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ABSTRACT
Tobacco columns are extreme examples of heterogenous packed beds, which have various cut-filler shapes and a wide range of size distribution. The behavior of mechanical filtration through tobacco columns has been investigated by using polystyrene latex (PSL) standard particles to compare the actual filtration efficiency with the predicted filtration efficiency calculated by theoretical equations for spherical packed beds. The influence of cut-filler shape and the range of cut-filler size distribution on filtration efficiency have been examined. The effect of diffusion in tobacco columns was lower and the effect of interception and inertia were higher than in spherical packed beds. These results show that a partially faster flow could have occurred in tobacco columns. It means that it is difficult to utilize the theoretical equations for spherical packed beds to heterogenous packed beds as proposed. Filtration efficiency through tobacco columns had a relationship with the factor that shows cut-filler shape and size distribution (r = 0.894, p < 0.05) and the factor that shows cut-filler size distribution (r = 0.683, p < 0.15). The factor showing cut-filler shape and size distribution was expected to be an effective factor of filtration efficiency for heterogenous packed beds. From these experiments, empirical equations that can be applied to tobacco columns have been proposed, and the prediction accuracy during burning was validated. It has been found that the prediction accuracy was precise, revealing the importance of taking the influence of cut-filler shape and size distribution into account in the filtration equations.
Copyright © 2016 American Association for Aerosol Research
EDITOR:
Nomenclature
| Cm | = | slip correction efficiency (−) |
| D | = | distribution factor (−) |
| DG | = | granular particle diameter (μm) |
| Di | = | sieve size i (mm) |
| Dm | = | average of sieve size (mm) |
| DP | = | aerosol particle diameter (μm) |
| Ε | = | filtration efficiency (−) |
| fi | = | normal cumulative distribution ratio as i sieve size (−) |
| fm | = | average of normal cumulative distribution ratio (−) |
| G | = | gravity parameter (−) |
| K | = | shape-size factor (−) |
| L | = | length of packed bed (mm) |
| R | = | interception parameter = DP /DG (−) |
| Re | = | Reynolds number (−) |
| Sc | = | Schmidt number (−) |
| Stk | = | Stokes number (−) |
| Stkeff | = | modified Stokes number (−) |
| v | = | liner velocity (m/s) |
| α | = | packing ratio (−) |
| ϵ | = | void ratio (−) |
| η | = | single collection efficiency (−) |
| ηD | = | single collection efficiency of diffusion (−) |
| ηG | = | single collection efficiency of gravity (−) |
| ηI | = | single collection efficiency of inertia (−) |
| ηR | = | single collection efficiency of interception (−) |
| μ | = | air viscosity (Pa.s) |
| ρa | = | air density (10−3 g/cm3) |
| ρP | = | aerosol particle density (g/cm3) |
| ΔP | = | pressure drop through packed beds (Pa) |