Design Criteria for Ventilated Filters

A number of filters were studied to determine the effect of air dilution on smoke filtration, both in well characterized acetate tow items and also in commercial filters that incorporated air dilution. A direct reduction of condensate and nicotine was observed in proportion to the degree of air dilution. Particulate filtration efficiency increased with air dilution. Gas phase delivery of aldehydes and CO decreased in greater proportion than the amount of air dilution. The commercial brands tested closely fitted the model developed in the filter tow study, except where mouthpieces or other flow channeling devices altered the filtration characteristics of the cigarette in varying degrees. Significantly, the results of the studies showed that the amount of air dilution, and not the physical means of air mixing, was the defining parameter to predict filter performance. Ventilation gives a useful design capacity that extends control of smoke filtration behaviour. By appropriate selection of tow denier per filament, total denier and cross-section shape, filter length and diameter, and the level of air dilution, filter properties can be adjusted to control gas and particulate phase deliveries, and the proportionality between the two.