عنوان مقاله [English]
One of the most important and essential parameters in studying the behavior of material drying and industrial dryer design is the materials moisture sorption isotherm curves. These curves show the relation between the equilibrium relative humidity of the surrounding of the material, which is called water activity and moisture content. Determination of the material moisture sorption isotherm is possible by static or dynamic systems. It could take many days, even weeks, to reach equilibrium in the static system. For this reason, a laboratory device, developed for / determining moisture sorption, using the dynamic method, was designed and constructed. Moisture sorption tests of wheat our in the dynamic device were undertaken at 25, 35, and 50 0C, at different water activities. The BET, GAB, Oswin, Smith, Iglesias-Shirife, Chung-Pfost, Halsey and Henderson sorption models were used for fitting the experimental data that resulted from the absorption process. The GAB, Chung-Pfost and Henderson models fitted the experimental data well. The net isosteric heat of sorption was determined by using the Henderson model and the Clausius-Clapeyron equation. This amount decreased from 33.34 to 2.98 (KJ/mole), with increasing moisture content from 0.02 to 0.20 (Kg water/Kg d.b) for wheat flour.