Representation of average drop sizes in sprays

Abstract

Procedures are presented for processing drop-size measurements to obtain average drop sizes that represent overall spray characteristics. These procedures are not currently in general use, but they would represent an improvement over current practice. Clear distinctions are made between processing data for spatial-and temporal-type measurements (also referred to as concentration-sensitive and flux-sensitive, respectively). The conversion between spatial and temporal measurements is discussed. The application of these procedures is demonstrated by processing measurements of the same spray by two different types of instruments, a laser-diffraction drop sizer and a phase-Doppler particle analyzer. C J D Nomenclature fraction of total spray cross section occupied by ring j SFS instruments, drops per unit volume (number density) in y th ring TFS instruments drops per unit area (number flux) in y th ring averaging process, designated by overbar on D average diameter; integer values p and q determine averaging procedure as shown in Eq. (1) arithmetic mean diameter D 20 = surface area mean diameter 5zo, Ao 530, surface area mean diameter of drops in j th ring volume mean diameter volume mean diameter of drops in the y th ring Sauter mean diameter (SDM) (volume/surface mean _ diameter) D vo 5 = volume median diameter; that diameter for which half the spray volume is contained in drops of larger size, and half in drops of smaller size HIJ = fraction of drops measured in size class / for ring j (not equivalent for SFS and TFS instruments) Ni = number of drops sampled in the /th size class (not equivalent for SFS and TFS instruments) ,SFS ^ number of drops sampled in the /th size class, where drops are counted proportional to drops per unit volume (number density) ,TFS = number of drops sampled in the ith size class, where drops are counted proportional to drops per unit time per unit area (number flux) N c = number of drop-size classes N R = number of rings in spray cross section u t = average velocity of drops in size class /' Subscripts i = number of size class j = ring number for various annuli in .spray cross section

Development of the Spray Drift Task force database for aerial applications

“…Details of the measurement procedures are described elsewhere [25]. Representative sampling for the nonuniform sprays was achieved using a continuous scan technique or multiple measurements at different heights within the spray plume [26].…”