Coaxial flow

Developed by Freeman and Tavlarides [45,46], and based on the liquid jet technique [47,48], the LJRR provides a method of measuring liquid-liquid reaction kinetics with direct contact, known interfacial area, renewable interface, and reasonably defined hydrodynamics. This method operates by employing an aqueous liquid jet in a concurrent, coaxially flowing organic solution, shown schematically in Fig. 8. 

Equation (5b), in Table VII, established by Lin et al. (L9) for coaxial flow in annuli with k = 0.5, was originally taken by them to be a striking confirmation of the theoretically derived correlation, Eq. (27), with 0=1. The latter condition, however, corresponds only to the limiting case of Eq. (27), at /c->0, that is, mass transfer to the wall of an outer cylinder, without an inner cylinder present. On these grounds, and because of other experimental conditions, the correlation of Lin et al. (L9) was criticized by Friend and Metzner (F9), who calculated that the constant in Eq. (5b) of... 

The first ESI design at the end of the 1980s proved to work properly as the HPLC interface with mobile phase flow rates between 1 and lOpL/min. Meanwhile, the development of the HPLC instrumentation and columns was oriented in the mL/min flow rate mode. In addition, the nebulization process based only on the application of an electrical field does not produce a stable spray from aqueous mobile phases. A modified ESI source, called ionspray, was then introduced [39], in which the nebulization of a liquid solution is pneumatically assisted by a coaxial flow of nitrogen (sheath gas) that allows the formation of a stable aerosol at mobile-phase flow rates between 10 and 500 pL/ min and the use of aqueous mobile phases. When working at higher flow rates (500-1000 pL/min), an additional nittogen flow rate can be used (auxiliary gas) to assist the desolvation of the droplets. This modified source is called turboionspray. 

Pneumatically assisted electrospray,24 also called ion spray, is illustrated in Figure 22-17a. Liquid from the chromatography column enters the steel nebulizer capillary at the upper left, along with a coaxial flow of N2 gas. For positive ion mass spectrometry, the nebulizer is held at 0 V and the spray chamber is held at —3 500 V. For negative ion mass spectrometry, all voltages would be reversed. The strong electric field at the nebulizer outlet, combined with the coaxial flow of N2 gas, creates a fine aerosol of charged particles. 

In atmospheric pressure chemical ionization, heat and a coaxial flow of N2 convert eluate into a fine mist from which solvent and analyte evaporate (Figure 22-19). Like chemical ionization in the ion source of a mass spectrometer, atmospheric pressure chemical ionization creates new ions from gas-phase reactions between ions and molecules. The distinguishing feature of this technique is that a high voltage is applied to a metal needle in the path of the aerosol. An electric corona (a plasma containing charged particles) forms around the needle,... 

Figure 27.1 (a) C02 Laser Pyrolysis System, (b) Detail of the gas nozzle, R = gas mixture of reactant gases Ig = coaxial flow of inert gas, usually argon. 

The technical term for this is hydrodynamic focusing, flow of a sample stream within the center core of a sheath stream is called coaxial flow. The exact diameter of that central sample core within the sheath stream is related to, among other things, the rate at which the sample is injected into the sheath stream a 100 pm sheath stream may, depending on sample injection velocity, have a core width of perhaps 5-20 pm (Fig. 3.4). Because hydrodynamic focusing tends to confine the cell sample to this central core, there is little mixing of sample with sheath fluid (but diffusion of small molecules will occur). The reason that this type of coaxial sample flow suits flow cytometry... 

Coaxial flow Coaxial flow is flow of a narrow core of liquid within the center of a wider stream. This type of flow is important in flow cytometry because it provides a means by which particles flowing through a relatively wide nozzle can be tightly confined in space, allowing accurate and stable illumination as they pass one by one through a light beam. 

Sheath Sheath is the fluid within which the central sample core is contained during coaxial flow within and from the flow cell of a flow cytometer. 

Fuel Injection/Premix Section, As is seen from Figure 2, premixing is accomplished via a coaxial flow scheme where the fuels are injected at the bell-mouthed entry to a 5.22-cm (2.07-in.) diameter straight cylindrical tube, 20.32 cm (8.00 in.) long. The flow area provides a space... 

In some systems, the restriction apparatus is a simple transfer tube restriction used for low-flow experiments. In others, a variable restrictor or back-pressure regulator is used between the outlet and the source. In the configuration used by Pinkston and Baker [7], the restriction apparatus is a series of tees to add a coaxial flow of nebulizing gas, electrospray buffer sheath flow, and another to introduce liquid from a syringe pump to regulate mobile-phase pressure. In Fig. lb, a direct interface is shown in which a split directs a fraction of the effluent flow toward the API source while the remainder is sent to waste through a back-pressure regulator or some controlled restriction to maintain system pressure. 

Lin, Z., et al.. On-column coaxial flow chemiluminescence detection for underivatized amino acids by pressurized capillary electrochromatography using a monolithic column. Anal. Chem., 78, 5322, 2006. 

Chemiluminescence detection (CL) with a on column coaxial flow detection interface... 

Simple Dripping, Electrostatic Extrusion, Flow Focusing, and Coaxial Flow..193... 

FIGURE 9.3 Different droplet production processes by dripping and jet break-up techniques, (a) Simple dripping, (b) electrostatic extrusion, (c) coaxial flow, (d) vibrating nozzle, (e) jet cutting, and (f) spinning disk atomization. 

The diameter of the beads produced under the influence of the gravitational force is usually larger than 1000 pm and the production rate is less than 0.5 mL min. In order to improve the production rate and reduce the bead diameter, external forces such as an electrostatic potential, a coaxial flow or vibrations can be used to release the droplet before its maximum... 

The flow rate through the electrically charged ESI capillary is kept in the range of 1-10 /fL/min by a syringe pump or the LC system. The electrospray process (depicted in Figure 1.14) may be assisted by the coaxial flow of a... 

Valid only for a coaxial flow nozzle containing a round liquid jet Water must be the liquid used Studied for a nozzle used in dust granulation Gas must be air, liquid must be water... 

One with coaxial flow guidance. An inner tube carries hot helium and an outer annulus carries cold helium. The inner tube is provided on its outer surface with a Kaowool-mat-insulation and the inner wall of the pressure bearing tube with a Kaowool-mat-insulation also. 

Fig. 33 Longitudinal section through a hot gas duct bent with coaxial flow...

It appears possible to use a less expensive version of ducts, with an inner metallic liner (e. g. made of Inconel 617) and no coaxial flow guidance for helium temperatures up to 950 °C or even 1000 C. Moreover it became evident that a coating at the sliding transitions or sliding supports (thermal expansions) might not necessarily be needed. A final confmnation test is still required however. 

Where Sis the distance from the wall. In the process of iteration at the given valne of velocity of the coaxial flow of a reacting mixture the tangential tension Tvalne and effective viscosity can be calculated using Equation 2.10 ... 

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