Two‐phase flow patterns in large diameter vertical pipes at high pressures

Abstract

in Wiley InterScience (www.interscience.wiley.com).The flow pattern characteristics for a mixture of naphtha and nitrogen in a 52-m high, 189-mm diameter vertical pipe at 20 and 90 bar are reported. Time varying, void fraction and pressure variations along the riser were measured. For the former, gamma densitometers were employed. It was found that the classic slug flow pattern was not present in these experiments. The observed flow patterns are classified as bubble, intermittent, semiannular, and annular. All the methods for flow pattern transitions in vertical two-phase flow tested against the present experiments give poor predictions. The identification and delineation of flow patterns using probability density function distribution of the cross-sectionally averaged void fraction is consistent with the methods of employing pressure gradient fluctuations and structure velocity. Gas superficial velocities: top, 0.21 m/s (intermittent), bottom, 1.0 m/s (semiannular). U GS 5 0.372m/s and U LS 5 0.072 m/s.Figure 15. Flow pattern transitions at: (a) 20 bar; (b) 90 bar.

Experimental Study of Two-Phase Air–Water Flow in Large-Diameter Vertical Pipes

“…In case of the latter higher diameters, the work has been confined to a very small length-todiameter ratio (Shipley, 1984, (z=D) air-water ¼ 12.34;Ohnuki et al, 1996, (z=D) air-water ¼ 4.16;Hasanein et al, 1997, (z=D) steam-water ¼ 7.87); hence, the two-phase flow is still evolving or developing, which may not depict the true two-phase flow behavior in a longer length vertical pipe. In most of the above works with the exception of Cheng et al (1998); Prasser et al (2002); Omebere-Iyari et al (2007; and Schlegel et al (2009), the major multiphase flow parameter, i.e., flow patterns, was studied by flow visualization only and hence can be subjective (Hills, 1976;Shoukri et al, 2000;Ohnuki and Akimoto, 2000;Oddie et al, 2003;Shen et al, 2005Shen et al, , 2012. Additionally, in some of the other large-diameter work, flow patterns were vaguely dealt or completely ignored (Shipley, 1984;Van der Welle, 1985;Clark and Flemmer, 1986;Hirao et al, 1986), while in others the objective of the study was determination of a local flow structure, i.e., local void phase and velocity distributions (Ohnuki and Akimoto, 2000;Shoukri et al, 2000;Prasser et al, 2005;Shen et al, 2005;Prasser, 2007;Prasser et al, 2007;Shen et al, 2012;Schlegel et al, 2009;Lucas et al, 2010); hence any comparison performed with smaller diameter pipes was limited to these parameters only.…”

“…Although many studies have contributed to the topic of the large-diameter vertical pipes (Hills, 1976(Hills, , 1993Shipley, 1984;Hirao et al, 1986;Ohnuki and Akimoto, 1996;Hasanein et al, 1997;Cheng et al, 1998;Ohnuki and Akimoto, 2000;Shoukri et al, 2000;Prasser et al, 2002;Sun et al, 2002;Oddie et al, 2003;Hibiki and Ishii, 2003;Shen et al, 2005;Prasser et al, 2005;Omebere-Iyari et al, 2007Schlegel et al, 2009;Lucas et al, 2010;Shen et al, 2012), a majority of the work performed was restricted to pipe diameter of intermediate sizes (D 200 mm) because this was considered to be an optimum choice from a cost analysis point of view. Only a few studies have been conducted for very large-diameter sizes (300 <D < 500 mm) (Shipley, 1984;Ohnuki and Akimoto, 1996;Hasanein et al, 1997;Yoneda et al, 2002).…”

“…It is quite interesting to note that although vast research exists on two-phase vertical pipe upflow, it is based on smalldiameter pipes (D < 100 mm), and the experimental work on predicting the two-phase flow behavior in a pipe of diameter D > 100 mm is scarce. Moreover, some previous research works suggest that the flow behavior of the two-phase flow in larger diameter vertical pipes is likely to be different from that in smaller diameter pipes, e.g., slug flow, an alternate flow of liquid slugs, and large bullet-shaped smooth and elongated Taylor gas bubbles do not exist for large-diameter vertical pipes (Cheng et al, 1998;Ohnuki and Akimoto, 2000;Shoukri et al, 2000;Pickering et al, 2001;Omebere-Iyari et al, 2007). This notion introduces the uncertainty behind the predictive accuracy of the existing correlations and modeling tools.…”

A critical review of flow maps for gas-liquid flows in vertical pipes and annuli

“…We did not include in this study the limited number of reports for downward concurrent gas-liquid flows in vertical pipes [64][65][66] because conditions that draw gas bubbles or slugs down with liquid flows are less common in industrial applications than upward flow conditions. Although most of the co-current upward flow studies used air with water, eight studies report co-current experiments in vertical pipes with hydrocarbon liquids or glycerol-water solutions [21,52,58,[67][68][69][70][71]. Three studies report experiments with nitrogen gas instead of air [52,70,71].…”

“…Although most of the co-current upward flow studies used air with water, eight studies report co-current experiments in vertical pipes with hydrocarbon liquids or glycerol-water solutions [21,52,58,[67][68][69][70][71]. Three studies report experiments with nitrogen gas instead of air [52,70,71]. Figure 6 presents flow maps generated from flow regimes described in the air-water studies listed in Table 2 and Table 3.…”