Dynamics and Thermodynamics of Dense and Dilute Clusters of Drops

Abstract

Collective drop behavior is encountered in sprays produced for a variety of applications: fuel sprays produced for combusting devices, metal sprays produced for coating, paint sprays, printer sprays, atmospheric clouds, etc. There is experimental evidence that clusters of drops exist both in combusting [1], [2], [3], [4], [5], and non-combusting sprays for atomizers used in combusting devices [6], [3], [4]. Clusters of drops have also been observed in round jets laden with solid glass beads [7], although the glass beads (of 55p radius) did not behave entirely like liquid drops due to their large inertia. The existence of these clusters of drops indicates that the interaction among the drops is important in determining the dynamics of the drops because the drop proximity changes the flow around the individual drops in ways that affects the drag on each drop. Additionally, if there is a phase change between the liquid drops and the gaseous surroundings (either evaporation or condensation), this will also influence the flow around the individual drops; and phase change is also affected by the drop proximity. If evaporation occurs, it is the drop heat up that is affected by drop proximity and the build up of fuel vapor in the interstitial space among drops might lead to saturation of the gas, resulting in termination of evaporation. If condensation occurs, such as in atmospheric clouds, the rate of mass transfer to the hotter liquid drops from the colder gas results in the reduction of the temperature differential between phases and thus might terminate phase change; and the rate of mass transfer depends upon drop proximity.