1. Scope
1.1 The purpose of this test method is to obtain data that characterizes the sizes of liquid particles or drops produced by a spray nozzle or similar device under specified conditions using a specified liquid. Parts of the test method are applicable to the use of laser diffraction instruments for the measurement of similar physical phenomena such as naturally occurring rain or clouds, but the intended scope is limited to artificially generated sprays. The drops will generally be in the size range from 1 m to the order of 9000-m diameter; they will occur in sprays that may be contained within a volume as small as a few cubic centimetres or as large as several cubic metres. Typically, the number density of the particles can vary significantly from one point to another. 1.2 This test method is intended primarily for use in standardizing measurements of the performance of spray-producing devices using laser diffraction instruments. 1.3 Although common practice is to make laser diffraction measurements along a single line of sight through the spray centerline, this test method defines a procedure requiring measurements across the entire spray cross section or through several chords representative of the overall spray cross section. This gives average spray characteristics representative of the entire spray rather than values preferentially weighted by the characteristics near the center of the spray obtained with a single, centerline measurement. 1.4 Use of this test method requires that the presence of the instrument, or any portions thereof, in proximity to the spray shall not interfere with the process of producing the spray (by atomization of the liquid) or the air patterns in the region being examined--this technique is described as nonintrusive. 1.5 The computation of drop-size distributions from the light-scattering distributions is based on the assumption that all particles are spherical. Measurement of nonspherical particles may introduce errors. 1.6 The instruments shall include data-processing capabilities to convert the laser-diffraction-scattering intensities into drop-size distributions parameters in accordance with Practice E 799 and Terminology E 1620. 1.7 The physical size and shape of the spray nozzle presents no special problem provided the spray is visible and accessible to the light beam. The shape and size of the spray, however, shall be considered in relation to the sampling volume of the optical system used. It may be necessary, as well, to contain the spray in a test chamber with provisions for exhausting. When measurements are made in a wind tunnel, the width of the working section shall be sufficiently large to avoid blockage and allow a full sample of the spray plume cross section (typically ~46 cm). For sampling in air velocities 20 m/s, the minimum working section width and height are 60 cm. For air velocities 50 m/s, 40-cm width and height will suffice. The air velocity variations shall be within 5 % of the specified velocity measured using an appropriate technique such as Pitot tube or laser-Doppler anemometry. Spatial variations in velocity shall not differ by more than 10 % from the specified velocity for a region from the centerline to 80 % of the distance from the centerline to the walls of the working section. 1.8 The measurements made with laser diffraction instruments are sensitive to the drop number density rather than the drop number flux. This is defined in Practice E 799 as a spatial sampling process. 1.9 This test method may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety problems associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific precautionary statements, refer to Section 8.
The purpose of this test method is to provide data on liquid drop-size characteristics for sprays representative of the entire cross section of the spray. The results obtained will be statistical in nature and give information on mean drop sizes and measures of dispersion of size. Classes of instruments other than laser diffraction instruments might be expected to give different results on similar sprays because of differences in sample volumes, sampling weighting factors resulting from particle velocities (spatial or flux weighted), size range capabilities, and other factors. However, the sampling of the entire cross section of the spray does remove the line-of-sight integral sampling volume usually associated with laser-diffraction particle-sizing instruments and provides a basis for comparison with measurements by other classes of instruments when those measurements are processed to determine cross-section average spray characteristics.
Keywords
laser diffraction instrument; liquid drop size characteristics; spray
The title and scope are in draft form and are under development within this ASTM Committee.
Citing ASTM Standards
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