Drying equipment is a kind of mechanical equipment that uses thermal energy to reduce material moisture, and is used to dry objects. The drying equipment vaporizes and escapes the moisture content (generally refers to moisture or other volatile liquid components) by heating to obtain a solid material with a specified moisture content. The purpose of drying is for the use of materials or further processing. For example, the drying of wood before making wooden molds and woodware can prevent deformation of the product, and the drying of ceramic blanks before calcination can prevent cracking of the finished product. In addition, the dried material is also convenient for transportation and storage, such as drying the harvested grain below a certain moisture content to prevent mildew. As natural drying is far from meeting the needs of production development, various mechanized drying equipments are more and more widely used.
The drying process of the drying equipment requires a large amount of thermal energy. In order to save energy, some materials with a high moisture content, suspensions or solutions containing solid materials are generally mechanically dehydrated or heated and evaporated, and then dried in a dryer to obtain a dry solid.
During the drying process, the drying equipment needs to complete the transfer of heat and mass (moisture content) at the same time to ensure that the wet partial vapor pressure (concentration) on the surface of the material is higher than the wet partial vapor pressure in the external space, and that the heat source temperature is higher than the material temperature.
The heat is transferred to the wet material from the high-temperature heat source in various ways, so that the moisture content on the surface of the material vaporizes and escapes to the external space, thereby causing a difference in moisture content between the surface of the material and the interior. The internal moisture content diffuses to the surface and vaporizes, 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 conditions of drying remain unchanged, the drying rate and surface temperature of the material remain stable. This stage is called the constant-speed drying stage; when the moisture content of the material decreases to a certain level To the extent that the internal moisture diffusion rate decreases to the surface and is less than the surface vaporization rate, the drying rate is mainly determined by the internal diffusion rate and continues to decrease as the moisture content decreases. This stage is called the reduced-speed drying stage.
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