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Restrictor device

Figure 19 Raman chemical images of the anodic bonded region-flow channel interface of the control (A) and flow-treated (B) MEMs silicon flow-restrictor devices. [Pg.239]

Restrictor devices such as venturi tubes, orifice plates, and nozzles operate on the basis of the Bernoulli equation [10, 11]. A venturi tube is depicted in Figure 12.13. [Pg.611]

The liquid enters the micro channel device via a large bore that is connected to a micro channel plate via a slit (Figure 5.2). The slit acts as a flow restrictor and serves for equipartition of the many parallel streams [1, 3, 4]. The liquid streams are re-collected via another slit at the end of the micro structured plate and leave the device by a bore. The gas enters a large gas chamber, positioned above the micro channel section, via a bore and a diffuser and leaves via the same type of conduit. [Pg.578]

The instrumental requirements for supercritical fluid extraction are quite simple. A pump is essential to generate the extraction pressure in a themostated extraction vessel. The soluble sample components are then swept from the vessel through a flow restrictor into a collection device that is normally at ambient pressure. The fluid used for supercritical fluid... [Pg.409]

There are a variety of restrictor types that control the pressure of the fluid during the chromatographic process. Each manufacturer has patented their individual restriction devices. It is beyond the scope of this text to go into the detail about all of these restrictors. However, by way of explanation, most of the mechanical restrictors that are used in commercial equipments operate under the principle of decreasing a volume or a space that the mobile phase must pass through by some mechanical means. This decrease in volume, if metered accurately, increases the pressure in the system in a controlled manner. As a safety precaution, for any equipment where elevated pressures are used, tubing should be rated with a safety factor of at least 1.5 times the maximum pressure the SFC system can achieve. [Pg.571]

Off-line SFE is conceptually a simple experiment to perform and requires only relatively basic instrumentation. The instrumental components necessary include a source of fluid, most often CO2 or CO2 with an organic modifier, a means of pressurizing the fluid, an extraction cell, a method of controlling the extraction cell temperature, a device to depressurize the supercritical fluid (flow restrictor), and a device for collecting the extracted analytes. [Pg.595]

One important application of pneumatic transmission is in the operation of diaphragm actuators. These are the elements generally employed to drive the spindles of control valves (Section 7.22.3) and, if hard-wired transmission systems are employed, require devices which convert electric current into air pressure or air flowrate, i.e. electropneumatic (E/P) converters. The basic construction of a typical E/P converter is illustrated in Fig. 6.77. A coil is suspended in a magnetic field in such a way that when a current is passed through the coil it rotates. This rotation is sensed by a flapper/nozzle system (Section 7.22.1). The nozzle is supplied with air via a restrictor and its back pressure actuates a pneumatic relay. The output from the latter is applied to the feedback bellows and also acts as output from the E/P converter. Electropneumatic valve positioners employ the same principle of operation. [Pg.551]

The use of a restrictor to control pressure and density in supercritical fluid extraction has also been eliminated. Prior to this, restriction and restriction devices have been the Achilles heel of SFE. With this system, this will no longer be a problem. [Pg.167]

Some support structures are also included for detachably retaining the various components of the system. Preferably the support structure can be of the assembly board type , which provides prearranged flow channels and connector ports. The desired components of the system can be fastened into these connectors by pins. The flow control system that makes up the ICS system can include pumps, flow channels, manifolds, flow restrictors, valves, etc. These components are equipped with the necessary fittings that allow them to be sealed with the prearranged or selectively located flow channels or connectors. The flow system can also include detachable mixing devices, e.g., static or ultrasonic, or with a chip-like design. The reaction units, whether chip-like or not, can be of thermal, electrochemical, photochemical or pressure type [84]. [Pg.546]

It should also be mentioned that the parallelization of reactors raises other problems such as the maldistribution of the reactants to the single units. While here usually passive devices such as flow restrictors are effectively applied, more severe problems are encountered if the process temperature should be controlled actively. One solution is to heat the whole micro reactor (assuming isothermal conditions due to large heat transfer coefficients) at a constant temperature controlled by the temperature of the flow at the reactor exit [13]. [Pg.609]

One solution to the problem mentioned above is not to rely solely on flow symmetry, but to achieve equidistribution by pressure-loss adjustment by means of flow resistors (see Figure 4.98) [140, 141, 148). In the flow sequence consisting of a main stream tube, fluid inlet, damping tank, distribution tubes and micro device such as a micro mixer, the main pressure drop is nearly always on the last side. The separation layer mixer acts here as a pressure restrictor similar to the sparger mentioned above. This requires accurate control over structural precision of micro fabrication. [Pg.615]

As previously mentioned, the SFE pump should produce a constant pressure of supercritical fluid with a rate controlled by a flow restrictor after the extraction vessel. There are a number of types of flow control devices, including a capillary made from fused silica, a pinched stainless steel tube, or a variable orifice allowing for electronic control of the pressure. [Pg.131]

Fig. 5.5. (A) Scheme of a flow digestion system and the principle of pressure equilibration A pressure reactor, B heating zone, C cooling zone, D digestion coil, E cooling device, F connection for gas supply, G restrictor tube, H collector vial, I temperature sensor, J high-pressure pump, K injection valve, L sample loop, M sample, N and O peristaltic pumps. (Reproduced with permission of the American Chemical Society.) (B) Manifold for dynamic microwave-assisted extraction I solvent, 2 pump, 3 microwave oven, 4 extraction chamber, 5 temperature set-point controller, 6 thermocouple, 7 fluorescence detector, 8 recording device, 9 restrictor, 10 extractor. (Reproduced with permission of Elsevier.)... Fig. 5.5. (A) Scheme of a flow digestion system and the principle of pressure equilibration A pressure reactor, B heating zone, C cooling zone, D digestion coil, E cooling device, F connection for gas supply, G restrictor tube, H collector vial, I temperature sensor, J high-pressure pump, K injection valve, L sample loop, M sample, N and O peristaltic pumps. (Reproduced with permission of the American Chemical Society.) (B) Manifold for dynamic microwave-assisted extraction I solvent, 2 pump, 3 microwave oven, 4 extraction chamber, 5 temperature set-point controller, 6 thermocouple, 7 fluorescence detector, 8 recording device, 9 restrictor, 10 extractor. (Reproduced with permission of Elsevier.)...
The depressurization system acts as an interface between the supercritical conditions in the extraction cell and the atmospheric conditions to which the extract is eventually subjected when the extractor is not connected on-line to a chromatographic system for the individual separation of extracted species with a view to their subsequent detection. A wide variety of commercially available devices for this purpose exists that range from straightforward glass capillaries — the end of which can be readily cut off in the event of clogging — to hand-operated restrictors to computer-controlled units. This is one of the characteristic components of commercial SF extractors (one that can differ markedly among manufacturers). [Pg.289]

The restrictor controls the flow rate of the SFE system. It is positioned after the extraction cell and ends in a collection device (off-line SFE) or in the injection port of another analytical device (on-line SFE). A shutoff valve is typically placed between the restrictor and extraction cell to enable static extractions to occur. A review of the literature indicates that the restrictor is one of the more problematic aspects of SFE. Restrictors are prone to plugging by ice formation, caused by expansion cooling of the supercritical fluid at the outlet of the restrictor, or by extracted material from the sample matrix. The technology of restrictors as flow-control devices in SFE has made significant advances since initial descriptions30 and has redefined restrictors as either fixed flow or variable flow. [Pg.187]

Restrictors have been described as one of the more problematic aspects of SFE. Collection for on-line and off-line SFE has common issues, but on-line SFE is intimately dependent on the connected analytical device. Therefore, only off-line collection techniques with the end result of a chromatography-compatible sample will be summarized here. [Pg.188]

The cyclone separator consists, in part, of a large-diameter cylinder with its central axis mounted vertically. A restrictor or BPR introduces the sample into the cylinder through a tube, pointed slightly down from horizontal, parallel to and nearly touching the inner wall. The cylinder acts as an expansion chamber. Its large volume allows the velocity of the expanded fluids to slow down. Heavier, nonvolatile components hit the wall, coalesce, and run down to the bottom, which is often tapered to a smaller diameter. A gas exit tube, often on the axis of the cylinder, allows the gas phase to escape out the top of the device. The density of the gas may still be 0.05-0.1 g/ cm. This fluid is sometimes recompressed and reused if it is pure enough. [Pg.516]


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See also in sourсe #XX -- [ Pg.611 ]




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