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Abstract
A new technique, based on sideward scattering, is presented for evaluating the modal drop size in non-absorbing liquid sprays.
The method relies on the additive contributions, in the 90°-110° scattering angle range, of the external reflection and of peripherally travelling surface waves which are respectively more polarized on the vertical than the horizontal plane.
The principle has been tested for water and light oil sprays in a preliminary fashion by comparing the experimental angular light scattering distribution on the horizontal and vertical planes with the theoretical Mie-Lorenz computations, averaged for a polydispersion. The technique has been applied to the dense early region of a pressure atomized, hollow cone, light oil spray to obtain values of the modal size, number concentration and volume fraction of drop clouds with very high spatial resolution.
It is shown that in a quiescent environment or in a coaxially-oriented fluid-dynamic air pattern a large number of small droplets, which are not easily detected by other sizing techniques, are entrained toward the central part of the spray, jusl downstream of the droplet formation region. The technique has been applied of the study of the interaction between swirled flow and sprays in three different fluid-dyamic configurations.
The suppression of the axial air flow induces a considerable decrease of the modal droplet size at the periphery of the spray and a radial broadening of the number concentration and of volume fraction. The increase of the swirl level yields an almost uniform radial distribution of sizes, while the number concentration is higher, and indicates that the reverse flow counteracts the classification effect which operates in quiescent sprays.
