The Use of Pressure Drop Measurements for Estimating Ventilation and Paper Porosity

Abstract

The recent increase in the number and volume of ventilated cigarette brands has created a need for a simple, non-destructive means of measuring the degree of air dilution. Two techniques currently in use require the use of auxiliary equipment or specialized analyses. One of these is the sleeve method of Norman (1) which encloses the ventilation portion of the cigarette in a small chamber and measures the flow into this chamber while a puff or alternatively a constant flow is withdrawn from the cigarette. The degree of air dilution is thus estimated from the ratio of the volumetric flow rates. A second method is that described by Reynolds and Wheeler (2), which encloses the cigarette except for the burning coal in an atmosphere of argon. The amount of argon in the mainstream smoke provides a measure of the dilution. Since both of these techniques require enclosing the burning or unlit cigarette in a chamber and separating the diluting flow from the mainstream flow by means of seals, they can sometimes be difficult to use in routine measurements. A method which avoids these difficulties is to utilize the encapsulated and unencapsulated pressure drop of the unlit or lit cigarette to estimate the amount of air dilution. Since pressure drop and volumetric air flow are essentially directly proportional to each other in cigarette filters (3, 4), the difference between the encapsulated and unencapsulated pressure drop provides a measure of the degree of filter ventilation. This was recognized by Reif (5), who derived the appropriate equations for a ventilated filter. While it is known that pressure drop in a tobacco rod is only approximately proportional to flow, the non-linear effects are small enough so that pressure drops can also be used to estimate ventilation in this portion of the cigarette. Figure 1 illustrates the dilution processes occurring in a cigarette, and the various pressure drop measurements that can be used to estimate these. Each of these pressure drops can be conveniently measured using an accurate pressure drop machine, and a rubber sleeve encapsulator. For the measurements reported herein, a critical flow orifice pressure drop tester with an adjustable length rod encapsulator of Celanese design was used. The orifice was calibrated to a flow of 17.50 ± 0.15 mVs at 760 torr and• Presented, in part, at the Coruta Technology Study Group meeting held in Munich, Germany, in September 1977.

The Effect of Filter Ventilation on the Yield and Composition of Mainstream and Sidestream Smokes

“…The cigarettes were smoked to 33 mm butt lengths in the standard conditioned atmosphere. Filter ventilations were calculated using the pressure drop method of K eith ( 14). Ventilation calculated r in this way using an unlit cigarette is somewhat lower than for the lit cigarette, but this should not influence the main conclusions.…”

Physical parameters of the ventilated filter cigarette

“…The linear flow model of the VFC, Fig.6, for P T = 0 and R i0 = R T = 0 corresponds to the filter with K perforated segments detached from the tobacco part. Therefore, from steps (1-4) and (8), the ventilation V FD and pressure P FD are obtained, respectively, by setting R i0 = 0 in step (2). The values of A, R iK , and R' iK obtained from the K-th iteration in step (3) correspond to this filter, while the values of V F , step (4), and P M , step (8), correspond to the values of V FD and P FD , respectively.…”

“…Thus, Q Vk is the total lateral flow entering the filter from the k-th ventilated segment, Fig.1.b. It is known that total ventilation increases once the cigarette is lit [2]. The order of the V T degree is 0.05 (or 5%) which is low compared to the V F degree and V F degree is usually higher than 0.2 (or 20%).…”

“…The pressures P FC , P ME , P MC , and P MBk , k=1,2,…,K can be measured using an accurate pressure drop machine calibrated to the standard air flow Q M which has a rubber sleeve encapsulator with adjustable length [2]. The measurements of P MBk still require an apparatus which must also has a rubber sleeve encapsulator with adjustable length, from l T to l T +l F -l M -l' VK , and a rubber stopper for closing the entrance of the flow Q E .…”

“…Till now, the recommended pressure measurements were P FC , P ME , P MC , and P Mpressure on the VFC [1,2,3] and P FP -the pressure on the filter prototype (filter detached from the tobacco part which has one ventilated segment of the length l' V = AT placed at end T), [4]. The distribution of the lateral flows used here and in the references [1,3,4] represents a better approximation than those reported by Keith [2]. However, using this better distribution and pressures P FC , P ME , P MC , and P M , it is impossible to estimate V F , V T and V without the knowledge of the air permeabilities of the PWP and TP, except in the case when TP has only one row of holes [1].…”