Temperature distributions in a paper sheet subjected to a short pressure pulse from a heated plate

The temperature and thickness of dry papers were measured during compressio n with a heated plate using short pressure pulses. The papers used were han dsheets Into which thermocouples were imbedded at different positions in th e thickness direction when the sheets were made. Assuming a semi-infinite p late, the thermal diffusivity of the papers was then evaluated in terms of the distance from the heated plate and the applied pressure. The calculated thermal diffusivity was in general somewhat lower than values reported in the literature which may be partly due to the fact that it was calculated f rom dynamic data. The calculated thermal diffusivity increased with increas ing distance from the heated plate which is attributed to an effect of the heat transfer coefficient. The calculated thermal diffusivity also increase d with increased applied pressure, due to compaction of the web and the sho rter diffusion distances. An apparent thermal conductivity of the sheets wa s calculated from the experimental results, and it was found to increase wi th increasing distance from the heated plate and with increasing compaction of the sheet. A simple model of parallel plates of cellulose is suggested to explain the increase in thermal conductivity. Despite the simplicity of the model, it explains the experimental data relatively well.