Abstract View
The Influence of the Water Activity Estimation Method on the Accuracy of the Hygroscopic Particle Growth Model
PATRICK O'SHAUGHNESSY, Alessandra Pratt, University of Iowa
Abstract Number: 81
Working Group: Health-Related Aerosols
Abstract
This research was motivated by the need to accurately determine deposition sites of pharmaceutical compounds that alleviate airway diseases with the use of computational fluid dynamic (CFD) modeling of the human lung. A fundamental aspect of the mathematical model developed to predict the hygroscopic growth of pharmaceutical particles is the relationship between the solute content of the droplet solution and its water activity – the ratio of the water vapor pressure near the surface of the droplet relative to the water vapor pressure in the atmosphere. A comparison between the use of Raoult’s Law and the use of a polynomial expression to model water activity relative to solute solution mass percent based on direct measurements was conducted. 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 as the test substance. Differential equations were solved using a MATLAB ordinary differential equation solver function. Experimental validation of the model was accomplished with the novel use of video photography to measure the growth of a salt particle frame-by-frame on a microscope slide placed on a light microscope. The experimental data indicated an initial growth phase that is consistent with the model when adjusted to simulate the dissolution of the salt core. Application of the polynomial expression proved to be more accurate than when applying Raoult’s Law for estimating water activity. Model accuracy during the initial growth phase is particularly important for particles entering the humid environment of the lung that are too large to reach equilibrium before entering the lower branches of the pulmonary system, which will therefore improve the accuracy of deposition site estimation within the lung. Future research will incorporate this added aspect of the hygroscopic growth model applied to more complex pharmaceutical compounds.