Predicting the Droplet Size and Yield Factors of a Phosphorus Smoke as a Function of Droplet Composition and Ambient Relative Humidity under Tactical Conditions.

摘要

The equilibrium vapor pressure over the surface of a droplet containing an aqueous solution of volatile solvent and nonvolatile solute is uniquely determined by the Kelvin and solute effects. A general thermodynamic relationship is developed for the equilibrium vapor pressure (saturation ratio) over the surface of a droplet as a function of diameter and droplet composition (solute and solvent). From the general relationship, a particular expression is formulated for the saturation ratio over the surface of a phosphoric acid droplet as a function of droplet diameter and moles of acid contained by the droplet. It is assumed that vapor diffusional equilibrium exists between the surface of the acid droplet and the environment under tactical conditions. Consequently, a predictive relationship between the ambient relative humidity and the diameter of a phosphoric acid droplet follows. With this relationship, numerical values for the droplet diameters of a representative phosphorus smoke are generated for environmental relative humidities ranging from 10% to 98%. The representative phosphorus smoke is characterized by a mole spectrum of condensation nuclei ranging from 0.30 x 10 to the minus 15th power to 0.14 x 10 to the minus twelth power moles or, equivalently, a diameter spectrum varying from 0.30 to 2.5 micrometers. To verify the validity of diffusional (vapor) equilibrium, an investigation on the kinetics of condensational growth is executed. With the introduction of the 'modified' growth law, a discussion on bounded and unbounded growth is presented. An analytical solution (droplet radius as a function of time) is offered for the growth equation as applied to the physical phenomenon of bounded growth.