Collection of aerosol particles by packed beds

Abstract

b The Kuwabara flow model in a system of multiple spheres is used to predict the collection of aerosol particles from flow through a packed bed. Diffusional and interceptional collection efficiencies are predicted by a theoretical procedure which was derived using a boundary layer approach accounting for the flow interference effects of neighboring collecting spheres in packed beds. The results were compared with available experimental data and satisfactory agreement was obtained.Packed beds have been used widely for many industrial operations such as absorption, adsorption, and distillation due to their large contact area between gas phase and solid media or between liquid and solid. Recently there has been increasing interest in employing the packed bed concept for removing aerosol particles. A major advantage of aerosol filtration by packed beds is that by selecting the proper bed media, both particulate and gaseous pollutants can be simultaneously collected, the particulates removed by filtration, and the gases removed by adsorption. The possibilities for using packed beds a t high temperatures and pressures also make their development more attractive.It is well known that in packed beds consisting of fine media and operating a t a low flow rate, small particles are collected primarily by Brownian diffusion. As particle size increases, direct interception and gravitational settling become important. Eventually, inertial impaction will dominate if particle size and flow rate are further increased.In filtration study, it is first necessary to understand flow field inside the filter media. For packed beds, the individual collectors or granules either have or can be assumed to have a spherical or nearly spherical shape. These individual granules or spheres are closely packed together and the mutual interference effects of neighboring spheres on the flow field have to be taken into consideration. However, most previous theoretical studies such as those by Fuchs ( I ) and by Friedlander ( 2 ) are based on the model of an isolated sphere collector. It is therefore necessary to employ an additional empirical correction factor when these results are to be applied to packed beds. Consequently, many theoretical studies of aerosol filtration that are based on an improved model have been reported recently (3-7).A single sphere efficiency may be defined as the ratio of the cross-sectional circular area surrounded by limiting streamlines of the flow approaching the collecting sphere to the projected area of the sphere. The limiting streamlines are such that all the particles passing within them will be collected by the sphere while all the particles outside the streamlines will escape it. With this representation, the concentration ratio of the particles collected inside the packed bed to those approaching it, or the overall efficiency of particle collection by the bed, can be shown to relate to the single sphere efficiency as follows:(1)where E = overall collection efficiency of packed bed, 7 = single sphere efficiency, L ...

Aerosol Capture in Granular Beds in the Sedimentation and Diffusion Dominated Regimes

“…In an attempt to test this formula, Lee and Gieseke (1979) prepared a graph of q Pe R/(1 + R) as a function of A1/3Pe1/3~/ (1 + R), using selected data of Thomas and Yoder (1956), Paretsky et al (1971), Gebhart et al (1973), and Schmidt et al (1978). Lee and Gieseke point out that very little of the data fall in the interception dominated regime, owing to the small values of R encountered in most experiments and the onset of other capture mechanisms.…”

Experimental study on mechanical filtration through tobacco columns: Influence of cut-filler shape and size distribution on filtration efficiencies

“…Comparison of previous research on filtration models for spherical packed beds In order to investigate the suitability of the filtration equations for spherical packed beds reported by previous research (Lee and Gieseke 1979;Kimura et al 1983;Mann and Goren 1984;Mori, et al 1985;Otani et al 1989) to tobacco columns, a comparison study on filtration efficiency between the predicted value by the research and the experimental value was carried out. It is assumed that the collection mechanism through tobacco columns would be dominated by diffusion and interception because a number of small cut-fillers are included in tobacco columns due to fragmentation in the manufacturing process and the low linear velocity through tobacco columns under smoking conditions.…”

Sensitivities Of Diesel Particulate Filter Clean And Loading Models

“…The changes of the filtration efficiency and pressure drop across the particulate filter porous wall, as well as the particulate deposit thickness, density, porosity, and permeability was studied. Their model was based on Kuwabara, Lee and Gieseke [9,10]. The model was later modified and outlined in Konstandopoulos [5,11].…”