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Air dryer is a mechanical equipment that makes the wet content in the material (generally refers to water or other volatile liquid components) vaporize and escape through heating, so as to obtain the solid material with specified wet content.
Since ancient times, human beings have been used to dry materials with natural heat source and natural ventilation, which is completely restricted by natural conditions and has low production capacity. With the development of production, they are gradually replaced by artificial controllable heat source and air dehumidifier.
Modern air driers began to use intermittent operation of the fixed bed air drier. In the middle of the 19th century, the use of tunnel type air drier marked the development of air drier from intermittent operation to continuous operation. The rotary cylinder air dryer can better realize the stirring of granular materials, and the drying capacity and strength can be improved. Some industries have developed continuous operation air driers to meet the requirements of the industry, such as textile and paper industry drum air driers.
In the early 20th century, spray air dryers were applied in dairy production, which provided a powerful tool for large-scale drying of liquid materials. Since the 1940s, with the development of fluidization technology, high strength and high productivity of the fluidized bed and air flow dryer have appeared. Freezing sublimation, radiation and dielectric air driers provide new means to meet special requirements. In the 1960s far infrared and microwave air driers were developed.
The drying process needs to consume a lot of heat energy, in order to save energy, some materials with high wet content, suspension or solution containing solid substances are generally first by mechanical dehydration or heating evaporation, and then dried in the air dryer, to get dry solid.
The purpose of drying is for material use or further processing needs. Such as wood in the production of wood mold, carpentry before the drying can prevent the deformation of products, ceramic blank in the drying before calcination can prevent the finished product cracking. In addition, the dried material is also easy to transport and storage, such as the harvest of grain dry to a certain moisture content below, to prevent mildew. Due to the natural drying can not meet the needs of production development, a variety of mechanized air driers are more and more widely used.
In the drying process, it is necessary to complete the transfer of heat and mass (wet content) at the same time to ensure that the partial pressure (concentration) of wet content steam on the surface of the material is higher than the partial pressure of wet content steam in the external space, and to ensure that the temperature of the heat source is higher than the temperature of the material.
The heat from the high temperature heat source is transferred to the wet material in various ways, so that the wet part on the surface of the material vaporizes and escapes to the external space, so that the difference of the wet content between the surface and the inside of the material appears. The internal moisture diffuses to the surface and vaporizes, so that the moisture content of the material decreases continuously and the overall drying of the material is completed step by step.
