How Air Dryers Work

During the drying process, heat and mass transfer need to be completed at the same time, to ensure that the partial pressure of moisture vapor on the surface of the material is higher than that of the external space, and to ensure that the temperature of the heat source is higher than the temperature of the material. The 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 is vaporized and dissipated to the external space, so that there is a difference in the moisture content between the surface and the inside of the material. The internal moisture 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. Usually 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 will remain stable. This stage is called the constant-speed 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 lower 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 deceleration drying stage.