ASTM WK24544

    New Test Method for Determining Cross-Section Averaged Characteristics of a Spray Using Laser-Diffraction Instruments in a Wind Tunnel Apparatus

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    Developed by Subcommittee: E29.02 | Committee E29 | Contact Staff Manager



    WK24544

    1. Scope

    1.1 The purpose of this test method 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 coflow conditions using a specified liquid. The intended scope is limited to artificially generated sprays with high speed coflow. The droplets are assumed to be in the size range of 1 to 2000 m 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 nonuniformly within the spray volume. 1.2 This test method is intended primarily for use in standardizing measurements for the performance of nozzles and atomizers using LD instruments. 1.3 Nonuniform 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 test method requires that the instrument, or any portions thereof, in proximity to the spray does not interfere with spray production and does not significantly impinge upon or disturb the coflow 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 one quarter the size of the measured droplet diameter at which 10 % of the spray volume is contained in smaller droplets, DV0.1 (see Terminology E456). 1.9 Units-The values stated in SI units are to be regarded as the 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 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.

    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.

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    Work Item Status

    Date Initiated:
    06-10-2009

    Technical Contact:
    Gordon Holloway

    Item:
    002

    Ballot:
    E29 (14-01)

    Status:
    Ballot Item Approved as E2872-2014 and Pending Publication