Effects of Liquid Superheat on Droplet Disruption and Vaporization in Supersonic Conditions
WASHINGTON UNIV SEATTLE DEPT OF AERONAUTICS AND ASTRONAUTICS
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Individual neat 70mum diameter droplets of 1-propanol, ethanol, and methanol, were smoothly accelerated after injection into a convergent-free expansion test section of a draw-down supersonic wind tunnel to examine the effects of liquid superheat on droplet disruption and vaporization. Superheating of the initially unheated droplets was accomplished upon injection into the freely expanding jet as the static pressure dropped below the vapor pressures of the droplet fluids. The rate and degree of superheating of the droplets varied with test fluid vapor pressure. Droplets were imaged by shadowgraphy over sufficiently short intervals to capture clear images. A simple computational model suggested that the droplets achieved supersonic velocities relative to the air stream. Examination of 888 droplet images indicates that superheating results in faster and more violent disruption and vaporization than would be expected based upon correlations from previous studies, due to flash vaporization originating in the region of low pressure on the aft of the droplet. More rapid superheating seems to increase the speed and violence of droplet breakup, and result in lower degrees of superheat necessary to completely disrupt a droplet.
- Physical Chemistry
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- Fluid Mechanics