DESIGN AND PERFORMANCE TESTING OF AN INDUSTRIAL-SCALE INDIRECT SOLAR DRYER

In this paper, an indirect solar dryer was developed and tested for drying food. This unit operation is an interesting technique for preservation in agricultural applications. The dryer was designed at industrial scale in order to carry out experiments in real applications and to get concrete results. It operated without additional energy in the passive and active modes, allowing the comparison between the two. The relationship between the solar collector air temperature and the relevant ambience parameters was deduced. The collector efficiency reached 66.56 % with forced ventilation and 46.32 % with natural ventilation. It also increased linearly with the solar radiation varying between 400-800 W/m(2) for air velocities ranging between 1 and 1.40 m/s. The effect of the air velocity on the collector efficiency was negligible for solar intensities close to 800 W/m(2). The tomato drying occurred mainly in the falling drying rate period. On average, the moisture content in dry basis was reduced from 14.32 kg water/kg dry matter to 0.14 kg water/kg dry matter. The equilibrium moisture content of tomatoes was reached after 12 h when the system was used with one layer. In the case it was used with four layers, the difference among the four durations of drying was one hour between each tray.