Spray Formation from Pressure Cans by Flashing

The formation of spray through flashing, from containers pressurized by volatile propellants dissolved into the spray liquid, is studied. A model for the flashing process is proposed. While the pressurized solution is discharged from the container into the atmosphere, vapor bubbles are produced. These bubbles grow rapidly through evaporation of the propellant. When they touch each other, flashing is assumed to occur-the bubbles “explode” and an aerosol is formed. The energy contained in these exploding bubbles is, in part, transformed into surface energy of the droplets of the aerosol. On the basis of this model of the flashing process, a mathematical derivation is presented, expressing the average spray droplet diameter in terms of the physical properties of the binary fluid system. An experimental program was carried out in which the droplet size distribution of an aerosol generated by a flashing process was measured. The average droplet diameter was correlated with the pressure in the container and with the relative concentration of the propellant in the mixture. Experiments were carried out at different temperatures. Comparing the experimental results with the proposed theory, it was found that deviations from the thermodynamic equilibrium have to be taken into account. Doing so, incorporating deviations from equilibrium for water vapor, the experimental data fitted the theoretical prediction for the average drop size quite well over the range of experimental pressures and temperatures.