THIN LAYER DRYING OF GARLIC SLICES USING CONVECTION AND COMBINED (CONVECTION - INFRARED) HEATING MODES

Thin layer drying of garlic slices has been studied under convection and combined infrared–convection heating modes. Four levels of inlet air temperature 45, 55, 65, and 75°C and three levels of air velocity of 0.25, 0.75, and 1.25 m/s were used for the convection drying experiments. While, for the combined infrared-convection, three levels of radiation intensity of about 0.075, 0.15 and 0.225 W cm-2 and three levels of air temperatures 45, 55 and 65°C were studied at inlet air velocity of 0.75 m/s. Three mathematical models (Page, Modified Page, and Henderson and Pabis) were examined for describing the drying behavior of garlic slices under the above mentioned experimental parameters. The results were compared to their goodness of fit in terms of coefficient of determination (R2), Standard deviation (SD), average percentage of error (% E), chi-square (χ2) and the modeling efficiency (EF). The results showed increases in drying rate, thermal efficiency, rehydration ratio, flavor strength, and colour difference, and showed decreases in drying time and specific energy consumption for the combined (infrared–convection) heating mode in comparison with convection only. The Page model satisfactorily described the drying behavior of garlic slices and predicted the changes in garlic slices moisture content as compared with the modified Page and the Henderson and Pabis models. Meanwhile, for the convection heating mode, the drying constant (k) increased with the increase of air temperature and air velocity while, the constant (n) decreased, while, for the combined mode, the drying constant (k) increased with the increase of radiation intensity and air temperature. However, the constant (n)decreased.