THE EFFECT ON REGIONAL LUNG DEPOSITION OF COUPLED HEAT AND MASS-TRANSFER BETWEEN HYGROSCOPIC DROPLETS AND THEIR SURROUNDING PHASE

A procedure for coupling the heat and mass transfer between inhaled ae rosol droplets and the continuous phase that carries the droplets is d escribed and incorporated into a hygroscopic human lung deposition mod el. Heat and mass transfer coefficients at the airway walls are used t o account for the effect of the coupling on wall heat and mass transfe r. At 50% ambient RH, 20-degrees-C, and typical inhalation and nebuliz er flow rates, by far the largest effect of coupling is on extrathorac ic dosages, which are up to 137% and 50% greater than that predicted w ithout coupling for initially isotonic 2.5 mum MMAD (GSD 1.7) and 6.0 mum MMAD (GSD 1.7) aerosols respectively, with 10(6) droplets cm-3. Co upling affects dosages by <10% for all regions only if <25,000 droplet s cm-3 are present in the inhaled stream, indicating that coupling bet ween the aerosol droplets and the continuous phase is an important con sideration for modelling deposition of most hygroscopic medical aeroso ls.