The heat of the desiccant dryer is transferred from the high temperature heat source to the wet material in various ways, so that the moisture on the surface of the material vaporizes and escapes to the outer space, so that the difference in moisture content appears on the surface and inside of the material. The internal moisture diffuses and vaporizes to the surface, so that the moisture content of the material is continuously reduced, and the overall drying of the material is gradually completed.
The drying rate of the material depends on the surface vaporization rate and the diffusion rate of internal moisture. During the drying process, it is necessary to complete the transfer of heat and quality (moisture) at the same time to ensure that the partial pressure (concentration) of moisture on the surface of the material is higher than the partial pressure of moisture on the external space, and to ensure that the temperature of the heat source is higher than the temperature of the material.
Generally, the drying rate in the early stage of drying is controlled by the surface vaporization rate; then, as long as the external conditions for drying remain unchanged, the drying rate and surface temperature of the material remain stable. This stage is called the constant-rate drying stage; when the moisture content of the material decreases to a certain When the diffusion rate of internal moisture to the surface decreases and is less than the surface vaporization rate, the drying rate is mainly determined by the internal diffusion rate, and decreases continuously with the decrease of moisture content. This stage is called the reduced-rate drying stage.
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