A NEW CORRELATION FOR THE ESTIMATION OF MOISTURE DIFFUSIVITY IN CORN KERNELS FROM DRYING KINETICS

The modelisation of cereal drying kinetics is more and more often perf ormed by the diffusion equation (Fick's law) for homogeneous materials rather than lumped or semi-empirical equations. The heterogeneity of the material is accounted for by the use of an effective diffusivity t he prediction of which is essential for the determination of the funct ional relationship between diffusion coefficient and grain moisture co ntent and temperature. For this dependence, the method of resolution m ay be analytical or numerical. In this study, the estimation of diffus ion coefficient is based on drying curves obtained with grains in the range of initial moisture content of 18-50% and a temperature of 50-12 0 degrees C. The important result corresponds to the finding that the moisture diffusivity is a function not only of variables of the state i.e. moisture content and temperature, but also of the initial moistur e content as in the following: D = A(D) X(o) exp(B X). A(D) and B are both dependent on temperature respectively as in Arrhenius and linear functions. This law reduces the universality of the diffusion concept. It has been validated in other experiments carried out under differen t operating conditions.