Self-aspirating

Example 22 Process characteristics of a self-aspirating hollow stirrer and the determination of its optimum process conditions... 

Self aspirating devices (hollow stirrers, ejectors, funnel-shaped nozzles) have to overcome the hydrostatic pressure Aphydr = pg H. This is taken into account by the combination Fr = Fr (d/H ). By the way, this extended Froude number, Fr, represents the reciprocal value of the Euler number, Eu ... 

Fig. 68 Comparison of the heat transfer behaviour of a mixing vessel with a self-aspirating hollow stirrer [58/2] and a bubble column [90].

In contrast, Fig. 72 shows the results of mass transfer in the system aqueous 1-n sodium sulphite solution/air. These measurements were carried out under steady-state conditions in vessels with hollow stirrers on the scale p = 1 5 [58/1, 92]. In this material system, the high salt concentration (70 g/1) fully suppresses bubble coalescence. In the case of the self-aspirating hollow stirrer (see Fig. 28), the stirrer power and gas throughput were coupled via the stirrer speed and were therefore dependent on each other. Consequently, v does not occur explicitly in the representation in Fig. 72, because it is a function of (P/V)". 

Only with self-aspirating hollow stirrrers, where v is not an independent process parameter, the following correlation was found ... 

Fig. 3 A typical self-aspirating CE-ICP-MS interface. The make-up buffer/sheath electrolyte reservoir is positioned above the interface to provide the correct pressure and flow of buffer to the pneumatic nebulizer.

Day, J.A. Sutton, K.L. Soman, R.S. Caruso, J.A. A comparison of capillary electrophoresis using indirect UV ahsorhance and ICP-MS detection with a self-aspirating nebulizer interface. Analyst 2000, 125, 819-823. 

These have been known since the work of Gouy [107] in the middle of the 19th century, and in principle are they are self-aspirating. They can be made of metal, plastic or of glass. In atomic absorption spectrometry, Pt-Ir capillaries are often used so as to allow the aspiration of highly acidic solutions. In plasma atomic... 

Fig. 1.22 Gas entrainment via vortex in comparison to the volume aeration by self-aspirating hollow stirrers (type "three-edged stirrer ) from [609]. 

Stirred tanks in scales n = 1-5 with the material system 1 N sodium sulfite solution [610/2, 624]. In self-aspirating hollow stirrers v is not a freely selectable process parameter The dependence (kto) = /(P/V) is shown in Fig. 4.6. The sorption characteristic was ... 

Heim A., Rzyski E., Stelmach ]., Diameters of gas bubbles generated by self-aspirating mixers, Chem. and biochem. Quart. 11 (1997) 3, p. 143-146... 

The difficulty in connecting CZE with other than on-line UV detectors is that most of the other detection systems require a certain fiow. This is generally done with a sheath flow between the outlet of the capillary and the nebulizer of the detector. Concentric nebulizers used in ICP-MS are self-aspirating and they induce a suction flow in the CE capillary, which causes dispersion. The employed sheath flow rates should not be too high because they result in dilution of the analyte ions. 

The nebulizer described is a self-aspirating, pneumatic nebulizer and is the one shown schematically on the lower left of Fig. 6.8(b). The nebulizer capillary is usually made of stainless steel but other materials such as Pt, Ta, and polymers may be used for corrosive solvents when contamination from the elements in steel must be avoided. A variety of other nebulizer designs have been developed for specific applications but are not commonly used in AAS. These other nebulizers are often used in atomic emission spectrometry and will be described in Chapter 7. 

Furthermore, some pulse combustors are self-aspirating so they do not require a separate fan to supply combustion air. Becanse of the high temperature and large volume of the combustion products, there is in general no need for a blower. 

According to Kentfield (1993), a pulse combustor is a combustion-driven device with self-aspirating feature, and this effect is achieved as a consequence of the internal unsteady flow events. In contrast, a pulsed combustor is a device with cyclic but nonresonant combustion as dictated by wave events. Pulsed combustors usually operate at a much lower than natural frequency, often controlled by an ignition, fuel injection, or a valve sequence. Therefore, valveless or flapper valve combustors fall into category of pulse combustors while mechanically driven valves (e.g., rotary valve) used to control either air or fuel inflow, flue gas outflow, or both should be categorized as pulsed combustors, unless the operation of a mechanical valve is controlled by resonant phenomena in a feedback mode. Such a design is known as a frequency-tunable pulse combustor. 

The continuous-flow profile of the mobile phase in OPLC and RPC has provided an opportunity to couple them to mass spectrometry through an API interface. In an OPLC/ESI-MS system, the coupling is achieved by connecting the OPLC outlet with the inlet of the ESI probe, which can accept a solvent flow rate of 60 to 120 p.L min [108]. Coupling of a commercial CycloGraph RPC system with APCI mass spectrometry has also been demonstrated [109]. Details of this coupling are shown in Figure 5.18. The self-aspiration of the heated APCI nebulizer delivers about 20 p.Lmin of the total 3.0 mLmin RPC flow to the mass spectrometer. The remainder of the flow is diverted to a fractional collector. 

At low power inputs, extra CO added. Results strictly not for self-aspirating conditions. 

Ben Brahim A, Prevost M, Bugarel R. (1984) Momentum transfer in a vertical down flow liquid jet ejector case of self-aspiration and emulsion flow. Int. J. Multiphase Flow, 10(l) 79-94. 

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