10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Verifying the Hygroscopic Particle Growth Model during the Time Relevant to Lung Inspiration
PATRICK O'SHAUGHNESSY, Ralph Altmaier, Ross Walenga, Ching-Long Lin, University of Iowa
Abstract Number: 1257 Working Group: Aerosols in Medicine
Abstract Under high humidity, hygroscopic compounds attract, absorb, and retain water molecules resulting first in deliquescence, during which the salt core dissolves and a film of salt solution increases, followed by an increase in the resulting droplet solution up to an equilibrium size. The human airways provide an environment suitable for hygroscopic particle growth which will ultimately affect their deposition sites. This research is therefore motivated by the need to accurately determine deposition sites of pharmaceutical compounds that alleviate airway diseases with the use of computational fluid dynamic modeling of the human lung. A set of published coupled differential equations for predicting droplet growth and droplet temperature change were used to predict the growth of sodium chloride particles. Sodium chloride was used as the test substance because its properties to be incorporated into the growth model are well known and accurate. The added effect of salt core dissolution during the initial fast growth phase of the particles was also explored. Differential equations were solved using the MATLAB ordinary differential equation solver function (ODE45). Experimental validation of the model was accomplished with the novel use of video photography to measure frame-by-frame the growth of a salt particle on a microscope slide placed on an inverted light microscope. Using an apparatus containing computer-activated solenoid valves, room air was instantly replaced with air of a known humidity and the subsequent growth of the particle was then videotaped. The numerical model was validated through comparison with the experimental data over the initial 0.2 seconds of growth, consistent with the average residence time needed for transport of air from the top of the trachea to the first lung bifurcation. The experimental data indicated an initial growth phase that is consistent with the model when adjusted to simulate the dissolution of the salt core. This was achieved in the model by holding the solution concentration of the film of salt solution surrounding the salt core at saturation until the droplet grew to have a volume sufficient to hold the entire mass of the original salt particle in solution at saturation. The conventional hygroscopic model then proved to be sufficiently accurate when modeling further growth of the homogeneous salt solution droplet to its equilibrium size. Without incorporating model enhancement to account for salt core growth, the hygroscopic growth model overestimated droplet diameter by an average of 32.1% compared to the measured values during the time span < 0.2 sec. When incorporating salt core growth, the modeled values slightly underestimated droplet diameter by -3.1% over that time span. The deliquescence phenomenon during which the salt core dissolves is therefore a critical component missing from currently published particle growth models. Future research will incorporate this added aspect of the hygroscopic growth model applied to more complex pharmaceutical compounds.