Dynamics of a radially expanding circular liquid sheet and its atomization characteristics

Publication date: Available online 6 July 2018

Source: Fire Safety Journal

Author(s): Chetankumar S. Vegad, Satyanarayanan R. Chakravarthy, Amit Kumar

Abstract

The present study pertains to unsteady behavior of the radially expanding circular liquid (water) sheet that emerges from the lip of a cone-disc deflector subjected to the orthogonal liquid jet impingement from a nozzle. This test configuration is a simplified version of a pendent fire sprinkler head. The goal is to correlate the dynamical characteristics of the liquid sheet with those of the ligaments and droplets formed during its atomization. Time-resolved high-magnification imaging at kilohertz of framing rates is adopted for shadowgraphy, Mie scattering of high-repetition-rate laser sheet, and planar laser induced fluorescence (PLIF) of the liquid sheet is carried out for different Weber numbers over a range of 745 < Wejet < 2484. The threshold amplitude and growth rate of the radial Kelvin-Helmholtz wave until it shears abruptly over a narrow radial zone into ligaments are qualitatively reported. The radial and azimuthal wavenumbers are correlated with ligament length and thickness respectively. The relationship between ligament and droplet volumes Vdroplet = 0.5 Vligament specifies the disintegration of ligaments in to droplets. Further, the droplet diameter D10, ligament length Llig and ligament thickness tlig reveal that Llig > D10 > tlig for given conditions. The correlations of D10 and D32 with Wejet are obtained. Finally, the dependence of the droplet diameter on the discharge pressure is derived.

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