The purpose of drying is for material use or further pr […]
The purpose of drying is for material use or further processing. For example, drying of wood before making wooden molds and woodenware can prevent product deformation, and drying of ceramic blanks before calcination can prevent finished products from cracking. In addition, the dried materials are also easy to transport and store, such as drying the harvested grain to a certain moisture content to prevent mildew. Since natural drying is far from meeting the needs of production development, various mechanized air dryers are more and more widely used.
Heat 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 external space, so that there is a difference in moisture content between the surface and the 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 internal moisture diffusion rate. Generally, the drying rate in the early stage of drying is controlled by the surface vaporization rate; then, as long as the external drying conditions 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 drops 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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