Experimental study of the moisture distribution inside a pulp sheet using MRI. Part II: Drying experiments

A spin-echo MRI sequence has been employed to measure moisture profiles during the drying of industrial never-dried pulp samples and was able to detect moisture even at very low:moisture content (6%). For the first time, moisture profiles have been measured for pulp samples approximately 2.5 mm thick with a spatial resolution of 0.15 mm under quite severe drying temperatures (up to 87 degrees C). The results highlight strong moisture gradients near the sample surfaces and no classical constant mass flux period, which leads to the conclusion that the evaporation at the surface is never fully compensated by the internal capillary flow during our drying experiments.