Reflux drying of aerosols.

The goal of our efforts has been to generate high aerosolized drug concentrations, so that the entire inhaled dose may be delivered to the animal in a relatively short time interval, typically one minute or less. In this report, we have examined the use of a reflux condenser coupled with an external heat source as a means to dry aerosol particles. The specific interest was to examine the parameters influencing the drying process and identify practical experimental conditions that would allow drying of aerosol particles. Aqueous solutions of cesium chloride were atomized with an ultrasonic driver, and the resulting cloud was subsequently passed through an externally heated column with an inner condenser cooled with flowing water. Increasing the airflow rate increased the output of total mass(water + CsCl) but decreased the particle transit efficiency. At a constant airflow rate, decreasing the wall-to-condenser temperature ratio led to a progressive increase in particle loss, but a maximum was observed in the water removal efficiency. While thermal diffusion and the thermophoretic effect may have an impact on the drying process, non-steady state conditions, convective currents, inertial impaction, turbulence, and changes in the condenser boundary layer are likely to have a role in particle drying. In spite of the numerous complexities, practical operating conditions were identified for efficient particle drying with high dry mass transit efficiency.