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

Abstract : This report describes the development and application of flash x-ray radiography for studying the core structure of atomizing jets at high temperatures (to 2,300 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. Similar experiments involving injections at 40 m/s through thin, annular orifices 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 cores of circular jets were found to develop helical structure whose pitch angle decreased with axial distance from the orifice. As expected, the core penetration distance decreased with increase in ambient gas density. A surprising result was that for the same global ambient gas density, the length of evaporating cores decreased with increase in ambient pressure (and temperature) up to a "critical" value, then increased with further rise in pressure. The minimum corresponds to a transition to a pressure and temperature regime above the thermodynamic critical point of the liquid. jg p.3