Numerical model for solar drying mechanism of grapes using double glazed cabinet type solar dryer

Abstract

AbstractA development of an integrated mathematical model based on heat and mass transfer process was used to predict the shrinkage, moisture content, and thermal properties of grapes under different climatic conditions. A lab‐scale experimental test setup has also been developed, and tests are performed. The results obtained from the mathematical model are compared with experimental results and found to be in agreement with a maximum error of 14%. The moisture content evaluated from the model showed a fair agreement with the experimental results. An energy balance equation is used to obtain the cabinet temperature. A time‐dependent radiation flux density (I(t)) at a certain day is obtained through meteorological records. The effective moisture diffusivity (Deff) is obtained using Fick's diffusion equation for all the investigated conditions. The model is also validated with the results reported in the literature. Moisture is reduced from the initial moisture content of 4.88 kg of water per kg of dry matter to the final moisture content of approximately 0.38 kg of water per kg dry matter. The average radius of the grape decreased by 34.67% at the end of drying process (moisture content ~13%). The maximum water activity is 0.37 for the highest moisture content. The maximum radius change was found 4.9 mm from 7.5 mm for 50°C case. The maximum temperature increase of grapes with respect to drying time is 18°C. The results obtained using the proposed mathematical model can be used to predict product temperature, moisture content, and drying time for cylindrical‐shaped products.