Spray drying mixed flow operation
For mixed-flow operation, it is actually a combination of co-flow and counter-flow, and its characteristics are in between. This method is most suitable for materials that can withstand high temperatures.
In the spray dryer, the drying process of the material is exactly the same as that in the conventional drying equipment, and it also undergoes two stages of constant speed drying and reduced speed drying. When the droplets contact the hot air, the heat is transferred to the droplets by the hot wind through the saturated vapor film on the surface of the droplets, so that the moisture in the droplets evaporates, as long as the amount of moisture inside the droplets diffuses to the surface to compensate for the loss of moisture on the surface , The evaporation is carried out at a constant speed; at this time, the surface temperature of the droplets is equivalent to the temperature of the wet bulb of hot air, which is the stage of constant speed drying. When the diffusion of moisture inside the droplets to the surface is not enough to maintain the wet state of the surface, the surface of the droplets gradually forms a dry shell. The dry shell thickens with time, and the moisture diffuses from the inside of the droplet through the dry shell The speed will also decrease, that is, the evaporation rate gradually decreases. At this time, the surface temperature of the material is higher than the wet bulb temperature of the hot air, which is the speed-down drying stage.