The convective drying of grape seeds: Effect of shrinkage on heat and mass transfer

Detailed knowledge of thermal, hydric and mechanical phenomena within a product during drying helps decrease energy costs by reducing the exposure time and improve product quality by respecting the severe standards requirements. In this context, we simulate the spatiotemporal behavior of a highly deformable product saturated with water during convective drying. The numerical simulation of heat and mass transfer states consists of solving the full conductive solid phase conservation equation, the convecto-diffusive conservation equation of the liquid water together with the energy equation. These equations are coupled by the solid phase contraction rate due to water removal, which represents the shrinkage. The thermo-physical properties of the considered product, grape in our case, were determined from characterization experiments. Measurement series were carried out in a laboratory-drying loop and the obtained numerical results are found to be in good agreement with the experimental ones. The simulation allows the monitoring of the time evolution of temperature and humidity inside the product for different drying conditions. At 20% relative humidity of drying air, the ideal temperature was found to be 55 °C and not 60 °C, which minimizes the cost of drying and conserves better the structure of the product. The simulation results of a deformable product can be extended to deformable foodstuffs to minimize the exposure time needed for predefined final water content. Practical applications The research of optimization of drying process of grapes led to the finding of the corresponding temperature and relative humidity of convective drying air. A proposed simulation model which takes the shrinkage of this product into account describes its behavior, gives the exposure time needed for predefined final water content. The model can be extended to other deformable products.