DROPLET VAPORIZATION IN EXPANSIBLE DENSE SPRAYS AT SUBCRITICAL AND SUPERCRITICAL CONDITIONS

Droplet vaporization in expansible dense sprays is studied numerically in sub- to supercritical pressure environments (5-60 bar). The concep t of the variable-sized sphere of influence is adopted in accounting f or the interaction among movable droplets in dense sprays. High-pressu re effects on droplet vaporization are taken into account by solving b oth gas- and liquid-phase transient flows, as well as by including the effects of ambient gas solubility, property variation, thermodynamic nonideality, and transient diffusion. Numerical results for expansible dense n-pentane sprays reveal chat in a low-pressure environment, the cloud of droplets first contracts due to ambient temperature drop for droplet heatup, and then expands due to gas mass addition by droplet vaporization, while in a high-pressure environment, it contracts throu gh its whole vaporization history. Droplets in an expansible spray can also reach the mixing critical state before complete vaporization at lower ambient pressures than those in a stationary spray, since a subs tantial ambient pressure drop occurs in the latter during the droplet heatup and vaporization period. For expansible dense sprays, the dropl et heating process is entirely transient in a supercritical pressure e nvironment, and the D-2 law is not valid at either sub- or supercritic al ambient pressures.