Stratified/slug transition

Stratified/Slug Transition, along the ZNS, H > 0.5, 355 Stratified-Smooth/Stratified-Wavy Transition, along the ZNS, H < 0.5, 360... 

Andritsos, N., Williams, L and Hanratty, T. J., Effect of Liquid Viscosity on the Stratified-Slug Transition in Horizontal Pipe Flow, Int. J. Multiphase Flow, Vol. 15, pp. 877-892 (1989). 

Except for the transition from wavy to stratified-slug flow, the agreement is good. 

In view of Figures 14, the regions of thick liquid layers (and laminar gas phase) is associated with liquid-controlled transition. Consequently, the stratified/slug... 

The transition of slug to annular or slug to stratified flow can be interpreted as a flooding condition. This approach describes the condition in which a wave, formed on the liquid film, may become unstable and increase indefinitely until it forms a slug (Bankoff and Lee, 1983). 

Additional research on the prediction of flow patterns is a necessity, for until detailed stability criteria are developed for the transition from one flow pattern to another, there is no alternative to the empirical flow pattern charts. Some progress in theoretically defining the transition from stratified to wavy or slug flow has been made by Russell and Etchells (R3). Inaccuracy and uncertainty in flow pattern prediction makes estimation of the in situ hydrodynamic quantities and the rate of heat transfer a difficult task. 

Experimental data for the limiting conditions of smooth stratified flow also are included in Figure 2. Inspection of the figure indicates that for relatively thick water layers (above H = 0.5 line), the neutral stability line represents a reasonable prediction for the departure from smooth-stratified configuration. Waves growing over thick layers tend to block the upper gas phase flow area, and the transition to stratified wavy regime coincides with the transition to slug flow. However, with... 

O stratified-smooth/slug, stratified-smooth/wavy, A stratified wavy/annular, turbulent/laminar transition of upper phase. 

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. 

Crowley, C. J., Wallis, G. B., and Barry, J. J., Validation of a One-dimensional Wave Model for the Stratified to Slug Flow Regime Transition, with Consequences for Wave Growth and Slug Frequency, Int. J. Multiphase Flow, Vol. 18, pp. 249-271 (1992). 

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...

The transition to annular flow either from the stratified wavy or slug flow is determined by the entrainment process. Thus if the gas (or relative) velocity exceeds the onset of entrainment velocity, the entrainment of wave crests or liquid slugs occurs. In case of slug flow, this leads to the elimination of liquid slugs. Since the part of entrained droplets are deposited on the wall surface, the onset of entrainment leads to the formation of annular flow with liquid wetting the whole surface. However, due to the gravity effect it is expected that the liquid film thickness at... 

When the liquid starts to flow as a film, three different regimes are possible as discussed previously. The stratified to slug flow transition criterion gives the required gas velocity of 300 m/s, which is about twice the expected gas velocity. However, the more important transition is that to the annular flow, which is determined by the entrainment process. As shown below, for the case of the sample calculation the onset of entrainment velocity is exceeded by the expected gas... 

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