Non-uniformity investigation in a combined thermal and microwave drying of silica gel

Local temperature and moisture were determined to analyze the uniformity in vertical and horizontal planes in a combined thermal and microwave (CTMW) drying chamber. Furthermore, the effects of microwave power and temperature of hot air on drying uniformity were also investigated. It could be concluded that the dried silica gel in the center area of the drying chamber obtained the highest drying rate and temperature, followed by the silica in the outermost and the middle portions. The dehydration difference of the three layers decreased with the drying time, whereas the drying uniformity increased. Overall, the change in uniformity in the horizontal direction of the drying cavity was not obvious, and the temperature and moisture content gradients mainly occurred in the vertical direction. The temperature gradient between the layers reached 5°C. As the hot air temperature and microwave power increased, the drying rate improved and the drying uniformity decreased.