Sampling Techniques to Determine Droplet Size Spectrum for Fan Nozzles

2009 ◽  
pp. 238-238-8
Author(s):  
RD Mitchel ◽  
LF Bouse ◽  
LE Bode
Keyword(s):  
Droplet Size ◽  
Size Spectrum ◽  
Sampling Techniques

scholarly journals Broadening of Cloud Droplet Spectra through Eddy Hopping: Turbulent Entraining Parcel Simulations

2018 ◽  
Vol 75 (10) ◽  
pp. 3365-3379 ◽  
Author(s):  
Gustavo C. Abade ◽  
Wojciech W. Grabowski ◽  
Hanna Pawlowska
Keyword(s):  
Droplet Size ◽  
Turbulent Mixing ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Cloud Microphysics ◽  
Droplet Growth ◽  
Size Spectrum ◽  
Entrainment Rate ◽  
The Mean ◽  
The Impact

This paper discusses the effects of cloud turbulence, turbulent entrainment, and entrained cloud condensation nuclei (CCN) activation on the evolution of the cloud droplet size spectrum. We simulate an ensemble of idealized turbulent cloud parcels that are subject to entrainment events modeled as a random process. Entrainment events, subsequent turbulent mixing inside the parcel, supersaturation fluctuations, and the resulting stochastic droplet activation and growth by condensation are simulated using a Monte Carlo scheme. Quantities characterizing the turbulence intensity, entrainment rate, CCN concentration, and the mean fraction of environmental air entrained in an event are all specified as independent external parameters. Cloud microphysics is described by applying Lagrangian particles, the so-called superdroplets. These are either unactivated CCN or cloud droplets that grow from activated CCN. The model accounts for the addition of environmental CCN into the cloud by entraining eddies at the cloud edge. Turbulent mixing of the entrained dry air with cloudy air is described using the classical linear relaxation to the mean model. We show that turbulence plays an important role in aiding entrained CCN to activate, and thus broadening the droplet size distribution. These findings are consistent with previous large-eddy simulations (LESs) that consider the impact of variable droplet growth histories on the droplet size spectra in small cumuli. The scheme developed in this work is ready to be used as a stochastic subgrid-scale scheme in LESs of natural clouds.

scholarly journals Model based decision support system of operating settings for MMAT nozzles

2016 ◽  
Vol 56 (2) ◽  
pp. 178-185 ◽  
Author(s):  
Bradley Keith Fritz ◽  
Zbigniew Czaczyk ◽  
Wesley Clint Hoffmann
Keyword(s):  
Decision Support ◽  
Experimental Design ◽  
Decision Support System ◽  
Droplet Size ◽  
Flow Rate ◽  
Support System ◽  
Computational Models ◽  
Ease Of Use ◽  
Size Spectrum ◽  
Orifice Size

Abstract Droplet size, which is affected by nozzle type, nozzle setups and operation, and spray solution, is one of the most critical factors influencing spray performance, environment pollution, food safety, and must be considered as part of any application scenario. Characterizing spray nozzles can be a timely and expensive proposition if the entire operational space (all combinations of spray pressure and orifice size, what influence flow rate) is to be evaluated. This research proposes a structured, experimental design that allows for the development of computational models for droplet size based on any combination of a nozzle’s potential operational settings. The developed droplet size determination model can be used as Decision Support System (DSS) for precise selection of sprayer working parameters to adapt to local field scenarios. Five nozzle types (designs) were evaluated across their complete range of orifice size (flow rate*) and spray pressures using a response surface experimental design. Several of the models showed high level fits of the modeled to the measured data while several did not as a result of the lack of significant effect from either orifice size (flow rate*) or spray pressure. The computational models were integrated into a spreadsheet based user interface for ease of use. The proposed experimental design provides for efficient nozzle evaluations and development of computational models that allow for the determination of droplet size spectrum and spraying classification for any combination of a given nozzle’s operating settings. The proposed DSS will allow for the ready assessment and modification of a sprayers performance based on the operational settings, to ensure the application is made following recommendations in plant protection products (PPP) labels.

scholarly journals Broadening of Cloud Droplet Size Spectra by Stochastic Condensation: Effects of Mean Updraft Velocity and CCN Activation

2018 ◽  
Vol 75 (2) ◽  
pp. 451-467 ◽  
Author(s):  
Gaetano Sardina ◽  
Stéphane Poulain ◽  
Luca Brandt ◽  
Rodrigo Caballero
Keyword(s):  
Chemical Composition ◽  
Droplet Size ◽  
Isotropic Turbulence ◽  
Cloud Condensation Nuclei ◽  
Collision Probability ◽  
Droplet Radius ◽  
Droplet Growth ◽  
Size Spectrum ◽  
Similar Reduction ◽  
Size Spectra

Abstract The authors study the condensational growth of cloud droplets in homogeneous isotropic turbulence by means of a large-eddy simulation (LES) approach. The authors investigate the role of a mean updraft velocity and of the chemical composition of the cloud condensation nuclei (CCN) on droplet growth. The results show that a mean constant updraft velocity superimposed onto a turbulent field reduces the broadening of the droplet size spectra induced by the turbulent fluctuations alone. Extending the authors’ previous results regarding stochastic condensation, the authors introduce a new theoretical estimation of the droplet size spectrum broadening that accounts for this updraft velocity effect. A similar reduction of the spectra broadening is observed when the droplets reach their critical size, which depends on the chemical composition of CCN. The analysis of the square of the droplet radius distribution, proportional to the droplet surface, shows that for large particles the distribution is purely Gaussian, while it becomes strongly non-Gaussian for smaller particles, with the left tail characterized by a peak around the haze activation radius. This kind of distribution can significantly affect the later stages of the droplet growth involving turbulent collisions, since the collision probability kernel depends on the droplet size, implying the need for new specific closure models to capture this effect.

scholarly journals BLADE ANGLE EFFECT ON DROPLET SIZE SPECTRUM OF ROTARY ATOMIZERS USED IN BRAZIL

2016 ◽  
Vol 36 (6) ◽  
pp. 1118-1125 ◽  
Author(s):  
Fernando K. Carvalho ◽  
Ulisses R. Antuniassi ◽  
Rodolfo G. Chechetto ◽  
Alisson A. B. Mota ◽  
Greg R. Kruger
Keyword(s):  
Droplet Size ◽  
Size Spectrum ◽  
Blade Angle ◽  
Angle Effect

scholarly journals Spray volume distribution pattern and droplet size spectrum from ceramic nozzles

2018 ◽  
Vol 22 (11) ◽  
pp. 804-809
Author(s):  
Mateus P. Massola ◽  
Vandoir Holtz ◽  
Marcos P. de O. Martins ◽  
Anderson da S. Umbelino ◽  
Elton F. dos Reis
Keyword(s):  
Experimental Design ◽  
Distribution Pattern ◽  
Droplet Size ◽  
Size Spectrum ◽  
Target Coverage ◽  
Volume Distribution ◽  
Working Pressure ◽  
Median Diameter ◽  
Spray Volume ◽  
Test Table

ABSTRACT Droplet size spectrum and uniformity of spray volume distribution are important parameters for selecting spray nozzles. The objective of this study was to evaluate the average spray volume distribution and droplet size spectrum from ceramic nozzles. The spray volume distribution pattern was evaluated on a test table for hydraulic spray nozzles using spray heights of 0.4, 0.5, 0.6, 0.7, and 0.8 m, and working pressures of 500, 600, and 700 kPa. Computer simulations were used to analyze the spray volume distribution using arrangements of bar heights, working pressures, and spacing between spray nozzles in a bar of 12 m. The droplet size spectrum from the spray nozzles was evaluated using a randomized complete experimental design in a 2 × 3 split-plot arrangement consisting of two types of nozzles (ATR-1.0, and TVI-800075) and three working pressures (500, 600, and 700 kPa), with four replications. The uniformity of spray volume distribution was improved when using ATR-1.0 spray nozzles spaced 0.4 or 0.6 m apart, regardless of the working pressure. Regarding the droplet size spectrum, the volume median diameter decreased with increasing the working pressure for both types of nozzles, reaching 210 μm (ATR-1.0) and 483 μm (TVI-800075). Contrastingly, the percentage of droplets with diameter smaller than 100 μm increased with increasing working pressure; the target coverage presented the same trend, with 8.4% of coverage when using ATR nozzles with working pressure of 700 kPa.

scholarly journals Optimizing Overhead Irrigation Droplet Size for Six Mississippi Soils

Agronomy ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 574 ◽  
Author(s):  
J. Connor Ferguson ◽  
L. Jason Krutz ◽  
Justin S. Calhoun ◽  
Drew M. Gholson ◽  
Luke H. Merritt ◽  
...  
Keyword(s):  
Droplet Size ◽  
Soil Type ◽  
Crop Production ◽  
Water Infiltration ◽  
Size Spectrum ◽  
Total Water ◽  
Rainfall Simulator ◽  
Irrigation Water Use ◽  
Overhead Irrigation ◽  
Droplet Sizes

Optimizing overhead irrigation practices will ensure that water loss is minimized, and each unit of water is used most effectively by the crop. In order to optimize overhead irrigation setup, a study was conducted over two years in Mississippi to quantify the optimal overhead irrigation duration and intensity for six soil types commonly found in row-crop production regions in the state. Each soil type was transferred to containers and measured for total water infiltration and water infiltration over time using a two-nozzle rainfall simulator in a track sprayer. The rainfall simulator was calibrated to apply 2.1 mm of water per minute. The rainfall simulator ran on a 2.4 m track for 90 s, with 3.2 mm total water applied during that time. After the 90 s overhead irrigation event, each container was undisturbed for 150 s and assessed for irrigation penetration through the soil profile. Commercially available irrigation nozzles were measured for droplet size spectrum. Results showed that across soil type, organic matter was the primary factor affecting water infiltration through the profile, followed by soil texture. Irrigation nozzle volumetric median droplet sizes ranged from 327 µm to 904 µm. The results will improve overhead irrigation setup in Mississippi, improving irrigation water use efficiency and reducing losses from soil erosion over the application of water and reduced crop yield.

scholarly journals A continuous spectral aerosol-droplet microphysics model

2011 ◽  
Vol 11 (23) ◽  
pp. 12297-12316 ◽  
Author(s):  
Z. J. Lebo ◽  
J. H. Seinfeld
Keyword(s):  
Droplet Size ◽  
Wrf Model ◽  
Grid Cell ◽  
Droplet Size Distribution ◽  
Mass Conservation ◽  
Size Spectrum ◽  
Cloud Droplets ◽  
Microphysics Scheme ◽  
Aerosol Droplet ◽  
Bin Microphysics

Abstract. A two-dimensional (2-D) continuous spectral aerosol-droplet microphysics model is presented and implemented into the Weather Research and Forecasting (WRF) model for large-eddy simulations (LES) of warm clouds. Activation and regeneration of aerosols are treated explicitly in the calculation of condensation/evaporation. The model includes a 2-D spectrum that encompasses wet aerosol particles (i.e., haze droplets), cloud droplets, and drizzle droplets in a continuous and consistent manner and allows for the explicit tracking of aerosol size within cloud droplets due to collision-coalescence. The system of differential equations describing condensation/evaporation (i.e., mass conservation and energy conservation) is solved simultaneously within each grid cell. The model is demonstrated by simulating a marine stratocumulus deck for two different aerosol loadings (100 and 500 cm−3), and comparison with the more traditional microphysics modeling approaches (both 1-D bin and bulk schemes) is evaluated. The simulations suggest that in a 1-D bin microphysics scheme, without regeneration, too few particles are produced and hence the mode of the droplet size spectrum occurs at a larger size relative to the 2-D bin model results. Moreover, with regeneration, the 1-D scheme produces too many small droplets and thus shifts the mode toward smaller sizes. These large shifts in the droplet size distribution can potentially have significant effects on the efficiency of the collision-coalescence process, fall speeds, and ultimately precipitation.

scholarly journals Evaluation of Aerial Spray Technologies for Adult Mosquito Control Applications

2013 ◽  
Vol 53 (3) ◽  
pp. 222-229 ◽  
Author(s):  
Wesley Clint Hoffmann ◽  
Bradley Keith Fritz ◽  
Muhammad Farooq ◽  
Todd William Walker ◽  
Zbigniew Czaczyk ◽  
...  
Keyword(s):  
High Pressure ◽  
Wind Tunnel ◽  
Vector Control ◽  
Droplet Size ◽  
High Speed ◽  
Laser Diffraction ◽  
Operating Conditions ◽  
Adult Mosquito ◽  
Size Spectrum ◽  
Spray Droplet

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

scholarly journals Large-Eddy Simulations of Trade Wind Cumuli Using Particle-Based Microphysics with Monte Carlo Coalescence

2013 ◽  
Vol 70 (9) ◽  
pp. 2768-2777 ◽  
Author(s):  
Sylwester Arabas ◽  
Shin-ichiro Shima
Keyword(s):  
Monte Carlo ◽  
Droplet Size ◽  
Cloud Condensation Nuclei ◽  
Cloud Droplet ◽  
Large Eddy Simulations ◽  
Trade Wind ◽  
Type Model ◽  
Size Spectrum ◽  
Large Eddy ◽  
Condensational Growth

Abstract A series of simulations employing the superdroplet method (SDM) for representing aerosol, cloud, and rain microphysics in large-eddy simulations (LES) is discussed. The particle-based formulation treats all particles in the same way, subjecting them to condensational growth and evaporation, transport of the particles by the flow, gravitational settling, and collisional growth. SDM features a Monte Carlo–type numerical scheme for representing the collision and coalescence process. All processes combined cover representation of cloud condensation nuclei (CCN) activation, drizzle formation by autoconversion, accretion of cloud droplets, self-collection of raindrops, and precipitation, including aerosol wet deposition. The model setup used in the study is based on observations from the Rain in Cumulus over the Ocean (RICO) field project. Cloud and rain droplet size spectra obtained in the simulations are discussed in context of previously published analyses of aircraft observations carried out during RICO. The analysis covers height-resolved statistics of simulated cloud microphysical parameters such as droplet number concentration, effective radius, and parameters describing the width of the cloud droplet size spectrum. A reasonable agreement with measurements is found for several of the discussed parameters. The sensitivity of the results to the grid resolution of the LES, as well as to the sampling density of the probabilistic Monte Carlo–type model, is explored.

A 2D Simulation Method for Computing Droplet Size Spectrum During the Atomization of High-Speed Liquid Jets

2004 ◽  
Author(s):  
Gian Marco Bianchi ◽  
Piero Pelloni ◽  
Stefano Toninel ◽  
Davide Paganelli ◽  
Daniele Suzzi
Keyword(s):  
Sensitivity Analysis ◽  
Stability Analysis ◽  
Linear Stability ◽  
Droplet Size ◽  
Linear Stability Analysis ◽  
High Speed ◽  
Simulation Method ◽  
Droplet Formation ◽  
Size Spectrum ◽  
Computational Domain

Based on both experimental observations and available numerical methods, an innovative 2D approach for determining droplet size during the atomization process has been developed. Based on experimental evidences (see [1] and [2]) atomization of turbulent high speed jets is assumed to occur in a two stage process: ligaments detachment and droplets formation. The simulation method here proposed wants to take the advantages typical of the two most effective methods in spray investigation. It joins LES (i.e Large Eddy Simulations) approach and Linear Stability Analysis: the first one is used to solve the liquid-air fluid dynamics interaction and in particular the instabilities leading to ligament formation. The second one is finally adopted to compute the droplet size spectrum from ligament break-up. Therefore dynamics of ligament formation is directly computed while droplet formation is modelled by using a Linear Stability Analysis. The numerical simulation adopts a VOF (i.e. Volume of Fluid) method to track liquid-gas interface. Turbulence effects on liquid surface are accounted for by adding a turbulent flow field at the nozzle exit which represents a part of the boundary condition of the computational domain. A physical criterion is then applied to detach ligaments from liquid jet surface which will reduce in diameter during simulation. The droplet formation is then computed by applying the linear stability analysis to the ligaments, assumed being circular and subject to circulation. An extensive validation and sensitivity analysis has been carried out in order to assess method advantages and limits. The experimental results of Wu et al. [3] and Horoyasu et al. [4] were used as test cases. A sensitivity analysis has been performed under typical HSDI Diesel engine injection conditions. The method proved to exhibit promising attitude in the reconstruction of the droplet size spectrum depending on injection parameter or conditions.

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