Two-phase flow pattern

Figure 2-41. Representative forms of horizontal two-phase flow patterns same as indicated in Figure 2-40. By permission, Heim, H., Oil and Gas Journal, Aug. 2,1982, p. 132.

Weisman, J., Duncan, D Gibson, J. and Crawford, T. Inti. JL Multiphase Flow 5 (1979) 437-462. Effects of fluid properties and pipe diameter on two phase flow patterns in horizontal lines. 

Two-phase flow pattern maps, observed by Revellin et al. (2006), are presented in Fig. 2.31 in mass flux versus vapor quality, and superficial liquid velocity versus superficial vapor velocity formats calculated from the test results as follows ... 

Figure 2.39a-o illustrates a typical example of alternate two-phase flow patterns at a distance of 1,000-1,500 pm downstream from the inlet of the test section. In... 

Hetsroni G, Mosyak A, Pogrebnyak E, Yarin LP (2005c) Heat transfer in micro-channels comparison of experiments with theory and numerical results. Int J Heat Mass Transfer 48 5580-5601 Hetsroni G, Mosyak A, Segal Z, Pogrebnyak E (2003b) Two-phase flow patterns in parallel microchannels. Int J Multiphase Flow 29 341-360... 

However, our current knowledge is still limited and in reality only a small number of literature sources are available. One of the questions is whether the two-phase flow patterns in small size channels are different from those encountered in ordin-... 

The experiments of co-current upward air-water two-phase flow patterns in vertical triangular micro-channels were carried out by Zhao and Bi (2001a). Three equilateral triangular channels 270 mm in length, having side lengths of 5.0, 2.5, and 1.5 mm, corresponding to hydraulic diameters of 2.886,1.443, and 0.866 mm, were tested. 

Knowledge of dominant two-phase flow patterns in micro-channels is a key factor in developing accurate and physically sound predictive tools for heat sink design. Unfortunately, interfacial interactions between the vapor and liquid phases during flow boiling in a micro-channel are often far too complex to permit accurate measurement or quantitative assessment of flow patterns. 

Serizawa et al. (2002) studied experimentally, through visualization, the two-phase flow patterns in air-water two-phase flows in round tubes. The test section for air-water experiments consisted of a transparent silica or quartz capillary tube with circular cross-section positioned horizontally. The two-phase flow was realized through a mixer with different designs, as shown in Figs. 5.4 and 5.5. The air was injected into the mixer co-axially while water was introduced peripherally. 

Figure 5.6 shows typical two-phase flow patterns observed in an air-water flow in a 25 pm silica tube at nearly atmospheric pressure. 

As demonstrated in Fig. 5.7, the result indicates that two-phase flow patterns observed in a 100 pm quartz tube are almost similar to those observed in a 25 pm silica capillary tube with several exceptions. One such exceptions is that in slug flow encountered at low velocities, small liquid droplets in a gas slug stick to the tube wall (Fig. 5.8). This fact is evidence that no liquid film exisfs befween fhe gas slug and the tube wall. 

In order to examine how two-phase flow patterns in small channels are sensitive to surface contamination, Serizawa et al. (2002) observed visually the flow patterns... 

Fig. 5.7 Two-phase flow patterns in a 100 pm quartz tube. Reprinted from Serizawa et al. (2002) with permission...

Figure 5.9 shows various interesting aspects of two-phase flow patterns obtained in this observation. It should be noticed from these pictures that a variety of two-phase flow patterns were encountered in a clean micro-channel. The authors noticed that in a very clean tube, many small individual bubbles flow in a discrete way in the tube without coalescence in bubbly flow. The most interesting thing is the special flow pattern given in Fig. 5.9d, where several bubbles with various shapes are connected in a series by the gas stems located at the tube center line. The liquid ring flow is also clearly seen in Fig. 5.9e. 

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). 

Fig. 5.17 Adiabatic micro-channel two-phase flow pattern map. Reprinted from Qu et al. (2004) with permission...

Me et al. (2006) addressed the differences in gas-liquid two-phase flow characteristics that occur in conventional size channels and micro-channels by examining the two-phase flow pattern, interfacial wave, void fraction and friction pressure drop data obtained in circular and rectangular channels with a hydraulic diameter ranging from 50 pm to 6.0 mm. 

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. 

Kawahara A, Chung PM, Kawaji M (2002) Investigation of two-phase flow pattern, void fraction and pressure drop in a micro-channel. Int J Multiphase Plow 28 1411-1435 Kawaji M (1999) Fluid mechanics aspects of two-phase flow Flow in other geometries. In Kand-likar SG, Shoji M, Dhir VK (eds) Handbook of phase change boiling and condensation. Taylor and Francis, Washington, DC, pp 205-259... 

Taitel Y, Bamea D, Dukler AE (1980) Modeling flow pattern transitions for steady upward gas-liquid flow in vertical tubes. AlChE J 26 345-354 Triplett KA, Ghiaasiaan SM, Adbel-Khalik SI, Sadowski DL (1999a) Gas-liquid two-phase flow in microchannels. Part 1 two-phase flow patterns. Int J Multiphase Flow 25 377-394 Triplett KA, Ghiaasiaan SM, Abdel-Khalik SI, LeMouel A, McCord BN (1999b) Gas-liquid two-phase flow in microchannels. Part 11 void fraction and pressure drop. Int J Multiphase Flow 25 395 10... 

Zhao TS, Bi QC (2001a) Co-current air-water two-phase flow patterns in vertical triangular microchannels. Int J Multiphase Flow 27 765-782... 

Hetsroni G, Mosyak A, Segal Z, Pogrebnyak E (2003) Two-phase flow pattern in parallel microchannels. Int J Multiphase Flow 29 344-360... 

Figure 3.1 Typical two-phase flow patterns (A) flow patterns in vertical flow (B) flow patterns in horizontal flow.

Since the pressure drop in two-phase flow is closely related to the flow pattern, most investigations have been concerned with local pressure drop in well-characterized two-phase flow patterns. In reality, the desired pressure drop prediction is usually over the entire flow channel length and covers various flow patterns when diabatic condition exist. Thus, a summation of local Ap values is necessary, assuming the phases are in thermodynamic equilibrium. The addition of heat in the case of single-component flow causes a phase change along the channel consequently, the vapor void increases and the phase (also velocity) distribution as well as the momentum of the flow vary accordingly. 

Williams, C. L., and A. C. Peterson, Jr., 1978, Two Phase Flow Patterns with High Pressure Water in a Heated Four-Rod Bundle, Nuclear Sci. Eng. 65 155. (3)... 

Hewitt GF, DN Roberts. Studies of Two-Phase Flow Patterns by X-Ray and Flash Photography. Report AERE-M 2159. London HMSO, 1969. 

Rouhani SZ, MS Sohal. Two-phase flow patterns A review of research results. Prog Nucl Energy 11(3) 219-259, 1983. 

Hewitt, G.F. and Roberts, D.N., Studies of two-phase flow patterns by simultaneous X-ray and flash photography. Report AERE-M 2159. London, HMSO (1969). 

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