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ICLASS 94<br>Proceedings of the Sixth International Conference on Liquid Atomization and Spray Systems

ISBN:
978-1-56700-019-1 (Print)
978-1-56700-445-5 (Online)

LIQUID CORE STRUCTURE OF EVAPORATING SPRAYS AT HIGH PRESSURES - FLASH X-RAY STUDIES

Avi Birk
U.S. Army Research Laboratory, Weapons Technology Directorate Aberdeen Proving Ground, MD 21005

Michael McQuaid
U.S. Army Research Laboratory, Aberdeen Proving Ground, Maryland, USA

M. Gross
US Army Research Laboratory MD, USA

Abstract

This paper describes the development and application of flash x-ray radiography for studying the core structure of atomizing jets at high temperatures (to 2300 K) and pressures (1.4 - 13.8 MPa). Methyl iodide (CH3I) was injected at approximately 75 m/s through a 1 mm circular orifice into (hot) nitrogen, or the post combustion products of an H2/Air/Ar mixture. Injections at 40 m/s through a thin annular orifice into these environments were also conducted. Radiographs which resolve core details to less than 0.1 mm were achieved. We observed that the core structure is strongly affected by heat transfer under these conditions. The core structures of circular jets were found to develop helical structures with wavelengths longer than the jets diameter, and the core penetrations decreased for denser ambient gas. A surprising result was that for the same gas density, the lengths of evaporating cores decreased with increase in pressure up to a "critical" value, then increased with further rise in pressure. The minimum corresponds to a pressure and temperature near the thermodynamic critical point of the liquid.