Conduit technique

Figs 6.72 and 6.73). Sparking components (e.g. fuses, contactors, circuit breakers) inside or parts not complying with the temperature class of the assembly are individually protected by an independent type of protection (for the most part in a flameproof housing). More recently, attempts have been made to introduce pressurized switchgear assemblies onto the market (Fig. 6.19). In the USA, the classic solution has been a flameproof enclosure with the conduit technique, see Fig. 6.83. 

Laser Doppler Velocimeters. Laser Doppler flow meters have been developed to measure Hquid or gas velocities in both open and closed conduits. Velocity is measured by detecting the frequency shift in the light scattered by natural or added contaminant particles in the flow. Operation is conceptually analogous to the Doppler ultrasonic meters. Laser Doppler meters can be appHed to very low flows and have the advantage of sensing at a distance, without mechanical contact or interaction. The technique has greatest appHcation in open-flow studies such as the deterrnination of engine exhaust velocities and ship wake characteristics. 

In some systems, known as continuous-flow analy2ers, the reaction develops as the sample —reagent mixture flows through a conduit held at constant temperature. In such systems, the reaction cuvettes are replaced by optical reading stations called flow cells. In most analy2ers, whether of discrete- or continuous-flow type, deterrnination of electrolyte tests, eg, sodium and potassium levels, is done by a separate unit using the technique of ion-selective electrodes (ISE) rather than optical detection. 

The flow profiles of electrodriven and pressure driven separations are illustrated in Figure 9.2. Electroosmotic flow, since it originates near the capillary walls, is characterized by a flat flow profile. A laminar profile is observed in pressure-driven systems. In pressure-driven flow systems, the highest velocities are reached in the center of the flow channels, while the lowest velocities are attained near the column walls. Since a zone of analyte-distributing events across the flow conduit has different velocities across a laminar profile, band broadening results as the analyte zone is transferred through the conduit. The flat electroosmotic flow profile created in electrodriven separations is a principal advantage of capillary electrophoretic techniques and results in extremely efficient separations. 

Until recently, epithelial cells were considered to function solely as the ciliated barrier lining in the airways and as conduits for gas exchange at the air/blood interphase. As techniques have improved to isolate and culture these cells and measure their gene products, it has become clear that they have a key role in lung defense and repair. Epithelial cells secrete a number of anti-microbial compounds and immunoregulatory cytokines [52], and are also capable of ingesting and killing bacteria [53],... 

Malheureusement, les variations portent sur la 3eme decimale de I indice, et n ont pu etre mises directement en evidence. La technique interferometrique, que nous avons developpee recemment pour la mesure des indices de refraction [1], nous a bien conduit a mettre en evidence vers 3 fx une forte zone de dispersion anomale, due au vibrateur OH, mais ne possedait pas assez de precision pour montrer la variation avec le degre de dilution de l alcool isopropylique avec CC14. 

The application is derived from new microsurgical techniques that can repair small blood vessels and nerves by sutures with optical equipment. The well-known synthetic implant materials for conduits of larger vessels (in-... 

The word flow implies fluid moving through (or across) a rigid framework or conduit (a container, tube, or packed bed) and not being carried with it as in the case of mechanical transfer. Flow is an integral part of many separation techniques, including chromatography, field-flow fractionation, ultrafiltration, and elutriation. The flow process is not itself selective, but it enables one to multiply by many times the benefits of separations attempted without flow. This point is explained in Chapter 7. 

The modem microstmcture applications led to increased interest in convection heat transfer in micro conduits. Huid transport in micro channels has found applications in a number of technologies such as biomedical diagnostic techniques, thermal control of electronic devices, chemical separation processes, etc. 

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