Annular and Parallel Flow

The comparison of annular (or parallel) flow with Taylor flow, another stable regime, is presented in Table 7.3. The additional advantages of slug flow over parallel flow allow it to use for wide range of applications. 

There are some case-specific applications where annular flow is used. Falling film reactor is one of the examples. In this case, the liquid flows downward because of gravity in the form of film and gas flows through the open space, which lies in the top cover of the housing. 

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The mass transfer coefficients investigated for annular and parallel flow are depicted in Table 7.9. As explained in the flow regime section, this flow exists over a wide range of flow velocities giving from 0.07 to 17.35 s . ... 

Table 7.9 Mass transfer literature data on annular and parallel flow.

As in gas-liquid systems, this flow is formed based on the type of microchannel geometry used flow symmetric geometry forms annular flow, while flow asymmetric forms parallel flow. This flow regime is observed at elevated flow rates in the microchannel without static internals - the higher the flow velocity, the better the stability. The shear force of the continuous phase is dominant over the surface tension force and, therefore, the dispersed phase flows straight forming annular or parallel flow. 

The flow patterns are combined into three regions surface tension-dominated region (slug flow), transition (slug-drop and deformed interface flow), and inertia dominated-region (annular or parallel flow). The following criteria were obtained ... 

Thus, d for a narrow space between two parallel plates, of which b is sufficiently large compared withz, is almost equal to 2z. Values offluid flow through the annular space between the outer and inner tubes of the double tube-type heat exchanger or fluid flow outside and parallel to the tubes of multitubular heat exchanger can be calculated using Equation 5.11. 

When the inlet length is expressed in terms of number of gap widths , the difference between the flow in a tube and the flow in an annulus of narrow gap differs only by 25% [(0.05 - 0.04)/0.05]. This situation is an indication that the growth of the laminar boundary layers from the wall to the center of the channel is similar in both cases. Because duct friction coefficients, a measure of momentum transfer, do not vary by more than a factor of 2 for ducts of regular cross sections when expressed in terms of hydraulic diameters, the use of the inlet length for tubes or parallel plates can be expected to be a reasonable approximation for the inlet lengths of other cross sections under laminar flow conditions. In the annular denuder, the dimensionless inlet length for laminar flow development, L, can be expressed as... 

Note that in [51] a nonisothermal flow of a power-law fluid between two parallel planes one of which moves at a constant velocity (a Couette flow) was studied, as well as a gravity flow in an annular gap and a flow between two rotating cylinders of a fluid with exponential consistence factor (6.6.5) under constant wall temperature. 

Three aspects are common to all shaft kiln designs, namely charging, drawing of the ore, and combustion. A shaft kiln is essentially a vertical refractory lined cylinder or ellipse. The ore is charged in at the top of the furnace, along with, in some cases, a solid fuel such as coke or anthracite coal. Other fuels such as natural gas and oil can also be employed. There are a number of different variants of shaft kilns, such as the mixed feed, traditional type and modern basic design, annular, parallel-flow regenerative, double inclined, and multichamber. 

The flow regimes observed in liquid-liquid flow in microchannels such as drop, slug, slug-drop, deformed interface, annular, parallel, and dispersed flow are depicted in Figure 7.9. 

Figure 1 Varied flow patterns in microchannels. (A) Liquid plug flow. (B) Droplet flow. (C) Liquid/liquid parallel flow. (D) Bubble droplet alternate flow. (E) Parallel water/oil flow containing gas slugs. (F) Bubbles embedded in liquid/liquid annular flow. (G) Multiemulsions. (H) Janus fluid particles generated in a cross-junction microchannel. All scale bars are 0.5 mm. Panel (D) Adapted from Wang et al (2015a) with permission of Wiley, panel (E) adapted from Yue et al (2014) with permission of The Royal Society of Chemistry, panel (G) adapted from Deng eta (2013 a) with permission of The Royal Society of Chemistry, and panel (H) adapted from Nisisako and Hatsuzawa (2010) with kind permission from Springer Science and Business Media.

SSEs and SSCs are used in incremental dewaxing and SSCs in DILCHILL dewaxing. SSEs and SSCs are double pipe exchangers with slurry inside the central tube and the cooling media (filtrate or relfigerant) in the annular area aroimd the inside tube (pipe). Tubes are t5q)ically stacked in groups of 8, 10 or 12 and internal flow may be in parallel or series. Internal pipe diameters are t3 ically 6, 8, 10, 12 inches. 

Figure 9.16 Flow pattern for the nitrogen-ethanol system, for rectangular channels of 100 pm X 200 pm, transition from slug to annular and stratified (parallel) flow occurs for...

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