Spray Dryer Atomizer, What Is It And What Are the Types?
Spray dryer atomizer, what is It？
The spray dryer atomizer is the heart of the spray drying machine. It directly affects product quality and economic indicators. The higher the dispersion of the atomizer, the greater the drying efficiency; the more uniform the atomization, the smaller the change of the product’s water content. Therefore, the atomizer must not only ensure the dispersion of the material liquid but also control the particle size change to a minimum.
Spray dryer atomizer, what are the types?
Spray dryer atomizer type — centrifugal atomizer
The material liquid is thrown out from the edge of the disc by centrifugal force in the high-speed turntable (circumferential speed 90~160m/s) and atomized. The centrifugal atomizer uses the action of a high-speed rotating disc. When the liquid is injected into the disc surface, the liquid is subjected to two forces. One is the combination of the centrifugal force and gravity, and the combined force accelerates the splitting and atomizing of the liquid.; the other is the friction where the liquid and the surrounding air contact the surface at the same time, which promotes the formation of droplets. The former is centrifugal atomization, and the latter is velocity atomization. In fact, the two exist at the same time. The atomization effect of the centrifugal atomizer is directly related to the characteristics of the liquid, the flow rate, the diameter of the disc, and the speed.
Features of the centrifugal atomizer
1)It can directly split the liquid into droplets. When the flow of the material liquid is small, the material liquid is subjected to centrifugal force and bulges into a hemispherical shape around the disc. Its diameter depends on the centrifugal force, viscosity, and surface tension of the material liquid. When the centrifugal force is greater than the surface tension, the droplets around the disk are immediately thrown out and split and atomized;
2)The centrifugal atomizer can split the filaments into droplets. When the flow rate of the material liquid is large and the speed increases, the hemispherical material liquid is drawn into many filamentary jets. As the liquid volume increases, the liquid filaments around the disc also increase. If the liquid volume reaches a certain amount, the liquid filaments become thicker, and the number of filaments no longer increases. The thrown liquid filament is extremely unstable, and is separated into small spherical droplets not far from the periphery;
3)The centrifugal atomizer can split the membrane mitosis into droplets. When the flow rate of the material liquid continues to increase, the number of liquid filaments and the filament warp no longer increase, and the liquid filaments merge into a thin film. After the liquid film is thrown out a certain distance from the periphery of the disk, it will be split into widely distributed droplets. If the sliding energy of the liquid on the surface of the disc is minimized, the liquid can be ejected at a high speed, rubbing against the air around the disc to split and atomize.
Spray dryer atomizer type — pressure atomizer
The pressure atomizer uses a high-pressure pump to obtain high pressure for the liquid. When the high-pressure liquid passes through the nozzle, it converts the pressure energy into kinetic energy and disperses into droplets
Features of the pressure atomizer:
1) Simple structure, no noise in operation;
2) Change the internal structure of the nozzle to easily obtain the desired atomization shape;
3) Multi-nozzle spray can be used for mass production.
Spray dryer atomizer type —airstream atomizer
The spray dryer with airstream atomizer is usually small spray dryer that is widely used in a lab. Airstream atomizer uses compressed air to spray the material liquid out from the nozzle at a high speed (≥300 m/s), relying on the friction generated by the speed difference between the gas and liquid phases to split the material liquid into mist droplets. It uses the high-speed motion of steam or compressed air to make the material liquids meet at the nozzle outlet to make the liquid film split and atomized. Because the material liquid velocity is not high, but the gas flow velocity is very high, the relative velocity of these two fluids exists, and the liquid film is drawn into filaments and then split into small droplets. The size of the droplets depends on the relative velocity and viscosity of the material liquid. Air-flow atomization has limitations. It only makes sense to use steam injection when the hot air temperature is higher than 300℃. Generally, the steam pressure is 0.3-0.7MPa, and the compressed air pressure is 0.2-0.5MPa. The average droplet diameter is 10-60μm.