ASTM E2872
Scope
1.1 The purpose of this guide is to define a test procedure for applying the laser diffraction (LD) method to estimate an average droplet size distribution
that characterizes the flux of liquid droplets produced by a specified spray generation device under specified gas co-flow conditions using a specified liquid. The intended scope is limited to
artificially generated sprays with high speed co-flow. The droplets are assumed to be in the size range of 1 µm to 2000 µm in diameter and occur in sprays that are contained within a volume as
small as a few cubic centimetres or as large as a cubic metre. The droplet sizes are assumed to be distributed non-uniformly within the spray volume.
1.2 This guide is intended primarily to guide measurement of performance of nozzles and atomizers using LD instruments.
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 aim of multiple-chord measurements is to obtain a single droplet size distribution that characterizes the whole spray rather than values from a single chordal
measurement.
1.4 Use of this guide requires that the instrument does not interfere with spray production and does not significantly impinge upon or disturb the co-flow
of gas and the spray. This technique is, therefore, considered non-intrusive.
1.5 The computation of droplet size distributions from the light-scattering distributions is done using Mie scattering theory or Fraunhofer diffraction
approximation. The use of Mie theory accounts for light refracted through the droplet and there is a specific requirement for knowledge of both real (refractive) and imaginary (absorptive)
components of the complex index of refraction. Mie theory also relies on an assumption of droplet homogeneity. The Fraunhofer diffraction approximation does not account for light refracted
through the droplet and does not require knowledge of the index of refraction.
1.6 The instruments shall include data-processing capabilities to convert the LD scattering intensities into droplet size distribution parameters in
accordance with Practice E799 and Test Method E1260.
1.7 The spray is visible and accessible to the collimated beam produced by the transmitter optics of the LD instrument. The shape and size of the spray
shall be contained within the working distance of the LD system optics as specified by the instrument manufacturer.
1.8 The size range of the LD optic should be appropriate to the spray generation device under study. For example, the upper bound of the smallest droplet
size class reported by the instrument shall be not more than 1/4 the size of DV0.1.
1.9 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.10 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if
any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.11 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision
on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Keywords
drop size distribution; laser diffraction instrument; liquid droplet size characteristics; spray;
ICS Code
ICS Number Code 55.130 (Aerosol containers)
DOI: 10.1520/E2872-14R24