Thin channel

These expressions are independent of L but depend on H and suggest to distinguish between two separate cases. 

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Typical column dimensions i.d. 7—10 mm Length 25-30 cm Several columns may be coupled in series i.d. 0.1—3 fjLtn Length 100-500 cm Similar to SEC Thin channel Thickness 50-150 /mi Width 1-2 cm Length 30-50 cm... 

Plate and frame systems offer a great deal of flexibility in obtaining smaller channel dimensions. Equations 4 and 5 show that the Increased hydrodynamic shear associated with relatively thin channels Improves the mass-transfer coefficient. Membrane replacement costs are low but the labor involved is high. For the most-part, plate and frame systems have been troublesome in high-pressure reverse osmosis applications due to the propensity to leak. The most successful plate and frame unit from a commercial standpoint is that manufactured by The Danish Sugar Corporation Ltd. (DDS) (Figure 15). 

Tubular systems can also be converted to thin-channel devices with the use of "volume displacement rods". In one such design ( 7), manufactured by Amlcon and Romicon, a splined core has the membrane wrapped around it, sealed, and braided to form thin-channels between the core and the membrane (Figure 17). These braided tubes are then potted in a shell and tube module where the permeate is collected on the shell side (Figure 18). 

American Institute ef Chemical Engineers Sympasium Series Figure 17. Thin-channel tube with splined core (1)... 

N 0 33 as predicted in equation 4 (see reference ). UF data (human albumin-laminar flow) taken by the author in a spiral thin-channel unit (Figure 36) confirm the 0.5 power dependence on the Reynolds number (Figure 37) rather than the usual 0.33 power dependence predicted by equation 4 and observed experimentally in linear thin-channel units (Figure 38). ... 

Likewise, the Increased pressure drop associated with some thin-channel systems, turbulence promoters, and static mixers must be weighed against the increased flux obtained. 

Electro-osmosis is widely used in microfluidics to drive aqueous media through thin channels. 

Figure 6.8 The effect of pressure on membrane flux for styrene-butadiene polymer latex solutions in a high-turbulence, thin-channel test cell [13]...

Figure 6.9 Ultrafiltration flux with a latex solution at an applied pressure of 60 psi (in the limiting flux region) as a function of feed solution latex concentration. These results were obtained in a high-turbulence, thin-channel cell. The solution recirculation rate is shown in the figure [13]...

Metal monoliths can be shaped rather freely. A good example is given in Figure 4 (9), where it can be seen that in these parallel-channel systems the structure of the channels is such that the turbulence increases. The reasoning behind that is the wish to counteract the low mass transfer rates associated with laminar flow in the thin channels of the monolith. 

Let s use the steady, two-dimensional flow in a thin channel or a narrow gap between solid objects as schematically represented in Fig. 5.11. The channel height or gap width... 

The EOF-induced flow has been amplified by using multiple capillary channels (of width 1-6 pm), so that the multiple flow streams are combined to produce adequate hydraulic pressure for liquid pumping (see Figure 3.7) [115]. The multiple channels (100) ensure the generation of sufficient flow rate (10-400 nL/min), while the small dimensions (of depth 1-6 pm) result in the necessary hydraulic pressure to prevent pressurized backflow leakage (up to 80 psi) [115]. Based on a similar approach, a narrow-gap EOF pump was constmcted to produce 400 Pa pressure with 850-nm-deep channels cascaded in three stages to produce a 200-pm/s flow velocity [390]. Another pump was constructed with 130-nm-thin channels cascaded in 10 stages to produce 25 kPa pressure [264]. 

High flow rates across the membrane surface help reduce the accumulation of solutes rejected by the membrane (referred to as concentration polarization) and impurities lodged on the membrane surface (i.e. fouling ). (See Section lbii.) Tubular membranes and flat-sheet membranes installed in thin channel plate-and-frame... 

In field-flow fractionation, a component undergoing flow transport through a thin channel is forced sideways against a wall by an applied field or gradient. The component is confined to a narrow region adjacent to the wall, by a combination of the wall s surface, which it cannot pass, and the driving force, which prevents its escape toward the center of the channel. The component molecules or particles soon establish a thin steady-state distribution in which outward diffusion balances the steady inward drift due to the field. The structure and dimensions of this layer determine its behavior in the separation process. 

In the fourth subtechnique, flow FFF (F/FFF), an external field, as such, is not used. Its place is taken by a slow transverse flow of the carrier liquid. In the usual case carrier permeates into the channel through the top wall (a layer of porous frit), moves slowly across the thin channel space, and seeps out of a membrane-frit bilayer constituting the bottom (accumulation) wall. This slow transverse flow is superimposed on the much faster down-channel flow. We emphasized in Section 7.4 that flow provides a transport mechanism much like that of an external field hence the substitution of transverse flow for a transverse (perpendicular) field is feasible. However this transverse flow—crossflow as we call it—is not by itself selective (see Section 7.4) different particle types are all transported toward the accumulation wall at the same rate. Nonetheless the thickness of the steady-state layer of particles formed at the accumulation wall is variable, determined by a combination of the crossflow transport which forms the layer and by diffusion which breaks it down. Since diffusion coefficients vary from species to species, exponential distributions of different thicknesses are formed, leading to normal FFF separation. 

Crossflow Gradients in Thin Channels for Separation by Hyperlayer FFF, SPLITT Cells, Elutriation, and Related Methods, J. C. Giddings, Sep. Sci. Technol., 21, 831 (1986). 

Separation in Thin Channels Field-Flow Fractionation and Beyond, J. C. Giddings, in J. D. Navratil and C. J. King, Eds., Chemical Separations, Vol. 1, Litarvan, Denver, 1986, pp. 3-20. 

Fig. 10.16. Pulsed flow current response for the oxidation of 3 x 10-6 mol dm-3 Fe(CN) at 0.4 V versus SSCE in 0.1 mol dm-3 KC1 and phosphate buffer, pH 7.4. (A) Wide channel tubular electrode (3 mm diameter, 4 mm long). (B) Thin channel tubular electrode (0.2 mm diameter, 1 mm long). H and L represent flow rates of 6 and 3 ml min 1 respectively (after Reference [74]).

An Amicon Model TCE thin channel multiple disc system is suitable for laboratory fractionation work of lignin. It has an UF surface area of 137 cm2 and a... 

This is useful, but the value obtained may not be, and generally is not, easily interpreted. First, the carriers are confined to a very thin channel near the CP-insulator interface of the transistor, and such a region may be structurally different from the bulk and contain different impurities. Second, this is an effective value, influenced by any trap present and by the surface states. These difficulties are shown clearly by the fact that the value of ixpe in a given material depends on the nature of the insulating material used, by up to an order of magnitude [226]. 

Focusing S-FFF suffers from the problem that the density gradient has to be formed instantaneously which is not the case in practice even for thin channels [107]. This may be the reason why published results obtained with focusing S-FFF are rare [27,74,83,308-315]. 

Sample-wall interactions may also be encountered with all other FFF techniques. The sample interaction with the accumulation wall can become a problem especially if thin channels are used to shorten elution times and to improve efficiency. For such cases, a rinsing procedure has been suggested [455]. 

In FLM, the LM organic solution flows in a thin channel between two hydrophobic microporous membranes separating the LM phase from an aqueous feed and strip solutions. The FLM differs from the HLM and MHS modules with hydro-phobic membranes by application of a spiral-type module. A schematic diagram of the spiral-type FLM module is shown in Figure 13.11. 

Flow field-flow fractionation (flow FFF or FIFFF) is one of the FFF subtechniques in which particles and macromolecules are separated in a thin channel by aqueous flow under a field force generated by a secondary flow. As with other FFF techniques, separation in FIFFF is based on the applied force directed across the axis of separation flow. In FIFFF, this force is generated by cross-flow of liquid delivered across the channel walls. In order to maintain the uniformity of cross-flow moving in a typical rectangular channel, two ceramic permeable frits are used as channel walls and the flow stream enters and exits through these walls. The force applied in FIFFF is a Stokes force that depends only on the sizes of sample components. 

Kaur, J. Agrawal, G.P. Studies on protein transmission in thin channel flow module the role of Dean vortices for improving mass transfer. J. Membr. Sci. 2002, 196, 1-11. 

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