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Diffusion process and speed of out-diffusion of rotary flash dryer
Oct 18, 2018

The heat exchange of the rotary flash dryer is mainly based on the air flow and the particles, and the heat exchange between the wall and the particles. The essence of the drying process is the diffusion of water, mainly Outward diffusion and internal diffusion are the processes in which the surface moisture of the particles diffuses from the surface to the surrounding medium in the form of steam. Internal diffusion is the process by which moisture moves inside the particles.


The rotary flash dryer mainly uses its high-speed hot air flow tangential direction to enter its cylinder. During operation, due to the spiral motion of the airflow in the cylinder, on the one hand, the temperature of the medium around the particles can be lowered, during operation.

At the same time, the medium flow rate and temperature are increased, which greatly increases the speed of out-diffusion. On the other hand, the high-temperature airflow impacts the particles or small wet materials located at the lower part of the cylinder at a high speed, and at the same time, the stirring action of the stirring blades in the cylinder causes the particles to be broken, the particle size is reduced, and the length of the internal capillary is also reduced, and the inner diameter is strengthened. The effect of diffusion reduces the resistance to internal diffusion.


The flow of the particles of the rotary flash dryer and the flow of the hot gas flow have both convection and cocurrent flow in the lower part of the cylinder during the operation, and convection and cocurrent heat exchange for the coarse material. For fine-grained materials, it is parallel with the hot gas flow, so the drying process can be completed in an instant. Drying of the granules is actually a hot air drying with high temperature and low humidity. These particles are mainly adsorbed by water and filled in the interstices of the particles. The conditions of high temperature and low humidity are adopted, and the heat conduction of the whole particles is slow, causing local stress concentration, dry cracking, crushing, dispersing and accelerating the drying process

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