Simplex atomizer

All Lfe values are applicable to pure and composite transformations, and to formal overall transformations as well vide supra). This is a consequence of the fact that the formal ligogenic representation ignores all the intermediate steps of a multistep process. The overall process ligogenicity is broken down into contributions from the reacting atoms, simplexes and molecular moieties. In the case of Lfoj = 0, there is no net new o bonds hence, the process is nonligogenic. 

Sangsila, S. Labinaz, G. Poland, J. S. et al. An Experiment on Sequential Simplex Optimization of an Atomic Absorption Analysis Procedure, /. Chem. Educ. 1989, 66, 351-353. 

This experiment describes a fixed-size simplex optimization of a system involving four factors. The goal of the optimization is to maximize the absorbance of As by hydride generation atomic absorption spectroscopy using the concentration of HCl, the N2 flow rate, the mass of NaBH4, and reaction time as factors. 

Hollow Sprays. Most atomizers that impart swid to the Hquid tend to produce a cone-shaped hoUow spray. Although swid atomizers can produce varying degrees of hoUowness in the spray pattern, they aU seem to exhibit similar spray dynamic features. For example, detailed measurements made with simplex, duplex, dual-orifice, and pure airblast atomizers show similar dynamic stmctures in radial distributions of mean droplet diameter, velocity, and Hquid volume flux. Extensive studies have been made (30,31) on the spray dynamics associated with pressure swid atomizers. Based on these studies, some common features were observed. Test results obtained from a pressure swid atomizer spray could be used to iUustrate typical dynamic stmctures in hoUow sprays. The measurements were made using a phase Doppler spray analyzer. 

One of the limitations of plain-orifice atomizers is the narrow spray cone generated. For most practical applications, large spray cone angles are desired. To achieve a wide spray cone, a simplex, i.e.,... 

A hollow-cone spray can be generated via a simplex atomizer. The spray pattern varies depending on the injection pressure. At very low pressures, liquid dribbles from the nozzle orifice. With increasing pressure, the liquid emerges from the orifice as a thin,... 

Various hollow-cone simplex atomizers (Fig. 2.1) have been developed for combustion applications, differing from each other mainly in the way that swirl is imparted to the issuing liquid jet. In these atomizers, swirl chambers may have conical slots, helical slots (or vanes), or tangential slots (or drilled holes). Using thin, removable swirl plates to cut or stamp the swirl chamber entry ports leads to economies of the atomization systems if spray uniformity is not a primary concern. Large simplex atomizers have found applications in utility boilers and industrial furnaces. Oil flow rates can be as high as 67 kg/min. 

Solid-cone spray atomizers usually generate relatively coarse droplets. In addition, the droplets in the center of the spray cone are larger than those in the periphery. In contrast, hollow-cone spray atomizers produce finer droplets, and the radial liquid distribution is also preferred for many industrial applications, particularly for combustion applications. However, in a simplex atomizer, the liquid flow rate varies as the square root of the injection pressure. To double the flow rate, a fourfold increase in the injection pressure is... 

Figure 2.1. Schematic of various types of hollow-cone simplex atomizers.

A spill-return atomizer (Fig. 2.4) is essentially a simplex atomizer. The difference between the two types of atomizers is that the rear wall of the swirl chamber is solid in a simplex, while in a... 

The simplex atomizer has many other variants. 1 Designs are aimed at achieving good atomization over a wide range of flow rates by varying the effective flow area without the need for excessive hydraulic pressures. In practice, pressure-swirl atomizers used in gas... 

As mentioned in the previous section, a major drawback of the simplex atomizer is the poor atomization quality at the lowest flow rate due to too-low pressure differential if swirl ports are sized to allow the maximum flow rate at the maximum injection pressure. This problem may be resolved by using dual-orifice, duplex, or spill-return atomizers. Alternatively, the atomization processes at low injection pressures can be augmented via forced aerodynamic instabilities by using air or gas stream(s) or jet(s). This is based on the beneficial effect of flowing air in assisting the disintegration of a liquid j et or sheet, as recognized in the application of the shroud air in fan spray and pressure-swirl atomization. 

Parker, L.R., Jr., Morgan, S.L., and Deming, S.N. (1975), Simplex Optimization of Experimental Factors in Atomic Absorption Spectrometry, Appl. Spectrosc., 29, 429-433. 

In the second configuration (moderate swirl) tested (see Fig. 20.2a), only the air stream was forced and no liquid-fuel pulsations were imposed. The experiments were performed with a Parker-Hannifan Research Simplex Atomizer. The atomizing nozzle consisted of a primary liquid ethanol feed with a coaxial primary air stream. The air stream passed through a set honeycomb, flow-straightener, and swirl vanes to provide the necessary level of swirl. Three loudspeakers were used to excite the primary air. 

Thus, (2R)-pumiliotoxin C (214) has been prepared from (R)-norvaline (212). The asymmetric center in the triene (213) controls the configuration at three carbon atoms 210). a-Kainic acid, isolated from the algae Digena simplex and Centrocerus clavulatum, was prepared by total synthesis. Its enantioselective synthesis involved a stereocon trolled intramolecular cycloaddition of a (S)-glutamic acid211). Asymmetric cycloadditions also play a decisive role in the synthesis of chiral cytochalasins. In this case 212> the primary chiral information was carried by (S)-alanine and (S)-phenylalanine, respectively. 

Table 2.35 Examples of practical applications of simplex optimisation in atomic spectrometry.

S. A. Pergantis, W. R. Cullen and A. P. Wade, Simplex optimisation of conditions for the determination of arsenic in environmental samples by using electrothermal atomic absorption spectrometry, Talanta, 41(2), 1994, 205-209. 

J. Echeverria, M. T. Arcos, M. J. Fernandez and J. Garrido Segovia, Simplex method strategy for optimisation in flames atomic absorption spectrometry, Quim. Anal., 11(1), 1992, 25-33. 

R. J. Stolzberg, Optimizing signal-to-noise ratio in flame atomic absorption spectrophotometry using sequential simplex optimisation, J. Chem. Educ., 76(6), 1999, 834-838. 

J. A. McGuire and E. H. Piepmeier, The characterisation and simplex optimisation of a variable-diameter, multi-electrode, direct current plasma for atomic emission spectroscopy. Can. J. Appl. Spectrosc., 36(6), 1991, 127-139. 

P. J. Galley, J. A. Horner and G. M. Hieftje, Automated simplex optimisation for monochromatic imaging inductively coupled plasma atomic emission spectroscopy, Spectrochim. Acta, Part B, 50(1), 1995, 87-107. 170. L. M. Cabezon, M. Caballero, J. M. Diaz, R. Cela and J. A. Perez-Bustamante, Multielemental separation and determination of some heavy metals (copper, cobalt, cadmium and nickel) in tap water and high salinity media by CGA (colloidal gas aphron)-coflotation, Analusis, 19(4), 1991, 123-127. 

C. D. Stalikas, G. A. Pilidis and M. I. Karayannis, Determination of lead and cadmium in environmental samples by simplex optimised atomic absorption methods, J. Anal. At. Spectrom., 11(8), 1996, 595-599. 

B. Hilligsoe and E. H. Hansen, Application of factorial designs and simplex optimisation in the development of flow injection-hydride generation-graphite furnace atomic absorption spectrometry (FI-HG-GFAAS) procedures as demonstrated for the determination of trace levels of germanium, Fresenius J. Anal. Chem., 358(7-8), 1997, 775-780. 

G. A. Zachariadis and J. A. Stratis, Optimisation of cold vapour atomic absorption spectrometric determination of mercury with and without amalgamation by subsequent use of complete and fractional factorial designs with univariate and modified simplex methods, J. Anal. At. Speetrom., 6(3), 1991, 239-245. 

M. T. Siles Cordero, E. I. Vereda Alonso, P. Canada Rudner, A. Garcia de Torres and J. M. Cano Pavon, Computer-assisted simplex optimisation of an on-line preconcentration system for determination of nickel in seawater by electrothermal atomic absorption spectrometry, J. Anal. At. Spectrom., 14(7), 1999, 1033-1037. 

---