Literatura científica selecionada sobre o tema "Phase Doppler Particle Analyser (PDPA)"

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.

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.

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.

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).

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.

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.

Les nanodiamants (NDs) font l'objet de recherches intenses dans les domaines biomédical, militaire et de la mécanique quantique. Pour produire ces NDs, le recours à la détonation d'un mélange RDX/TNT, aussi appelé hexolite, est souvent préféré. Cependant, pour produire des NDs aux propriétés physico-chimiques performantes, il est nécessaire d’avoir au préalable des particules fines d’hexolites, et des mélanges intimes et homogènes. Pour parvenir à cela, le laboratoire NS3E a développé le procédé de recristallisation par évaporation flash de spray (Spray Flash Evaporation, SFE). Cependant, l'influence des différentes conditions opératoires du procédé sur les caractéristiques physico-chimiques des particules est encore mal comprise. Améliorer cette compréhension permettrait une plus grande maîtrise des propriétés des particules recristallisées. Cette thèse vise donc, à l'aide d'analyses in situ telles que l'ombroscopie et le PDPA (Phase Doppler Particle Analyzer), à apporter des réponses. Les recherches se structurent en deux axes principaux. Le premier axe explore en profondeur les phénomènes physico-chimiques de l'évaporation flash d'un solvant (acétone) et l'impact du soluté (hexolite) sur le comportement du spray d'acétone. Le second axe porte quant à lui sur la caractérisation des particules d'hexolite, notamment en ce qui concerne leur sensibilité, leur taille et leur morphologie et les raisons qui ont conduit à de telles propriétés par rapport au comportement du spray
Nanodiamonds (NDs) are the subject of extensive research in biomedical, military, and quantum mechanics applications. To produce these NDs, the detonation of a RDX/TNT mixture, commonly referred to as hexolite, is frequently employed. However, to achieve NDs with high-performing physicochemical properties, it is essential to begin with finely divided hexolite particles and to ensure that the mixture is both intimate and homogeneous. In pursuit of this goal, the NS3E laboratory has developed a recrystallization process based on Spray Flash Evaporation (SFE). Despite this advancement, the influence of various operating conditions on the physicochemical characteristics of the resulting particles remains poorly understood. Gaining a deeper understanding of these influences would enable more precise control over the properties of the recrystallized particles. This thesis therefore aims to address these issues by employing in situ analytical techniques, such as shadowgraphy and Phase Doppler Particle Analysis (PDPA).The research is organized around two principal axes. The first focuses on an in-depth investigation of the physicochemical phenomena underlying the flash evaporation of a solvent (acetone) and examines how the presence of a solute (hexolite) affects the behavior of the acetone spray. The second axis centers on characterizing the resulting hexolite particles—specifically their sensitivity, size, and morphology—and elucidating the underlying reasons for these properties considering the spray’s behavior

Les effets anthropogéniques sur l’environnement posent un défi majeur pour l’industrie aéronautique. Des réglementations de plus en plus strictes et la nécessité de rendre le transport aérien durable orientent les recherches actuelles vers des systèmes propulsifs innovants. Dans ce contexte, Safran Helicopter Engines développe sa technologie brevetée de combustion giratoire (SCT), visant à améliorer les performances des moteurs d’hélicoptères. Déjà implémentée sur le moteur Arrano, cette technologie est davantage optimisée pour réduire significativement les émissions de NOx et de suies. Dans le cadre du programme européen LOOPS, deux nouveaux systèmes d’injection de carburant sont étudiés : l’un conçu pour un régime riche dans une chambre RQL, et l’autre pour une combustion pauvre. Cette thèse évalue expérimentalement ces systèmes à l’aide de diagnostics laser avancés, adaptés aux environnements réactifs à haute pression. Le banc HERON, développé au CORIA, permet d’analyser leurs performances de combustion et évaluer les émissions dans des conditions représentatives des moteurs d’hélicoptères : pressions de 8 à 14 bar, températures d’entrée d’air de 570 à 750 K, et richesses de 0,6 à 1,67. Des diagrammes de stabilité de flamme sont établis, suivis d’analyses des propriétés du spray liquide par PDPA (Phase Doppler Particle Anemometry). Les champs aérodynamiques sont mesurés en conditions réactive et non-réactive par PIV (Particle Imaging Velocimetry) ultra-rapide à 10 kHz. La structure des flammes est caractérisée par PLIF-OH, tandis que la PLIF-kérosène permet d’étudier l’évaporation du carburant en détectant les mono- et di- aromatiques. Les diagnostics couplés simultanément PLIF-NO, PLIF-OH et PLIF-kérosène corrèlent les structures des flammes, les distributions des phases liquide et vapeur, et les zones de formation de NO. De même manière, la PLII (Planar Laser-Induced Incandescence) couplé avec PLIF-OH, PLIF-kérosène permets d’analyser les mécanismes de formation et d’oxydation des suies. Des méthodes spécifiques déterminent des distributions 2D des concentrations de NO, OH et des fractions volumiques de suies. Les résultats montrent une flamme asymétrique pour l’injecteur riche, avec une efficacité de combustion élevé dans la partie supérieure grâce à une injection liquide augmenté localement. Malgré des richesses élevées, les niveaux de suies restent modérés, tandis que le NO se forme principalement près de la flamme, confirmant le mécanisme thermique de Zeldovich. L’injecteur en régime pauvre présente une structure de flamme typique des flammes swirlées stratifiées, malgré la légère asymétrique. Une meilleure évaporation du carburant y favorise une combustion plus efficace, réduisant la longueur de flamme et les NO, grâce à des températures de flamme plus basses. Cependant, des niveaux modérés de suies sont également observés malgré le régime pauvre. Les conditions opératoires influencent fortement les performances. À haute pression, l’atomisation du spray est accélérée, l’angle d’expansion du spray augmente, et les zones de recirculation interne sont renforcées, modifiant la structure des flammes. L’augmentation des émissions de suies par la haute pression est observée pour l’injecteur en régime riche, gardant une richesse constante sur l’ensemble des conditions testées, tandis que les niveaux de NO restent stables. Pour l’injecteur en régime pauvre, les conditions réactives avec une richesse minimale à haute pression atténuent les effets de la pression, stabilisant la production de suies tout en réduisant les concentrations de NO. Ces résultats mettent en évidence le potentiel des deux systèmes d’injection pour optimiser les performances tout en réduisant les émissions des futurs moteurs d’hélicoptères
Anthropogenic effects on the environment present a major challenge for the aeronautical industry. Increasingly stringent pollution regulations and the necessity for sustainable air transport are driving the nowadays research toward innovative propulsion systems. In this context, Safran Helicopter Engines is advancing its patented Spinning Combustion Technology (SCT), aimed at improving helicopter engine performance. Already implemented in the Arrano engine, SCT is now being refined to significantly reduce NOx and soot emissions. As part of the European LOOPS program, two novel fuel injection systems are under investigation: one operating in a rich combustion regime tailored for an RQL combustion chamber and the other designed for lean combustion. The scientific activity of this thesis focuses on the experimental characterization of these injection systems using state-of-the-art laser diagnostics optimized for high-pressure reactive environments. The HERON combustion facility at CORIA enables the analysis of combustion and pollutant performance under conditions representative of helicopter engines, with pressures from 8 to 14 bar, air inlet temperatures from 570 to 750 K, and equivalence ratios ranging from 0.6 to 1.67. Initial flame stability maps are established, followed by in-depth analyses of liquid spray properties using Phase Doppler Particle Anemometry (PDPA). High-speed Particle Imaging Velocimetry (PIV) captures aerodynamic fields under reactive and non-reactive conditions at 10 kHz. Flame structures are examined via OH-PLIF fluorescence imaging, while kerosene-PLIF evaluates liquid and vapor fuel distributions, particularly probing aromatic components in Jet A-1 kerosene. Furthermore, NO-PLIF imaging, combined with OH-PLIF and kerosene-PLIF, enables spatial correlations between flame structure, fuel distribution, and NO production zones. Soot formation and oxidation mechanisms are explored through Planar Laser-Induced Incandescence Imaging (PLII), integrated with OH-PLIF and kerosene-PLIF. Specific methods are developed to obtain 2D distributions of quantitative concentrations of NO, OH and soot volume fraction. Results reveal that the rich-burn injector produces an asymmetrical flame with enhanced upper-zone combustion efficiency due to locally intensified liquid fuel injection. Moderate soot levels are observed despite high equivalence ratios, while localized NO production, primarily near the flame, is attributed to the Zeldovich thermal mechanism. Conversely, the lean-burn injector forms a flame structure characteristic of stratified swirl flames, despite the minor asymmetry. Improved fuel evaporation leads to higher combustion efficiency, shorter flame lengths, and a reduction in NO formation, attributed to lower flame temperatures. In spite of the lean combustion conditions, moderate soot levels are measured for the second injector. Operating conditions strongly influence performance. Higher pressures accelerate spray atomization, increase spray expansion angles, and strengthen internal recirculation zones, reshaping flame structures. The increase in soot production at higher pressure is particularly demonstrated by the rich-burn injector due to constant equivalence ratios across all test conditions, while NO levels remain stable. For the lean-burn injector, leaner operation at elevated pressures moderates pressure effects, maintaining consistent soot levels and reducing NO concentrations. These findings highlight the potential of both injection systems for optimizing performance and reducing emissions in future helicopter engines

Abstract This study focused on the measurement of solid mass flux in the riser of a CFB cold pilot. The investigations were carried out using a Phase Doppler Particle Analyzer (PDPA). Inconsistencies in PDPA results were observed when investigating flows with high particle densities. It appears that the performance of the measuring technique was affected by the optical thickness of the measured medium, thus producing substantial overestimation of the global solid phase quantity (e.g., solid mass flux). To determine the origin of these inconsistencies, the measuring system was subjected to complete recalibration. It was found that in flows with high particle densities, noisy doppler signals tend to be split into several parts by the burst detector system, thus producing inconsistencies in the number of particles counted. The parameters associated with the splitting events were analyzed, and a post-processing algorithm was developed to limit PDPA measuring errors. The aim of the post-processing algorithm was to rebuild the data and to recover the original measurements. The reconstitution process was applied to solid mass flux measurements in a CFB cold pilot.

A Phase-Doppler-Particle-Analyzer (PDPA) was used to screen candidate water mist nozzles for use in a scaling validation aimed to allow scaled-down testing of water mist systems. A custom-designed iso-kinetic sampling probe (IKSP) was developed to independently measure water mist fluxes at the same locations where PDPA measurements were made. Measurements were taken at two elevations in selected full-cone water mist sprays. The water drop size was found to increase with radial distance from the spray centerline, while the mean drop velocity and drop concentration decrease with radial distance. Gross drop size distributions of water mist sprays were derived from local drop size distributions and water fluxes measured in two spray cross sections. It was found that, for the water mist sprays investigated in this study, both Rosin-Rammler and log-normal distributions are required to correlate the entire drop size spectrum. In general, the agreement between the mist fluxes measured with the PDPA and iso-kinetic sampling was within 7% near the spray centerline. The selected nozzles show appropriate intended scaling in terms of the drop size, nozzle discharge pressure, and water discharge rate.

Recent research on biofuels for power generation has typically focused on biodiesel because the biodiesel feedstrock, e.g., vegetable oil, poses significant combustion problems related to poor atomization. Existing injectors cannot effectively atomize high viscosity fuels such as vegetable oil. However, a new, novel flow-blurring (FB) injector concept has shown promise in overcoming the atomization problems. In this study, a FB injector is compared to a commercial air-blast (AB) injector operated with water at ambient conditions of temperature and pressure. Laser sheet visualization and Phase Doppler Particle Analyzer (PDPA) systems are used to obtain the spray characteristics for a range of air to liquid (ALR) ratios. Results show significant difference in distributions of Sauter Mean Diameters (SMDs), and mean and root-mean square axial velocity for the two injectors operated at a fixed ALR. In comparison to the AB injector, the FB injector produced spray with smaller SMDs, a smaller SMD range over the spray volume, higher RMS and mean axial velocities in the center region, and a compact spray with spray angle nearly independent of ALR. Results show that the FB injector is an effective way of atomizing liquids at relatively low ALRs compared to a traditional AB injector, without the additional pressure drop penalty.

Abstract Numerous practical applications exist where dispersed solid particles are transported within a turbulent accelerating or deceleration gaseous flow. The large density variation between phases creates the potential for significant differences in velocity known as slip. Flow over a backward facing step provides a well characterized, turbulent, decelerating flow useful for measuring the relative velocities of the solid and gaseous phases in order to determine velocity slip and particle drag. Numerous investigations have been conducted to determine the gas phase velocity in a backward facing step for both laminar and turbulent flows and therefore the gas phase flow is well known and documented. Furthermore, some studies have also been conducted to determine the velocity of various sizes of spherical particles in a backward facing step and compared with their corresponding gas phase velocities. Few, if any, velocity measurements have been made for non-spherical particles in a backward facing step. In this work, a Phase Doppler Particle Analyzer (PDPA) was used to measure gas and particle phase velocities in a backward facing step. The step produced a 2:1 increase in cross sectional area with a Reynolds number of 22,000 (based on step height) upstream of the step. Spherical particles of 1–10 μm with an average diameter of 4 μm were used to measure the gas phase velocity. At least three sizes in the range of 38–212 μm for four different particle shapes were studied. The shapes included spheres, flakes, gravel, and cylinders. Since the PDPA is not able to measure the size of the non-spherical particles, the particles were first separated into size bins and a technique was developed using the Photo Multiplier Tubes (PMT) gain to isolate the particles size of interest for each size measured. The same technique was also used to measure terminal velocities of particles in quiescent air. This paper will discuss the results of the measurement of the particles and show that for the gas phase velocity and spherical solid phase particles that the measurements were in good agreement with previous measurements in the literature. However, for the non-spherical particles it will be shown that the drag coefficients were an order of magnitude higher in turbulent flows when compared to the literature values which are based on particles moving through a still fluid. This information is valuable for modeling turbulent two-phase flows since most assumptions of the drag are based on correlations from empirical data with particles moving through still fluid.

In this work we used deep-molding manufacture of three kinds to fabricate micro pressure-swirl atomizers to promote their performance, and a Phase Doppler Particle Analyzer (PDPA) to measure the characteristic distributions of the spray flow field of these atomizers. The deep-molding techniques were X-ray LIGA process, ICP-LIGA process (inductive coupling plasma etching), and injection molding LIGA process. Parameters of atomizers examined here include configuration of flow channel, diameter of exit orifice, the ratio of diameters of swirl chamber and discharge orifice, and the thickness of atomizer. Experimental results showed that the manufacturing process combining injection molding with electroplating had large yields and that the technique is highly reliable; enable manufacture of an atomizer at small cost and great quality. Moreover, these microatomizers are assembled well with other components and be readily applied. The results of PDPA diagnosis further revealed that the spray features are related with the design parameters of atomizer dimensions.

Abstract A two-fluid atomizer has been frequently used in a wide range of industries for various purposes such as painting, cleaning particles and snow making. In particular, the manufacturing of advance semiconductors using sensitive devices such as organic light emitting diodes (OLED) and dynamic random access memory (DRAM), require high performance nozzle. The droplets sprayed with a high relative gas velocity are widely used for cleaning particles. In this paper, two-fluid atomizer is numerically studied according to four variables to confirm the effect on the atomizer performance. The numerical results using the discrete phase model (DPM) with several break-up models are compared with the experimental data measured by the phase doppler particle analyzer (PDPA). Design of experiment (DOE) and genetic algorithm (GA) were used to obtain design points, and conduct sensitivity analysis, respectively. The results showed that the WAVE model has a good agreement compared to the other models, and the orifice diameter is a crucial factor for this model to determine the performance of Weber number and pressure.

We propose a computationally tractable model for film formation and breakup based on data from experiments and direct numerical simulations. This work is a natural continuation of previous studies where primary atomization is modeled based on local flow information from a relatively low-resolution tracking of the liquid interface [1]. Sub-models for film formation are supported by direct numerical simulations obtained with the Refined Level Set Grid (RLSG) method [2]. The overall approach is validated by a carefully designed experiment [3], where the liquid jet is cross flow-atomized in a rectangular channel so that a film forms on the wall opposite to the injection orifice. The film eventually breaks up at the downstream exit of the channel. Comparisons with Phase Doppler Particle Analyzer (PDPA) data and with non-intrusive film thickness point measurements complete this study.

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 1 are re-examined and more in-depth physics is revealed. It is found that the location of optimum cooling effectiveness is coincided 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.

Abstract In order to understand the details of the mechanism of the occurrence of wetness loss between blade rows, the blades of an HP nuclear turbine were modeled in an atmospheric subsonic wind tunnel, and a flow field with wet loss was analyzed in its totality using a three-hole Pitot tube and Phase Doppler Particle Analyzer (PDPA) system. In the secondary flow loss region and the end wall loss region, a significant increase in pressure loss was confirmed under wet conditions. Analysis by measurement and the Eulerian-Lagrangian coupled solver showed that these loss increases can occur due to the agitation of water droplets and water films in the passage vortex or corner vortex. Finally, this report contains a breakdown of profile loss, thermodynamic loss and acceleration loss of the wet air flow through the sub-sonic blade row.

Particle size analysis is an essential analytical task in a large variety of processes of industrial and laboratorial relevance. Phase doppler anemometer (PDA) is one of well-established techniques allowing simultaneous measurement of velocity and size of particles, droplets, or bubbles in two-phase flows including spray atomization. The method is based upon the principle of light scattering interferometry. When a particle passes through the probe volume defined by the intersection of two laser beams, the phase of the light scattered by the particle carries information about the particle size, whereas its frequency provides the information of particle velocity. This research work has been devoted to the development of a one-dimensional PDA instrument by using He-Ne laser with wavelength of 632.8 nm and two detectors for measuring velocity and size distribution of water droplets generated by binary and ultrasonic nozzles. The calibration of the developed PDA with the transparent glass spheres of precisely known size was conducted before investigating the reliability and accuracy of the developed system by comparing the measurement results obtained from the developed with that of the commercial PDA instruments. It was found that the relative difference of the droplet mean velocity and diameter measured by the developed system were less than 15% and 25% respectively. These results demonstrate the potential of the PDA instrument developed in this work.