1、 Definition

A dryer is a mechanical device that uses heat to dry wet materials. It is a device that uses thermal energy to reduce the moisture content of materials and is used for drying objects. Drying machines vaporize and release moisture (usually referring to water or other volatile liquid components) from materials through heating, in order to obtain solid materials with a specified moisture content. The purpose of drying is to meet the needs of material use or further processing.

2、 Classification

There are the following types of dryers: "tube dryer", "drum dryer", "shaft dryer", "boiling layer dryer" and "spiral dryer".

3、 Working principle of 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 mechanically dehydrated or heated and evaporated before being dried in a dryer to obtain dry solids.

Working principle of box dryer

During the drying process, it is necessary to simultaneously transfer heat and mass (moisture) to ensure that the surface moisture vapor pressure (concentration) of the material is higher than the moisture vapor pressure in the external space, and to ensure that the heat source temperature is higher than the material temperature.

Heat is transferred from the high-temperature heat source to the wet material in various ways, causing the surface moisture of the material to vaporize and escape to the external space, resulting in a difference in moisture content between the surface and interior of the material. The internal moisture diffuses and vaporizes towards the surface, continuously reducing the moisture content of the material and gradually completing the overall drying of the material.

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 speed drying stage; When the moisture content of the material decreases to a certain extent, the diffusion rate of internal moisture towards the surface decreases and is less than the surface vaporization rate. The drying rate is mainly determined by the internal diffusion rate and continuously decreases with the decrease of moisture content. This stage is called the deceleration drying stage.