Evaluation on microwave drying of waste paper towel with multi-magnetron and mode stirrer

The thin-layer drying performance for a typical solid waste (paper towel) was evaluated at hot air temperatures of 90–130 °C (0.5 m/s air velocity) and microwave powers of 200–800 W in a bench-scale microwave combined convective drying setup. Influences of hot air and radiation modes (multi-magnetron and mode stirrer) on the temperature distribution uniformity were examined. The effective moisture diffusivities of sample during pure hot air drying ranged from 6.07 × 10−9 to 1.31 × 10−8 m2/s, while those for pure microwave drying were from 3.54 × 10−8 to 1.52 × 10−7 m2/s. The apparent activation energy of sample in pure hot air drying was estimated as 23.17 kJ/mol, while that for pure microwave drying was 22.64 W/g. The effective moisture diffusivities of sample in combined drying ranged from 5.71 × 10−8 to 2.05 × 10−7 m2/s. The heating uniformity for microwave was improved effectively by the combined drying. The application of the mode stirrers and multi-magnetron radiation modes further improved the microwave heating uniformity. Midilli model can well describe moisture content of paper towel over time.