Firstly, the particles are placed in a heat transfer medium with a relatively high temperature and a relative humidity of less than 100%. In a short period of time, the surface is heated to the wet bulb temperature of the drying medium, the evaporation rate of water is increased rapidly, and the heat absorbed by the particles after a certain time is Evaporation of water consumes the same amount of heat and reaches equilibrium. The time in this phase is very short, the amount of water discharged is not large, and then enters the constant speed phase.
Then there is the constant speed drying stage. In some stages, the water evaporated from the surface of the particles is continuously replenished from the inside to the surface of the particles, and the surface is always kept wet. At this time, the drying rate remains unchanged, and the surface temperature of the particles remains unchanged. Therefore, the velocity of the surface airflow of the particles is increased, and the air film is thinned, and the drying rate can be increased.
After the water evaporates to a certain amount, the internal moisture of the particles is insufficient to completely wet the surface, the wet surface is gradually reduced, and the drying rate is gradually decreased. In this stage, the evaporation rate and heat consumption are greatly reduced, and the surface temperature of the particles is higher than the wet bulb temperature of the medium. Gradually increasing, the temperature difference with the carrier decreases until it is close to or the same. Finally, the equilibrium phase, when the moisture moisture and evaporation of the surface of the particles reaches equilibrium, the drying rate is zero.