Flow manifold

A numerical study of the effect of area ratio on the flow distribution in parallel flow manifolds used in a Hquid cooling module for electronic packaging demonstrate the useflilness of such a computational fluid dynamic code. The manifolds have rectangular headers and channels divided with thin baffles, as shown in Figure 12. Because the flow is laminar in small heat exchangers designed for electronic packaging or biochemical process, the inlet Reynolds numbers of 5, 50, and 250 were used for three different area ratio cases, ie, AR = 4, 8, and 16. 

Also a simulation of the flow field in the methanol-reforming reactor of Figure 2.21 by means of the finite-volume method shows that recirculation zones are formed in the flow distribution chamber (see Figure 2.22). One of the goals of the work focused on the development of a micro reformer was to design the flow manifold in such a way that the volume flows in the different reaction channels are approximately the same [113]. In spite of the recirculation zones found, for the chosen design a flow variation of about 2% between different channels was predicted from the CFD simulations. In the application under study a washcoat cata-... 

Capillary zone electrophoresis coupled with fast cyclic voltammetric detection was developed by Zhou et al. [27] for the separation and determination of OTC, TC, and CTC antibiotics. All compounds were well separated by optimization of pH and complexation with a boric acid sodium tetraborate buffer. The detection limit using fast on-line cyclic voltammetric detection with Hg-film-microm electrode was 1.5 x 10-6 mol/L for OTC (signal to noise ratio > 2). A continuous flow manifold coupled on-line to a capillary electrophoresis system was developed by Nozal et al. [28] for determining the trace levels of OTC, TC, and DC in surface water samples. 

A. Manz, D.J. Harrison, J.C. Verpoorte, H. Ludi, and H.M. Widmer, Integrated electroosmotic pumps and flow manifolds for total chemical analysis systems. Proceedings Transducers (San Francisco, USA) 939-941 (1991). 

Table 1 Selected Applications of Continuous Flow Manifolds with CL Detection... 

Number of flow streams The number of reagent and/or carrier streams is a very important aspect when designing a flow manifold. In contrast to other detection techniques in FTA, with CL detection there is a very important limitation... 

In some applications, additional components acting as reactors for specific chemical pretreatment are incorporated within the flow manifold. Typical examples are ion-exchange microcolumns for preconcentration of the analyte or removal of interferences and redox reactors, which are used either to convert the analyte into a more suitable oxidation state or to produce online an unstable reagent. Typical examples of online pretreatment are given in Table 2. Apart from these sophisticated reactors, a simple and frequently used reactor is a delay coil (see also Fig. 4), which may be formed by knitting a segment of the transfer line. This coil allows slow CL reactions to proceed extensively and enter into the flow cell at the time required for maximum radiation. The position of the reactors within the manifold is either before or after the injection port depending on the application. 

Fig. 12). External numbering-up by flow manifolding to separate reactor units is here one concept for future production reactors with another tenfold increase in structured area.

In parallel with improvements in chemical sensor performance, analytical science has also seen tremendous advances in the development of compact, portable analytical instruments. For example, lab-on-a-chip (LOAC) devices enable complex bench processes (sampling, reagent addition, temperature control, analysis of reaction products) to be incorporated into a compact, device format that can provide reliable analytical information within a controlled internal environment. LOAC devices typically incorporate pumps, valves, micromachined flow manifolds, reagents, sampling system, electronics and data processing, and communications. Clearly, they are much more complex than the simple chemo-sensor described above. In fact, chemosensors can be incorporated into LOAC devices as a selective sensor, which enables the sensor to be contained within the protective internal environment. Figure 5... 

Combining flow manifolds, 73 272 Combipress, molecular formula and structure, 5 161t Combustible masking materials, 10 91 Combustion, See also Fire entries in diesel engines, 72 420-421 energy loss from, 70 138 of ethers, 70 579-580 explosives and propellants during, 70 719... 

Divergent exo-receptors, 26 774 DiverseSolutions software, 6 17 Diversity searches, 6 14-18 DiversitySolutions software, 6 15, 17 Dividing flow manifolds, 23 272 Dividing wall distillation columns, 20 750-751... 

Flow-injection and continuous-flow systems are very similar. The major differences are outhned here. Continuous-flow systems are characterized by a relatively long start-up time prior to instrument stabilization, whereas the flow-injection approach requires little more time than that needed to stabilize the detector output. Tubing diameters on a flow-injection manifold are usually much smaller and the samples are injected into the flow line rather than aspirated. No wash cycle is employed in the flow-injection regime, since the sample is a discrete slug. Flow rates in continuous-flow manifolds are often larger than in the flow-injection regime. 

Figure 3.8 — (A) Biosensors used in different FI manifolds to perform reaction-rate measurements (I) stopped-flow manifold (II) iterative flow-reversal system (III) open-closed configuration S sample B buffer P pump IV injection valve PC personal computer IMEC immobilized enzyme cell D detector W waste SV switching valve. (B) Types of recordings obtained by using the three types of biosensors and measurements to be performed on them in order to develop reaction-rate methods. (Reproduced from [50] with permission of Elsevier Science Publishers).

Figure 3.10 — Flow manifolds for implementation of flow-through biosensors. (A) Flow injection merging-zones manifold for the bioluminescence detennination of ATP. ATP standards (30 fiL) and luciferin (30 fiL) are injected into the buffered carrier streams, each pumped at 0.7 mL/min and synchronously merged 12.5 cm downstream. Distance from merging point to immobilized enzyme coil, 2.2 cm. (Reproduced from [59] with permission of Elsevier Science Publishers). (B) Completely continuous flow manifold for the determination of NADH. (Reproduced from [71] with permission of the Royal Society of Chemistry). (C) Segmented-flow manifold for the determination of L-(+)-lactate. (Reproduced from [65] with permission of Marcel Dekker, Inc.). (D) Single-channel flow injection manifold with immobilized reagent for the detennination of glucose. (Reproduced from [77] with permission of Elsevier Science Publishers).

Miniaturization as a general trend in science and technology has also reached flow-through sensors as regards both design and construction of the sensor proper and the experimental set-up or flow manifold used prior to detection. 

Glucose oxidase (GOD) was immobilized on the sample inlet by using bovine serum albumin (BSA) and glutaraldehyde. The flow manifold included a buffer carrier line circulated at 0.3 mL/min into which sample volumes of 0.2 nL were injected [110]. 

Flow systems are developed mainly for liquid samples and their complexity can range from simple to very complex manifolds to deal with ultratrace amounts of the target analyte in complex matrices, which often require on-line separation/preconcentration steps. As a wide variety of chemical manipulations can be carried out in an FI manifold, the scope of the FI applications is enormous. Not only liquid samples, but also both gas and solid samples, can be also introduced into the liquid flow manifold if special adaptations are made. Gas samples simply require impermeable tubing. Solids can be either introduced into the system and leached with the help of auxiliary energy e.g. ultrasound) or introduced as slurries. 

Nowadays, the outstanding advantages of using flow manifolds as sample preparation systems for atomic detectors have been demonstrated for a variety of techniques. Characteristic examples of the instrumentation required and typical applications are presented in a comprehensive monograph dedicated to FI and atomic spectrometric detectors [21]. 

The on-line interface of flow manifolds to continuous atomic spectrometric detectors for direct analysis of samples in liquid form typically requires a nebuliser and a spray chamber to produce a well-defined reproducible aerosol, whose small droplets are sent to the atomisation/ionisation system. A variety of nebulisers have been described for FAAS or ICP experiments, including conventional cross-flow, microconcentric or Babington-type pneumatic nebulisers, direct injection nebuliser and ultrasonic nebulisers. As expected, limits of detection have been reported to be generally poorer for the FIA mode than for the continuous mode. 

Finally, we should consider that the intrinsic discontinuous nature of the ETAAS technique has limited the interest in interfacing basic continuous flow manifolds to this detector. However, several flow approaches offer special attraction for their combination with ETAAS, particularly ... 

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