EFFECTS OF MW-HOT AIR PARAMETERS ON DRYING SOYBEANS IN THE ROTATING DRUM
The influence of microwave power, temperature and velocity of the hot air stream on drying rate, uniformity of drying and temperature of the material in microwave and microwave-convective drying of soybeans in the rotating drum was studied experimentally. Temperature of the material surface and drying uniformity were visualized and analyzed with the IR Thermal Imager. Compared with the sole microwave drying it was found that in the accelerating drying rate stage blowing hot air through the cascading bed of MW-heated soybeans is highly beneficial to reduce the material surface temperature, enhance drying rate and improve drying uniformity. However, in the falling drying rate stage the effect of hot air on drying rate was not so advantageous since the drying uniformity was worsened and the material temperature increased with hot air temperature. On the other hand, higher hot air velocity increases drying uniformity and reduces material temperature in the falling rate period which dominates the drying process but worsens the quality of soybeans quantified in terms of the cracking ratio.