Flow regime transitional line

Fig. 5.15 Comparison between the experimental flow patterns obtained by Triplett et al. (1999a) and the experimental flow regime transition lines of Damianides and Westwater (1988) representing their 1 mm diameter cireular test section. Reprinted from Triplett et al. (1999a) with permission...

For the sake of clarity, the focus in Figure 18 is on the interplay and practical relevance of the stability boundaries (ZNS or ZNS) and the L-T laminar/turbulent flow regime transitional line in predicting the stratified-smooth/wavy flow pattern transition. Other transitional boundaries, which confine the stratified-smooth and stratified-wavy zones, are shown in Figure 19. For relatively low gas rates, the stratified-smooth zone is bounded by the slug or bubbly patterns while the stratified-wavy zone, at high gas rates, is bounded by the transition to annular pattern. 

This flow regime map can be compared with other maps developed previously for air-water two-phase flow in small-diameter horizontal and vertical channels. Figure 5.21a-d shows comparisons with the results of Damianides and Westwa-ter (1988), Fukano and Kariyasaki (1993), Triplett et al. (1999a) and Zhao and Bi (2001 a), respectively. The solid lines represent the flow regime transition boundaries observed in the 1 mm diameter channels and the flow regime names in parentheses are those given by the respective authors. 

Figure 5.6 Flow pattern map for a gas/liquid flow regime in micro channels. Annular flow wavy annular flow (WA) wavy annular-dry flow (WAD) slug flow bubbly flow annular-dry flow (AD). Transition lines for nitrogen/acetonitrile flows in a triangular channel (224 pm) (solid line). Transition lines for air/water flows in triangular channels (1.097 mm) (dashed lines). Region 2 presents flow conditions in the dual-channel reactor ( ), with the acetonitrile/nitrogen system between the limits of channeling (I) and partially dried walls (III). Flow conditions in rectangular channels for a 32-channel reactor (150 pm) (T) and singlechannel reactor (500 pm) (A) [13].

The it "zero neutral stability boundary predicted by Equation 33.2 has been denoted as ZNS lines while the stability boundary predicted by Equation 33.1 has been denoted by ZNS. The interplay between the stability of the smooth interface and the flow regime transition in the upper phase is elucidated with reference to Figure 7, which represents air-water flow in various conduit sizes. 

The existence of two branches points out the multiplicity of solutions, which become even more complicated along the ZNS, ZNS boundaries, also due to the discontinuities which evolve from laminar-turbulent flow regime transitions in either of the two phases (and the associated change in the shear stresses). Note, that for low gas holdup (H/D > 0.5), the destabilizing effect of may be dampened even when the gas flow is turbulent due to the strong effect of the upper wall on the turbulent structures. Therefore, the ZNS line in Figure 8 is extended (beyond gas phase L-T transitional boundary) up to the H/D = 0.5 line. 

Figure 5.16c indicates that as the channel size was reduced to Jh = 0.866 mm, the dispersed bubbly flow pattern vanished from the flow regime map. Figure 5.16a-c indicates that the slug-churn flow transition line shifted to the right, as the channel size was reduced. Similar trends were also found in small circular tubes by the... 

There has been relatively little work done on the development of two-phase flow regime maps for micro-channels. The general trends of how the transition lines are shifted as the diameter is decreased are unclear. Figure 5.19 shows a flow pattern map obtained for air-water two-phase flow in a 20 pm i.d. silica tube by Serizawa et al. (2002) at nearly atmospheric pressure. 

Fig. 4.4.5 Gradual blurring (staring on locations marked by arrow) of MRI spin-tagging spin-echo images of Taylor—Couette—Poiseuille flow as the axial flow is increased (from left to right). The images correspond to longitudinal sections of the flow and the axial flow is upwards. The dashed line marks the location of one of the stationary helical vortices which characterize the SHV mode. This flow regime corresponds to the transition from the SHV (steady) to partial PTV (unsteady) regimes as Re increases, as shown in Figure 4.4.2.

Figure 3.22 is a plot of slug-to-annular transition lines for different pressures. Thus the boundaries between flow regimes shift from adiabatic lines depending on the... 

The lines on this diagram which separate the flow regimes are actually transition regimes rather than points of abrupt change from one flow type to another. It is also worth noting that... 

Figure 5. Normalized flowrate variation in the slip and early transitional flow regimes for various aspect ratio (AR) duct flows. Symbols show the linearized Boltzmann solutions. Comparisons with the proposed model are also presented by lines.

Figure 9.7 Maps of the water-nitrogen two-phase flow regimes in the microchannels (I) 100 X 50 pm [40], (II) 50 X 50 pm [45], (III) 300 x 100 pm [40], (IV) Ref [46], (V) Ref [47], and (VI) Ref [44]. The lines represent the boundaries of the transitions between regimes (la), (lb) slug/slug-annular (2a), (2b), (2c) slug-aimular/annulai (3a), (3b) annular/churn and (4) slug/ churn regimes.

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