Two-phase stratified flows

Sachs, P., and Long, R. A. K., A correlation for heat transfer in stratified two-phase flow with vaporization, Intern. J. Heat Mass Transfer 2, 222 (1961). 

ROLE OF INTERFACIAL SHEAR MODELLING IN PREDICTING STABILITY OF STRATIFIED TWO-PHASE FLOW... 

For simple flow geometries, as in the case of stratified two-phase flow between two parallel plates, the velocity field varies only in the perpendicular direction and expressions for the shear stresses, in terms of the phases average velocities, U, U, and the layer depth, H, can be analytically derived by solving the Navier-Stokes equations in the two-phases domains (see, for example, Hanratty and Hershman [61]). Coutris et al. showed that even for the simplest case of fully developed laminar two-layer flow the closure relations which evolve for the wall and inteifacial shear stresses are quite complicated [62]. 

Brauner, N., Rovinsky, J., and Moalem Maron, D, Analytical Solution for Laminar-Laminar Stratified Two-Phase Flows with Curved Interfaces, ANS, NUREG/CP-0142, Vol. 1, pp. 192-211, NURETH-7 International meeting, Saratoga Springs, NY, Sept. 10-15 (1995). 

Sinai, Y. L., An Extended Charnock Estimate of Interfacial Stress in Stratified Two-Phase Flows, Int. J. Multiphase Flow, Vol. 12, pp. 839-844 (1986). 

Strand, O., An Experimental Investigation of Stratified Two-Phase Flow in Horizontal Pipes, Ph.D. thesis. University of Oslo, Dept, of Mechanics (1993). 

There is a range of volume velocity of two-phase flow, which corresponds to the cone-channel confused with optimal diameter of the diffuser to confuser (further indicated as d /d, ). The distance is limited from bottom by seating stratified two-phase flow, and is limited from top by energy costs arising from the increased pressure on the ends of the device (Dp w ). In particular, the ratio d /d = 3 corresponds to the interval 44 < w < 80 cmVs, and d /d =1.6 corresponds to the interval 80 < w < 180 cm%, and further increase in the velocity of the dispersed system (w > 180 cm%) determines the need to further reduce the ratio d /d imtil d /d = 1,... 

In the study by Qu et al. (2004), experiments were conducted with adiabatic nitrogen-water two-phase flow in a rectangular micro-channel. The bubbly, stratified and churn flow patterns commonly encountered in macro-channels were never observed in the study. No water droplets were observed in the nitrogen bubble, nor were any nitrogen bubbles present in the water slugs. 

For all flow conditions tested in that study, a bubbly flow pattern with bubbles much smaller than the channel diameter (100 pm) was never observed. While liquid-only flows (or liquid slugs) containing small spherical bubbles were not observed, small droplets were observed inside gas core flows. Furthermore, no stratified flow occurred in the micro-channel as reported in previous studies of two-phase flow patterns in channels with a diameter close to 1 mm (Damianides and Westwater 1988 Fukano and Kariyasaki 1993 Triplett et al. 1999a Zhao and Bi 2001a). 

In large tubes, as well as in tubes of a few millimeters in diameter, two-phase flow patterns are dominated in general by gravity with minor surface tension effects. In micro-channels with the diameter on the order of a few microns to a few hundred microns, two-phase flow is influenced mainly by surface tension, viscosity and inertia forces. The stratified flow patterns commonly encountered in single macro-channels were not observed in single micro-channels. 

Figure 7.6 illustrates a gas-liquid two-phase flow through an inclined pipe. For clarity the diagram is drawn for stratified flow but the equations to be derived are not limited to that flow regime. A momentum equation can be written for each phase but it will be sufficient for the present purposes to treat the whole flow. In this case the interfacial shear force SFs makes no direct contribution but it would have to be considered in writing the momentum equation for either of the phases individually. The net force acting in the positive x-direction is... 

Second, a peak-intensity ultrasound echo can be used to detect the gas-liquid interface, but in this case the aim is the development of a flow meter capable of estimating the ratio of component phases accurately and in real time. Our results are promising for the estimation of the liquid flow rate of gas-liquid two-phase flow further research will produce valuable data that will allow the estimation of flow rates for the two phases simultaneously. The results presented here show the liquid flow rate estimated by the peak echo intensity method can provide an accurate estimate of the actual liquid flow rate. This method can be applied to pure liquid as well as to a two-phase flow where the void fraction is as high as 50%. The flows tested are of the stratified, elongated bubble, and slug flow types. Other types of flow such as wave flow and dispersive flow were not tested the present experimental setup does not provide the gas and liquid flow rates needed to achieve such flows. 

THIS PROGRAM CALCULATES THE TWO PHASE FLOW MODULUS AND PRESSURE DROPS FOR STRATIFIED FLOW REGIME... 

The background research in the field of multiphase transport started more than 40 years ago with the study of two-phase flow (27—31), mostly gas and liquid, that exhibits different regimes from stratified (or separated) to annular flow, passing through bubbly and slug flow. 

By increasing Ca, alternating droplet-based flow is generated with decreased droplet size. Droplet size (R) in a two-phase flow depends on the channel size (h) and the capiUaiy numben R h/Ca [7]. Finally, stratified flow is obtained for Ca > 0.15 at a water fraction of 0.2. 

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