DEHYDRATION OF POTATO: 3. INFLUENCE OF PROCESS PARAMETERS ON DRYING BEHAVIOR FOR NATURAL CONVECTION SOLAR DRYING CONDITIONS

Abstract

Conditions for conducting laboratory simulations of natural convection solar-drying were investigated. In the solar-drying experiments, air speed in the empty drying chamber (called the air flow potential, AFP) varied from 1.3 to 1.8 m/s, while inlet temperature to the loaded drying tower varied from 57 to 71°C. In laboratory simulations of solar-drying, the influence of variation of air flow rate, product loading density and inlet air temperature on drying behavior of potato sticks (12.5 × 6 × 40 mm) was investigated. It was determined that potato sticks could be solar-dried in 5–6 h to a water activity of 0.7 (15 g water/100 g solids) under natural convection conditions. Drying rate increased with increase of inlet air temperature and/or AFP, with the effect of AFP being most noticeable at the beginning of the drying process. The time required to remove 96% of the original moisture varied by ± 5% for the AFP variation noted in solar-drying (1.54 ± 0.23 m/s) and varied ± 10% for the variation of inlet air temperature noted in solar-drying (65 ± 5°C), indicating a higher sensitivity for natural convection solar-drying to variability of inlet air temperature than fluctuating AFP. The ratio of increase in drying time to increase in bed depth is less than 1, so overall dryer productivity increased with increasing bed depth.