MODELING OF MICROWAVE DRYING OF GRAPES

Thompson seedless grapes were dried into raisins under combined convec tive and microwave drying in a single mode cavity type of applicator a t 2450 MHz with varying operating parameters viz., air temperature, mi crowave power density, and superficial air velocity. A number of exper iments designed to determine the relationships between grape physical and electrical properties and grape moisture content were executed. Th ese relationships were then used in the development of a model of micr owave drying. The model was based on the continuum approach and includ ed the terms describing internal heat generation, convective heat tran sfer, and evaporation. The internal resistance to moisture transfer wa s described by a Fick's type diffusion equation. The effective diffusi vity parameter included the combined effect of microwave power and liq uid diffusion on moisture transport. A moving co-ordinate system based on non-variate dry solids was adopted to handle the problem of shrink age. The model was solved by the ''Method of Lines''. The simulated re sults were tested with the experimental data and good agreement was fo und proving the validity of the procedures.