Factors affecting drying rate of drying equipment and classification of drying equipment

1. Drying rate of drying equipment
  
  1. The weight lost by the material in unit time and unit area is called drying rate.
  
  2. Drying process
  
  (1) Initial period: the time is relatively short, which is to adjust the material to the same condition as the dryer.
  
  (2) Constant rate period: This is the period when the drying rate is large. The water evaporated on the surface of the material is just replenished internally, so the water film on the surface is still there and kept at the wet bulb temperature.
  
(3) Deceleration Phase 1: At this time, the evaporated water cannot be completely replenished inside, so the surface water film begins to break and the drying rate begins to slow down. The material is called the critical point at this point, and the water contained at this time is called It is the critical moisture.
  
  (4) The second phase of deceleration: In this phase, only dense materials are available, because water is not easy to come up; but porous materials do not. Most of the evaporation of the water in the first stage takes place on the surface. In the second stage, the water film on the surface is completely gone, so the water diffuses to the surface in the form of water vapor.
  
2. Factors affecting constant drying rate
  
  1. Air temperature: If the temperature is increased, the diffusion rate and the evaporation rate of sweat will increase.
  
  2. Humidity of the air: When the humidity is lower, the evaporation rate of water becomes larger.
  
  3. The speed of the air flow: the faster the speed, the better the mass transfer and heat transfer effects.
  
  4. Shrinkage and surface hardening: Both of these phenomena will affect drying.
  
3. Classification of drying equipment
  
  Excess water should be removed as much as possible before the material enters the equipment.
  
  1. Dryer for solids and pastes
  
  (1) Disc dryer
  
  (2) Screen conveyor dryer
  
  (3) Rotary dryer
  
  (4) Screw conveyor dryer
  
  (5) Take-up dryer
  
  (6) Stirring dryer
  
  (7) Flash evaporation dryer
  
  (8) Cylindrical dryer
  
  2. The solution and slurry are dried by thermal evaporation
  
  (1) Drum dryer
  
  (2) spray dryer