Solar drying of Ayas tomato using a natural convection solar tunnel dryer

An experimental study was conducted to determine the thin layer drying characteristics of Ayas tomato in a natural convection solar tunnel dryer. Open sun drying runs were also performed for comparison at the same time. The dryer was 20 in long and 5.4 m wide. This system can be used for drying various agricultural products. Also, it is simple in construction and can be constructed at a low cost with locally obtainable materials. Moisture content of tomato was reduced from 11.71 to 0.10 kg [H2O]/kg [DM] in about 101 h for open sun drying, whereas the solar tunnel dryer took only about 86 h. Depending on weather conditions, the solar tunnel dryer was found to be more efficient than the open sun drying and resulted in saving to extent of about 17.4% of drying time. Samples dried in the solar tunnel dryer were completely protected from insects, rain and dusts and the dried samples were of high quality in terms of colour and hygienic. In falling rate period, moisture transfer from the test samples was described by applying the Fick's diffusion model and the effective diffusivity was calculated. The experimental drying data of tomato were used to fit the Page, Logarithmic, Approximation of diffusion, Two-term and Midilli el at. models, and drying rate constants and coefficients of models tested were determined by non-linear regression analysis. Among the various models tested to interpret the drying behaviour of tomato, the Midilli el al. model was in good agreement with the experimental data obtained.