TY - JOUR
T1 - Modeling of solid particle formation during solution aerosol thermolysis
T2 - The evaporation stage
AU - Jayanthi, G. V.
AU - Zhang, S. C.
AU - Messing, Gary L.
N1 - Funding Information:
The authors gratefully acknowledge NASA through Battelle's Advanced Materials Center for Commercial Development of Space (Grant No. NAGW-811), and the Fluid, Particulate and Thermal Systems, and the Metals, Ceramics and Electronic Materials programs of the NSF (Grant No. CTS-9202418) for financial support.
PY - 1993/1/1
Y1 - 1993/1/1
N2 - The evaporation state of solution aerosol thermolysis (SAT) was modeled to study the effect of various parameters on solid particle formation by solute precipitation. A comparison of the characteristic time constants for various processes demonstrated that droplet shrinkage and solute diffusion are the slowest processes, and that the fast processes, i.e., vapor diffusion and heat conduction in the gas phase and the liquid phase, can be assumed to have reached steady state. Differential equations for these faster processes were thus simplified and were solved numerically along with a modified solute diffusion equation, using an explicit first-order finite difference scheme. The computations were done until the solute concentration at the droplet surface reached the critical supersaturation. Then, if the solute concentration at the droplet center is higher than the equilibrium saturation, volume precipitation is proposed to occur. Solutes with a large difference between critical supersaturation and equilibrium saturation were observed to favor volume precipitation. High initial concentrations and low ambient temperatures were demonstrated to favor volume precipitation. Percolation theory was invoked to provide insights about the space filling capacity of the precipitated solids, and a second criterion, the percolation criterion, for solid particle formation was proposed; the solute concentration at the droplet center should be high enough so that the volume fraction of the precipitated solids is higher than the critical volume fraction. Volume precipitation only ensures that there are precipitated solids at the droplet center. The percolation criterion ensures that there is a sufficient volume of precipitated solids at the droplet center to form a coherent three-dimensional network. For solid particle formation by SAT, both the volume precipitation and the percolation criteria must be satisfied.
AB - The evaporation state of solution aerosol thermolysis (SAT) was modeled to study the effect of various parameters on solid particle formation by solute precipitation. A comparison of the characteristic time constants for various processes demonstrated that droplet shrinkage and solute diffusion are the slowest processes, and that the fast processes, i.e., vapor diffusion and heat conduction in the gas phase and the liquid phase, can be assumed to have reached steady state. Differential equations for these faster processes were thus simplified and were solved numerically along with a modified solute diffusion equation, using an explicit first-order finite difference scheme. The computations were done until the solute concentration at the droplet surface reached the critical supersaturation. Then, if the solute concentration at the droplet center is higher than the equilibrium saturation, volume precipitation is proposed to occur. Solutes with a large difference between critical supersaturation and equilibrium saturation were observed to favor volume precipitation. High initial concentrations and low ambient temperatures were demonstrated to favor volume precipitation. Percolation theory was invoked to provide insights about the space filling capacity of the precipitated solids, and a second criterion, the percolation criterion, for solid particle formation was proposed; the solute concentration at the droplet center should be high enough so that the volume fraction of the precipitated solids is higher than the critical volume fraction. Volume precipitation only ensures that there are precipitated solids at the droplet center. The percolation criterion ensures that there is a sufficient volume of precipitated solids at the droplet center to form a coherent three-dimensional network. For solid particle formation by SAT, both the volume precipitation and the percolation criteria must be satisfied.
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U2 - 10.1080/02786829308959653
DO - 10.1080/02786829308959653
M3 - Article
AN - SCOPUS:0027703614
VL - 19
SP - 478
EP - 490
JO - Aerosol Science and Technology
JF - Aerosol Science and Technology
SN - 0278-6826
IS - 4
ER -