The trend of droplet expansion and the formation of hollow particles in pressure spray dryers play a significant role in the loose density of the dried product. Hollow particles can be formed through four mechanisms.
At the droplet surface, a semi-permeable surface layer is formed. As the temperature of the droplet increases, it expands and emits steam generated within its interior.
(2) The rate of water evaporation is slightly faster than the rate of solid diffusing back into the liquid droplet interior. Pressure spray dryers, particularly when the evaporation process is complete, contain numerous pores, especially in the case of crystalline products.
Due to the capillary action, during drying, the liquid within moves through the fine pores between solid particles to the surface of the droplet. The liquid leaves the center of the droplet, creating a void. This mechanism applies to clay paste.
(A) The air introduced into the liquid aids in forming an air space within the droplet.
The above outlines the four mechanisms for the formation of hollow particles in the pressure spray drying machine.
