Energy and Exergy Analysis of Microwave Drying Kinetics in Cucumber Peels With Quality Assessment

Abstract

This study investigates the effects of microwave drying on cucumber peels, focusing on how drying time varies with power levels and material thickness. Experiments were conducted using a household microwave at power levels of 90, 360, and 600 W on samples with 2.5 and 5 mm thickness. A digital balance recorded a mass loss at 1-min intervals, and drying continued until moisture content was below 0.5% d.b. It finds that drying time decreases significantly as power increases. Drying at the 90 W power level took 27 min, while at drying 360 and 600 W, it takes 9 and 5.5 min, respectively. Doubling the sample thickness from 2.5 to 5 mm significantly increases drying time, indicating that thicker materials require more time for moisture to diffuse. Microwave drying was also found to influence nutrient retention, with high-power drying preserving more polyphenols and flavonoids, which are sensitive to prolonged heating. Specific moisture extraction rate (SMER) was highest at 360 W for 5 mm samples, showing optimal moisture removal efficiency at this setting. Specific energy consumption (SEC) was lowest at 360 W and 5 mm, indicating this combination as the most energy-efficient. Also, high-power drying retains more sugar, while lower-power settings lead to greater sugar degradation due to prolonged heat exposure. Moreover, the exergy efficiency for drying cucumber peels at different microwave power levels and thicknesses shows that at 90 W, the exergy efficiency is 76.43% for 5 mm and 40.51% for 2.5 mm, while at 360 W, it is 40.18% for 5 mm and 24.88% for 2.5 mm, and at 600 W, it is 31.77% for 5 mm and 16.40% for 2.5 mm. Thicker peels at 5 mm consistently exhibit higher exergy efficiency across all power levels, with the highest efficiency observed at 90 W.