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 dif ferential equations for moisture transfer within a sphere. Volume decr ease was assumed to be equivalent to the volume of moisture removed. A n 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 t he 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 thos e used to develop the model and different grape sizes could be predict ed.