Spray Formation from Pressure Cans by Flashing

Abstract

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.

Aspects of Numerical Modelling of Flash-Boiling Fuel Sprays

“…Sher and Elata [12] were among the first to develop empirical models to predict bubble growth rates and droplet sizes caused by flashboiling. A relationship between average droplet size, nozzle pressure ratio and fuel properties was developed and validated against flashing sprays formed using a "pressure-can" apparatus.…”

“…At high superheat degrees, the spray is deemed to be fully flashing as the flow exiting the nozzle can consist already of a large amount of fuel vapor cloud housing liquid droplets. The size of these liquid droplets diminishes as the severity of flashboiling increases, resulting in the initial droplet diameter becoming much smaller than the nozzle diameter for highly superheated fuels [12]. The influence of initial droplet size on spray formation was investigated for both n-Pentane and isoOctane at superheated conditions where the onset of plume merging was witnessed, T f = 90 °C, P ∞ = 1.0 bar, and T f =120 °C, P ∞ = 0.5 bar, respectively.…”

Current Status of Superheat Spray Modeling with NCC

“…It seemed to have a value of 0.61 based on the research identified in [15]. Incidentally, this condition for criticality also coincides with the packing limit of spheres beyond which it can not accommodate any more bubbles and results in shattering [27]. In order to calculate this state of critical limit, they employed the homogeneous relaxation model (HRM) for calculating the mass fraction of gas, x, also known as quality.…”

Spray Formation of a Liquid Carbon Dioxide-Water Mixture at Elevated Pressures

“…In general, the dissolved gas at the exit orifice nucleates to form gas bubbles, as in effervescent atomization, and can rapidly evaporate by flashing as well [10]. The result shows that the mean droplet diameter is mainly influenced by the sudden release of the gas dissolved in the liquid.…”