Optimization of hybrid solar drying of okra by using response surface planes

In order to optimize solar drying, a study by surface plane of centered response composite types was used. After the choice of 3 factors, 16 experiments were carried out and led to a mathematical model of the second degree linking the responses (drying time and energy consumption) to the factors considered influential.After carrying out the experiments and analyzing the results using Minitab software, the study has allowed determined the optimal conditions needed to obtain a drying time and a minimum energy consumption to obtain a dry product with a water content of 15% in wet base. The analysis of the main effect profiles as well as the mathematical correlation show the following: • energy consumption was proportional with the thickness of the slice, the temperature and the speed of the air; • the drying time was proportional to the thickness of the slice and inversely proportional to the temperature (from the center of the domain to its upper level) and the air velocity; • a good concordance between the selected models and the experimental results was observed with correlation factors of 99.3% and 99.8% respectively for drying time and energy consumption. The optimal values of drying time DS=318.2922 minutes and energy consumption CE=7.1859 kwh with an overall desirability of 90.29% were obtained with the following optimal operating conditions: • Drying air temperature of 40°C; • Product thickness of 11.5mm; • Air velocity of 1.02m/s.