Segmentation, open tubes

For the sake of simplicity, we may replace the packed segment by a hypothetical open tube of length, Le, that is the same as the distance traveled by the neutral and inert tracer in the packed segment. The lumen of this hypothetical tube, A packed, is assumed to be the same as the free cross-sectional area of the packed column so that Apacked = 7rae, where, ae is the radius of the hypothetical tube. The equivalent length, Le, is determined from the ratio of the conductivities of the packed and the open... 

Open tubes with optimal geometric orientation. 3) Open tubes with liquid or gas segmentation 4) Coiled open tubes... 

Another often-used reactor type (especially for relatively long-lasting derivatization reactions) is the open tube with liquid or gas segmentation [94]. Segmentation prevents the formation of a parabolic flow profile (axial dispersion), and peak dispersion is due mainly to the phase separator, which is responsible for removal of the segments prior to detection. The principle of segmentation was first used by Moore and Stein [102], who developed an amino acid autoanalyzer (ninhydrin reaction) in 1958. 

In hardwoods, morphological structural elements in longitudinal series comprise the segmented structure termed vessel . Vessels, which are exposed in transverse section, constitute about 10-46% of the stem volume in deciduous hardwoods and are cells of relatively large diameters (50-300 p.m). Vessels have in short the appearance of open vertical tubes within the wood structure because their end walls have partially dissolved. By comparison, the hardwood vessel diameter can be as much a 10 times the diameter of a softwood fiber. 

Fig. 7.1.1 Left Two parchment-like tubes inhabited by Chaetopterus variopedatus. The tubes are usually buried in muddy sand, exposing only the openings at both ends. Center The worms after removal of the casings. Right Diagram showing luminous area (after Panceri, 1878) the third pair from the top corresponds to the 12th segment.

Fig. 2.4p shows three types of post-column reactor. In the open tubular reactor, after the solutes have been separated on the column, reagent is pumped into the column effluent via a suitable mixing tee. The reactor, which may be a coil of stainless steel or ptfe tube, provides the desired holdup time for the reaction. Finally, the combined streams are passed through the detector. This type of reactor is commonly used in cases where the derivatisation reaction is fairly fast. For slower reactions, segmented stream tubular reactors can be used. With this type, gas bubbles are introduced into the stream at fixed time intervals. The object of this is to reduce axial diffusion of solute zones, and thus to reduce extra-column dispersion. For intermediate reactions, packed bed reactors have been used, in which the reactor may be a column packed with small glass beads. 

Columns in CEC often have a packed and an open segment with a detection window in between. The conductivities of the open and packed segments, a open and gpacked, are then evaluated from the currents measured with the capillary tubing in the absence, iopen, and presence, ipacked, of the packing by using Eqs. 1.1 and 1.8 as... 

A great amount of proprietary research has been conducted by a few companies into the workings of helical baffled heat exchangers. The only known open literature method for estimating helical baffle performance has been Comparison of Correction Factors for Shell-and-Tube Heat Exchangers with Segmental or Helical Baffles by Stehlik, Nemcansky, Krai, and Swanson [Heat Transfer Engineering, 15(1), 55-65]. 

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