The working principle of a dryer

The working principle of a dryer
        The drying process requires a large amount of heat energy. In order to save energy, certain materials with high moisture content, suspensions or solutions containing solid substances are generally first mechanically dehydrated or heated for evaporation, and then dried in a dryer to obtain dry solids. During the drying process, it is necessary to simultaneously transfer heat and mass (moisture content), ensuring that the surface moisture vapor pressure (concentration) of the material is higher than the moisture vapor pressure in the external space, and ensuring that the heat source temperature is higher than the material temperature.

        Heat is transferred from a high-temperature heat source to a wet material in various ways, causing the surface moisture to vaporize and dissipate to the external space, resulting in a difference in moisture content between the surface and interior of the material. The internal moisture diffuses to the surface diffusion and vaporizes, so that the moisture content of the material is constantly reduced and the drying of the whole material is gradually completed.

        The drying rate of materials depends on the surface vaporization rate and the diffusion rate of internal moisture. The drying rate in the early stage of drying is usually 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, and this stage is called the constant rate drying stage; When the moisture content of the material decreases to a certain extent, the diffusion rate of internal moisture to the surface decreases and is less than the surface vaporization rate, and the drying rate is mainly determined by the internal diffusion rate, which continuously decreases with the decrease of moisture content. This stage is called the rate reduction drying stage.