Patterns intermittent flow

Fig. 4.2 Photographs of ionic liquid-water two-phase flow patterns in microchannels, a Plug flow, b Disturbed plug, c Plug and drain, d Intermittent flow, e Dispersed flow. f. Quasi annular flow, g Throat annular flow, h Rivulet annular flow, i Drop flow, j Irregular flow...

As already done for the Friedel model, the possible influence of the specific flow pattern has been checked also for the Lockhart-Martinelli model. However, since the influence of the vapor quality has been already found negligible from the previous results, the ratio of the predicted pressure drop over the experimental one, has been plotted as a function of the inlet pressure (Fig. 7). It can be seen that, apart from the expected marked dispersion of the data (based on the RMS value already reported in Fig. 6), a general increase of the ratio is observed at increasing inlet pressures. Again, an apparent dependency of the predictions with the flow pattern is found, with the intermittent flow regime always characterized by larger ratios of the pressure drop, compared with the dispersed bubble. 

Siace the mid-1980s, contaminated storm mnoff has become an object of increasing concern within iadustrial complexes. Storm flow is intermittent and unpredictable ia aature, and tittle data has been collected to typify its characteristics. The level of flow and degree of contamination not only varies within an iastallation it has its own geometric characteristics, which influence patterns of surface mnoff. 

Intermittent (I) - In this flow pattern the liquid inventory in the pipe is non-uniformly distributed axially. Plugs or slugs of liquid that fill the pipe are separated by gas zones that contain a stratified liquid layer flowing along the bottom of the... 

Hetsroni G, Hu BG, Yi JH, Mosyak A, Yarin LP, Ziskind G (1998b) Heat transfer in intermittent air-water flows Part II. Int J Multiphase Flow 24(2) 189-212 Hetsroni G, Mewes D, Enke C, Gurevich M, Mosyak A, RozenbUt R (2003b) Heat transfer of two-phase flow in inclined tubes. Int J Multiphase Flow 29 173-194 Hetsroni G, Mosyak A, Segal Z, Pogrebnyak E (2003a) Two-phase flow patterns in parallel microchannels. Int J Multiphase Elow 29 341-360... 

Two-phase flows are classified by the void (bubble) distributions. Basic modes of void distribution are bubbles suspended in the liquid stream liquid droplets suspended in the vapor stream and liquid and vapor existing intermittently. The typical combinations of these modes as they develop in flow channels are called flow patterns. The various flow patterns exert different effects on the hydrodynamic conditions near the heated wall thus they produce different frictional pressure drops and different modes of heat transfer and boiling crises. Significant progress has been made in determining flow-pattern transition and modeling. 

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

In gas-liquid two-phase flow, several flow patterns exist such as bubbly, slug, plug, and annular flow depending on the pipe configuration, geometry, and flow conditions. Of these types of flows, slug flow is one of the most complex, owing to its intermittent and transient nature. Despite its complexity, industrial processes often require an online, accurate, and noninvasive estimation of such flow. If this is accomplished, industrial processes can be kept within acceptable quality limits and additionally, financial losses may be reduced. 

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