Gr. Shaub et al., RADIAL MODEL FOR PARTICLE FORMATION FROM THE RAPID EXPANSION OF SUPERCRITICAL SOLUTIONS, The Journal of supercritical fluids, 8(4), 1995, pp. 318-328
A numerical model for the rapid expansion of supercritical-fluid solut
ions (RESS) is presented, Considering the complete expansion of the fl
uid into a vacuum, the process is modeled as inviscid, radial flow. Th
e particulate material is described by the moments of the particle siz
e distribution by numerically integrating the moments with the equatio
ns describing an inviscid flow of a non-ideal solution. By varying the
initial process conditions, we examine the trends due to changes in s
pecific operational parameters for typical RESS solutions. These calcu
lations show that in the limit of a very rapid expansion with no preci
pitation in the nozzle itself, an increase in solute concentration pro
duces a large increase in the particle size of the solids produced. In
creasing the initial temperature causes a decrease in the calculated m
ean particle size, while an increase in pressure produces larger parti
cles. However, both temperature and pressure have a much smaller effec
t on the calculated particle sizes than does concentration. The calcul
ations demonstrate that small particles with a narrow size distributio
n can be achieved by using as low a solute concentration as possible a
nd operating at relatively low preexpansion pressures and high preexpa
nsion temperatures.