When the temperature of the mustard rises to the wet bulb temperature of the air energy, and all the heat absorbed from the air energy is used to evaporate the water, the drying speed shall remain constant at this time.
After entering the second drying stage, most of the evaporated water is free water, and most of the free water and colloidally bound water are removed during the drying process. The evaporation speed in the Chinese turnip is not entirely determined by the temperature of the drying air, but by the humidity of the air. The lower the relative humidity, the faster the moisture migration and evaporation. The temperature shall be gradually increased, thus the moisture content could reach an equilibrium moisture content. When the dry moisture content of the Chinese turnip is about 15%, the evaporation is stopped and the drying process is completed.