Pressure Drop - Flow Relationships in Cigarette Filter Rods and Tobacco Columns

With a liquid displacement flow system, pressure drop and flow measurements were performed on filter rods, tobacco columns and multicapillary pressure drop standards. The purpose of these measurements was to determine the relative contributions of laminar or viscous flow, inertial flow, and entry and exit effects to pressure drop. Pressure drops were obtained both by forcing and drawing air through the article. No difference in pressure drop was obtained by either method provided that the flow was the same at a common point in the rod. This specification was necessary because of the change in flow rate due to gas expansion inside the rod. Pressure drop contributions from gas expansion, thermal effects and rod collapse were negligible. From regression equations, the major pressure drop component in all three types of article was viscous flow, ranging from 98 % of the total pressure drop in filter rods to 79 % in tobacco columns. Entry and exit effects were small in both filter rods and tobacco columns but were appreciable and the only other pressure drop contributor in multicapillaries. These measured entry and exit effects in multicapillaries agreed well with those estimated by flow theory. Inertial flow was found to contribute 1.5 % and 19 % of the total pressure drop in filter and tobacco rods, respectively. These contributions are reasonable from flow theory for packed columns.