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 determ ined experimentally for several conditions of convective drying of pla ster. 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) a nd to determine the equivalent moisture diffusivity at the external su rface of plaster which was found to be equal to 3.9 x 10(-9) m(2)/s. O n the other hand, expressions of the internal humidity profiles were d etermined without solving the second FICK's law and were found to be s ame that the ones obtained by KEEY [1] for thick products and KRISCHER and KROLL [3] for thin products by solving this law. The moisture dif fusivity at the surface previously obtained was used in these equation s to predict the internal humidity profiles during the constant rate p eriod, Comparison between theoretical predictions and experimental hum idity profiles obtained on plaster shows a quite good agreement.