Aerosols nozzle atomization

A colloid is a broad category of mixtures, and is defined as one phase suspended in another. A perfume spray is made up of a liquid (the perfume) dispersed in a gas (the air). The principle underlying the perfume atomizer is the same as the nozzle on a can of polish, and the jets within the carburettor in the internal combustion engine. In each case, the colloid formed is an aerosol. 

Sprays of fine droplets can be generated by first mixing a liquid with liquefied gas under pressure and then expanding the mixture through a nozzle. This technique, referred to ssliquefied gas atomization, has been used in many applications such as commercial aerosol cans. The mean droplet size generated with this technique is very small. In very few systematic studies, the measured droplet size distribution was found rather widely spread.[881 It is not clear, however, how the liquid amount, pressure, and nozzle design affect the mean droplet size and size distribution. 

Tests with Aerosol Sprays. One of the chief means of applying concentrated oil sprays is in aerosol form. An aerosol generally remains suspended in the air for some time and is carried by normal wind or air currents. Aerosols are probably best adapted to interior applications but have been used with some success outdoors. They may be produced by liquefied-gas formulations released through capillary nozzles, by steam and air atomization, by centrifugal disks and rotors, by extremely high pressure, and by heat vaporization. 

Aerosol Solvent Extraction System (ASES) Here, the solution is sprayed through atomization nozzle into a chamber L lied with SCF. Expansion of solution occurs within the Lne droplets of solvent being sprayed, thus creating supersaturation and precipitation of solids as Lne particles. 

Laskin-Type Nozzle Generator. A third type of atomizer, the Laskin-type nozzle generator, is used to create test atmospheres of particulate or aerosol and vapor mixtures. A pure liquid or melt is used, and no solvent is necessary. Again, this is important for evaluating filter and solid sorbent combination sampling trains. 

Gas antisolvent processes can be performed in a semicontinuous mode. In this case the solution and the antisolvent are continuously introduced in the system until the desired amount of the product is formed. The introduction of the solution is then stopped and the DG flux extracts the residual solvent from the system. The system is then depressurized to enable collection of the product. The solution is generally introduced through an atomization nozzle that favors the prompt expansion of the solution and the formation of small particles. Different process configurations have been utilized, i.e., co- and countercurrent introduction of the solution and antisolvent fluxes and various nozzles have been designed. The process is referred to by different acronyms such as ASES (aerosol solvent extraction system), SAS (supercritical antisolvent), SEDS (solution enhanced dispersion by supercritical fluids), PCA (precipitation with a compressed fluid antisolvent), GASR (gas antisolvent recrystallization), GASP (gas antisolvent precipitation). 

ASES (aerosol solvent extraction system) This is the first modification of the gas antisolvent process and involves spraying the solution through an atomization nozzle as fine droplets into compressed carbon dioxide (Figure 8.4). The dissolution of the SCF into the liquid droplets is accompanied by a large volume expansion and, consequently. 

Electrohydrodynamic atomizers are used to make monodisperse aerosols of liquid droplets. A hquid is sprayed from a nozzle in the presence of an electric... 

The morphology and size of particles prepared by the LPSP process are different from those produced by CSP using either an ultrasonic nebulizer or a two-fluid nozzle as atomizers under an atmospheric environment. For example, nickel oxide (NiO) nanoparticles can be formed via the LPSP route whereas, only submicronsized NiO particles are produced by ultrasonic spray pyrolysis [9]. It is evident that the nanoparticle formation mechanism in the LPSP process is different from that in the CSP process. The calculated particle size based on the ODOP principle is much larger than 100 nm, indicating that the nanoparticles are formed based on one-droplet-to-multiple-particles (ODMP). The reason can be attributed to the difference in operating pressures and aerosol formation mechanisms between the two types of aerosol generators. 

To overcome these problems, another comminution technique—atomization—was developed. Atomization produces solid or aerosol particles with reduced sizes by spraying molten material or material solution or suspension under conditions such that it breaks down and then solidifies as fine powder [32]. In a typical atomization process, a molten material passing through a nozzle scatters into fine droplets by a highspeed medium (e.g., gas or water) and then the droplets solidify to powder. Obviously, the atomization technique is highly efficient for preparing micron and submicron powders at industrial scales and recent development has enabled atomization to produce nanoparticles of sizes down to 20nm [33]. 

FIGURE 13.4. Of many possible mechanisms for liquid aerosol formation, four of the most common include (a) surface impact of a high-pressure liquid stream, (b) the collision of high-velocity liquid and gas streams, (c) high-pressure spray nozzles, and (d) spinning-disk centrifugal atomizers. 

Figure 14.2 Schematic of a nebulizer The compressed air expands as it leaves the nozzle. This causes reduced pressure which induces the drug solution to flow up and out of the nozzle where it atomized by contact with the air stream. Cop)U ight (1996) from Lung Biology in Health and Disease, Vol. 94, Dalby et al, Inhalation Aerosols, p. 452. Reproduced by permission of Routledge/Taylor Francis Group, LLC...

In metalworking operations, mist is the by-product from the atomization of a metalworking fluid which has been subjected to shear and extensional flow forces. A qualitative method to measure the reduction of aerosol mist was developed by incorporating the use of a spray nozzle as a source for continuous atomization of the... 

Figure 3.12 shows the pneumatic Aerosol-Jet printing process in diagrammatic form. The ink, a suspension with a solids content of approximately 60 to 70%, is pneumatically atomized and mixed with an inert carrier gas. The suction effect is the basis for atomization. Plastic tubes deliver the aerosol to the print head. In the print head a metered feed of clean inert gas aerodynamically collimits the aerosol, which is then applied to the substrate surface in a tight jet by a nozzle. 

---