi.org/10.1115/1.2910279.
Testo completoAbstract (sommario):
Measurements of the droplet behavior near the wall in a vertical rectangular duct were conducted by a phase Doppler particle analyzer (PDPA). The test Reynolds number and drop size range is from 18,500 to 89,300 and from 5 μm to 110 μm, respectively. Results show that the negative slip-velocity of the drops near the free-stream region normally results in the reversed slip-velocity phenomenon in the boundary layer region. No negative slip-velocity of all drops are discovered for Reynolds number less than 38,300. This indicates no reversed slip-velocity phenomenon for the test drop size range under low Reynolds number conditions. However, when the Reynolds number is over 38,300, the free-stream slip-velocity of the bigger drops becomes negative. It is found that the negative slip-velocity and, hence, the reversed slip-velocity phenomenon may take place for drop size larger than 52 μm to 90 μm depending on the flow Reynolds number.
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MARTÍNEZ-BAZÁN, C., J. L. MONTAÑÉS e J. C. LASHERAS. "On the breakup of an air bubble injected into a fully developed turbulent flow. Part 1. Breakup frequency". Journal of Fluid Mechanics 401 (25 dicembre 1999): 157–82. http://dx.doi.org/10.1017/s0022112099006680.
Testo completoAbstract (sommario):
The transient evolution of the bubble-size probability density functions resulting from the breakup of an air bubble injected into a fully developed turbulent water ow has been measured experimentally using phase Doppler particle sizing (PDPA) and image processing techniques. These measurements were used to determine the breakup frequency of the bubbles as a function of their size and of the critical diameter Dc defined as Dc = 1.26 (σ/ρ)3/5ε−2/5, where ε is the rate of dissipation per unit mass and per unit time of the underlying turbulence. A phenomenological model is proposed showing the existence of two distinct bubble size regimes. For bubbles of sizes comparable to Dc, the breakup frequency is shown to increase as (σ/ρ)−2/5ε−3/5 √D/Dc−1, while for large bubbles whose sizes are greater than 1.63Dc, it decreases with the bubble size as ε1/3D−2/3. The model is shown to be in good agreement with measurements performed over a wide range of bubble sizes and turbulence intensities.
20
Prasad, Athira, Dhalin D. e Dipak S. Khatawkar. "Sampling, quantification and mathematical modeling in agricultural spray drift: A review". Environment Conservation Journal 25, n. 3 (30 aprile 2024): 881–96. http://dx.doi.org/10.36953/ecj.25462715.
Testo completoAbstract (sommario):
An effective spray of agrochemicals is inevitable for crop production for viable agriculture. Spraying inherently suffers from drift, which has always been one of the major concerns in agriculture, affecting the intent of agrochemical spraying and posing serious environmental hazards. Complete elimination of spray drift is impractical under field conditions but can be minimized using precision spraying techniques. Agricultural spray drift has several detrimental effects, such as environmental damage, polluting water bodies, human and animal health risks, chemical exposure, and economic losses, and may also lead to conflicts between neighboring farmers. Hence, the assessment of spray drift is a salient part of the design process of plant protection equipment to achieve maximum deposition in both chemical and biological pesticide applications. The different methods used to study the drift of a sprayer include test bench, wind tunnel and phase Doppler particle analyzer (PDPA) methods. In the field-level assessment, the fluorometric tracer sampling method conforming to ISO-22866:2005 was used. Plume dispersion, particle tracking and computational fluid dynamics (CFD) are the major mathematical modeling approaches for spray drift simulation studies. Among various methodologies and techniques, an appropriate method for spray drift assessment should be adopted in accordance with factors such as crop parameters, mode of application, and environmental conditions.
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Bren˜a de la Rosa, A., S. V. Sankar, G. Wang e W. D. Bachalo. "Particle Diagnostics and Turbulence Measurements in a Confined Isothermal Liquid Spray". Journal of Engineering for Gas Turbines and Power 115, n. 3 (1 luglio 1993): 499–506. http://dx.doi.org/10.1115/1.2906736.
Testo completoAbstract (sommario):
This work reports an experimental study of the behavior and structure of a liquid spray immersed in a strong swirling field. In order to simulate some of the aerodynamic conditions experienced by a spray in a model combustor, an experimental setup using an acrylic chamber, a vane type swirler, and separate air supplies for both the secondary air and the swirl air were integrated to perform the experiments in the wind tunnel. A vane-type swirler exhibiting a high swirl number was used to produce a strong recirculation flow field downstream of a pressure swirl atomizer. Properties of the dispersed phase such as velocity, size distribution, and size-velocity correlation were measured at several locations within the swirling flow field. In addition, mean velocity and turbulence properties were obtained for the gas phase. Flow visualization was performed with a laser sheet to gain further understanding of the formation and influence of the recirculation region on the spray. A two-component PDPA system with a frequency-based Doppler signal analyzer was used throughout the measurements, and proved most valuable in the toroidal vortex region where low SNR conditions and nonuniform concentration of seed particles prevail. The results show that flow reversal of the drops is present at this swirl intensity within the recirculation region at distances up to X/D = 2.0. Small variations of drop size distribution within the recirculation region are observed; however, large variations outside of it are also present. Plots of the normal Reynolds stresses and Reynolds shear stresses show double-peak radial distributions, which indicate regions in the flow where high mean velocity gradients and large shear forces are present. The decay of turbulence velocities in the axial direction was observed to be very fast, an indication of high diffusion and dissipation rates of the kinetic energy of turbulence.
22
Guo, Tao, Ting Wang e J. Leo Gaddis. "Mist/Steam Cooling in a Heated Horizontal Tube—Part 1: Experimental System". Journal of Turbomachinery 122, n. 2 (1 febbraio 1999): 360–65. http://dx.doi.org/10.1115/1.555460.
Testo completoAbstract (sommario):
To improve the airfoil cooling significantly for the future generation of advanced turbine systems (ATS), a fundamental experimental program has been developed to study the heat transfer mechanisms of mist/steam cooling under highly superheated wall temperatures. The mist/steam mixture was obtained by blending fine water droplets (3∼15 μm in diameter) with the saturated steam at 1.5 bars. Two mist generation systems were tested by using the pressure atomizer and the steam-assisted pneumatic atomizer, respectively. The test section, heated directly by a DC power supply, consisted of a thin-walled (∼0.9 mm), circular stainless steel tube with an ID of 20 mm and a length of 203 mm. Droplet size and distribution were measured by a phase Doppler particle analyzer (PDPA) system through view ports grafted at the inlet and the outlet of the test section. Mist transportation and droplet dynamics were studied in addition to the heat transfer measurements. The experiment was conducted with steam Reynolds numbers ranging from 10,000 to 35,000, wall superheat up to 300°C, and droplet mass ratios ranging from 1∼6 percent. [S0889-504X(00)02402-8]
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Stężycki, P., M. Kowalski, A. Jankowski e Z. Sławinski. "Laser Research of the Fuel Atomization Process of Internal Combustion Engines". Science & Technique 19, n. 1 (5 febbraio 2020): 34–42. http://dx.doi.org/10.21122/2227-1031-2020-19-1-34-42.
Testo completoAbstract (sommario):
The paper presents test methods (mechanical, electrical and optical) for the fuel spray research in combustion engines. Optical methods, imaging and non-imaging can be used in laboratory and engine tests. Imaging methods include flash photography and holography. Their use is limited to testing droplet dimensions larger than 5 µm. Imaging methods have an advantage over non-imaging ones because they allow the droplet to be seen at the point and time where its measurement is required. Non-imaging methods can be divided into two groups: the first, which counts and measures, individual droplets one at a time, and the second, which measures a large number of droplets simultaneously. Exemplary results of research of droplet size distribution in fuel sprays are shown. In tests of atomized fuel spray, in conditions reflecting the conditions of the internal combustion engine, the size of droplets, their distribution in the spray and the velocity of individual droplets are presented. To determine the quality of the fuel spray, two substitute diameters Sauter (D32) and Herdan (D43) were selected, the first of which refers to heat transfer and the second to combustion processes. Laser research equipment including Particle Image Velocimetry laser equipment (PIV), Laser Doppler Velocimeter (LDV) and Phase Doppler Particle Analyzer (PDPA) were applied for testing fuel spray distribution for two kind of fuel. The atomization process from the point of view of combustion and ignition processes, as well as emission levels, is characterized by the best substitute diameter D43, which value is close to the median volume. The most harmful droplets of fuel in the spray are large droplets. Even a few such droplets significantly change the combustion process and emission of toxic exhaust components, mainly NOx.
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Bren˜a de la Rosa, A., W. D. Bachalo e R. C. Rudoff. "Spray Characterization and Turbulence Properties in an Isothermal Spray With Swirl". Journal of Engineering for Gas Turbines and Power 112, n. 1 (1 gennaio 1990): 60–66. http://dx.doi.org/10.1115/1.2906478.
Testo completoAbstract (sommario):
The present work reports an experimental study of the effect of swirl on the dynamic behavior of drops and on the velocity and turbulence fields of an isothermal spray using a two-component Phase Doppler Particle Analyzer (PDPA). It represents the first phase of an effort to investigate the effect of swirl on the structure of liquid spray flames, the stability of the flame, and its effect on the emission of pollutants. A vane-type swirler was placed on the liquid supply tube of a pressure atomizer and tested in the wind tunnel under specified conditions. Mean velocity and turbulence properties were obtained for the gas phase. In addition, drop velocity and drop size distributions, particle number densities, and volume flux were measured at different locations within the swirling flow. Large differences in the spatial distribution of the drops over its size, velocity, and number density are observed when the spray in coflowing air with the same axial velocity is compared with the atomizer spraying into the swirling flow field. Large drops seem to be recirculated into the core of the swirling flow, while rather small drops surround this central region. The radial distribution of particle number density and the liquid volume flux are also different when the atomizer spraying into the coflowing air and into the swirling field are compared. Particle number densities for the latter exhibit higher peak values close to the nozzle; but show almost the same peak values as in the coflowing case but at a different radial location further downstream. The velocity of specific drop sizes was also obtained. Drops as large as 5μm are seen to follow closely the mean velocity of the gas. The turbulence properties of the swirling flow show significant influence on the dynamic behavior of the drops. Radial distributions of turbulence kinetic energy, normal Reynolds stresses, and Reynolds shear stresses exhibit double peak values, which delineate the boundaries of the central recirculation region and the external free stream. Within these boundaries the radial distribution of both particle number density and volume flux are seen to attain their maximum values.
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LI, FEI, HAIYING QI e CHANGFU YOU. "Phase Doppler anemometry measurements and analysis of turbulence modulation in dilute gas–solid two-phase shear flows". Journal of Fluid Mechanics 663 (27 settembre 2010): 434–55. http://dx.doi.org/10.1017/s0022112010003587.
Testo completoAbstract (sommario):
Flow velocities of a dilute gas–solid two-phase flow in a vertical sudden expansion were measured using phase Doppler anemometry to study the behaviour of the turbulence modulation for the stronger shear for various particle mass loadings, inlet Reynolds numbers and particle diameters. The measurements show that the particles changed the gas turbulence by elongation of the entire gas flow field in the downstream direction, which displaced the axial profile of the section-averaged fluctuation velocity in comparison with that of the single-phase flow, and by either the particle inertia reducing the local turbulence or the wake eddy effects enhancing the turbulence. Both mechanisms resulted in an apparent turbulence modulation, which has not been referred to in the related literature, and have led to an ambiguous understanding of turbulence modulation. The elongation and inlet effects should be eliminated to estimate whether the gas turbulence was really modified. The linear relationship between the gas mean velocity gradient and the root-mean-square fluctuation velocity, which was found to be similar to that in single-phase flows, gradually disappeared as the flow developed and the shear intensity reduced. The linear relationship also varied with different conditions. Specifically, the turbulence modulation was enhanced by higher particle mass loadings and the linear relationship disappeared with increasing particle mass loading. This linearity can perhaps be regarded as a criterion for determining the effect of stronger turbulence modulation.
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Radenz, Martin, Johannes Bühl, Patric Seifert, Hannes Griesche e Ronny Engelmann. "peakTree: a framework for structure-preserving radar Doppler spectra analysis". Atmospheric Measurement Techniques 12, n. 9 (10 settembre 2019): 4813–28. http://dx.doi.org/10.5194/amt-12-4813-2019.
Testo completoAbstract (sommario):
Abstract. Clouds are frequently composed of more than one particle population even at the smallest scales. Cloud radar observations frequently contain information on multiple particle species in the observation volume when there are distinct peaks in the Doppler spectrum. Multi-peaked situations are not taken into account by established algorithms, which only use moments of the Doppler spectrum. In this study, we propose a new algorithm that recursively represents the subpeaks as nodes in a binary tree. Using this tree data structure to represent the peaks of a Doppler spectrum, it is possible to drop all a priori assumptions on the number and arrangement of subpeaks. The approach is rigid, unambiguous and can provide a basis for advanced analysis methods. The applicability is briefly demonstrated in two case studies, in which the tree structure was used to investigate particle populations in Arctic multilayered mixed-phase clouds, which were observed during the research vessel Polarstern expedition PS106 and the Atmospheric Radiation Measurement Program BAECC campaign.
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Guo, Tao, Ting Wang e J. Leo Gaddis. "Mist/Steam Cooling in a 180-Degree Tube Bend". Journal of Heat Transfer 122, n. 4 (28 gennaio 2000): 749–56. http://dx.doi.org/10.1115/1.1287794.
Testo completoAbstract (sommario):
An experimental study on mist/steam cooling in a highly heated, horizontal 180-deg tube bend has been performed. The mist/steam mixture is obtained by blending fine water droplets (3∼15 microns) with the saturated steam at 1.5 bar. The test section consists of a thin wall (∼0.9 mm), welded, circular, stainless steel 180-deg tube (20-mm inside diameter) with a straight section downstream of the curved section, and is heated directly by a DC power supply. The experiment was conducted with steam Reynolds numbers ranging from 10,000 to 35,000, wall superheat up to 300°C, and droplet to steam mass ratio at about 1∼2 percent. The results show that the heat transfer performance of steam can be significantly improved by adding mist into the main flow. The highest enhancement occurs at a location about 45-deg downstream of the inlet of the test section. Generally, only a small number of droplets can survive the 180-deg turn and be present in the downstream straight section, as observed by a phase Doppler particle analyzer (PDPA) system. The overall cooling enhancement of the mist/steam flow ranges from 40 percent to 300 percent. It increases as the main steam flow increases, but decreases as the wall heat flux increases. [S0022-1481(00)02003-X]
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Roten, R. L., R. J. Connell e A. J. Hewitt. "Phase Doppler technology for infield assessment of drift potential". New Zealand Plant Protection 66 (8 gennaio 2013): 381. http://dx.doi.org/10.30843/nzpp.2013.66.5690.
Testo completoAbstract (sommario):
Laserbased technologies for droplet analysis have existed for decades but most of these devices are not suitable to be moved once calibrated PhaseDoppler interferometer (PDI) technology has enabled the capture of live infield spray particle data such as the particle size distribution velocity and flux which are essential to accurately measure and model the drift of agricultural equipment The objective of this study was to develop and implement methods to determine if drift could be detected and if so to use the data obtained to crossreference its validity with spray drift models AGDISP and WTDISP The spray apparatus consisted of a 12V trailertype sprayer outfitted with a 50 cm high fournozzle boom with 110SG02 nozzles delivering 238 litres/ha at 34 bar This setup was selected to maximise the output of the sprayer and produce the worstcase drift scenario for the given spray system It was observed that driftable particles of a passing and a static sprayer could be detected within close proximity of 8400 cm2 These results also agreed with the model output generated
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Hoffmann, Wesley Clint, Bradley Keith Fritz, Muhammad Farooq, Todd William Walker, Zbigniew Czaczyk, Jonathan Hornsby e Jane Annalise Sara Bonds. "Evaluation of Aerial Spray Technologies for Adult Mosquito Control Applications". Journal of Plant Protection Research 53, n. 3 (1 luglio 2013): 222–29. http://dx.doi.org/10.2478/jppr-2013-0034.
Testo completoAbstract (sommario):
Abstract Spray droplet size has long been recognized as an important variable that applicators of vector control sprays must be aware of to make the most effective spray applications. Researchers and applicators have several different techniques available to assess spray droplet size from spray nozzles. The objective of this study was to compare the droplet size spectrum produced by three nozzles commonly used in vector control in a high-speed wind tunnel, when characterized using three different laser-based droplet size measurement systems. Three droplet sizing systems: Malvern Spraytec laser diffraction, Sympatec HELOS laser diffraction, and TSI Phase Doppler Particle Analyzer (PDPA), were simultaneously operated, but under different operating conditions, to measure the spray droplet size-spectra for three spray nozzles. The three atomizers: a TeeJet® 8001E even flat fan nozzle, a BETE® PJ high pressure fog nozzles, and a Micronair ® AU5000 rotary atomizer were evaluated in a high speed wind tunnel at airspeeds of 53 and 62 m/s (120 and 140 mph). Based on the results of this work, only the BETE® PJ high pressure fog nozzles met the label requirements for both Fyfanon® and Anvil®. While the other nozzle might met the Dv0.5 (VMD - volume median diameter) requirement for Fyfanon®, the resulting Dv0.9 values exceeded labeled size restrictions. When applying Anvil with the BETE PJ high pressure fog nozzles, it is important to use the smaller two orifice sizes. The larger sizes tended to result in Dv0.9 values that exceeded label recommendations
30
Van den Moortel, T., E. Azario, R. Santini e L. Tadrist. "Experimental analysis of the gas–particle flow in a circulating fluidized bed using a phase Doppler particle analyzer". Chemical Engineering Science 53, n. 10 (maggio 1998): 1883–99. http://dx.doi.org/10.1016/s0009-2509(98)00030-x.
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Edwards, Christopher F., e K. D. Marx. "ANALYSIS OF THE IDEAL PHASE-DOPPLER SYSTEM: LIMITATIONS IMPOSED BY THE SINGLE-PARTICLE CONSTRAINT". Atomization and Sprays 2, n. 3 (1992): 319–66. http://dx.doi.org/10.1615/atomizspr.v2.i3.70.
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Fohanno, S., e R. J. Martinuzzi. "A Phase-Averaged Analysis of Droplet Dispersion in the Wake of a Square Cylinder in a Uniform Stream". Journal of Fluids Engineering 126, n. 1 (1 gennaio 2004): 110–19. http://dx.doi.org/10.1115/1.1637637.
Testo completoAbstract (sommario):
Time-averaged and phase-averaged size and velocity distributions of water droplets in the turbulent wake of a square cross-section cylinder, measured with a phase-Doppler anemometer, are presented for a Reynolds number ReD=18,500, based on the free stream velocity, U∞, and cylinder side dimension, D. It is shown that the coherent motion strongly influences the particle distribution and that the mean flow representation can be misleading in interpreting mixing. The results show that small particle concentration is largest in the very near wake. The mean particle distributions are homogeneous as early as 4D downstream of the cylinder, but the influence of vortex shedding on instantaneous distributions persists much longer. It is also observed that at the point of maximum mean streamline curvature, which also coincides with the region of maximum streamwise velocity fluctuations, particle separation is most effective.
33
Sijs, R., S. Kooij, H. J. Holterman, J. van de Zande e D. Bonn. "Drop size measurement techniques for sprays: Comparison of image analysis, phase Doppler particle analysis, and laser diffraction". AIP Advances 11, n. 1 (1 gennaio 2021): 015315. http://dx.doi.org/10.1063/5.0018667.
Testo completo
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Li, Shougen, Chongchong Chen, Yaxiong Wang, Feng Kang e Wenbin Li. "Study on the Atomization Characteristics of Flat Fan Nozzles for Pesticide Application at Low Pressures". Agriculture 11, n. 4 (2 aprile 2021): 309. http://dx.doi.org/10.3390/agriculture11040309.
Testo completoAbstract (sommario):
Spraying is the most widely used means of pesticide application for pest control in agriculture and forestry. The atomization characteristics of the nozzles are directly related to the spray drift, rebound, and deposition. Previous research studies have mainly focused on the change pattern of atomization characteristics. Mathematical descriptions of the atomization characteristics of flat fan nozzles are rare, and pesticide application theories are also insufficient. Atomization characteristics mainly include droplet size and velocity. This study analyzes the influence of the spray parameters (spray angle, pressure, and equivalent orifice diameter of nozzles) and the spatial position in the flow field. To obtain the atomization characteristics of flat fan nozzles, the phase Doppler particle analyzer (PDPA) was selected for the accurate measurement of the droplet sizes and velocities at distances 0.30–0.60 m, using low spray pressures (0.15–0.35 MPa). The droplet size and velocity models were then established and validated. The results revealed that the average absolute error of the droplet size model was 23.74 µm and the average relative error was 8.23%. The average absolute and relative errors of the droplet velocity model were 0.37 m/s and 7.86%, respectively. At a constant spray pressure and angle, there was a positive correlation between the droplet size and the equivalent orifice diameter of the nozzles. The test also verified that the spray angle and distance had a negative correlation with the droplet velocity at a given pressure. The spray distance had no effect on the spray axial droplet size at constant spray pressure. In addition, the spray angle greatly affected the droplet velocity along the X-axis; similarly, the spray parameters, especially spray angle, greatly affected the droplet size.
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Schaub, Scott A., Dennis R. Alexander e John P. Barton. "Theoretical analysis of the effects of particle trajectory and structural resonances on the performance of a phase–Doppler particle analyzer". Applied Optics 33, n. 3 (20 gennaio 1994): 473. http://dx.doi.org/10.1364/ao.33.000473.
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LEE, SEONG W., e YUN LIU. "The Unique Phase Doppler Particle Analyzer Application and Analysis of Solid Particle Flow in the Fluidized Bed Combustor (FBC) Cold Model". Particulate Science and Technology 22, n. 1 (gennaio 2004): 65–73. http://dx.doi.org/10.1080/02726350490422482.
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Bühl, Johannes, Patric Seifert, Alexander Myagkov e Albert Ansmann. "Measuring ice- and liquid-water properties in mixed-phase cloud layers at the Leipzig Cloudnet station". Atmospheric Chemistry and Physics 16, n. 16 (26 agosto 2016): 10609–20. http://dx.doi.org/10.5194/acp-16-10609-2016.
Testo completoAbstract (sommario):
Abstract. An analysis of the Cloudnet data set collected at Leipzig, Germany, with special focus on mixed-phase layered clouds is presented. We derive liquid- and ice-water content together with vertical motions of ice particles falling through cloud base. The ice mass flux is calculated by combining measurements of ice-water content and particle Doppler velocity. The efficiency of heterogeneous ice formation and its impact on cloud lifetime is estimated for different cloud-top temperatures by relating the ice mass flux and the liquid-water content at cloud top. Cloud radar measurements of polarization and Doppler velocity indicate that ice crystals formed in mixed-phase cloud layers with a geometrical thickness of less than 350 m are mostly pristine when they fall out of the cloud.
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Oue, Mariko, Pavlos Kollias, Sergey Y. Matrosov, Alessandro Battaglia e Alexander V. Ryzhkov. "Analysis of the microphysical properties of snowfall using scanning polarimetric and vertically pointing multi-frequency Doppler radars". Atmospheric Measurement Techniques 14, n. 7 (12 luglio 2021): 4893–913. http://dx.doi.org/10.5194/amt-14-4893-2021.
Testo completoAbstract (sommario):
Abstract. Radar dual-wavelength ratio (DWR) measurements from the Stony Brook Radar Observatory Ka-band scanning polarimetric radar (KASPR, 35 GHz), a W-band profiling radar (94 GHz), and a next-generation K-band (24 GHz) micro rain radar (MRRPro) were exploited for ice particle identification using triple-frequency approaches. The results indicated that two of the radar frequencies (K and Ka band) are not sufficiently separated; thus, the triple-frequency radar approaches had limited success. On the other hand, a joint analysis of DWR, mean Doppler velocity (MDV), and polarimetric radar variables indicated potential in identifying ice particle types and distinguishing among different ice growth processes and even in revealing additional microphysical details. We investigated all DWR pairs in conjunction with MDV from the KASPR profiling measurements and differential reflectivity (ZDR) and specific differential phase (KDP) from the KASPR quasi-vertical profiles. The DWR-versus-MDV diagrams coupled with the polarimetric observables exhibited distinct separations of particle populations attributed to different rime degrees and particle growth processes. In fallstreaks, the 35–94 GHz DWR pair increased with the magnitude of MDV corresponding to the scattering calculations for aggregates with lower degrees of riming. The DWR values further increased at lower altitudes while ZDR slightly decreased, indicating further aggregation. Particle populations with higher rime degrees had a similar increase in DWR but a 1–1.5 m s−1 larger magnitude of MDV and rapid decreases in KDP and ZDR. The analysis also depicted the early stage of riming where ZDR increased with the MDV magnitude collocated with small increases in DWR. This approach will improve quantitative estimations of snow amount and microphysical quantities such as rime mass fraction. The study suggests that triple-frequency measurements are not always necessary for in-depth ice microphysical studies and that dual-frequency polarimetric and Doppler measurements can successfully be used to gain insights into ice hydrometeor microphysics.
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SCHOBER, PETER, ROBERT MEIER, OLAF SCHÄFER e SIGMAR WITTIG. "Visualization and Phase Doppler Particle Analysis Measurements of Oscillating Spray Propagation of an Airblast Atomizer under Typical Engine Conditions". Annals of the New York Academy of Sciences 972, n. 1 (ottobre 2002): 277–84. http://dx.doi.org/10.1111/j.1749-6632.2002.tb04585.x.
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Pfitzenmaier, Lukas, Yann Dufournet, Christine M. H. Unal e Herman W. J. Russchenberg. "Retrieving Fall Streaks within Cloud Systems Using Doppler Radar". Journal of Atmospheric and Oceanic Technology 34, n. 4 (aprile 2017): 905–20. http://dx.doi.org/10.1175/jtech-d-16-0117.1.
Testo completoAbstract (sommario):
AbstractThe interaction of ice crystals with supercooled liquid droplets in mixed-phase clouds leads to an enhanced growth of ice particles. However, such processes are still not clearly understood although they are important processes for precipitation formation in midlatitudes. To better understand how ice particles grow within such clouds, changes in the microphysical parameters of a particle population falling through the cloud have to be analyzed. The Transportable Atmospheric Radar (TARA) can retrieve the full 3D Doppler velocity vector based on a unique three-beam configuration. Using the derived wind information, a new fall streak retrieval technique is proposed so that microphysical changes along those streaks can be studied. The method is based on Doppler measurements only. The shown examples measured during the Analysis of the Composition of Clouds with Extended Polarization Techniques (ACCEPT) campaign demonstrate that the retrieval is able to capture the fall streaks within different cloud systems. These fall streaks can be used to study changes in a single particle population from its generation (at cloud top) until its disintegration. In this study fall streaks are analyzed using radar moments or Doppler spectra. Synergetic measurements with other instruments during ACCEPT allow the detection of liquid layers within the clouds. The estimated microphysical information is used here to get a better understanding of the influence of supercooled liquid layers on ice crystal growth. This technique offers a new perspective for cloud microphysical studies.
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Nissar, Zuhaib, Oyuna Rybdylova, Guillaume De Sercey e Steven M. Begg. "Precision in Spray Dynamics: Combining Advanced Imaging and Phase Doppler Anemometry". Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (8 luglio 2024): 1–10. http://dx.doi.org/10.55037/lxlaser.21st.203.
Testo completoAbstract (sommario):
Atomisation in sprays exhibits a stochastic nature, yet it underpins the functionality of technologies reliant on sprays. To accommodate this inherent randomness, it is important to assess all possible outcomes of droplet sizes and velocities at each location, which is crucial for advancing spray-based applications. Phase Doppler Anemometry (PDA) is typically employed to measure these properties, though its use is largely restricted to the far-field, dilute region of a spray where droplets are generally smaller and spherical compared to those in the breakup zone. A new approach involving high-resolution, high-speed, microscopic imaging was developed to complement PDA measurements. Firstly, in this method, a composite image of the spray was constructed by translating the small field of view across the entire spray region in steps, resulting in a set of non-overlapping images. Along the boundaries, the artefacts due to composition were taken care of by utilising four grids, each offset vertically and/or horizontally by half the height and/or width of the field of view to reconstruct data along the ’stitches’. Secondly, the image processing algorithm enabled identification of perforations in the liquid sheet, breakup region and local droplet size and velocity distributions in the spray. In total, 1,200 composite images were produced for each grid at a frame rate of 84 kHz. Droplet sizes greater than 10 μm could be measured, with PDA extending the measurable range down to 1-2 μm. In addition, particle image velocimetry was performed on temporally resolved composite images to derive velocities in the field. The characteristics of a steady-state flat fan water spray at a flow rate of 5 kg/h were analysed using both methodologies. The findings indicated a strong qualitative agreement between the techniques, showing consistent trends, though some quantitative discrepancies were noted. The velocity measurements varied by up to 20% between the two methods. These variations may stem from the exclusion of non-spherical droplets in PDA or from droplets within the depth of field in the images, which move slowly and lead to bias during image analysis.
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von Terzi, Leonie, José Dias Neto, Davide Ori, Alexander Myagkov e Stefan Kneifel. "Ice microphysical processes in the dendritic growth layer: a statistical analysis combining multi-frequency and polarimetric Doppler cloud radar observations". Atmospheric Chemistry and Physics 22, n. 17 (13 settembre 2022): 11795–821. http://dx.doi.org/10.5194/acp-22-11795-2022.
Testo completoAbstract (sommario):
Abstract. The dendritic growth layer (DGL), defined as the temperature region between −20 and −10 ∘C, plays an important role for ice depositional growth, aggregation and potentially secondary ice processes. The DGL has been found in the past to exhibit specific observational signatures in polarimetric and vertically pointing radar observations. However, consistent conclusions about their physical interpretation have often not been reached. In this study, we exploit a unique 3-months dataset of mid-latitude winter clouds observed with vertically pointing triple-frequency (X-, Ka-, W-band) and polarimetric W-band Doppler radars. In addition to standard radar moments, we also analyse the multi-wavelength and polarimetric Doppler spectra. New variables, such as the maximum of the spectral differential reflectivity (ZDR) (sZDRmax), allows us to analyse the ZDR signal of asymmetric ice particles independent of the presence of low ZDR producing aggregates. This unique dataset enables us to investigate correlations between enhanced aggregation and evolution of small ice particles in the DGL. For this, the multi-frequency observations are used to classify all profiles according to their maximum average aggregate size within the DGL. The strong correlation between aggregate class and specific differential phase shift (KDP) confirms the expected link between ice particle concentration and aggregation. Interestingly, no correlation between aggregation class and sZDRmax is visible. This indicates that aggregation is rather independent of the aspect ratio and density of ice crystals. A distinct reduction of mean Doppler velocity in the DGL is found to be strongest for cases with largest aggregate sizes. Analyses of spectral edge velocities suggest that the reduction is the combined result of the formation of new ice particles with low fall velocity and a weak updraft. It appears most likely that this updraft is the result of latent heat released by enhanced depositional growth. Clearly, the strongest correlations of aggregate class with other variables are found inside the DGL. Surprisingly, no correlation between aggregate class and concentration or aspect ratio of particles falling from above into the DGL could be found. Only a weak correlation between the mean particle size falling into the DGL and maximum aggregate size within the DGL is apparent. In addition to the correlation analysis, the dataset also allows study of the evolution of radar variables as a function of temperature. We find the ice particle concentration continuously increasing from −18 ∘C towards the bottom of the DGL. Aggregation increases more rapidly from −15 ∘C towards warmer temperatures. Surprisingly, KDP and sZDRmax are not reduced by the intensifying aggregation below −15 ∘C but rather reach their maximum values in the lower half of the DGL. Also below the DGL, KDP and sZDRmax remain enhanced until −4 ∘C. Only there, additional aggregation appears to deplete ice crystals and therefore reduce KDP and sZDRmax. The simultaneous increase of aggregation and particle concentration inside the DGL necessitates a source mechanism for new ice crystals. As primary ice nucleation is expected to decrease towards warmer temperatures, secondary ice processes are a likely explanation for the increase in ice particle concentration. Previous laboratory experiments strongly point towards ice collisional fragmentation as a possible mechanism for new particle generation. The presence of an updraft in the temperature region of maximum depositional growth might also suggest an important positive feedback mechanism between ice microphysics and dynamics which might further enhance ice particle growth in the DGL.
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Pfitzenmaier, Lukas, Christine M. H. Unal, Yann Dufournet e Herman W. J. Russchenberg. "Observing ice particle growth along fall streaks in mixed-phase clouds using spectral polarimetric radar data". Atmospheric Chemistry and Physics 18, n. 11 (4 giugno 2018): 7843–62. http://dx.doi.org/10.5194/acp-18-7843-2018.
Testo completoAbstract (sommario):
Abstract. The growth of ice crystals in presence of supercooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. However, such mixed-phase interaction processes remain relatively unknown, as capturing the complexity in cloud dynamics and microphysical variabilities turns to be a real observational challenge. Ground-based radar systems equipped with fully polarimetric and Doppler capabilities in high temporal and spatial resolutions such as the S-band transportable atmospheric radar (TARA) are best suited to observe mixed-phase growth processes. In this paper, measurements are taken with the TARA radar during the ACCEPT campaign (analysis of the composition of clouds with extended polarization techniques). Besides the common radar observables, the 3-D wind field is also retrieved due to TARA unique three beam configuration. The novelty of this paper is to combine all these observations with a particle evolution detection algorithm based on a new fall streak retrieval technique in order to study ice particle growth within complex precipitating mixed-phased cloud systems. In the presented cases, three different growth processes of ice crystals, plate-like crystals, and needles are detected and related to the presence of supercooled liquid water. Moreover, TARA observed signatures are assessed with co-located measurements obtained from a cloud radar and radiosondes. This paper shows that it is possible to observe ice particle growth processes within complex systems taking advantage of adequate technology and state of the art retrieval algorithms. A significant improvement is made towards a conclusive interpretation of ice particle growth processes and their contribution to rain production using fall streak rearranged radar data.
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Kun, Emma, e Attila Medveczky. "Multiwavelength Analysis of the IceCube Neutrino Source Candidate Blazar PKS 1424+240". Symmetry 15, n. 2 (18 gennaio 2023): 270. http://dx.doi.org/10.3390/sym15020270.
Testo completoAbstract (sommario):
The true nature of sources of cosmic neutrinos recorded by the Antarctic IceCube Neutrino Detector is still an enigma of high-energy astrophysics. Time-integrated neutrino source searches with the 10 years of IceCube data unfolded neutrino hot-spots of the sky; among them, one is associated with the blazar PKS 1424+240, which is the third most significant neutrino source candidate in the Northern sky. In this paper, we analyze VLBI radio data of PKS 1424+240 taken with the Very Large Baseline Array at 15 GHz as part of the MOJAVE Survey. We generate the adaptively binned gamma-ray light curve of the source, employing Fermi-LAT data between 100 MeV and 300 GeV. We find that the VLBI jet components maintain quasi-stationary core separations at 15 GHz. We find a quiescence and a perturbed phase of the VLBI core of PKS 1424+240, based on that its Doppler factor increased tenfold after 2016 compared to the quiescence phase. We do not find elevated gamma-ray activity after 2016, while archive Swift-XRT measurements show a highly increased 0.3–10 keV X-ray flux in the beginning of 2017. Substantial increase of the activity of the radio core might help us to identify episodes of particle acceleration in lepto-hadronic blazar jets that eventually lead to the emission of high-energy neutrinos.
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Ctibor, Pavel, e Milan Hrabovský. "Dependence of Particle Parameters in Flight and Coating Character on Power of the Electric Supply at Plasma Spraying of TiO2". Key Engineering Materials 434-435 (marzo 2010): 779–82. http://dx.doi.org/10.4028/www.scientific.net/kem.434-435.779.
Testo completoAbstract (sommario):
The influence of input power on the spayed powder and final coating was quantified for particular case of water-stabilized plasma spray torch (WSP®) and ceramic coating formed from titanium dioxide (TiO2). All other spray setup parameters were fixed during the experiment with electric supply power as the only variable factor. In-flight particles were characterized by Doppler particle velocimetry, microstructure of the coatings was observed by microscopic techniques and computer image analysis and phase composition was studied by X-ray diffraction. Various mechanical properties were measured – microhardness, surface roughness and wear resistance in a slurry. The results indicate that the higher power means better coating quality – its microstructure and mechanical performance. This substantial difference has the same trend for both power supplies utilized for the testing.
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Hubbert, J. C., S. M. Ellis, W. Y. Chang, S. Rutledge e M. Dixon. "Modeling and Interpretation of S-Band Ice Crystal Depolarization Signatures from Data Obtained by Simultaneously Transmitting Horizontally and Vertically Polarized Fields". Journal of Applied Meteorology and Climatology 53, n. 6 (giugno 2014): 1659–77. http://dx.doi.org/10.1175/jamc-d-13-0158.1.
Testo completoAbstract (sommario):
AbstractData collected by the National Center for Atmospheric Research S-band polarimetric radar (S-Pol) during the Terrain-Influenced Monsoon Rainfall Experiment (TiMREX) in Taiwan are analyzed and used to infer storm microphysics in the ice phase of convective storms. Both simultaneous horizontal (H) and vertical (V) (SHV) transmit polarization data and fast-alternating H and V (FHV) transmit polarization data are used in the analysis. The SHV Zdr (differential reflectivity) data show radial stripes of biased data in the ice phase that are likely caused by aligned and canted ice crystals. Similar radial streaks in the linear depolarization ratio (LDR) are presented that are also biased by the same mechanism. Dual-Doppler synthesis and sounding data characterize the storm environment and support the inferences concerning the ice particle types. Small convective cells were observed to have both large positive and large negative Kdp (specific differential phase) values. Negative Kdp regions suggest that ice crystals are vertically aligned by electric fields. Since high |Kdp| values of 0.8° km−1 in both negative and positive Kdp regions in the ice phase are accompanied by Zdr values close to 0 dB, it is inferred that there are two types of ice crystals present: 1) smaller aligned ice crystals that cause the Kdp signatures and 2) larger aggregates or graupel that cause the Zdr signatures. The inferences are supported with simulated ice particle scattering calculations. A radar scattering model is used to explain the anomalous radial streaks in SHV and LDR.
47
Zheng, Lei, Rui Zhao, Yong-Le Nian, Jun Liu e Wen-Long Cheng. "Numerical and experimental study of the effects of tangential to axial velocity ratio and structural parameters inside the nozzle on spray characteristics". Physics of Fluids 35, n. 4 (aprile 2023): 043303. http://dx.doi.org/10.1063/5.0140753.
Testo completoAbstract (sommario):
Pressure swirl nozzles are widely applied in spray cooling, dust removal, and fuel injection. To better connect the nozzle structure with the internal flow to analyze their influence on spray parameters, this paper designs a nozzle structure and uses experimental measurement and computational fluid dynamics simulation methods to investigate the influence of the nozzle's tangential velocity to axial velocity ratio ( vτin/ vzin) and the swirl diversion channel eccentric distance ( dl) on the spray parameters. A phase Doppler particle analyzer was used in the experiment study to determine the spray axial velocity ( vz) and sault mean diameter ( D32). In the simulation investigation, the Eulerian multiphase flow model was used to calculate the multiphase flow field of the spray. The results showed that dl and vτin/ vzin both have an obviously linear relationship to the peak location ( rpeak) of each spray parameter. It means that dl plays similar roles as the vτin/ vzin, which can enhance the swirl strength inside the nozzle and increase the spray cone angle. The rpeak of liquid phase volume fraction ( αw) and D32 of the droplet particle are always greater than the rpeak of vz. The analysis of the flow field inside the spray orifice indicates that as the vτin/ vzin rises, the liquid in the nozzle orifice tends to move farther from the central axis, causing atomization to occur more upstream. This study serves as a reference for the flow analysis and structure design of the pressure swirl nozzle.
48
Sassen, Kenneth, James R. Campbell, Jiang Zhu, Pavlos Kollias, Matthew Shupe e Christopher Williams. "Lidar and Triple-Wavelength Doppler Radar Measurements of the Melting Layer: A Revised Model for Dark- and Brightband Phenomena". Journal of Applied Meteorology 44, n. 3 (1 marzo 2005): 301–12. http://dx.doi.org/10.1175/jam-2197.1.
Testo completoAbstract (sommario):
Abstract During the recent Cirrus Regional Study of Tropical Anvils and Cirrus Layers (CRYSTAL) Florida Area Cirrus Experiment (FACE) field campaign in southern Florida, rain showers were probed by a 0.523-μm lidar and three (0.32-, 0.86-, and 10.6-cm wavelength) Doppler radars. The full repertoire of backscattering phenomena was observed in the melting region, that is, the various lidar and radar dark and bright bands. In contrast to the ubiquitous 10.6-cm (S band) radar bright band, only intermittent evidence is found at 0.86 cm (K band), and no clear examples of the radar bright band are seen at 0.32 cm (W band), because of the dominance of non-Rayleigh scattering effects. Analysis also reveals that the relatively inconspicuous W-band radar dark band is due to non-Rayleigh effects in large water-coated snowflakes that are high in the melting layer. The lidar dark band exclusively involves mixed-phase particles and is centered where the shrinking snowflakes collapse into raindrops—the point at which spherical particle backscattering mechanisms first come into prominence during snowflake melting. The traditional (S band) radar brightband peak occurs low in the melting region, just above the lidar dark-band minimum. This position is close to where the W-band reflectivities and Doppler velocities reach their plateaus but is well above the height at which the S-band Doppler velocities stop increasing. Thus, the classic radar bright band is dominated by Rayleigh dielectric scattering effects in the few largest melting snowflakes.
49
Wu, Kenan, Tianwen Wei, Jinlong Yuan, Haiyun Xia, Xin Huang, Gaopeng Lu, Yunpeng Zhang, Feifan Liu, Baoyou Zhu e Weidong Ding. "Thundercloud structures detected and analyzed based on coherent Doppler wind lidar". Atmospheric Measurement Techniques 16, n. 23 (5 dicembre 2023): 5811–25. http://dx.doi.org/10.5194/amt-16-5811-2023.
Testo completoAbstract (sommario):
Abstract. The studies of intracloud discharges may shed light on the microphysical structure of thunderclouds, as both the magnitude and the sign of charge separation due to graupel collides with ice crystals within the strong updrafts are influenced by the surrounding environment. Here, a compact all-fiber coherent Doppler wind lidar (CDWL) working at the 1.5 µm wavelength is applied for probing the dynamics and microphysics structure of thunderstorms. Thanks to the precise spectrum measurement, multi-component spectra signals of thunderstorms can be analyzed by the CDWL. The spectrum width, skewness, and Doppler velocity of CDWL is used to separate and identify the particle composition and polarity. In the experiment, the thundercloud properties are detected by the CDWL, 10.6 cm Doppler weather radar (DWR), and Advanced Geosynchronous Radiation Imager (AGRI) onboard Fengyun-4 satellites. In particular, the spectrum width and skewness of the thundercloud below the 0 ∘C isotherm are increased, and when a cloud-ground lightning occurs, there is additional graupel with a velocity greater than 5 m s−1. It indicates that this region is a melting layer, and lightning activity changes the motion characteristics of graupel, affecting the charge structure of the whole thundercloud. In general, our findings provide details on the velocity, phase, and composition of particles in the outside updraft region of the thunderstorm. The identification and analysis of graupel is particularly important. It is proved that the precise spectrum of CDWL is a promising indicator for studying the charge structure of thunderstorms.
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BORÉE, J., T. ISHIMA e I. FLOUR. "The effect of mass loading and inter-particle collisions on the development of the polydispersed two-phase flow downstream of a confined bluff body". Journal of Fluid Mechanics 443 (25 settembre 2001): 129–65. http://dx.doi.org/10.1017/s0022112001005134.
Testo completoAbstract (sommario):
The effect of mass loading and inter-particle collisions on the development of the polydispersed two-phase flow downstream of a confined bluff body is discussed. The bluff-body flow configuration, which is one of the simplest turbulent recirculating flows, is relevant for applications and forms the basis of numerous combustion devices. The present data are obtained for isothermal conditions by using a two-component phase-Doppler anemometer allowing size and velocity measurements. Polydispersed glass beads are introduced into the flow. The statistical properties of narrow particle size classes are displayed and analysed in order to allow for the wide range of particle relaxation times. The evolution of mass fluxes and mass concentration per size class is estimated from the PDA data. A correction is introduced to ensure that the mass flow rate of particles per size class from data integration is correct.We show that the development of the continuous phase is very sensitive to initial mass loading of the inner jet. An increase in mass loading corresponds to an increase in momentum flux ratio between the central jet and annular flow. In the present situation, this implies a complete reorganization of the recirculation zone and the turbulent field. The importance of direct modulation of turbulence induced by particles is demonstrated in the inner jet. Moreover, our data confirm that the prediction of fluid/particle velocity correlation is essential to take these effects into account for partly responsive beads.We show that the sensitivity to mass loading greatly affects the dispersion of the glass beads. Particles recirculate at the lowest mass loading and the mass concentration of the dispersed phase in the recirculation zone and in the external shear layer is high. On the other hand, the memory of the initial jet is detected far downstream at the highest loading and the dispersion of particles is reduced. Axial or radial profiles of mean and r.m.s. velocity of the dispersed phase are displayed and analysed. The role of large-scale intermittency is discussed. Relevant Stokes numbers are introduced to account for different driving mechanisms in the turbulent field. Non-Stokesian effects are particularly important. We show that the anisotropy of the particle fluctuating motion is large and associated with production mechanisms via interaction with mean particle velocity gradients. A focus on the jet stagnation region proves that the particulate flow is very sensitive to inertia effects and that no local equilibrium with the fluid turbulence can be assumed when modelling such a configuration.Finally, even at the small volume ratio considered here, we prove that it is highly probable that inter-particle collisions occur in the jet stagnation region at low mass loading and all along the inner jet flow at the highest mass loading. Redistribution of mean momentum and fluctuating kinetic energy between all colliding classes is therefore expected, which implies a fully coupled fluid and particle system.The data and analysis presented provide a severe test case for the recent development in two-phase flow modelling and offer further challenges both to experimentation and model development. The validated data set has been selected for benchmarking and is available on the internet.