Flow configuration

Use of well-defined convective systems allows the influence of mass transfer to be treated explicitly eind quantitatively thus the interpretation of impedance data in terms of interfacial processes can be emphasized. Several experimental systems are commonly employed. 

The rotating disk electrode, described in Section 11.6, has the advantage that the fluid flow is well defined emd that the system is compact and simple to use. The rotation of the disk imposes a centrifugal flow that in turn causes a radially uniform flow toward the disk. If the reaction on the disk is mass-transfer controlled, the associated current density is imiform, which greatly simplifies the mathematical description. As discussed in sections 5.6.1 and 8.1.3, the current distribution below the mass-transfer-limited current is not uniform. The distribution of current and potential associated with the disk geometry has been demonstrated to cause a frequency dispersion in impedance results. The rotating disk is therefore ideally suited for experiments in which the disk rotation speed is modulated while im-der the mass-transfer limited condition. Such experiments yield another t)q)e of impedance known as the electrohydrodynamic impedance, discussed in Chapter 15. 

Rotating cylinders, described in Section 11.8, are popular experimental systems because the system setup is relatively simple to use and, at moderate rotation speeds, the flow is turbulent and yields a uniform mass-transfer-controlled current density. Empirical correlations are available that relate the cylinder rotation speed to the mass-transfer coefficient.  

The rotating hemispherical electrode, introduced by Chin, ° has a uniform primary current distribution and would therefore be a suitable configuration for experiments conducted under conditions such that the current distribution is not in- 

---

Fig. 19. Comparison of the predictions of k-e model and experimental data for a confined swirling flow, (a) Flow configuration where 4. is the primary inlet, D = 25 mm, and B is the secondary inlet, = 31 mm, = 59 mm and the step height, H = 31.5 mm. (b) Predicted and measured streamline values where r/H is the ratio of the radial distance from the centerline to the step height.

In equation 26, F is the MTD correction factor and, in general, is a function of the flow configuration and the two temperature factors defined ... 

In general there are three main types of hoUow-fiber flow configurations. In the most common, for reverse osmosis and ultrafiltration, the feed... 

A reactor is termed a radial or panel-bed reactor when gas or vapor flow perpendicular to a catalyst-fiHed aimulus or panel. These are used for rapid reactions to reduce stresses on the catalyst or to minimize pressure drops. Similar cross-flow configurations also are used for processing soHds moving... 

Process Description Microfiltration (MF) separates particles from true solutions, be they liquid or gas phase. Alone among the membrane processes, microfiltration may be accomplished without the use of a membrane. The usual materi s retained by a microfiltra-tion membrane range in size from several [Lm down to 0.2 [Lm. At the low end of this spectrum, very large soluble macromolecules are retained by a microfilter. Bacteria and other microorganisms are a particularly important class of particles retained by MF membranes. Among membrane processes, dead-end filtration is uniquely common to MF, but cross-flow configurations are often used. 

Figure 12-9. Cross section of an annular combustor showing high dome flow configuration. (Courtesy of General Electric Company.)...

Because of fhe planar nafure of the cormterflow flame and the relatively high Reynolds number associated with the flow, the flame/flow configuration can be considered to be "aerodynamically clean," where the quasi-one-dimensional and bormdary-layer simplifications can be implemented in either analytical or computational studies. Useful insights into the thermochemical structure... 

Numbering-up can be performed in two ways (Figure 1.4). External numhering-up is referred to as the connection of many devices in a parallel fashion [8] (a similar, but less elaborate, definition was already provided in [9, 10] see also [11] for a realized industrial example). A device in the sense as it is used here is defined as a functional element, e.g. a micro-mixing flow configuration such as an interdigital... 

Figure 3.7 Alternated 90° turned adjacent platelets forming a stacked cross-flow configuration. Image of thermally bonded devices (top). Complete mounted multi-plate stack micro reactors (bottom) [45].

The chip micro reactor [R 5] comprises a long micro channel connected to two vertically positioned shorter channels at each end which lead to two reservoirs [17]. These shorter channels are oriented in opposite directions so that a Z-type flow configuration results. In the downstream section of the long channel, two other vertically oriented shorter channels are also attached. These channels are each connected to a liquid reservoir. A total of five reservoirs are made in this way (Figure 4.6). 

Reactor 7 [R 7] Chip Micro Reactor with Z-type Flow Configuration... 

Reactor type Chip micro reactor with Z-type flow configuration Heater type/material Nichrome wire... 

Reactor 14 [R14] Chip with Bi-/Tri-layer Flow Configuration Using Y-type Contact... 

The polymer chips comprise two feed micro channels which are connected in a Y-type flow configuration to one elongated micro channel which is folded multiple times for compact design [29]. At the end of this channel a split into two channels is made, again by a Y-type flow configuration. The two-channel flow configuration serves for preparing water-oil parallel (bi-laminated) streams. 

Reactor type Chip with bi/tri-layer flow configuration using Y-type Outer dimensions 30 X 15 X 1.7 mm ... 

OS 43] [R 14] [P 32] Using a three-liquid layer (water/oil/water) flow instead of a two-liquid layer flow at constant channel dimensions decreases the liquid lamellae width and doubles the absolute value of the organic/aqueous interface. As a consequence, mass transport is facilitated compared with the two-flow configuration. Hence it was found that a much higher yield was obtained for the three-liquid layer flow when performing experiments of both flow configurations imder the same experimental conditions (210 s, 0.2 pi min room temperature, 300 W, > 300 nm... 

Figure 4.70 Flow configuration for the Michael addition using 2,4-pentanedione and ethyl propiolate in a two-mixing tee microreactor [8].

Figure 4.85 Flow configuration for the aldol reaction of silyl enol ethers in a mixing-tee chip micro reactor [15],...

Figure 4.87 Flow configuration for a Wittig synthesis in a chip micro reactor with three vertical injections [13].

P 75/The protocol relies on sequential filling of selected charmels or parts of them in a chip micro reactor [17]. Thus, a short description of the micro reactor flow configuration is needed to understand details of the protocol. 

---