Carbon nanotubes (CNTs) are being used in many applications and filtration of airborne CNTs is very important for CNT control. Penetration of airborne multi-wall CNTs through a screen filter is studied using a numerical model and the results are compared to experiments. The flow through the screen filter is simulated using a three-dimensional model, and the particle capture due to diffusion, interception and inertial impaction are covered. The length and diameter of CNTs are determined from electron microscopic images and used in the model. In the filtration experiments, the challenging CNTs are classified by a differential mobility analyzer. Therefore we compute the drag force and diffusion coefficient for CNTs based on their mobility sizes. The effects of CNT rotation and orientation on the drag, diffusion coefficient and interception length are considered in the sense of average over a large number of particles. Both the modeling and experimental results show that the CNT penetration is less than the penetration for a sphere with the same mobility diameter, which is mainly due to the larger interception length of the CNTs. The modeling results for CNTs agree reasonably well with experiments when the mobility diameter is less than 250 nm, but significantly underestimate the penetration when the mobility diameter is larger than 250 nm. The discrepancy is attributed to possible curling and bending of the longer CNTs in the flow.
Bibliographical noteFunding Information:
The work was partially supported by the NSF grant (Award ID: 0646236) on “Experimental and Numerical Simulation of the Fate of Airborne Nanoparticles from a Leak in a Manufacturing Process to Assess Worker Exposure.” The authors thank the support of members of the Center for Filtration Research: 3M Corporation, Boeing Company, Cummins Filtration Inc., Donaldson Company, Inc., Entegris Inc, Hollingsworth & Vose Company, Samsung Semiconductor Inc., Shige-matsu Works CO., LTD, TSI Inc., and W. L. Gore & Associates and the affiliate member National Institute for Occupational Safety and Health (NIOSH).