Effervescent atomization

Atomization of melts has, in principle, some similarity to the atomization of normal liquids. The atomization processes originally developed for normal liquids, such as swirl jet atomization, two-fluid atomization, centrifugal atomization, effervescent atomization, ultrasonic piezoelectric vibratory atomization, and Hartmann-whistle acoustic atomization, have been deployed, modified, and/or further developed for the atomization of melts. However, water atomization used for melts is not a viable technique for normal liquids. Nevertheless, useful information and insights derived from the atomization of normal liquids, such as the fundamental knowledge of design and performance of atomizers, can be applied to the atomization of melts. 

Vacuum atomization is a method conceptually similar to effervescent atomization. As schematically depicted in Fig. 2.19, a vacuum atomization facility consists of two chambers, one above the other. The overall dimension is about 18 x 4 m. In the lower chamber, metal is first induction-melted under vacuum and subsequently... 

The studies on the performance of effervescent atomizer have been very limited as compared to those described above. However, the results of droplet size measurements made by Lefebvre et al.t87] for the effervescent atomizer provided insightful information about the effects of process parameters on droplet size. Their analysis of the experimental data suggested that the atomization quality by the effervescent atomizer is generally quite high. Better atomization may be achieved by generating small bubbles. Droplet size distribution may follow the Rosin-Rammler distribution pattern with the parameter q ranging from 1 to 2 for a gas to liquid ratio up to 0.2, and a liquid injection pressure from 34.5 to 345 kPa. The mean droplet size decreases with an increase in the gas to liquid ratio and/or liquid injection pressure. Any factor that tends to impair atomization quality, and increase the mean droplet size (for example, decreasing gas to liquid ratio and/or injection pressure) also leads to a more mono-disperse spray. 

Elemental composition Li 18.78%, C 16.25%, 0 64.96%. It evolves CO2 with effervescence when treated with dilute acids, which turns limewater milky. Lithium may be analyzed in an aqueous solution by atomic absorption or emission spectroscopy and carbonate anion may be determined by ion chromatography. 

Excess magnesium ribbon is added to dilute nitric acid. During this addition an effervescence is observed due to the production of hydrogen gas. In this reaction the hydrogen ions from the nitric acid gain electrons from the metal atoms as the reaction proceeds. 

Further evaporation also occurs within the discharge nozzle, and alternating segments of liquid and gas pass through the nozzle in a process of effervescent atomization. 

Do you know that the foods you eat, the fibers in your clothes, and the plastic in your CDs have something in common Foods, fibers, and plastic are produced when the atoms in substances are rearranged to form different substances. Atoms are rearranged during the flash of lightning shown in the photo on the opposite page. They were also rearranged when you dropped the effervescent tablet into the beaker of water and indicator in the DISCOVERY LAB. 

Thiobenzoyl isocyanate (313) may contribute four of the atoms (S—C—N—C) of the 1,2,4-thiadiazole ring system, the fifth being provided by a suitable nitrogenous compound. The reactant (313) is readily generated in situ from 2-phenylthiazoline-4,5-dione (312) in toluene.235 It reacts with ethereal hydrazoic acid with effervescence to yield 3-hydroxy-5-phenyl-... 

Schroder J, Kleinhans A, Serfert Y et al. (2012) V iscosity ratio A key factor for control of oil droplet size distribution in effervescent atomization of oil-in-water emulsions. Journal of Food Engineering 111 265-271. 

Abstract A bquid droplet may go through shape oscillation if it is forced out of its equilibrium spherical shape, while gas bubbles undergo both shape and volume oscillations because they are compressible. This can happen when droplets and bubbles are exposed to an external flow or an external force. Liquid droplet oscillation is observed during the atomization process when a liquid ligament is first separated from a larger mass or when two droplets are collided. Droplet oscillations may change the rate of heat and mass transport. Bubble oscillations are important in cavitation problems, effervescent atomizers and flash atomization where large number of bubbles oscillate and interact with each other. This chapter provides the basic theory for the oscillation of liquid droplet and gas bubbles. 

Gas bubbles are relevant to various aspects of the atomization and sprays. In flashing process or flash atomization, bubbles are formed inside the liquid which significantly alter the atomization process (see Chap. 10). Also in effervescent atomizers, high-pressure air is injected inside a liquid and disperses as small bubbles. In addition, bubbles are formed in cavitating nozzles, which significantly alter the atomization process. Gas bubbles go through volume oscillations in addition to shape oscillation discussed in the previous section. In this section, dynamic evolution and stability of a spherical bubble undergoing volume oscillation is discussed. 

Babinsky and Sojka [23] used DPF to study non-Newtonian liquid drop size distributions. For a single fluctuation, their results showed that fluctuations in ALR and interphase velocity slip ratio have the largest effect on effervescent atomizer/q. For two simultaneously fluctuating quantities, the influence on/o is found by adding... 

Gas and hquid can be brought in contact either within the nozzle (internal mix) or outside of the nozzle (external mix). In addition, nozzles can be categorized based on the flow rate of the atomizing gas and the way the gas is brought into contact with the liquid. These variations are airblasting, air-assisting, and effervescent nozzles. The main difference between each of the three is the velocity and quantity of air used in the atomizing process. Another difference relates to when the air is mixed with the liquid stream. 

Effervescent atomization is a special form of the twin-fluid atomization in which a small amotmt of gas is used to generate bubbles inside the body of the nozzle and then the resultant bubbly flow is forced through an orifice [1]. Effervescent... 

Effervescent atomizers are already employed or may potentially be used in various spray systems such as, the gas turbine combustors, furnaces, and boilers [10], combustion of diesel or gasoline fuel containing dissolved CO2 [11], atomization of viscoelastic liquids [13], atomization of liquids containing nanoparticles [35], etc. 

A typical effervescent atomizer is shown in Fig. 24.21. It consists of liquid and gas supply ports, a mixing chamber where the gas is bubbled into the liquid stream, and an exit orifice. Liquid is supplied to the atomizer through a port at the top and flows down inside a perforated central tube to the exit orifice. The gas, which is at a pressure slightly higher than that of the liquid, is supplied to an annular chamber surrounding the perforated central tube, and generates bubbles in the liquid. The generated bubbly flow exits the orifice. 

The successful operation of effervescent atomizers has been dependent on the ability to maintain a stable uniform sized bubble flow. Bubbly flows depend on nozzle geometry, air and liquid flow rates, and they become influenced by pressure and velocity instabilities. The stability of bubbly flows depends upon two factors (1) bubble coalescence and (2) characteristics of the bubble formation, which may affect their coalescence. The bubble formation may occur at various regimes, which... 

Fig. 24.21 Schematic design of atypical effervescent atomizer (From [10]. With permission from Elsevier)...

There are also few numerical and theoretical studies on the effect of various parameters on the effervescent spray characteristics. Neglecting the secondary atomization and following a stability analysis, Lund et al. [36] obtained the following theoretical correlation for the spray SMD... 

In order to obtain a correlation, the outflow of the effervescent spray was simulated by a numerical model based on the Navier-Stokes equations and the particle tracking method. The external gas flow was considered turbulent. In droplet phase modeling, Lagrangian approach was followed. Droplet primary and secondary breakup were considered in their model. Secondary breakup consisted of cascade atomization, droplet collision, and coalescence. The droplet mean diameter under different operating conditions and liquid properties were calculated for the spray SMD using the curve fitting technique [43] ... 

Xiong et al. [44] developed a three-dimensional model of droplet-gas two-phase flow and smdied the evolution of spray downstream along the exit orifice in an effervescent atomizer. The model was used to calculate the mean size and statistical distributions of atomized droplets under various operating conditions. Their key results show that the gas to Uquid mass ratio is one of the most important control parameters and increasing this parameter will decrease the droplet size gradually and finally tend to a certain limitation. They also foimd that a decreasing nozzle exit favors primary breakup, while high injection pressure has more influence on the secondary atomizatiOTi. 

Swirl nozzles are often used in twin-fluid nozzles, to enhance the overall atomization process in them. In some cases, the air is swirled before it comes in contact with the liquid. In other cases, both the air and liquid are swirled. An important design consideration in nozzles where both the hquid and gas are swirled is whether the gas should be swirled in the same direction, or in the opposite directions. Rotation in the same direction provides a strong circulation of fluid, while rotation in the opposite direction creates opposing shear forces, which helps in mixing the hquid and gas, and also in the atomization. Airblast, air-assist, and effervescent nozzles often contain swirling chambers. 

Lund, M. T., Sojka, P. E., Lefebvre, A. H., and Gosselin, P. G.. Effervescent Atomization at Low Mass Flow Rates. Part 1 The Influence of Surface Tension, AWm/zafton Sprays, Vol. 3,... 

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