What Is a Dryer?
Dryers are used to remove water or moisture from objects by means of condensation.
A dryer uses electricity or gas as a heat source to dry the object. There is a wide range of objects to be dried, from household use to industrial use, and the types and methods of dryers vary widely. In particular, industrial dryers are important equipment for a wide range of industries, including food, chemical, pharmaceutical, biomass power generation, and sludge treatment.
Types of Dryers
Dryers are used in industries such as food, pharmaceutical, industrial, etc., as well as in household products used to dry dishes and clothes.
Industrial dryers vary in size and construction, ranging from small tabletop dryers used for testing and research to large drying plants for manufacturing and production sites. In addition, the drying method differs greatly depending on the type, so it is necessary to understand the drying principle and use the dryer according to the purpose.
Dryers are broadly classified according to the internal temperature at the time of operation. For example, there are constant-temperature dryers that maintain a uniform temperature in the range of 5 to 200°C, high-temperature dryers that maintain a temperature of 50 to 700°C, and low-temperature dryers that maintain a temperature of 5 to 45°C. The higher the temperature, the easier it is for moisture to evaporate, but it is also easier for the object to be denatured by the heat, so it is necessary to determine the most efficient drying temperature.
Different types of dryers use different air circulation patterns. There are natural convection systems that circulate air using the natural convection of gases, forced airflow systems that circulate air inside the chamber using an airflow fan, etc. The appropriate system should be selected according to the object to be dried. Vacuum dryers, which create a vacuum by lowering the air pressure inside the chamber to dry at a lower temperature than normal pressure, are also commonly used.
Other types of dryers include far-infrared dryers and microwave dryers, which use far-infrared rays or microwaves to heat and dry the object itself, and vacuum freeze dryers, which freeze the object and then vacuum dry it.
1. Band Dryers
Band dryers or conveyor dryers are very common dryers in which the object to be dried is loaded on a conveyor such as wire mesh or perforated plate, and is dried by hot air blown from outside the drying chamber while the conveyor is moving. This type of dryer can be used for a wide range of items, such as foodstuffs, building materials that do not change shape (veneer boards, etc.), automobile parts, and electrical and mechanical parts.
2. Tunnel Dryers
Tunnel dryers are a type of dryer in which the materials to be dried are loaded on a cart, and the cart is inserted at the entrance of the tunnel chamber and moved through the drying chamber. The features of this type of dryer are that it is suitable for drying materials for a long period of time, it can process large quantities, and the dryers equipped with an automated system can save energy. Target materials include foodstuffs (especially those that are resistant to shape damage), construction materials, IC substrates, automotive parts, etc.
3. Box Dryers
Box dryers are a type of dryer that use air currents generated in the drying chamber to dry the materials to be dried. Containers or trays loaded with drying materials are placed on shelves in the drying room and dried by airflow. The airflow system can be either horizontal (one direction or alternating direction) or ventilation airflow, and the most efficient airflow system can be selected according to the object to be dried. The target material can be food, medicine, agricultural products, pigments, cosmetics, and a very wide range of other industrial products, and can be powdery, lumpy, muddy, or plate-like materials.
4. Rotary Dryers
Rotary dryers dry materials by means of an agitator installed inside a rotating cylinder. The agitator repeatedly crushes and disperses the material and improves contact with hot air for more efficient drying.
Characteristically, the drying time is very short, and the amount of gas used can be reduced, which has advantages in terms of cost and environment. It is suitable for drying materials that contain a lot of water, muddy or highly viscous materials.
Applications of Dryers
Dryers are used for more than just drying materials. For example, high-temperature dryers are used for baking, curing, heat treatment, and sterilization, while constant-temperature dryers are sometimes used as heat insulators to maintain the viscosity of paints and other materials. Because temperatures can be precisely controlled, they may also be used for environmental resistance testing, such as heat or cold resistance.