Measurement of z-direction moisture transport and shrinkage in the drying of paper

摘要

A new experimental rig has been constructed capable of measuring z-directional temperature, moisture and shrinkage during the drying of paperboard. The board to be tested was constructed from three 60 gsm sheets. Shrinkage was measured using eddy current displacement transducers and very thin copper meshes buried between the layers of the sheets. Moisture content was calculated from the impedance measured between pairs of the copper mesh electrodes. The temperature was measured using very thin thermocouples buried within the sheet. Preliminary results measured on an unbleached eucalyptus kraft pulp showed complex drying behaviour, with drying occurring first at the surface in contact with the hot plate and then secondly at the cooler surface where moisture was removed. The middle of the sample was the last part to fully dry out. This was in contrast to the shrinkage data, which showed that the bottom layer, from which the water was evaporated, was the last to shrink.