Studies on the Natural Smouldering of Cigarettes: III. Determination of the Thermal Properties of Tobacco Shreds Packed in Columns

The values of effective thermal conductivity, specific heat and thermal diffusivity of various kinds of tobacco shreds, which are necessary for the solution of heat transfer problems of a smouldering cigarette, were determined. Effective thermal conductivity of tobacco shred packed into simulated cigarette columns was measured by a transient hot-wire method as a function of packing fraction at conditions of 20°C and 60 % relative humidity. Specific heat was measured with the aid of a differential scanning calorimeter (DSC). The thermal diffusivity was obtained from the values of effective thermal conductivity, specific heat and packing density. Effective thermal conductivity increased with increasing packing fraction (1 - e) and was uniformly expressed as a function of the total void fraction (et) inside the column regardless of tobacco types and stalk positions, whereas thermal diffusivity decreased with the packing fraction. At the same packing fraction, bright shreds produced higher values of effective thermal conductivity as well as higher specific heats (although specific heat was independent of the packing fraction) but had lower thermal diffusivity values than Burley and Matsukawa shreds.