1、Designation: E2872 14Standard Guide forDetermining Cross-Section Averaged Characteristics of aSpray Using Laser-Diffraction Instruments in a Wind TunnelApparatus1This standard is issued under the fixed designation E2872; the number immediately following the designation indicates the year oforiginal
2、adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONIn this guide, test methodologies are described specifically relatin
3、g to the use of laser diffraction(LD) instrumentation to estimate the droplet-size distribution for liquid sprays released into movingair streams. This guide presented is primarily applicable to aerial agricultural spraying, aerial forestsprays, or air-blast spraying. Cases in which the spray is eje
4、cted into a quiescent gas environment thatlacks the unifying effect of a well-defined gas co-flow may require different techniques orinstrumentation or both. In this guide, an average droplet size distribution for the entire spray isdetermined. It requires that the spray be statistically steady in t
5、ime, but it may be polydisperse andspatially non-uniform.The droplet-size distribution used for characterization of a moving spray source must be determinedfrom a “flux-sensitive sample” or equivalent. This is because a flux-sensitive sample provides thefraction of the total liquid flow rate contrib
6、uted by each size class of droplets and, therefore, is directlyrelated to the spray coverage. In contrast, the LD instrument derives its droplet-size distribution froma “spatial sample,” and therefore, its use for spray characterization is limited to test conditions underwhich equivalence between fl
7、ux-sensitive samples and spatial samples can be established. Suchequivalence exists when the velocity of all droplets of the spray is equal and creating these conditionsis the basis of this guide.All tests relating to this guide require a wind tunnel with a test section of sufficient size that itcon
8、tains the entire spray plume up to the plane of measurement without droplets impacting the testsection walls under the prescribed operating conditions. The unobstructed wind tunnel air stream shallbe uniform and free of turbulence. The test air speed shall be chosen to match the relative speed ofthe
9、 sprayer to the ambient conditions.1. Scope1.1 The purpose of this guide is to define a test procedurefor applying the laser diffraction (LD) method to estimate anaverage droplet size distribution that characterizes the flux ofliquid droplets produced by a specified spray generation deviceunder spec
10、ified gas co-flow conditions using a specified liquid.The intended scope is limited to artificially generated sprayswith high speed co-flow. The droplets are assumed to be in thesize range of 1 to 2000 m in diameter and occur in sprays thatare contained within a volume as small as a few cubiccentime
11、tres or as large as a cubic metre. The droplet sizes areassumed to be distributed non-uniformly within the sprayvolume.1.2 This guide is intended primarily to guide measurementof performance of nozzles and atomizers using LD instru-ments.1.3 Non-uniform sprays require measurements across theentire s
12、pray cross section or through several chords providinga representative sample of the overall spray cross section. Theaim of multiple-chord measurements is to obtain a singledroplet size distribution that characterizes the whole sprayrather than values from a single chordal measurement.1This guide is
13、 under the jurisdiction of ASTM Committee E29 on Particle andSpray Characterization and is the direct responsibility of Subcommittee E29.02 onNon-Sieving Methods.Current edition approved April 1, 2014. Published May 2014. DOI: 10.1520/E2872-14.Copyright ASTM International, 100 Barr Harbor Drive, PO
14、Box C700, West Conshohocken, PA 19428-2959. United States11.4 Use of this guide requires that the instrument does notinterfere with spray production and does not significantlyimpinge upon or disturb the co-flow of gas and the spray. Thistechnique is, therefore, considered non-intrusive.1.5 The compu
15、tation of droplet size distributions from thelight-scattering distributions is done using Mie scatteringtheory or Fraunhofer diffraction approximation. The use of Mietheory accounts for light refracted through the droplet and thereis a specific requirement for knowledge of both real (refractive)and
16、imaginary (absorptive) components of the complex indexof refraction. Mie theory also relies on an assumption ofdroplet homogeneity. The Fraunhofer diffraction approxima-tion does not account for light refracted through the droplet anddoes not require knowledge of the index of refraction.1.6 The inst
17、ruments shall include data-processing capabili-ties to convert the LD scattering intensities into droplet sizedistribution parameters in accordance with Practice E799 andTest Method E1260.1.7 The spray is visible and accessible to the collimatedbeam produced by the transmitter optics of the LD instr
18、ument.The shape and size of the spray shall be contained within theworking distance of the LD system optics as specified by theinstrument manufacturer.1.8 The size range of the LD optic should be appropriate tothe spray generation device under study. For example, theupper bound of the smallest dropl
19、et size class reported by theinstrument shall be not more than14 the size of DV0.1.1.9 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.10 This standard may involve hazardous materials,operations, and equipment. This standard d
20、oes not purport toaddress all of the safety problems associated with its use. It isthe responsibility of the user of this standard to establishappropriate safety and health practices and determine theapplicability of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E799
21、 Practice for Determining Data Criteria and Processingfor Liquid Drop Size AnalysisE1260 Test Method for Determining Liquid Drop SizeCharacteristics in a Spray Using Optical NonimagingLight-Scattering InstrumentsE1620 Terminology Relating to Liquid Particles and Atomi-zation2.2 ISO Standards:3ISO 13
22、320:2009 Particle Size AnalysisLaser DiffractionMethods, General Principles3. Terminology3.1 DefinitionsFor definitions of terms used in thisstandard, refer to Terminology E1620 and ISO 13320:2009.3.2 Definitions of Terms Specific to This Standard:3.2.1 aerial spraying, npractice of delivering spray
23、 via anairborne vehicle such as a fixed-wing aircraft or helicopter.3.2.2 atomizer, nspray generation apparatus.3.2.2.1 DiscussionVarious definitions for “atomizer” aredefined in Terminology E1620 by construction and atomizationmethod.3.2.3 co-flow, ncoherent, moving gas phase surrounding aplume of
24、spray droplets that significantly influences the direc-tion of movement of droplets in a spray plume.3.2.4 co-flow generation device, nwind tunnel or otherdevice that creates a steady, uniform air stream in the plane ofmeasurement.3.2.5 concentration sensitive, adjstatistical quantity de-rived from
25、a spatial sample.3.2.6 droplet size distribution, DSD, nmathematical orgraphical representation of droplet sizes of a given sprayfrequently shown as a volume fraction, number fraction, orcumulative fraction distributions.3.2.7 laser diffraction, LD, nused in this guide to refer toa class of laser dr
26、oplet-sizing instruments known collectivelyas laser diffraction instruments, also used to qualify datagathered using an instrument of this type.3.2.8 monodisperse, adjrefers to a spray in which alldroplets have identical size.3.2.9 nozzle, nspray generation apparatus.3.2.9.1 DiscussionVarious defini
27、tions for “nozzle” aredefined in Terminology E1620 by construction and atomizationmethod.3.2.10 number concentration, nnumber of particles in aunit volume of space.3.2.11 obscuration , npercentage or fraction of incidentlight that is attenuated as a result of extinction (scattering orabsorption or b
28、oth) by droplets.3.2.12 obstructed, adjrefers to co-flow generation devicewhen the spray generation device is mounted such that itinterferes with the gas-phase co-flow.3.2.13 plume, nensemble of droplets that constitutes aspray.3.2.14 polydisperse, adjrefers to a spray in which dropletshave differen
29、t sizes.3.2.15 sample distance, nseparation between the samplevolume of the LD system and the spray nozzle.3.2.16 sample volume, nintersection of LD beam and theportion of the spray plume containing a measurable concen-tration of droplets.3.2.17 model liquid, nfluid used to simulate the propertiesof
30、 density, viscosity, and surface tension of another fluid.3.2.17.1 DiscussionTypically used to replace sprays thatare flammable, toxic, or otherwise deemed too dangerous touse in a spray test.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at ser
31、viceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.E2872 1423.2.18 spatial segregation, nspat
32、ial non-uniformity ofdroplet sizes resulting from aerodynamic forces or atomizationcharacteristics or both.3.2.19 spray characterization, nprocess of describing aspray based on a theory of measurement in terms of parameterssuch as liquid flow rate, flux, patternation, particle size, andvelocity.3.2.
33、20 spray generation apparatus, ndevice specially de-signed to transform a bulk liquid into droplets.3.2.21 traverse, ndevice used to move beam from oneposition to another in space with documented precision andaccuracy.3.2.22 traverse, vact of moving laboratory equipment inspace.3.2.23 vignetting, ni
34、n the context of this guide, refers tothe inability of an LD instrument to accurately estimate the sizeof those droplets in a spectrum whose contribution to thediffraction pattern falls outside the reach of the LD receiveroptics.3.2.24 volume concentration, nvolume of droplets in aunit volume of spa
35、ce.3.2.25 working distance, ndistance within which a dropletof the minimum diameter of the rangeas defined by the LDsystem manufacturerof a given optical arrangement is said tohave been measured accurately by the LD instrument.4. Summary of Guide4.1 A description of the principles of LD measurements
36、 isprovided in ISO 13320:2009.4.2 A method of data interpretation for LD data analysis isprovided in Practice E799.4.3 A typical LD sample volume is idealized as a long, thincylinder passing through the spray plume. The sample volumeis delineated by the diameter of the laser beam and the edgesof the
37、 spray plume. The procedure in this guide covers methodsof traversing the sample volume across the spray plumesuitable for LD measurements of spatially irregular and non-uniform sprays. The aim of the procedure is to determine asingle droplet size distribution that is equivalent to a fluxsensitive s
38、ample.4.4 It is important to position the LD instrument at anappropriate axial distance from the nozzle or atomizer alongthe mean direction of co-flow to ensure complete primary andsecondary droplet breakup, minimal droplet velocity variation,and avoidance of vignetting and multiple scattering. Them
39、anufacturers specification should be consulted regardingvignetting and multiple scattering limitations of a particularinstrument.5. Significance and Use5.1 This guide provides a means of using an LD instrumentto obtain a droplet size distribution from a spray in gas co-flowthat approximates a flux-s
40、ensitive sample.45.2 In many sprays, the experimenter shall account forspatial segregation of droplets by size. This guide provides ameans of spatial averaging the droplet distribution.5.3 The results obtained will be statistical in nature and referto the time average of droplet size distribution of
41、 the entirespray.5.4 This guide is used to calibrate a spray generation deviceto produce a desired droplet size distribution under prespecifiedenvironmental and co-flow conditions or characterize an un-known spray while minimizing the uncertainty in the measure-ment.6. Apparatus6.1 The measurement a
42、pparatus includes an LD system.This system should provide means for producing a collimatedlaser beam that passes through a region of the spray, a detector,or detectors for recording scattered light from droplets and ameans for transforming the observations into statistical dropletsize spectrum.6.2 S
43、pray generation apparatuses vary widely and provisionfor their mounting depends on the type of spray they produceand the conditions under which the spray is typically used. Thespray generation apparatus should be mounted in the testsection of a wind tunnel that provides a constant, uniform,low-turbu
44、lence, incident gas stream of a size sufficient toenclose the entire spray generation apparatus, its aerodynamicwake, and the plume up to the plane of measurement.6.3 Gas phase velocity at the measurement plane shall bemeasured for uniformity and steadiness with respect to turbu-lence intensity.Any
45、number of available instruments including,but not limited to, pitot tubes, hot-wire anemometers, andultrasonic anemometers may be used, Such equipment shall becalibrated against an appropriate primary standard.6.4 The wind tunnel used to enclose the spray shall providegas co-flow velocities represen
46、tative of relative velocity be-tween the sprayer and the environment in the simulated sprayapplication.6.5 Optical access to the spray may be direct or viaviewports (approved by the LD manufacturer), slots, or holesin the walls of the test section. Wherever possible, the LDinstrumentation should be
47、mounted such that its housing isentirely outside the spray and co-flow region or, at the veryleast, in a location where it does not significantly impinge onthe spray plume or uniform co-flow region. In situations inwhich aerodynamic fairing or waterproofing or both is appliedto the LD device to mini
48、mize the effect of the obstruction, careshall be taken to prevent any accumulation and shedding ofdroplets from the obstruction into the LD beam path.4Bagherpour et al., “Droplet Sizing and Velocimetry in the Wake of Rotary CageAtomizers,” Transactions of the ASABE, Vol 55, No. 3, 2012, pp. 579772.E
49、2872 1436.6 The spray may remain stationary in the center of the airstream and the beam traversed relative to it, or the beam mayremain stationary and the nozzle or atomizer traversed relativeto the beam. Choice of traversing method should reflect thesize of the spray and the dimension of the uniform gas phasevelocity region. At no time may a spray be traversed to alocation where wind tunnel walls or boundary layers alter thespray plume or the aerodynamic wake of the spray generationdevice. Traversing systems for either case should be robust,enab
