Mechanisms removable droplets The droplets are extracted from a vapor stream through series actions: collision and adhesion to target coalesce into larger droplets and drainage of the contacting element.
The sizes of the droplets is an important element because the empirical data show that the important target size in the first removal step should be in the order of magnitude as the particles to be removed.
These steps are shown schematically in Figure (A) for the Elimination of fog with metal mesh mist elimination.
For mists, wherein the majority of droplets are characterized by submicron diameters, the energy required to cause the collision with the target is derived from Brownian diffusion, the aleatory movement of fine liquid particles as they are pushed by action molecular as shown “inertial Impaction”. This includes removal of mists with the so-called fiber bed technology
For particles in the spray area between 4-20 microns, wire mesh is the most common type of mist eliminator used and interception is the main mechanism. Consider a droplet approaching a filament of a much larger diameter mesh « Direct interception ».
More the droplet is dense relative to the filament, and the gas velocity is elevated more likely it is that the droplets strike the filament.
If the velocity is too low, or droplets are small or too light compared with gas, the droplet will simply flow around the filament with the gas.
There are also particles in the gas stream that are smaller between 0.3 to 1 micron in diameter and these do not have sufficient momentum to break through the gas streamlines. Instead, they are carried around the target by the gas stream.
If the velocity is too high, liquid hooked to the filament will be re-trained, mainly in large droplets, and carried away by the gas. Re-entrainment is also favored by the low density of the liquid and low surface tension of the liquid
Even small particles, generally smaller than 0.3 microns in diameter, exhibit a random Brownian motion caused by collisions with gas molecules. This aleatory movement will cause these small particles to hit the target and be collected, even if the gas velocity is zero. The particles diffuse from the streamlines to the target surface when the concentration is zero. Diffusion is favored by low velocity and high concentration gradients.
Even small particles, generally smaller than 0.3 microns in diameter, exhibit a random Brownian motion caused by collisions with gas molecules. This aleatory movement will cause these small particles to hit the target and be collected, even if the gas velocity is zero. The particles diffuse from the streamlines to the target surface when the concentration is zero. Diffusion is favored by low velocity and high concentration gradients.
Baffles type of impingement mist extractor consists of a series of Vane or plates between which the gas must flow. As the gas stream circulates through the plates, the droplets strike the surface of the plate, coalesce, fall, and are routed to the liquid collecting section of vessel. The most common is Vane or Chevron -Shape.
