Aerosol generation, atomizer

Aerosol Generator. The atomizer shown in Figure 7 was designed to produce aerosols of certain organic materials that are soluble only in easily vaporized solvents such as isopropanol or toluene. Difficulties were encountered when using other nebulizers because of continual concentration of the solution resulting from evaporation of the solvent, making it impossible to predict or control the test air concentration and the particle size. 

The direct introduction of atomic vapour into the AAS flame can also be seen as an equipment variation [148, 152], Here, the evaporation of the steel samples can be carried out with the help of the glow-discharge lamp [148] or an aerosol generator with a low current d.c.-arc discharge [152]. Another example is the combination of gas chromatography and AAS [92], where AAS is used as an element detector. 

The second mechanism proposed for aerosol generation is based on the piezoelectric crystal operating at low frequency and imparting vibrations to the bulk liquid. This results in the formation of cavitation bubbles, which move to the air-liquid interface.The internal pressure within the bubbles equilibrates with that of the atmosphere, causing their implosion. When this occurs at the liquid surface, portions of the liquid break free from the turbulent bulk liquid, resulting in droplet formation. The dependence of atomization on cavitation phenomena has been demonstrated for frequencies between 0.5 and 2.0 MHz.Boguslavskii and Eknadiosyants combined these theories with-their proposal that droplet formation resulted from capillary waves initiated and driven by cavitation bubbles. 

Constant-ouput atomizer, tri-jet aerosol generator, electrostatic classifier, vibrating-orifice aerosol generator, fluidized-bed aerosol... 

Atomization. The main mechanism used for deaggregation of aerosol particles is the atomization process. Various mechanisms, such as a turbulent airstream and ultrasonication, are used in inhaler devices to separate dry particles or create fine liquid droplets. Methods of aerosol generation and the characterization of the various inhalers are available elsewhere [264]. 

In the flame atomization technique the sample is sprayed into the flame in the form of an aerosol generated by means of a nebulizer. It is also possible to introduce solid samples directly or as suspensions into the flame. 

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. 

The concept or the basis of spray pyrolysis method assumes that one droplet forms one product particle. To date, submicrometer- to micrometer-sized particles are typically formed in a spray pyrolysis process. A variety of atomization techniques have been used ftn- solution aerosol formation, such as ultrasonic spray pyrolysis, electrospray pyrolysis, low pressure spray pyrolysis using a filter expansion aerosol generator (FEAG), salt-assisted spray pyrolysis, two-fluid pyrolysis method, etc. [15-18]. These atomization methods differ in droplet size, rate of atomization, and... 

The mostly liquid samples are introduced into an ICP-mass spectrometer by different techniques. Each of these techniques aims to generate fine aerosol of the liquid sample to achieve efficient ionization of the sample atoms in the plasma. However, only 1-2% of the sample can find way into the plasma hence, the sample introduction system is considered as the weakest component of an ICP-MS. The introduction system works in two steps, namely, aerosol generation using nebulizer and droplet selection by the spray chamber. Most commonly, the liquid sample is pumped into the nebulizer by a peristaltic pump at a speed of 1 mL/min. When the liquid sample enters the nebulizer, it is transformed into fine aerosol under the pneumatic action of the nebulizer gas flow ( l L/min). However, some pneumatic nebulizers do not use a pump. They suck the sample through the tubing through the action of positive pressure of the nebulizer gas. 

Figure 1.6. Size ranges of droplets/particles found in nature and generated by atomization of normal liquids and melts in aerosol spray, spray combustion, powder production, and spray forming processes.

A similar technique has been applied to the generation of monodisperse suspensions in water. This type of method was first used in medical field and then widely used to spray monodisperse solid particles such as polystyrene latex particles. Aerosols of solutes have also been produced by atomizing solutions of salt, sugar or methylene blue dye dissolved in water. In practical operations, a low concentration of solid particles in a solvent is recommended in order to avoid possible agglomeration of suspensions in the solvent. 

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. 

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