WATER - CORN EQUILIBRIUM: TEMPERATURE DEPENDENCY OF THE G.A.B. MODEL PARAMETERS AND CALCULATION OF THE HEAT OF SORPTION

ABSTRACT

By using sorption data for com in the range of 4.4-60°C, the temperature (T) variations of the GAB. 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, Lb presented a maxinuin 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.

Key Words and Phrases:

• Equilibrium Moisture Content
• Heat of Sorption
• Water Activity.