Simulation Models Growth, Distribution Of Ultrafine Particles
Engineers from Penn State University (University Park, PA; txm11@psu.edu), have developed a simple, fast computer simulation for growing and distributing ultrafine particles. The simulation uses modest amounts of computing power. It may apply to processes ranging from ceramic-membrane development to powdered-milk production to air-pollution control.
The new simulation is based on a standard Monte Carlo method, a technique for estimating the solution of a mathematical problem by artificial sampling. In the new simulation, however, the Penn State researchers simplify the solution by using a sample of fixed size, regardless of whether the actual growth process results in a net loss via aggregation or gain via breakup. Through experiments, they have shown that the technique delivers accurate results for long growth times. Answers are delivered in about four minutes from a mainframe computer.
The new simulation can accurately predict the size and distribution of particle groups over time. Some results from the simulation have already been confirmed and verified by comparison with experimental results.
The research team has shown that stirring induces aggregation of nanoparticles and affects their stability but has little effect on the rate of breakup. The presence of alcohols also promotes aggregation as does coating the nanoparticles with polymers. They have found breakup to be promoted by the type of starting material (alkoxide type) and acidity.
Led by Themis Matsoukas, assistant professor of chemical engineering, the research team is using the simulation to understand the grouping and breakup processes that ultrafine titanium dioxide particles undergo before reaching their final size. The formation of ultrafine, nanometer-sized titanium dioxide particles is characterized by a rapid aggregation of large particle groups followed by the slow breakup of these groups. The breakup or de-aggregation can take hours or days depending on the processing conditions.
Matsoukas chose to model titanium dioxide nanoparticle formation because of current interest in using metal oxides in ceramic membranes for gas separation. The size of the particles is important to the activity of the membrane in this application; nanosized particles are difficult to obtain in non-aggregated form.
"We haven't yet applied the simulation to other particulate materials. However, it could potentially be done for any powder of interest—powdered milk, for example. The simulation could also be used to model the formation and behavior of aerosols, sol/gel particle-producing systems or even aggregates of pollutants in the atmosphere," Matsoukas says.
The research team's results on titanium dioxide were detailed in a series of papers at the '98 American Institute of Chemical Engineering meeting in November 1998. The simulation method and comparison with numerical and theoretical solutions is detailed in the paper, "Constant-Number Monte Carlo Simulation of Population Balances," in a recent issue of Chemical Engineering Science.
For more information, call 814-865-9481 or e-mail txm11@psu.edu.