Ultrafine Aerosol Deposition in Planar Channel

A technique was developed for measuring the deposition of aerosols from 0.01 to 1pm diameter in a turbulent, planar channel flow. The ultimate goal of this project was to investigate ultrafine aerosol deposition in lung passageways. A procedure was developed to measure ultrafine aerosol deposition in a turbulent planar channel. Titanium tetrachloride, TiCl4, reacting with atmospheric water vapour created a polydisperse titanium dioxide, TiO2, aerosol which was injected into the flow. The aerosol deposited on electron microscope grids mounted on the bottom of a test section. Then the grids were photographed at 20,000 magnification with a transmission electron microscope, and a digital image analysis computer program counted and sized the particles on the grids. Two sets of tests were performed using slightly different apparatuses. An initial battery of tests was performed the summer of 1992. Then another battery of tests was run in the spring of 1993 incorporating many design improvements to the apparatus. Both tests had a step upstream of the grids to study the effects of secondary flows, a common occurrence in the lung. The data taken during the summer of 1992 showed five times greater deposition within the secondary flow than before the step. Deposition at the reattachment point of the flow was still higher than the non-secondary flow case, but lower than within the secondary flow itself. It has been surmised that the vortex in the secondary flow entrained the smaller particles and brought them much closer to the bottom of the wall. This created a higher concentration gradient to drive mass transfer. The data taken during the spring of 1993 showed that the secondary flows inhibited mass transfer. Within the secondary flow deposition only reached 10 percent of what was attained upstream of the step. It was concluded that the secondary flow was affected by the design changes which caused the diffusive boundary layer to be too thick for enhanced mass transfer to occur. However, the sample size was much smaller in 1993 than in 1992, so further testing should be conducted. Thesis Supervisor: John H. Lienhard V Title: Associate Professor Ultrafine Aerosol Deposition in Planar Channel Flow by