Determination and interpretation of the critical moisture content (CMC) and the internal moisture content profile during the constant drying rate period.

In this study, the critical moisture content (C.M.C.) and the internal moisture content profiles during the constant rate period were determined experimentally for several conditions of convective drying of plaster. The experimental C.M.C values obtained allow us to validate the theoretical model of prediction of this parameter presented by KEEY [1] and SUZUKI [2] for drying rates higher than 3 x 10(-4) kg/(m(2).s) and to determine the equivalent moisture diffusivity at the external surface of plaster which was found to be equal to 3.9 x 10(-9) m(2)/s. On the other hand, expressions of the internal humidity profiles were determined without solving the second FICK's law and were found to be same that the ones obtained by KEEY [1] for thick products and KRISCHER and KROLL [3] for thin products by solving this law. The moisture diffusivity at the surface previously obtained was used in these equations to predict the internal humidity profiles during the constant rate period, Comparison between theoretical predictions and experimental humidity profiles obtained on plaster shows a quite good agreement.