I. Introduction to Drying Equipment 1. Drying refers to the removal of an appropriate amount of water or other liquid from the material.
2. The similarities and differences between drying and evaporation (1) are the same as removing water.
(2) Drying is mostly carried out below the boiling point, and air is removed from the material by air.
(3) Evaporation mostly removes water in the case of boiling.
3. One of the important operations in an industrial production process, usually the final stage of operation.
Drying equipment 2. Balanced humidity 1. The material is in contact with air of a specific temperature and humidity for a long time. At this time, the moisture contained in the material is called equilibrium humidity.
2. The equilibrium humidity of some materials is almost zero (eg glass, porcelain).
3. Some materials have a wide range of equilibrium humidity (eg wood, fabric, leather).
4. In combination with moisture incorporated into the material, the vapor pressure exhibited is lower than the vapor pressure of the free water.
5. The free water is the moisture contained in the equilibrium moisture of the material, that is, the water that can be removed by the drying operation.
6. The meaning of balance humidity is the ability of the material to dry? A process, and the ability of hot air to remove water,
Third, drying equipment drying rate 1. Unit time and unit area, the weight lost by the material, called the drying rate.
2. Drying process (1) Initial period: The time is short, in order to adjust the material to the same condition as the dryer.
(2) Constant speed period: This is the one with the largest drying rate. The water evaporated on the surface of the material is fully replenished inside, so the surface water film is still in and kept at the wet bulb temperature.
(3) Phase I of deceleration: At this time, the water evaporated, the interior cannot be completely replenished, so the surface water film begins to rupture, and the drying rate begins to slow down. The material is called the critical point at this point. The water contained at this time is called It is a critical moisture.
(4) Deceleration Phase II: Only dense materials are available in this period, because water is not easy to come up; but porous materials are not. Most of the evaporation of the first phase of water is carried out on the surface. In the second phase, the water film on the surface is completely gone, so the water diffuses to the surface in the form of water vapor.
Fourth, the factors affecting the constant speed drying rate 1. Air temperature: If the temperature is increased, the evaporation rate of the diffusion rate of sweat increases.
2. Humidity of air: At lower humidity, the evaporation rate of water becomes larger.
3. Speed ​​of airflow: If the speed is faster, the effect of mass transfer and heat transfer is better.
4. Shrinkage and surface hardening: Both of these phenomena can affect drying.
5. Drying equipment Classification Materials should remove excess water as much as possible before entering the equipment.
1. Dryer for solid and paste (1) Disc dryer (2) Screen conveyor dryer (3) Rotary dryer (4) Screw conveyor dryer (5) Strap dryer (6) Stirring Dryer (7) Rapid Evaporation Dryer (8) Cylinder Dryer 2. Solution and slurry water is dried by thermal evaporation (1) Drum dryer (2) Spray dryer
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