Aloe vera ( Aloe barbandensis Miller), is an ancient plant, being used since before Christ. This plant is known as a source of valuable elements used in functional foods, cosmetics, and pharmaceuticals. The gel extracted from aloe vera is effective in treating many diseses. High moisture content is a prominent feature of aloe vera leaves. On the other side, the powder obtained from the dehydrated gel is commonly used for producing the by-products. Therefore, drying of aloe vera gel is of great importance. Drying process is one of the oldest methods of food preservation, based on removal of moisture from product via complex procedures of simultaneous heat and mass transfer. In most commonly used dryers, energy is usually provided by fossil fuels. High expenses, environmental contamination, and diminishing of fossil energy sources, besides not being available in different urban and rural areas are some disadvantages of using fossil energies. Solar thermal technology is rapidly developing in agricultural practices as an alternative, clean, and renewable energy. In this regard, many solar dryers have been designed and fabricated. In present study, aloe gel slabs with dimensions of 10×10×100 mm and initial moisture content of 99.43% were dried using oven, hot air, open sun, natural and forced convection solar drying methods. A photovoltaic system was designed and installed to supply the electrical power required for the solar dryer fan. The color values, L, a, and b, antioxidant activity, and drying duration of different drying methods were determined and compared. Fourteen empirical and semi-theoretical models were fitted to experimental data to find the best model describing drying process, based on the statistical parameters R 2 , RMSE and SSE. Oven and sun dried samples indicated the best and the worst qualities regarding color values, respectively. The highest and lowest antioxidant activities were respectively observed in hot air and solar dried samples. Forced convection solar drying method took the longest drying time, while hot air drying method needed the shortest. Wang and Singh model satisfactorily predicted the drying process under oven, hot air, open sun, and forced convection drying methods. However, Midili et al. model presented the best fit to natural convection solar drying data. The results obtained from the numerical solution of Fick’s second law based on finite difference method in two-dimensional geometry, indicated an acceptable compatibility to the experimental data. Key Words : Aloe vera, Drying, Solar Dryer, Mathematical Modeling, Moisture Diffusity.
