Granular Filtration for Airborne Particles: Correlation Between Experiments and Models Laleh Golshahi, 1 Jalal Abedi 2 * and Zhongchao Tan 1 † 1. Department of Mechanical and Manufacturing Engineering, Schulich School of Engineering, University of Calgary, Calgary 2500 University Dr. N.W. Calgary, Alberta, Canada T2N1N4 2. Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, Calgary, Alberta, Canada Granular filtration has been widely used for liquid filtration and hot gas filtration, but less is known for the filtration of airborne particles, especially the ultrafine ones, at the room conditions. A cylindrical packed bed was designed and tested for the filtration of particles in the range of about 10 nm to 15 m in diameter at different configurations and kinetic conditions. Three sizes of uniform glass beads (2, 4, and 6 mm in diameter) were tested as the filtration media each at three media thicknesses (H = 2.5, 7.6, and 12.7 cm), and at two airflow rates (50 and 65 liters per minute). The filtration efficiencies were the lowest for particles between 0.1 and 1 m in diameter. The particle filtration efficiency decreased with the increase in the granule size and the airflow rate, but a thicker bed corresponded to higher filtration efficiency. The experimental results showed much higher efficiency than existing models can predict, therefore, an empirical model using least square method is reported. La filtration granulaire est utilis´ ee abondamment pour filtrer les liquides et les gaz chauds, contrairement ` a la filtration des particules a´ eriennes, surtout celles d’une taille ultrafine, aux grandeurs externes. On a conc ¸u puis mis ` a l’essai une tour de filtration cylindrique destin´ ee ` a la filtration des particules dans la plage des 10 nm ` a 15 m de diam` etre environ ` a diff´ erentes configurations et conditions cin´ etiques. On a fait l’essai de trois tailles de billes de verre uniformes (2, 4 et 6 mm de diam` etre) comme mat´ eriaux filtrants, et ce selon trois ´ epaisseurs (H = 2.5, 7.6, et 12.7 cm) et deux d´ ebits d’air (50 et 65 litres par minute). L’efficacit´ e de la filtration s’est av´ er´ ee la plus faible dans le cas des particules variant de 0.1 ` a1 m de diam` etre. L’efficacit´ e de la filtration des particules diminuait en fonction de l’augmentation de la taille des granules et du d´ ebit d’air, mais une tour de filtration plus ´ epaisse offre une meilleure filtration. Les r´ esultats exp´ erimentaux ont montr´ e une efficacit´ e beaucoup plus ´ elev´ ee que les mod` eles existants sont en mesure de pr´ edire; en cons´ equence, un mod` ele empirique utilisant la m´ ethode des moindres carr´ es est indiqu´ e. Keywords: granular filtration, packed bed, airborne particles, empirical model INTRODUCTION F ollowing the work by Tien’s group (Rajagopalan and Tien, 1976), extensive research has been conducted for granular filtration of particles in water or hot gas clean- ing. Recently, there is a growing interest in investigating its performance on airborne particle filtration, especially for ultrafine (sub-100 nm) ones (Ozis et al., 2004; Wu et al., 2005; Quevedo et al., 2008), likely due to the increasing envi- ronmental concerns of airborne nanoparticles. In fact, there has been evidence that some particles that are non-toxic in the micron size range may be toxic in the nanometer range. Studies using rats exposed to the same mass of 250 and 20 nm titanium oxide (TiO 2 ) showed that more nanoparti- cles were stored in the interstitial tissue of the lung, which developed noticeable inflammatory responses (Seaton et al., 1995). This article introduces a new simple design for a packed bed granular filter. Kinetic performance of the designed bed was eval- uated in the laboratory environment. Based on the obtained data and modeling results, a more precise empirical model was devel- oped for prediction of the filtration efficiency of the packed beds. EXPERIMENTAL METHODS The schematic diagram of the packed bed is depicted in Figure 1. The packed bed was designed with a cylindrical cross-section to ∗ Author to whom correspondence may be addressed. E-mail address: jabedi@ucalgary.ca † Alternate corresponding author E-mail address: tanz@ucalgary.ca Can. J. Chem. Eng. 87:726–731, 2009 © 2009 Canadian Society for Chemical Engineering DOI 10.1002/cjce.20215 | 726 | THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING | | VOLUME 87, OCTOBER 2009 |