Droplet Vaporization in a High-Pressure Gas

Evaporation of single, liquid droplets in a high-temperature, high-pressure gaseous environment has been investigated experimentally. The effects of gas temperature, pressure, and strength of naturally occurring convective flows were studied. Pure hydrocarbon (n-heptane) and trichlorotrifluoroethane (R-113) droplets were vaporized in a nitrogen atmosphere within a sealed chamber, which was developed to minimize forced convection. Experiments were carried out in normal and microgravity (~ 10⁻⁵ g) fields in order to examine the effect of natural convection. A single droplet was attached to the end of a quartz fiber. The gas temperature and pressure were raised quickly by a compressive process. The gas temperature and pressure were varied from 0.93<T_r<1.23 and 0.32<P_r<0.73. The droplet was located at the point of compressive symmetry. Droplet lifetime and instantaneous vaporization rate were determined from the data recorded by video camera. The results indicated that ambient gas temperature is a more significant parameter than ambient pressure for high-pressure droplet vaporization. This conclusion was based on comparisons of droplet vaporization rate for the range of temperatures and pressure tested. Ambient gas pressure was seen to have a weaker influence on vaporization rate. Removal of the gravity field during free-fall experiments resulted in an increase of droplet life time of about 30 percent for the case of R-113 liquid, and little change for the n-heptane droplets.