Moving boundary model for simulating moisture movement in grapes

A diffusional model for simulating grape dehydration with simultaneous shrinkage was developed using a finite difference method to solve differential equations for moisture transfer within a sphere. Volume decrease was assumed to be equivalent to the volume of moisture removed. An effective diffusivity coefficient was developed from drying data at air temperatures between 30 and 90 degrees C and constant air velocity. Effective diffusivity varied with drying air temperature following the Arrhenius equation. Experimental data at two different diffusional periods in drying were adequately represented by this moving boundary diffusivity model. Drying kinetics at temperatures different from those used to develop the model and different grape sizes could be predicted.