Phase Doppler Particle Analyzer Research Articles

Coupled droplet dynamics: Investigation of acoustic-spray interactions in a reacting flow field

Droplet dynamics in a self-excited thermoacoustic instability are not well understood due to the tight coupling of competing effects and difficulty in taking high-quality data. In this investigation, droplet data from a combustion instability is used to illustrate how a spray couples with a thermoacoustic instability. Commonly accepted ensemble averaging techniques such as the Sauter mean diameter (D32) is shown to be inadequate in describing the coupling phenomena, and instead, a new approach based on droplet surface area is used to characterize the spray. The present study extends literature concerning nonreacting acoustic-spray interactions and considers these in a fully self-excited instability. A lean direct injection (LDI) geometry is used at atmospheric pressure and phased averaged Phase Doppler Particle Analyzer (PDPA) measurements, acoustic pressure measurements, and OH* chemiluminescence images are taken to characterize the flow field. It is shown that while some of the trends found in nonreacting experiments apply to reacting systems, the mechanisms are notably different due to the presence of a flame. Flame response is shown to be important due to its influence on the evaporation of droplets.

Effect of liquid splattering on thermal performance of jets and sprays over plain and pillared surfaces

A comparative study of liquid jet and spray is explored over plain and pillared copper surfaces with coolant flow (water) ranging over 3000 < Re < 10500, and heat fluxes up to the critical heat flux limit. Liquid jets and sprays are hydrodynamically characterized using high-speed videography and the phase-Doppler particle analyzer system. The interaction of liquid jets and sprays with the respective metallic substrates is experimentally investigated and strong liquid splattering is observed over the pillared surfaces at higher coolant flow rates. The resulting splattering mass fraction is measured over a range of coolant flow rates and radial positions of the nozzle. Subsequently, the effect of splattering on heat transfer performance is compared for various heat flux conditions by measuring the steady-state surface temperature. Heat transfer coefficient is found to be a strong function of coolant flow rate, operating heat flux conditions, and splattered mass fraction. Significant differences are not seen in these quantities between the liquid jet and spray for a plain surface. However, spray cooling clearly shows superior heat transfer enhancement over a liquid jet for a pillared surface where the critical heat flux limit is significantly delayed. The apparent advantages of heat transfer performance enhancement with patterning of surfaces are not always guaranteed, and the design consideration must address the coolant interaction with it to ensure a net advantage, which may get diminished due to liquid splattering induced by the interaction of the coolant with the patterned surface.

Experiments on the breakup and evaporation of small droplets at high Weber number

Shock-driven multiphase mixing is present in numerous physical systems such as detonation-driven propulsion engines, liquid–vapor cloud explosions, and hypersonic flight droplet impacts. At the microscale, droplets experience deformation, breakup, and evaporation under extreme conditions (high Weber and Reynolds regimes). For small droplets, these phenomena are simultaneous and highly transient, making their interactions and interdependencies warrant further investigation. In this study, experiments are conducted in a shock tube facility to investigate these simultaneous droplet-scale phenomena. An interface consisting of small acetone droplets (⌀ 10–40 [μm]) is impulsively accelerated by a strong planar shock wave (Mach ∼2.09). The droplet size distribution is well-characterized in-situ utilizing a Phase Doppler Particle Analyzer (PDPA) and shadowgraphy. The development of child droplet clouds is captured through an ensemble of Mie scattering images. A simplified model is developed to interpret the experimental results, combining deformation, breakup, and evaporation models. The results indicate that the breakup of small droplets at high Weber numbers is likely dominated by the Rayleigh–Taylor (RT) mechanism, aligning with previous empirical models for low Weber numbers.

EFFERVESCENT SUSPENSION SPRAY IN A GASEOUS CROSSFLOW

A spray of suspension, forms mainly solid particles in a liquid phase from the atomization of two or multiphase flow, mainly solid particles in a liquid phase, and its transport phenomena by a gaseous crossflow have many natural and industrial applications. For example, injection of suspension jet in a high-speed flow is used in the emerging surface engineering process called suspension plasma spray. Typically, submicron ceramic oxide particles are mixed with water or ethanol to form a suspension that is injected in a plasma plume using different types of injectors. Injection parameters such as the type of injector and momentum flux influence the size, velocity, and trajectory of suspension droplets in the plasma and the microstructure of the deposited coatings. Using an effervescent atomizer, due to its capability in transporting flows with various rheological properties is promising for injection of suspension into the gaseous crossflow. In this study, an effervescent atomizer was employed to introduce a suspension radially into the flow of gas at room temperature. The spray of suspensions with different concentrations of glass particles in water was investigated in the crossflow by phase Doppler particle analyzer. The results were validated and supported by studying the spray by shadowgraph and light diffraction techniques. The results of this study provide a better understanding of the suspension spray generated by an effervescent atomizer in a crossflow configuration. It was found that the solid concentration of the suspension (up 10 wt.&amp;#37;) causes a slight decrease in size and brings the penetration of the suspension droplets in the gas flow.

Spray characterization in a multi-jet airblast injector with swirling air crossflow

Experimental spray characterization in a multi-jet airblast injector with swirling crossflow of air is the goal of the present work. The current injector allows radial injection of six liquid jets from a central hub into swirling and crossflowing air into the annular region around the hub. In the present study, three different aspects related to jet-in-crossflow are concurrently addressed viz. air flow confinement, air swirl and simultaneous atomization of multiple liquid jets. Such key features have been rarely reported in the past in spite of their relevance to practical injectors such as in Lean Premixed Prevaporized (LPP) gas turbine combustors. The spray structure and spatial distribution of droplets are visualized at different cross-sectional planes in the spray by application of the Laser Sheet Imaging (LSI) technique. The Droplet size, three components of droplet velocities and local liquid mass flux are measured at different axial and radial locations using the Phase Doppler Particle Analyzer (PDPA) technique. The injector is operated over a wide range of aerodynamic Weber number (Weg) of the liquid jets (Weg = 57 – 430). The physics behind the spatial evolution of characteristic droplet size is analyzed by estimating the droplet Weber number and the probability of droplet coalescence. The plume-to-plume interaction, subsequent to droplet generation from the primary atomization of adjacent liquid jets, is found to contribute to the variation of droplet size in the current injector. The influence of Weg on the evolution of spray characteristics is investigated in detail.

Experimental study of the spray characteristics of twin-fluid atomization: Focusing on the annular flow regime

The characteristics of twin-fluid atomization operating in the annular flow regime were studied experimentally under various gas-to-liquid ratios (GLRs) and injection pressures. The macroscopic morphology of the spray was obtained by shadowgraph, while the droplet size and velocity were measured using a phase-Doppler particle analyzer technique. It was found that the spray cone angle increases almost linearly with the GLR, and the axial distance required for droplet coalescence to outweigh the breakup decreases with increasing GLR. The Sauter mean diameter (SMD) first decreases and then increases along the axial direction due to the competition between turbulent breakup and droplet coalescence. The droplet size follows a lognormal distribution; the droplet velocity distribution is closer to a lognormal distribution under large GLRs, while it follows normal distribution with GLR = 3%. Regarding the radial distribution, low GLRs (3% and 5%) lead to a bimodal spatial velocity distribution, while for large GLRs, the droplet velocity decreases monotonically toward the far field. The spray tends to become more stable with increasing GLR and injection pressure Pinj, whereas the SMD increases with increasing Pinj. The underlying atomization mechanism in a twin-fluid injector in the annular flow state can be regarded as the disintegration of the initial liquid sheet by longitudinal Kelvin–Helmholtz instability followed by transverse Rayleigh–Taylor instability, which yields a direct proportionality of the droplet size to the initial liquid sheet thickness ΔL. Subsequently, for high Pinj, the gas core shrinks and ΔL increases, which results in an increased SMD but enhanced atomization efficiency ΔL/SMD.

Flow Field Measurement and Display Technology Based on Hand-Held Probe

Measuring flow field information in wind tunnel is an indispensable basic condition for aerodynamic research. Traditional measuring equipments include phase Doppler particle analyzer, hot wire anemometer, particle image velocimeter, etc. Particle image velocimeter can visualize the flow field, but its installation and debugging are complicated. To obtain flow field information quickly and realize visualization, a kind of technology based on hand-held probe is designed. The velocity of the flow field is calculated by the probe, and the position and attitude information of the probe is obtained by a kind of visual measurement system (Optotrak system), The spatial velocity distribution is fused with the position and attitude information of the probe, and then the flow field in the test area is graphically displayed by interpolation with mathematical tools. By using this technique to carry out test in wind tunnels, taking segment of the airfoil as the test object, and the dynamic measurement of the probe at the rear of the airfoil, the complex vortical flow generated by segment of the airfoil is successfully plotted. The test result shows the device used in this technology is simple in structure and flexible in use and can quickly acquire flow field information, which provides a new method and idea for flow field measurement.

Investigation on fine particle agglomeration and separation promoted by different bluff bodies

Using particle agglomeration to help separate fine particles receives increasing attention in air purification processes. Recent studies suggested that enhanced turbulence using bluff bodies can significantly improve the agglomeration of fine particles. However, since micron-sized particles are difficult to measure, the current exploration of flow fields and particles is mainly based on simulations and lacks experimental validation. This paper innovatively used a phase doppler particle analyzer to measure the flow field in terms of velocity, streamline and turbulence intensity, as well as particle size and number concentration in an agglomeration chamber with a bluff body located at the center. Different shaped bluff bodies were also considered. It was found that low-velocity recirculation region with different shapes appeared in the wake, and vortex flow with special structures were observed. From the perspective of particles, the development of the flow field generated by a single bluff body effectively caused an increase in particle size and a decrease in particle number, which is because that the flow field promotes collisional agglomeration. More specifically, for V-structure bluff body, the particle size improved from 6 μm to a maximum of 13 μm and the particle number concentration decreased by 8 times. The agglomeration efficiency for PM2.5 and PM10 reached 89.06% and 87.38% respectively. Furthermore, by analyzing the velocity of different sized particles, it was reasonable to assume that different sized particles appeared to have velocity differences due to recirculating vortex flow, while the overlapping trajectories of positive and negative moving particles was mainly responsible for the collision probability enhancement. This paper presents new insights into particle agglomeration separation for this environment-friendly and low-cost technology.

Impacts of preferential vaporization on flashback behaviors of multi-component liquid fuels

Liquid transportation fuels are composed of a wide range of molecular structures and weights, therefore exhibiting a relatively large distillation temperature range. When fuel chemical properties change along with the distillation temperature curve, preferential vaporization effects could play a role in near-limit combustion behaviors. The objective of this study is to experimentally evaluate the role of preferential vaporization on flame flashback behaviors. A unique spray burner is developed to control the extent of fuel spray vaporization by adjusting flow rates and/or the spray injection location from the burner exit. Spray characteristics are comprehensively determined using Phase Doppler Particle Analyzer. Two binary component mixtures are formulated (n-octane/iso-cetane and iso-octane/n-hexadecane) to exhibit common combustion behaviors in the fully vaporized condition but have considerably different preferential vaporization characteristics. Identical flashback behaviors of two mixtures are observed for fully pre-vaporized conditions by setting the burner temperature at 700 K, including both propagation- and ignition-driven flashback behaviors. Partially vaporized conditions are investigated at two global equivalence ratios (1.0 and 1.4) by setting the burner temperature at 450 K. The flashback behaviors for both global equivalence ratio conditions are found to be affected by the preferential vaporization characteristics represented by laminar flame speeds of the vaporized fuel mixture composition. The relative significance of local flow perturbation induced by instantaneous fuel droplet evaporation near the flame surface has been also investigated by analyzing planar laser-induced fluorescence images, as well as considering the changes of Markstein length with the extent of fuel vaporization. Finally, the relative contributions of local laminar flame speed representing local fuel vapor deposit, local flow perturbation, and preferential vaporization are evaluated through feature sensitivity analyses.

Experimental Study on a New Combined Gas–Liquid Separator

Gas–liquid separation at natural gas wellheads has always been a key technical problem in the fields of natural gas transportation and storage. Developing a gas–liquid separation device that is both universal and highly efficient is the current challenge. A new type of combined gas–liquid separation device was designed in this study, and the efficiency of the separator was studied using a laser Doppler anemometer and phase Doppler particle analyzer at a flow rate of 10–60 Nm3/h. The results showed that the separation efficiency of the combined separator was above 95% at each experimental flow rate, verifying the strong applicability of the combined separator. Moreover, the separation efficiency was as high as 99% at the flow rates of 10 and 60 Nm3/h, thereby realizing efficient separation. This study is significant to the development of gas–liquid separation devices.

Validation of a Two-Phase CFD Air/Mist Film Cooling Model With Experimental Details—Part I: Development of an Experimental Test Facility

Abstract 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 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 of about 7 µm (mist) is injected into the cooling air to enhance the cooling performance. One key feature in understanding mist cooling is the ability to capture droplet information. In order to thoroughly investigate a two-phase flow, experimental and computational studies are needed. 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 an air/mist film cooling study with both heat transfer and droplet measurements. A wind tunnel system and test facilities are built. A phase doppler particle analyzer (PDPA) system is employed to measure the two-phase flow characteristics, including droplet size, droplet dynamics, velocity, and turbulence. An 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 an 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 are presented.

Influence of Mass Flow Rate on the Atomization Characteristics of Screw Conveyor Swirl Injectors

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.

Response of PDPA to optical materials and thickness of test section window

The objective of this work is to study the response of phase calibrated Phase Doppler Particle Analyser (PDPA) in presence of various arrangement schemes of optical materials and thickness of the test section window. The standard “Mono sized droplet generator” (MDG) has been used as a source of mono sized droplets stream. Receiving optics collection angle, Bandpass filter, and Photo-multiplier tube (PMT) voltage has been optimized using a known mono-size droplet stream. The results indicate that maximum perturbation in response occurs in presence of 17.5 mm Plexiglas thickness. The reduction in 97% of data rate is noted in Scheme B, whereas no data has been observed for the case of Scheme D. The maximum data rate reduction of 15.9% is observed in 17.5 mm Plexiglas of Scheme D for aligned PDPA subsystem. The results of the experiment also reveal that when unpolished glass is used instead of Plexiglas, the maximum date rate reduction is 70% for 17.5 mm for Scheme D whereas when subsystems are aligned then maximum loss of data rate is 11.3%, which are significantly higher to losses due to Plexiglas.

Experimental investigation on the effects of fuel–air mixture temperature on the air-assisted kerosene spray characteristics

The air-assisted fuel injection (AAFI) system may be installed in the spark ignition aviation piston engine for the atomization of heavy fuels. However, studies on the effects of fuel–air mixture temperature on the spray characteristics are insufficient, which affects the design of AAFI engines. This study experimentally investigates the air-assisted kerosene spray characteristics over a wide range of fuel–air mixture temperatures (253–353 K). A high-speed backlit imaging technique was employed to monitor the temporal and spatial evolution of the spray, and a phase Doppler particle analyzer was used to measure the diameter and velocity of droplets. The results indicate that at low temperatures, room temperature, and high temperatures, the spray adopts a slender cylindrical, fusiform, and conical shape, respectively. As the fuel–air mixture temperature increases from 253 K to 353 K, the spray penetration and width first increase and then decrease. Moreover, the diameter and velocity of the droplets follow log-normal distributions. In particular, as the fuel–air mixture temperature increases, the probability that a droplet’s diameter is within the range of 0–10 μm increases from 34.7 % (253 K) to 59.8 % (353 K), while the probability that a droplet’s velocity is within the range of 0–10 m/s decreases from 44.1% (253 K) to 38.1% (273 K), and then increases to 57.5 % (353 K). Accordingly, as the fuel–air mixture temperature rises, the Sauter mean diameter of the droplets decreases, while the mass-average velocity of the droplets first increases and then decreases. The proportion of droplets with Stokes numbers less than 1 is positively correlated with the fuel–air mixture temperature, thus implying that droplets at high temperatures tend to follow the airflow, whereas droplets at low temperatures tend to move along their initial trajectories.

On the evolution of n-octane atomization characteristics using an air-assisted intermittent spray method

In this study, droplet size and velocity of an intermittent air-assisted n-octane spray were measured using a Phase Doppler Particle Analyzer, focusing on the effect of operating parameters on time-resolved droplet behavior and local gas flow characteristics. An electro-magnetically actuated air-assisted injector, which features internal gas-liquid premixing upstream and releasing through an annular nozzle, was used to generate intermittent sprays. The sampling time equalization method is employed to examine the time-resolved spray microscopic characteristics with various injection control parameters and spatial sampling positions. The droplet diameter range is found to be generally independent of air injection duration and sampling time while droplet velocity is correlated with these two parameters. A large air injection duration tends to accelerate droplets in the late spray period and leads to an increasing normalized gas flow velocity. Estimation of local gas flow turbulence intensity indicates a prominent radial sampling position dependence due to the rapid attenuation of the gas flow velocity away from the spray axis. A noteworthy finding for this intermittent air-assisted spray is that at 30 mm from the nozzle outlet, the zero point of droplet-gas mean slip velocity shifts toward the nozzle with sampling time. The time bin size employed to divide the sampling time has been proved to exert no influence on the statistical results of transient spray microscopic characteristics.

Atomization and droplet dynamics of a gas-liquid two-phase jet under different mass loading ratios

Atomization and droplet dynamics of a gas-liquid two-phase jet were investigated experimentally, with the particular interest in the influence of mass loading ratio (the ratio of droplet mass flow rate to the carrier-phase mass flow rate, ranging from 0.60 to 3.23) on the jet atomization. Droplet size and velocity at selected positions were obtained by employing Phase Doppler Particle Analyzer (PDPA), combined with backlit illumination for spray visualization. Droplet transport characteristics are substantially influenced by the mass load ratio. Characterization of the local gas flow velocity by using droplets smaller than 5μm reveals a highly turbulent jet with Reynolds number exceeding 5×104, implying the possibility of droplet turbulent breakup. Critical equilibrium location xcrit between droplet breakup and coalescence is close to the nozzle exit and a positive correlation is found between mass loading ratio and xcrit. Exaltation of mass loading ratio increases the droplet size and decreases the velocity. Quantification of droplet collision outcome indicates a relatively high probability of coalescence, which explicates the downstream increasing of measured droplet Sauter mean diameter along the centerline of far-field jet.

An Estimation of the Backscattering Strength of Artificial Bubbles Using an Acoustic Doppler Current Profiler.

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).

Spray dynamics and atomization characteristics of multi-hole GDI injectors under flash boiling conditions

• About 100 points on the 30 mm plane below the injector was measured by using PDPA. • The effect of hole angle and air entrainment on spray atomization was analyzed. • The atomization uniformity of flash boiling spray in the space was improved. In the gasoline direct injection (GDI) engine, spray atomization contributes significantly to the formation of a uniform mixture and the effective combustion of the spray. In this study, a phase Doppler particle analyzer (PDPA) was used to measure the spray atomization characteristics of two five-hole GDI injectors with different hole arrangements under subcooled and mild flash-boiling conditions (superheated degree = 20 °C). Based on the spray patterns of the two injectors on a plane 30 mm below the injector tip, the two injectors were called triangle-patterned and pentagon-patterned injectors. A total of 100 measuring points were selected on a plane 30 mm below the injector tip, and the spray droplet diameter and velocity at these points were measured to understand the overall atomization characteristics of the spray in space. The experimental results indicated that as the spray transitioned from subcooled to flash boiling conditions, a polarization phenomenon occurred in which the velocity in the center of the plume increased and the velocity in the peripheral region of the plume decreased. However, the spray droplet diameter significantly decreased under flash-boiling conditions. The average Sauter mean diameter (SMD) of the two injectors on a plane 30 mm below the injector tip decreased by approximately 4 μm, and the uniformity of the spatial distribution of the SMD also increased. Compared with the triangle-patterned injector (injector A), the average SMD of the pentagon-patterned injector (injector B) was slightly smaller; this was attributed to the stronger air entrainment inside the spray and the enhanced air flow caused by the larger plume spacing of the pentagon-patterned injector.

Deposition law of flat fan nozzle for pesticide application in horticultural plants

Pesticide spraying is to protect the plants with adequate target coverage and a minimum of off-target drift. Understanding the spatial distribution characteristics of spray droplets is essential for regulating pesticide deposition, in order to investigate the relationship between the two at the mechanistic level and provide an accurate basis for nozzle selection, this study compared the characteristics of the atomization field under different pressures, angles, and flow rate types by phase Doppler particle analyzer (PDPA), the unit spatial density of droplet was used as a link to explore the internal mechanism that affects the deposition efficiency by constructing a transport model and conducting actual spraying experiments. The results showed that the cumulative distribution of droplet diameter could be perfectly fitted by the Rosin-Rammler correlation, and the deposition efficiency had a strong correlation with the peak particle size range. For strawberry and chrysanthemum plants, the optimal droplet deposition particle size ranges were 250-270 μm and 240-260 μm, respectively. This article explained the deposition efficiency from a single droplet dynamics mechanism and deposition of droplet cloud, which provided a new research idea for the study of precision plant protection. Keywords: pesticide transport, deposition, atomization field, PDPA DOI: 10.25165/j.ijabe.20221504.7502 Citation: Wu X Y, Jia Y L, Luo B, Chen C C, Wang Y X, Kang F, et al. Deposition law of flat fan nozzle for pesticide application in horticultural plants. Int J Agric & Biol Eng, 2022; 15(4): 27–38.

이류체 노즐 분무 해석을 위한 분열모델 상수 최적화 연구

Over the past few decades, investigations on a dual-fluid nozzle for a wafer cleaning process have been actively conducted. Especially, developments of the dual-fluid nozzle using a numerical analysis is attracting many researchers. Breakup model constants, however, must be determined precisely to perform the numerical analysis of the dual-fluid nozzle. To select the suitable breakup model constants, validation study with experiments should be carried out. In this paper, optimization using a multi-objective genetic algorithm (MOGA) was conducted to determine the most suitable breakup model constants to use the discrete phase model (DPM) during the numerical analysis. Then, experimental results using a phase doppler particle analyzer (PDPA) were compared to validate the numerical analysis. For the design parameters, the sheet, ligament, droplet diameter, and breakup time constant, were selected. Also, the Sauther mean diameter (SMD) and mean velocity of the droplets were considered as objective functions. Consequently, the most suitable values of the sheet ligament, droplet diameter and breakup time constants were predicted to be 1.8645, 10.142, 1.4922, and 23.101, respectively.