Comparison of drying kinetics of mint leaves by photovoltaic / thermal solar dryer and natural drying

In this research, a combined photovoltaic / thermal solar dryer containing phase change materials (PCM) was designed and fabricated for drying mint leaves. The performance of this dryer was evaluated under the climatic conditions of Mashhad city with a longitude of 59.62 and a latitude of 36.26. The components of this dryer mainly include: photovoltaic panel, solar collector, blowers, phase change material chamber containing paraffin wax and drying chamber. Solar dryer and natural drying in shade as two different drying types were used to perform experiments on mint leaves. The initial moisture content of the mint leaves was 80% which reduced to 12%. The required drying time for the combined solar drying and natural drying was 290 minutes and 1560 minutes, respectively. Eight thin layer drying models available in the literature were fitted to the experimental data in which the Two-term model and the Wang and Singh model were the best fit models for natural and combined solar drying respectively. These models have the highest correlation (highest coefficient of determination and least root mean square error and Chi-square) with the experimental moisture ratio among the other models.