ASTM E2872-14

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Designation: E2872 − 14
Standard Guide for
Determining Cross-Section Averaged Characteristics of a
Spray Using Laser-Diffraction Instruments in a Wind Tunnel
1
Apparatus
This standard is issued under the fixed designation E2872; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
In this guide, test methodologies are described specifically relating to the use of laser diffraction
(LD) instrumentation to estimate the droplet-size distribution for liquid sprays released into moving
air streams. This guide presented is primarily applicable to aerial agricultural spraying, aerial forest
sprays, or air-blast spraying. Cases in which the spray is ejected into a quiescent gas environment that
lacks the unifying effect of a well-defined gas co-flow may require different techniques or
instrumentation or both. In this guide, an average droplet size distribution for the entire spray is
determined. It requires that the spray be statistically steady in time, but it may be polydisperse and
spatially non-uniform.
Thedroplet-sizedistributionusedforcharacterizationofamovingspraysourcemustbedetermined
from a “flux-sensitive sample” or equivalent. This is because a flux-sensitive sample provides the
fraction of the total liquid flow rate contributed by each size class of droplets and, therefore, is directly
related to the spray coverage. In contrast, the LD instrument derives its droplet-size distribution from
a “spatial sample,” and therefore, its use for spray characterization is limited to test conditions under
which equivalence between flux-sensitive samples and spatial samples can be established. Such
equivalence exists when the velocity of all droplets of the spray is equal and creating these conditions
is the basis of this guide.
All tests relating to this guide require a wind tunnel with a test section of sufficient size that it
contains the entire spray plume up to the plane of measurement without droplets impacting the test
section walls under the prescribed operating conditions.The unobstructed wind tunnel air stream shall
be uniform and free of turbulence. The test air speed shall be chosen to match the relative speed of
the sprayer to the ambient conditions.
1. Scope are contained within a volume as small as a few cubic
centimetres or as large as a cubic metre. The droplet sizes are
1.1 The purpose of this guide is to define a test procedure
assumed to be distributed non-uniformly within the spray
for applying the laser diffraction (LD) method to estimate an
volume.
average droplet size distribution that characterizes the flux of
liquid droplets produced by a specified spray generation device
1.2 This guide is intended primarily to guide measurement
under specified gas co-flow conditions using a specified liquid.
of performance of nozzles and atomizers using LD instru-
The intended scope is limited to artificially generated sprays
ments.
with high speed co-flow. The droplets are assumed to be in the
size range of 1 to 2000 µm in diameter and occur in sprays that 1.3 Non-uniform sprays require measurements across the
entire spray cross section or through several chords providing
a representative sample of the overall spray cross section. The
1
This guide is under the jurisdiction of ASTM Committee E29 on Particle and
Spray Characterization and is the direct responsibility of Subcommittee E29.02 on aim of multiple-chord measurements is to obtain a single
Non-Sieving Methods.
droplet size distribution that characterizes the whole spray
Current edition approved April 1, 2014. Published May 2014. DOI: 10.1520/
rather than values from a single chordal measurement.
E2872-14.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E2872 − 14
1.4 Use of this guide requires that the instrument does not 3. Terminology
interfere with spray production and does not significantly
3.1 Definitions—For definitions of terms used in this
impinge upon or disturb the co-flow of gas and the spray. This
standard, refer to Terminology E1620 and ISO 13320:2009.
technique is, therefore, considered non-intrusive.
3.2 Definitions of Terms Specific to This Standard:
1.5 The computation of droplet size distributions from the 3.2.1 aerial spraying, n—practice of delivering spray via an
light-scattering distributions is done using Mie scattering airborne vehicle such as a fixed-wing aircraft or helicopter.
theoryorFraunhoferdiffractionapproximation.TheuseofMie
3.2.2 atomizer, n—spray generation apparatus.
theoryaccountsforlightrefr
...