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1
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.
Testo completo
2
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.
Testo completo
3
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.
Testo completo
4
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.
5
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.
6
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.
Testo completo
7
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.
8
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).
9
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.
10
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.
11
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.
12
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).
13
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.
14
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.
15
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.
16
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]
17
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.
18
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.
19
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.
20
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]
21
Li, Xiang, Xuewen Zhang, Tianya Zhang, Ce Ji, Peiyong Ni, Wanzhong Li, Yiqiang Pei, Zhijun Peng e Raouf Mobasheri. "Insights into Microscopic Characteristics of Gasoline and Ethanol Spray from a GDI Injector Under Injection Pressure up to 50 MPa". Sustainability 16, n. 21 (31 ottobre 2024): 9471. http://dx.doi.org/10.3390/su16219471.
Testo completoAbstract (sommario):
Nowadays it has become particularly valuable to control the Particulate Matter (PM) emissions from the road transport sector, especially in vehicle powertrains with an Internal Combustion Engine (ICE). However, almost no publication has focused on a comparison of the microscopic characteristics of gasoline and ethanol spray under injection pressure conditions of more than 30 MPa, except in the impingement process. By using a Phase Doppler Particles Analyser (PDPA) system, the microscopic characteristics of gasoline and ethanol spray from a Gasoline Direct Injection (GDI) injector under injection pressure (PI) up to 50 MPa was fully explored in this research. The experimental results demonstrate that under the same PI, the second peak of the probability (pd) curves of droplet normal velocity for gasoline is slightly higher than that of ethanol. Moreover, gasoline spray exceeds ethanol by about 5.4% regarding the average droplet tangential velocity at 50 mm of jet downstream. Compared to ethanol, the pd curve’s peak of droplet diameter at (0, 50) for gasoline is 1.3 percentage points higher on average, and the overall Sauter mean diameter of gasoline spray is slightly smaller. By increasing PI from 10 MPa to 50 MPa, pd of the regions of “100 ≤ Weber number (We) < 1000” and “We ≥ 1000” increases by about 23%, and the pd of large droplets over 20 μm shows a significant reduction. This research would provide novel insights into the deeper understanding of the comparison between gasoline and ethanol spray in microscopic characteristics under ultra-high PI. Additionally, this research would help provide a theoretical framework and practical strategies to reduce PM emissions from passenger vehicles, which would significantly contribute to the protection and sustainability of the environment.
22
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
23
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.
24
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.
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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.
Testo completo
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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.
27
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.
28
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.
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Van Den Moortel, T., R. Santini, L. Tadrist e J. Pantaloni. "Experimental study of the particle flow in a circulating fluidized bed using a phase doppler particle analyser: A new post-processing data algorithm". International Journal of Multiphase Flow 23, n. 6 (novembre 1997): 1189–209. http://dx.doi.org/10.1016/s0301-9322(97)00033-5.
Testo completo
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Gindroz, B., e M. L. Billet. "Influence of the Nuclei on the Cavitation Inception for Different Types of Cavitation on Ship Propellers". Journal of Fluids Engineering 120, n. 1 (1 marzo 1998): 171–78. http://dx.doi.org/10.1115/1.2819643.
Testo completoAbstract (sommario):
In order to relate nuclei size distributions with inception cavitation in cavitation facilities, a test program was conducted at the Grand Tunnel Hydrodynamique (GTH) of the Bassin d’Essais des Care`nes. The GTH, which has a complete air control system including dissolved gas and nuclei (microbubbles) control, offers the opportunity to answer this question. The tests were conducted on the three 34 mm diameter propellers used by Kuiper (1981), each of these propellers being characterized by a different cavitation type: bubble, sheet and vortex cavitation. The water nuclei content correspond to strong degassed water (maximum tension), low injection of medium size nuclei (medium tension-low content), large injection of medium size nuclei (medium tension-high content) and large injection of large nuclei (minimum tension). By injecting medium size nuclei for a low content and a high content, we can examine the influence of the number of nuclei on the cavitation inception characteristic. During all the tests, the dissolved air content was kept constant. The GTH online Cavitation Nuclei Counter (Centerbody Venturi) was used to measure both the water nuclei distribution and the liquid tension. Comparisons are made with the calibrated Centerbody Venturi, a Phases Doppler Particles Analyzer (PDPA) and Holographic measurements.
31
Lee, Sanghoon, Yunjung Oh e Sungwook Park. "Characterization of the spray atomization process of a multi-hole gasoline direct injector based on measurements using a phase Doppler particle analyser". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 227, n. 7 (8 aprile 2013): 951–65. http://dx.doi.org/10.1177/0954407013483244.
Testo completo
32
Trujillo, M. F., W. S. Mathews, C. F. Lee e J. E. Peters. "Modelling and experiment of impingement and atomization of a liquid spray on a wall". International Journal of Engine Research 1, n. 1 (1 febbraio 2000): 87–105. http://dx.doi.org/10.1243/1468087001545281.
Testo completoAbstract (sommario):
An experimental and computational investigation of spray impingement on a flat surface is presented. Different angles of incidence are studied, namely 30, 45 and 60°C measured from the normal to the surface. Back-lit photographs of the wall spray taken at various times during the impingement period give a qualitative view of the secondary atomization process. A stochastic model based on the sampling of velocity and size distributions of secondary droplets is used to simulate the creation of incident droplet fragments created by the numerous splashing events occurring during the impingement period. Size characteristics of the secondary droplet cloud are computed at various points in the impingement region and these are compared against phase/Doppler particle analyser (P/DPA) measurements yielding reasonable agreement. The effect of surface roughness is incorporated into the model and is found to play a major role in affecting the splashing threshold and the sizes of splashing fragments. The secondary droplet distributions are virtually unchanged among the different angles of incidence. This behaviour is explained by considering the shift in the splashing droplet distribution as a function of incident angle.
33
Zhao, Lei, e Ting Wang. "An Experimental Study of Mist/Air Film Cooling On a Flat Plate With Application to Gas Turbine Airfoils—Part II: Two-Phase Flow Measurements and Droplet Dynamics". Journal of Turbomachinery 136, n. 7 (2 gennaio 2014). http://dx.doi.org/10.1115/1.4025738.
Testo completoAbstract (sommario):
A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air-mist coolant jet flow spreads and eventually blends into the hot main flow is proposed. This proposed profile is found to be well supported by the measurement results of the turbulent Reynolds stresses. The coolant film envelope is identified with shear layers characterized by higher magnitudes of turbulent Reynolds stresses. In addition, the separation between the mist droplet layer and the coolant air film is identified through the droplet measurements—large droplets penetrate through the air coolant film layer and travel further into the main flow. With the proposed air-mist film profile, the heat transfer results on the wall presented in Part I are re-examined and more in-depth physics is revealed. It is found that the location of the optimum cooling effectiveness coincides with the point where the air-mist coolant stream starts to bend back towards the surface. Thus, the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface, which improves the cooling effectiveness for mist cooling.
34
Hui, Yue, Hao Wu e Zhenyu Zhang. "Droplet dynamics and spray mechanism of air-assisted intermittent atomization under different injection timings". Physics of Fluids 36, n. 11 (1 novembre 2024). http://dx.doi.org/10.1063/5.0237835.
Testo completoAbstract (sommario):
The droplet dynamics and spray mechanism of air-assisted intermittent atomization were experimentally investigated, with a particular focus on the effect of injection timing (duration of fuel injection ranged from 1 to 10 ms, and the interval between fuel injection and air injection varied from −0.5 to 2 ms) on jet atomization. Droplet velocities, sizes, and arrival times at a selected location were obtained by applying a phase Doppler particle analyzer (PDPA) with the combination of high-speed photography for spray visualization. The results indicate that droplet dynamics and velocity distribution are substantially influenced by fuel injection duration. Specifically, two peaks in the droplet velocity distribution are identified when the fuel injection duration exceeded 6 ms. Reconstruction of the gas-phase velocity using tracer particles reveals that the gas-phase velocity and stability are similarly affected by the fuel injection duration, and the gas flow tends to be stable for fuel injection durations longer than 6 ms. Droplets in the two velocity peaks exhibit different dynamic characteristics. The phenomenon of two peaks in droplet velocity is attributed to fuel accumulation inside the air-assisted atomizer, with the analysis given in terms of spray concentration and fuel state in the atomizer. Fuel accumulation and twin-peak droplet velocity caused by extended fuel–air injection intervals are predicted and validated.
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Panchasara, Heena, Pankaj S. Kolhe e Ajay K. Agrawal. "Spray Flame Characteristics of Bio-Derived Fuels in a Simulated Gas Turbine Burner". Journal of Engineering for Gas Turbines and Power 142, n. 8 (31 luglio 2020). http://dx.doi.org/10.1115/1.4047782.
Testo completoAbstract (sommario):
Abstract Fuel injection plays an important role in liquid-fueled gas turbine combustion. The strong interdependence of liquid breakup and atomization, turbulent dispersion of these droplets, droplet evaporation, and fuel–air mixing make the spray modeling an extremely challenging task. The physical processes are even more difficult to predict for alternative fuels with different thermophysical properties. In this study, spray flames of unheated and preheated vegetable oil (VO) produced by an air-blast (AB) atomizer in a swirl stabilized combustor are investigated experimentally. Phase Doppler particle analyzer (PDPA) is used to measure the instantaneous diameter and axial velocity of droplets at different axial and radial locations in both flames. Experiments are conducted at an equivalence ratio of 0.79 and atomizing air to liquid ratio by a mass of 2.5 to obtain stable VO flames. Radial profiles of mean axial velocity and Sauter mean diameter (SMD) are presented to show the effect of fuel preheating. Joint probability density functions (joint PDF) are presented to show the correlation between droplet diameter and axial velocity. Results are analyzed to show that both sprays exhibit self-similar droplet diameter distributions at different axial and radial locations when normalized properly. Thus, the vast amount of PDPA data in the spray can be reduced to simple distribution functions. A method to reconstruct the joint PDF from experimentally determined distribution functions is presented. We envision that the joint PDF approach outlined in this study could be implemented in high-fidelity computational fluid dynamic models to improve spray predictions in future studies.
36
Ragab, Reda, e Ting Wang. "An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part II: Two-Phase Flow Measurements and Droplet Dynamics". Journal of Heat Transfer 140, n. 4 (12 dicembre 2017). http://dx.doi.org/10.1115/1.4037642.
Testo completoAbstract (sommario):
A phase Doppler particle analyzer (PDPA) system is employed to measure the two-phase mist flow behavior including flow velocity field, droplet size distribution, droplet dynamics, and turbulence characteristics. Based on the droplet measurements made through PDPA, a projected profile describing how the air–mist coolant jet flow spreads and eventually blends into the hot main flow is prescribed for both cylindrical and fan-shaped holes. The mist film layer consists of two layers: a typical coolant film layer (cooling air containing the majority of the droplets) and a wider droplet layer containing droplets outside the film layer. Thanks to the higher inertia possessed by larger droplets (>20 μm in diameter) at the injection hole, the larger droplets tend to shoot across the coolant film layer, resulting in a wider droplet layer than the coolant film layer. The wider droplet layer boundaries are detected by measuring the droplet data rate (droplet number per second) distribution, and it is identified by a wedge-shaped enclosure prescribed by the data rate distribution curve. The coolant film layer is prescribed by its core and its upper boundary. The apex of the data rate curve, depicted by the maximum data rate, roughly indicates the core region of the coolant film layer. The upper boundary of the coolant film layer, characterized by active mixing with the main flow, is found to be close to relatively high values of local Reynolds shear stresses. With the results of PDPA measurements and the prescribed coolant film and droplet layer profiles, the heat transfer results on the wall presented in Part I are re-examined, and the fundamental mist-flow physics are analyzed. The three-dimensional (3D) droplet measurements show that the droplets injected from the fan-shaped holes tend to spread wider in lateral direction than cylinder holes and accumulate at the location where the neighboring coolant film layers meet. This flow and droplet behavior explain the higher cooling performance as well as mist-enhancement occurs between the fan-shaped cooling holes, rather than along the hole's centerline as demonstrated in the case using the cylindrical holes.
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Pabbisetty, Mallikarjuna Rao, e B. V. S. S. S. Prasad. "Effect of Blowing Ratio on Mist-Assisted Air Film Cooling of a Flat Plate: An Experimental Study". Journal of Thermal Science and Engineering Applications 13, n. 3 (27 ottobre 2020). http://dx.doi.org/10.1115/1.4048209.
Testo completoAbstract (sommario):
Abstract A novel mist-assisted air film cooling scheme is proposed by Li and Wang (2006, “Simulation of Film Cooling Enhancement With Mist Injection,” ASME J. Heat Transfer, 128, pp. 509–519) to increase the film cooling effectiveness of a gas turbine cooled vane/blade. This scheme is further investigated experimentally in this article to determine the effect of the blowing ratio. The coolant is made to pass through the film holes on a flat plate mounted in a test facility. Tiny water droplets, characterized by Rosin-Rammler mean diameter of about 36.7 μm measured with a phase Doppler particle analyzer (PDPA) system is introduced into the cooling air. The effectiveness values are evaluated by measuring the plate surface temperature with the infrared (IR) camera. The maximum percentage of the mist-assisted film cooling effectiveness is 26% more than air film cooling effectiveness when 2.1% of mist is added to the air. In addition, the coolant coverage on the plate is found to be much better with mist cooling in both the streamwise and the spanwise directions. The net enhancement due to the mist-assisted air film cooling effectiveness (Δη) decreases with the increasing values of the blowing ratio in the range of 0.55–2.58 at a density ratio of 2.2.
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Abdelmaksoud, Ramy, e Ting Wang. "An Experimental Investigation of Sweeping Air/Mist Jet Film Cooling Through a Row of Passive Fluidic Oscillators". ASME Journal of Heat and Mass Transfer, 21 maggio 2024, 1–16. http://dx.doi.org/10.1115/1.4065573.
Testo completoAbstract (sommario):
Abstract This paper presents an experimental study of employing two-phase (air/mist) flow through a row of passive fluidic oscillators in film cooling applications for gas turbine aerofoil cooling. The objective of this study is to investigate the potential enhancement of film cooling by using sweeping jets injected with water mist. Three blowing ratios (BR=0.85, 1.46, 2.40) and two mist ratios (MR=2.75% and 6.92%) are used (i.e., a total of nine cases including the air-only cases). Infrared thermography and E-type thermocouples were used to measure the wall temperature, while a phase Doppler particle analyzer (PDPA) was used to measure the droplets' size distributions. The initial mean droplet size is 11.6&#181;m. An interesting observation was found where thin water liquid streaks were formed at the exit of the fluidic oscillators and traveled for very long distances (about 140D) providing excellent local film cooling under the laboratory low heating condition. The forming of liquid streaks is due to the significant droplets coalescence phenomenon caused by large oscillating vortical flows inside the fluidic oscillator. Adding small mist ratios provided better cooling effectiveness with an overall time-averaged cooling enhancement of 15-90% and a maximum local cooling enhancement of 300-350% in all the cases studied. The sweeping jet provided better film cooling effectiveness at the centerline and spanwise direction (87% and 76%, respectively) when compared to steady jets under the laboratory conditions with low temperatures and low pressure.
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Wang, Ting, Lei Zhao e Ramy Abdelmaksoud. "Validation of a Two-Phase CFD Model Air/Mist Film Cooling with Experimental Details – Part I: Development of an Experimental Test Facility". Journal of Thermal Science and Engineering Applications, 18 maggio 2022, 1–19. http://dx.doi.org/10.1115/1.4054624.
Testo completoAbstract (sommario):
Abstract Motivated by the need to further improve the turbine hot section cooling performance, a mist/air film cooling scheme is investigated. A small amount of tiny water droplets with an average diameter about 7 µm (mist) is injected into the cooling air to enhance the cooling performance. Designing an experimental setup for a two phase flow experiment is challenging, therefore, the authors will dedicate this paper as Part I to discuss all the challenges faced in order to create a successful experimental facility for air/mist film cooling while Part II will discuss how to conduct a high-fidelity computational model for air/mist film cooling accompanied with a validation study by including detailed experimental conditions. This paper presents the experimental facility and instrumentation of a air/mist film cooling study with both heat transfer and droplet measurements. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure the two-phase flow characteristics, including droplet size, droplet dynamics, velocity, and turbulence. Infrared camera and thermocouples are both used for temperature measurements. An extensive uncertainty analysis is performed to assist in identifying large uncertainty sources and planning for experimental procedure. It was found during the experiment design process that resolving the mist agglomeration problem is the key in successfully generating a well-controlled mist/air mixture and reducing experimental uncertainties. The test apparatus has proven to serve the purpose well to investigate mist/air film cooling with both heat transfer and droplet measurements. Selected experimental data is presented.
40
Ahmed, Mahmoud, e M. S. Youssef. "Characteristics of Mean Droplet Size Produced by Spinning Disk Atomizers". Journal of Fluids Engineering 134, n. 7 (21 giugno 2012). http://dx.doi.org/10.1115/1.4006819.
Testo completoAbstract (sommario):
Characteristics of mean droplet size of spray produced by spinning disk atomizers were experimentally investigated. The phase-doppler particle analyzer (PDPA) was used to measure the droplet size of water spray in the downstream distance along the spray trajectory. Effects of various operating conditions on the mean diameter had been studied. The studied variables were: the rotational speed in the range of 838 to 1677 rad/s (8,000–16,000 rpm), the liquid flow rate in the range of 0.56 to 2.8 × 10−6 m3/s (2–10 L/h), the disk diameter in the range of 0.04 to 0.12 m, and the downstream tangential distance along the spray trajectory of up to 0. 24 m. The Sauter mean diameter (d32) was used to represent the mean of generated spray droplet sizes. The results indicated that the Sauter mean diameter can be correlated with dimensionless groups, such as the Reynolds number, Weber number, flow coefficient, and the ratio of downstream distance to disk diameter. Based on this correlation, it was found that the Sauter mean diameter (d32) increases as the downstream tangential distance, and liquid flow rate increase. Similarly, a decrease of rotational speed and disk diameter results in an increase in the Sauter mean diameter (d32). A comparison between the developed correlation and correlations obtained by other researchers has been presented and discussed in detail.
41
Wu, Guohua, Xin Yu, Jiangbo Peng, Chaobo Yang, Zhen Cao e Yingjie Song. "Quantitative measurement of the Sauter mean diameter in dense fuel sprays using simultaneous planar-laser-induced-fluorescence/Mie scattering technique". Measurement Science and Technology, 6 gennaio 2025. https://doi.org/10.1088/1361-6501/ada62d.
Testo completoAbstract (sommario):
Abstract The planar laser induced fluorescence (PLIF)/Mie scattering technique has been established as an effective method for measuring the Sauter Mean Diameter (SMD) distribution in dense fuel sprays. This technique typically utilized a 266 nm laser. However, the strong absorption of laser wavelengths ranging from 266 nm to 274 nm in dense fuel sprays affected the detection of Mie scattering signals. Therefore, it was proposed to use a 266 nm laser for fluorescence excitation and a 532 nm laser for Mie scattering radiation in dense fuel sprays. In this study, a look-up table (LUT) was created by correlating the PLIF/Mie ratio with the Sauter Mean Diameter (SMD) using the Phase Doppler Particle Analyzer (PDPA), reducing the SMDerror from 27% to 13%. Furthermore, the proposed method was successfully applied to investigate the atomization field of room temperature and atmospheric pressure in a dual-stage axial swirl combustion chamber. By comparing the time-averaged PLIF images and time-averaged Mie images, the vapor and liquid phases of the fuel in the spray were successfully imaged and identified. The results indicated that, under the same fuel flow, increasing the air mass flow led to a gradual increase in the spray cone angle inside the dual-stage axial swirl combustor. Additionally, at a constant fuel flow, increasing the air mass flow resulted in a more uniform droplet size distribution, thereby enhancing the atomization effect. The presented technique provides a reliable and accurate tool for studying fuel spray behavior under various operating conditions. This knowledge can contribute to the design of more efficient combustion systems and the optimization of fuel injection strategies.
42
Zhao, Lei, e Ting Wang. "An Experimental Study of Mist/Air Film Cooling on a Flat Plate With Application to Gas Turbine Airfoils—Part I: Heat Transfer". Journal of Turbomachinery 136, n. 7 (2 gennaio 2014). http://dx.doi.org/10.1115/1.4025736.
Testo completoAbstract (sommario):
Film cooling is a cooling technique widely used in high-performance gas turbines to protect the turbine airfoils from being damaged by hot flue gases. Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments in this study. A small amount of tiny water droplets (7 wt. %) with an average diameter about 5 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facility is specifically built for this unique experiment. A phase Doppler particle analyzer (PDPA) system is employed to measure the droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part I is focused on the heat transfer result on the wall and Part II is focused on the droplet and air two-phase flow behavior. Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. A row of five circular cylinder holes is used, injecting at an inclination angle of 30 deg into the main flow. For the 0.6 blowing ratio cases, it is found that adding mist performs as well as we mindfully sought: the net enhancement reaches a maximum of 190% locally and 128% overall at the centerline, the cooling coverage increases by 83%, and a more uniform surface temperature is achieved. The latter is critical for reducing wall thermal stresses. When the blowing ratio increases from 0.6 to 1.4, both the cooling coverage and net enhancement are reduced to below 60%. Therefore, it is more beneficial to choose a relatively low blowing ratio to keep the coolant film attached to the surface when applying the mist cooling. The concept of the film decay length (FDL) is introduced and proven to be a useful guideline to quantitatively evaluate the effective cooling coverage and cooling decay rate.
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Ragab, Reda, e Ting Wang. "An Experimental Study of Mist/Air Film Cooling With Fan-Shaped Holes on an Extended Flat Plate—Part 1: Heat Transfer". Journal of Heat Transfer 140, n. 4 (12 dicembre 2017). http://dx.doi.org/10.1115/1.4037641.
Testo completoAbstract (sommario):
Motivated by the need to further improve film cooling in terms of both cooling effectiveness and coolant coverage area, the mist/air film cooling scheme is investigated through experiments using fan-shaped holes over an extended downstream length in this study. Both an existing wind tunnel and test facility, used in previous work, have been retrofitted. The first modification was extending the length of the flat plate test section to cover longer distances downstream of the injection holes, up to X/D = 100, in order to investigate whether mist cooling can be harnessed farther downstream where single-phase film cooling is not effective. X represents the axial distance downstream of the cooling hole of diameter D. The second modification was to incorporate fan-shaped (diffusion) holes which are proven to have a higher film cooling efficiency, than cylindrical holes. The objective is to investigate whether mist can further enhance the film cooling performance of the already highly effective fan-shaped holes. A phase Doppler particle analyzer (PDPA) system is employed to measure the droplet size, velocity, and turbulence information. An infrared camera and thermocouples are both used for temperature measurements. Part I is focused on the heat transfer result on the wall. The results show that, at low blowing ratios when the film is attached to the surface, the enhancement of the mist film cooling effectiveness, compared to the air-only case, on the centerline of the hole ranges from 40% in the near hole region to over 170% at X/D = 100. Due to the diffusive nature of the fan-shaped hole, the laterally averaged enhancement is on par with that on the centerline. The significant enhancement over the extended downstream distance from X/D = 40–100 is attributed to the evaporation time needed to evaporate all of the droplets. Each droplet acts as a cooling sink and flies over a distance before it completely vaporizes. This “distributed cooling” characteristic allows the water droplets to extend the cooling effects farther downstream from the injection location. At higher blowing ratios, when the cooling film is lifted off from the surface, the cooling enhancement drops below 40%. Although the enhancement in the near hole region X/D < 40 is about 20% lower than that achieved by using the cylindrical holes, the magnitudes of the mist adiabatic film cooling effectiveness using fan-shaped holes are still much higher than those of the cylindrical holes. Part II of this study is focused on analyzing the two-phase droplet multiphase flow behavior to explain the fundamental physics involved in the mist film cooling.
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Subramani, Sivakumar, Narendra Laxman Gajbhiye, Venkatasudhahar Murugesan, Prabhu Mottaiyan e Ratchagaraja Dhairiyasamy. "Experimental investigations on spray characteristics of non-edible oils using phase doppler particle analyser". Matéria (Rio de Janeiro) 29, n. 3 (2024). http://dx.doi.org/10.1590/1517-7076-rmat-2024-0415.
Testo completo
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Li, Xiang, Dayou Li, Yiqiang Pei e Zhijun Peng. "Optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition (SI) engine by changing GDI injection pressure". International Journal of Engine Research, 1 marzo 2022, 146808742210827. http://dx.doi.org/10.1177/14680874221082793.
Testo completoAbstract (sommario):
Regarding reducing particle emissions from dual-injection spark ignition engines, most of the existing research focused on the benefits of using alcohol fuels. However, a comprehensive study of the effects of fuel injection pressure on microscopic spray characteristics and particle emissions in dual-injection spark ignition engines fuelled with gasoline has not been reported before. In this paper, with the assistance of phase Doppler particles analyser system and fast particle analyser, a study of optimising microscopic spray characteristics and particle emissions in a dual-injection spark ignition engine fuelled with gasoline by changing GDI injection pressure was conducted. The results show that by increasing injection pressure from 5.5 to 18 MPa, both normal and tangential components of droplet velocity increase, but the possibility of spray impingement would not increase a lot. Higher injection pressure would increase the probability of small droplets, and more droplets would collapse with a mode of continuous ripping or break down abruptly. From jet’s central axis to sides, Sauter mean diameter increases first, then reduces outside the spray boundary. Increasing injection pressure from 5.5 to 18 MPa reduces total particle number concentration, which is 53.98% and 45.44% at 2 bar and 10 bar, respectively. Meanwhile, the peak of particle number distribution curve decreases from 3.01 × 106 to 1.43 × 106 at 2 bar, whilst reducing from 1.08 × 106 to 5.33 × 105 at 10 bar. Overall, this paper comprehensively analyses the effects of fuel injection pressure on microscopic spray characteristics and particle emissions, whilst offering a practical approach to reduce particle emissions in dual-injection SI engines fuelled with gasoline.
46
Song, Jinkwan, Charles Cary Cain e Jong Guen Lee. "Liquid Jets in Subsonic Air Crossflow at Elevated Pressure". Journal of Engineering for Gas Turbines and Power 137, n. 4 (28 ottobre 2014). http://dx.doi.org/10.1115/1.4028565.
Testo completoAbstract (sommario):
The breakup, penetration, droplet size, and size distribution of a Jet A-1 fuel in air crossflow has been investigated with focus given to the impact of surrounding air pressure. Data have been collected by particle Doppler phased analyzer (PDPA), Mie-scattering with high speed photography augmented by laser sheet, and Mie-scattering with intensified charge-coupled device (ICCD) camera augmented by nanopulse lamp. Nozzle orifice diameter, do, was 0.508 mm and nozzle orifice length to diameter ratio, lo/do, was 5.5. Air crossflow velocities ranged from 29.57 to 137.15 m/s, air pressures from 2.07 to 9.65 bar, and temperature held constant at 294.26 K. Fuel flow provides a range of fuel/air momentum flux ratio (q) from 5 to 25 and Weber number from 250 to 1000. From the results, adjusted correlation of the mean drop size has been proposed using drop size data measured by PDPA as follows: (D0/D32)=0.267Wea0.44q0.08(ρl/ρa)0.30(μl/μa)-0.16. This correlation agrees well and shows roles of aerodynamic Weber number, Wea, momentum flux ratio, q, and density ratio, ρl/ρa. Change of the breakup regime map with respect to surrounding air pressure has been observed and revealed that the boundary between each breakup modes can be predicted by a transformed correlation obtained from above correlation. In addition, the spray trajectory for the maximum Mie-scattering intensity at each axial location downstream of injector is extracted from averaged Mie-scattering images. From these results, correlations with the relevant parameters including q, x/do, density ratio, viscosity ratio, and Weber number are made over a range of conditions. According to spray trajectory at the maximum Mie-scattering intensity, the effect of surrounding air pressure becomes more important in the farfield. On the other hand, effect of aerodynamic Weber number is more important in the nearfield.
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Suleiman, Baha, Hatem Selim, Alaaeldin Dawood, Jinkwan Song, Jongguen Lee, Abdurrahman Alkhalidi, Kamal M. AlAhmadi, Ibrahim A. AlGhamdi, Eid Badr e Mohammed Al-Gahatani. "Characterization of Spray Field for Water-Emulsified Diesel Using a Pressure Swirl Atomizer Under a Non-Reacting Environment". Journal of Engineering for Gas Turbines and Power, 17 ottobre 2023, 1–33. http://dx.doi.org/10.1115/1.4063778.
Testo completoAbstract (sommario):
Abstract Employing a mixture or an emulsion of water and diesel fuel is considered a way to reduce gas emissions such as NOx and soot in a gas turbine. This study presents detailed experimental results on the spray characteristics of a water-diesel emulsion injected by a pressure swirl atomizer with a 90-degree spray angle and a flow number of 0.58 under a non-reacting environment at high pressure and temperature conditions. Acquiring this data is a key step when configuring a combustor that will employ emulsified fuels. In addition, this study seeks to confirm that the emulsion stays intact when it gets sprayed into the combustor. Furthermore, this study attempts to understand if a water-diesel emulsion prepared by a sonicator improves fuel atomization as compared to a water-diesel mixture prepared by a static mixer, i.e., not a proper emulsion. Tests are conducted in a high pressure and temperature testing facility at two ambient pressures and three ambient temperatures and water to diesel ratio (W/D) is varied from 11% to 100% by mass. Phase Doppler Particle Anemometry (PDPA) is employed to measure the spray characteristics. Through a backlit high-speed photography, overall spray patterns over different test conditions are visualized. Mie-scattering and planar laser-induced fluorescence imaging are utilized to visualize the mixture field. In general, the results indicate that emulsion stays intact as it gets sprayed into the combustor; and emulsion is a better solution to reduce emissions than a statically mixed mixture.
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Ferran, Amélie, Nathanaël Machicoane, Alberto Aliseda e Martín Obligado. "An experimental study on the settling velocity of inertial particles in different homogeneous isotropic turbulent flows". Journal of Fluid Mechanics 970 (4 settembre 2023). http://dx.doi.org/10.1017/jfm.2023.579.
Testo completoAbstract (sommario):
We propose an experimental study on the gravitational settling velocity of dense, sub-Kolmogorov inertial particles under different background turbulent flows. We report phase Doppler particle analyser measurements in a low-speed wind tunnel uniformly seeded with micrometre scale water droplets. Turbulence is generated with three different grids (two consisting of different active-grid protocols while the third is a regular static grid), allowing us to cover a very wide range of turbulence conditions in terms of Taylor-scale-based Reynolds numbers ( $Re_\lambda \in [30\unicode{x2013}520]$ ), Rouse numbers ( $Ro \in [0\unicode{x2013}5]$ ) and volume fractions ( $\phi _v \in [0.5\times 10^{-5}\unicode{x2013}2.0\times 10^{-5}]$ ). We find, in agreement with previous works, that enhancement of the settling velocity occurs at low Rouse number, while hindering of the settling occurs at higher Rouse number for decreasing turbulence energy levels. The wide range of flow parameters explored allowed us to observe that enhancement decreases significantly with the Taylor–Reynolds number and is significantly affected by the volume fraction $\phi _v$ . We also studied the effect of large-scale forcing on settling velocity modification. The possibility of changing the inflow conditions by using different grids allowed us to test cases with fixed $Re_\lambda$ and turbulent intensity but with different integral length scale. Finally, we assess the existence of secondary flows in the wind tunnel and their role on particle settling. This is achieved by characterising the settling velocity at two different positions, the centreline and close to the wall, with the same streamwise coordinate.