Atomization and Sprays Journal of the International Institutes for Liquid Atomization and Spray Systems

ISSN for PRINT: 1045-5110

For Online Access

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1999, Volume9

Issue 2

122 pages

Issue price - $75.00

Sandeep D. Sovani
Maurice J. Zucrow Laboratories (Formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, U.S.A.

Paul E. Sojka
Maurice J. Zucrow Laboratories (formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, USA

Yudaya R. Sivathanu
En'Urga Inc.; Maurice J. Zucrow Laboratories (Formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, U.S.A.

A first principles analytical method for predicting drop size distributions in sprays, where primary atomization is the dominant process, has been developed. The method is able to predict the effects of fluctuations in gas-liquid relative velocity at the atomizer exit, and variations in fluid physical properties, on the spray drop size distribution. The method is based on applying the discrete probability function (DPF) to a fluid mechanic instability model. The dispersion equation for growth of fluid mechanic disturbances in cylindrical liquid ligaments relates the magnitude of the liquid-gas relative velocity and liquid physical properties to the size of drops formed. Fluctuations in relative velocity and fluid physical properties are introduced into the dispersion equation in the form of probability density functions (pdfs). The solution of the dispersion equation over the range of the pdf yields a drop size distribution. Results demonstrate how fluctuations in gas-liquid relative velocity at the atomizer exit, and variations in fluid physical properties (density, surface tension, and viscosity) can lead to a distribution of drop sizes. The width of the drop size distribution is found to be strongly dependent on the level of gas-liquid relative velocity fluctuations at the exit of the injector. Furthermore, the width of the drop size distribution increases with the level of velocity fluctuations in a slightly nonlinear manner. Finally, a distinct upper limit is found to exist for the drop size distribution, which cannot be exceeded by any amount of velocity fluctuation. Fluctuations in physical properties have a lesser effect on the drop size distributions than fluctuations in relative velocity, with variations in viscosity having the greatest impact. It is concluded that typically observed fluctuations in fluid physical properties are too small to produce experimentally observed drop size distribution widths in most practical sprays.

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