Supercritical droplet vaporization and combustion studies

Droplet vaporization and combustion studies in environments where the ambient pressure and temperature are supercritical relative to the droplet are reviewed. The conditions under which the droplet vaporization and combustion may be approximated as quasi-steady are discussed. It is shown that this approximation is not valid for paraffin fuels in conditions where the reduced temperature and pressure exceed approximately twice the fuel's critical values. Conditions in which the pseudo wet-bulb and critical mixing states are obtained are also discussed. Results indicate that for the paraffin fuels n-pentane through n-dodecane, a vaporizing droplet can reach the critical state for ambient pressures greater than approximately twice the fuel's critical pressure and for ambient temperatures approximately twice the fuel's critical temperature while combusting droplets can reach this state when ambient pressure is approximately 2.5 rimes that of the fuel's critical pressure. Droplet vaporization and combustion lifetimes are shown to be significantly influenced by the ambient temperature and pressure conditions, with a minimum in the latter occurring near the fuel's critical pressure. Key modeling assumptions and their relative importance in supercritical droplet vaporization and combustion are also reviewed. These include real gas effects, effects of liquid-phase gas solubility, and anomalies in thermophysical properties near the critical region. We outline areas of research in need of further study and the challenges in the held. Copyright (C) 1996 Elsevier Science Ltd.