Water-corn equilibrium: Temperature dependency of the GAB model parameters and calculation of the heat of sorption

By using sorption data for corn in the range of 4.4-60 degrees C, the temperature (T) variations of the G.A.B. model parameters (M(m), C(B) and k) were studied. As only the monolayer moisture (M(m)) varied (decreased) with temperature, a generalized GAB equation of four total parameters was obtained. This, together with the Clapeyron equation allowed a method to calculate the heat of sorption (L(b)) as a function of T and moisture content (M). For each temperature, L(b) presented a maximun some 30% above the heat of vaporization of water (L(f)), which occurred around the M(m), in congruence with the sorption theory. A similar behavior of L(b) was found using the Othmer method. In contrast, the Gallaher equation predicted an ever increasing L(b) up to 3 L(f) at very low moistures. The GAB-Clapeyron method is then proposed to calculate L(b) as a function of M and T.