FLOW PATTERNS IN VERTICAL AIR/WATER FLOW WITH AND WITHOUT SURFACTANT. Thesis. Submitted to. The School of Engineering of the UNIVERSITY OF DAYTON

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1 FLOW PATTERNS IN VERTICAL AIR/WATER FLOW WITH AND WITHOUT SURFACTANT Thesis Submitted to The School of Engineering of the UNIVERSITY OF DAYTON In Partial Fulfillment of the Requirements for The Degree Master of Science in Chemical Engineering By Jing Zhou Dayton, Ohio August, 2013

2 FLOW PATTERNS IN VERTICAL AIR/WATER FLOW WITH AND WITHOUT SURFACTANT Name: Zhou, Jing Approved by: Robert J. Wilkens, Ph.D., P.E. Advisory Committee Chairman Professor Department of Chemical and Materials Engineering Donald A. Comfort, Ph.D. Committee Member Assistant Professor Department of Chemical and Materials Engineering Michael Elsass, Ph.D. Committee Member Lecturer and Chemical Engineering Program Director Department of Chemical and Materials Engineering John G. Weber, Ph.D. Associate Dean School of Engineering Tony E. Saliba, Ph.D. Dean, School of Engineering & Wilke Distinguished Professor ii

3 ABSTRACT FLOW PATTERNS IN VERTICAL AIR/WATER FLOW WITH AND WITHOUT SURFACTANT Name: Zhou,Jing University of Dayton Advisor: Dr. Robert J. Wilkens Multiphase flow is a common phenomenon in many industrial processes. The influence of a surfactant on two-phase upward vertical flow regime was investigated in this study. With the addition of surfactant, the churn regime was extended towards lower gas velocity, and no bubble flow was observed at lower gas/liquid velocity for the range of conditions studied. The bubble sizes in all flow regimes were changed due to the lower surface tension caused by addition of the surfactant solution. The comparison between this experimental study with several predictive models was provided. iii

4 ACKNOWLEDGEMENTS I sincerely thank Dr. Robert Wilkens, my advisor, for his committed to this project and all his support throughout this time. I would like to thank Dr. Michael Elsass and Dr. Donald Comfort, for being my committee members and providing valuable advices. I would like to thank Saeid Biria and Innocent C. Akor for their cooperation; and special thanks to Mike Green for his assistance. This thesis is dedicated to my parents, Yanbin Zhou and Guoqing Dai, I would like to thank for their support and encouragement throughout these years. iv

5 TABLE OF CONTENTS ABSTRACT... iii ACKNOWLEDGEMENTS... iv LIST OF ILLUSTRATIONS... vi LIST OF TABLES viii LIST OF ABBREVIATIONS AND NOTATIONS...ix CHAPTER I INTRODUCTION... 1 CHAPTER II LITERATURE REVIEW... 3 CHAPTER III EXPERIMENTAL SET UP AND RESEARCH METHOD CHAPTER IV RESULTS AND DISCUSSION CHAPTER V CONCLUSIONS CHAPTER VI RECOMMENDATIONS REFERENCES APPENDIX 42 v

6 LIST OF ILLUSTRATIONS Figure 1. Typical flow patterns in gas/liquid vertical upward flow... 4 Figure 2. Air/Water vertical upward flow pattern map. 10 Figure 3. Air/Water flow pattern map with different L/D...,,,, 11 Figure 4. Air/ Water vertical upward flow pattern map 12 Figure 5. Ansari's Air/Water vertical flow pattern map. 13 Figure 6. Hasan & Kabir's air/water flow pattern map Figure 7. Experimental apparatus Figure 8. Observed flow pattern in air/water vertical upward flow. 24 Figure 9. Observed flow patterns in air/water vertical upward flow (cont d) Figure 10.The air/water system without surfactant flow pattern map Figure 11.Comparison of the bubble to slug transition for air/water flow Figure 12. Comparison of the slug to churn transition for air/water flow Figure 13. Comparison of the slug to annular transition for air/water flow vi

7 Figure 14. New flow pattern observed in 100 ppm SDS solution Figure 15. Photo images of flow pattern structures in air/water two-phase upward flow Figure 16. Photo images of flow pattern structures in 100 ppm surfactant solution.. 31 Figure 17. Flow pattern map of 100 ppm SDS solution Figure 18. Comparison of the bubble to slug transition for 100 ppm surfactant solution Figure 19. Comparison of the slug to churn transition for 100 ppm surfactant solution Figure 20. Comparison of flow pattern transition boundaries for water and 100 ppm surfactant solution vii

8 LIST OF TABLES Table 1. Flow pattern map coordinate parameters.. 7 Table 2. Physical and chemical properties of SDS 21 Table 3: Physical properties of the liquid in this study. 22 viii

9 LIST OF ABBREVIATIONS AND NOTATIONS Pipe inclination (rad) viscosity (kg/ms) Density (kg/m 3 ) Surface tension A Cross sectional area of pipe (m 2 ) D Pipe diameter (m) g Gravity (m/s 2 ) l L/D Nd Ngv Nlv Nx Ny Q Pipe length (m) Pipe length to diameter ratio Pipe diameter number Gas velocity number Liquid velocity number Normalized gas velocity Normalized liquid velocity Volumetric flow rate V m Mixture velocity (m/s) V SG Superficial gas velocity (m/s) V SL Superficial liquid velocity (m/s) ix

10 CHAPTER I INTRODUCTION Multiphase flow is a common phenomenon that occurs in many industrial processes, such as distillation, oil production, and fluid transportation. It consists of two or more immiscible fluids flowing simultaneously through a pipe. For example, in an oil production system, the fluid system of oil, water and natural gas flow through the well tubing from the reservoirs to the ground surface. However, the interaction of different phases can strongly influence the pressure drop, the hold up, and the system stability. Therefore, it would increase the operation expense and reduce the production rate. In order to overcome this problem, drag reduction agents (DRA) have been studied since 1949 (Tom, 1949). It has been introduced to gas/liquid flow since 1968 (Oliver and Young Hoon, 1968), and provides great performance while minimizing of pressure loss during fluid transportation. The fluid fluctuation and turbulence can be considerably reduced as well. Thus, DRA could extend the instruments lifetime. Several works have been done and showed that DRA in horizontal flows not only can reduce the pressure drop, but also influence the flow regime boundaries (Wilkens and Thomas, 2007). 1

11 However, there are very few studies on the influence of drag reducing agent addition on the flow pattern transition in multiphase vertical flow. This type of research has a wide industrial applications, such as oil drilling, but unfortunately lack of a strong database support. In most research on vertical multiphase drag reduction, a large amount of drag reducing polymer has been added into the solution. Such a high concentration of DRA may bring out other problems, such as foaming. The purpose of this study is to characterize the flow pattern behavior of two-phase vertical upward flow and to determine the flow pattern transition boundaries with the addition of surfactant drag reducing agent at a relatively low concentration. 2

12 CHAPTER II LITERATURE REVIEW Two Phase Flow Pattern The description of gas liquid flow in a vertical pipe is complicated due to the existence of an interface between the two phases. The different interfacial structure of two immiscible fluids is called a flow pattern. The flow patterns can be influenced by fluid properties, pipe inclination, flow rates and pipe geometry. There are many ways to describe the different flow patterns. However the flow patterns of gas and liquid two phase flow upward through a vertical pipe fall into two general categories: continuous flow and discontinuous flow. In continuous flow, one fluid phase is not interrupted by the other phase when travelling through the pipe. In discontinuous flow, both air and liquid are discrete. Hewitt and Hall-Taylor (1970) classified the gas/liquid vertical upward flow into four categories that can be described as bubble flow, slug flow, churn flow and annular flow. The flow patterns are sketched in Figure 1. These flow patterns are also observed and reported by many. (McQuillan and Whalley, 1985) 3

13 Figure 1 Typical flow patterns in gas/liquid vertical upward flow (1= Bubble, 2=Slug, 3=Churn, 4= Annular) 4

14 (i) Bubble (Figure 1-1). At a low gas rate, numerous spherical bubbles are observable as gas evenly disperses in a continuous liquid. The bubble sizes are almost the same. This is continuous flow, and the continuous phase is liquid. (ii) Slug (Figure 1-2). At a moderate gas flow, small bubbles coalesce to form a large bullet shaped gas pocket, the so called Taylor bubble. Usually these gas pockets have almost the same diameter as the pipe. As the Taylor bubble moves up, a thin liquid film between bubble and pipe wall is moving downward. Each Taylor bubble is followed by small bubbles. This is also a continuous flow, the continuous phase is liquid. The liquid region between bubbles is called slug region. (iii) Churn (Figure 1-3). As the gas flow rate is increased, the Taylor bubble is twisted and collapsed to form a highly disordered oscillation region. Both gas phase and liquid phase are no longer continuous. The liquid slug is destroyed by high gas concentration, to form liquid droplets in the center of the pipe. The falling thin film no longer can be observed. (iv) Annular (Figure 1-4). When the gas flow rate is very high, normally the gas superficial velocity is above 14m/s (Duns & Ros, 1963; Taitel, Bornea, & Dukler, 1980; Hasan & Kabir, 1998; Ansari, Sylvester, Sarica, Shoham, & Brill, 1994), the gas flows in the center of the pipe whereas the liquid flows along the pipe wall to form a thin film. Both gas and liquid phases are continuous and flowing upwardly. The flow pattern descriptions however are not limited by the above four types. For example, the annular flow regime may be divided in to wispy flow and non-wispy 5

15 flow, or mist flow. Some literature even combine the semi-annular and annular together (Rozenblit, Gurevich, Lengel, & Hetsroni, 2006). Furthermore, the transition of two flow patterns does not suddenly occur, it is possible to observe a number of transition flow patterns, and it may result in a very broad transition boundary between two distinct flow patterns. Flow pattern maps and flow pattern transitions In multiphase flow, the mass, momentum and energy change between two phases leads to great impact on the efficiency of fluid transportation, hence on the industrial production rate. The consequence of the multiphase interactions are all dependent on the fluid geometry. Bubble flow and annular flow have different relationships for pressure drop and heat transfer. In bubble flow, small gas bubbles are dispersed in a liquid channel, but in annular flow, liquid is a thin film along the pipe wall with a gas core in the center of the pipe. Therefore, it is important to use a flow pattern dependent model for better prediction of pressure drop and heat transfer. Usually, the flow patterns are recorded and plotted on a flow regime map. The flow regime map is used to identify the flow pattern occurrence and transition boundaries between two or more distinct flow regimes. In literature, there are a variety of flow pattern maps for vertical upward flow. They are based on different coordinate systems, such as modified superficial velocity (Hewitt & Roberts, 1969), dimensionless parameters (Duns & Ros, 1963), and superficial 6

16 velocity (Ansari, Sylvester, Sarica, Shoham, & Brill, 1994), as shown in Table 1. In general, these coordinate parameters are based on gas/liquid physical properties, superficial velocities, pipe material and diameter, and flow conditions. Govier (1958) and Brown s (1960) studies indicated that tube diameter and gas density have great impact on the flow pattern, pressure drop and holdup, especially at the slug/churn transition and churn/annular transition. Zubir and Zainon s (2011) experiment showed that the flow pattern transition and void fraction are preforming as a function of gas/liquid superficial velocity. Moreover, the flow pattern transition also strongly depends on the liquid viscosity (Furakawa & Fukano, 2001). Table 1 Flow pattern map coordinate parameters References Fluids Coordinate Parameters (Duns & Ros, 1963) Air-Water (Aziz, Govier, & Fogarasi, 1967) (Hewitt & Roberts, 1969) (Taitel, Bornea, & Dukler, 1980) (Ansari et,al., 1994) (Hasan & Kabir, 1998) Air-Water Air-Water Air-Water Air-Water Air-Water Gas/liquid physical properties include density, surface tension and viscosity. Superficial velocity can be calculated by (1) 7

17 where is the superficial velocity, is the volumetric flow rate, is the cross section area of pipe. Temperature, pipe inclination and pipe diameter also can affect the flow pattern transition boundaries. The boundaries between different flow patterns are not really distinct since the transition from one flow pattern to another does not occur abruptly. Therefore, the visual data collection would result in relatively broad transition boundaries. Early approaches generalized the empirical correlations, which involved several parameters to predict the flow pattern under certain flow conditions. The results of the prediction have to be validated by experimental data. Duns and Ros (1963) provided one of the early empirical approaches; they introduced dimensionless numbers for liquid velocity, gas velocity, pipe diameter and liquid viscosity. Liquid velocity number ( ) (2) Gas velocity number ( ) (3) Pipe diameter number ( ) (4) 8

18 Liquid viscosity number ( ) (5) The flow-pattern transition boundaries are defined as functions of the dimensionless groups and. For these transition boundaries, Duns and Ros proposed the following equations (Figure 2). Bubble/Slug boundary: (6) where and are functions of, Slug/transition boundary: (7) Transition/mist boundary: (8) Flow pattern prediction: Bubble flow exists if (9) Slug flow exists if (10) Mist flow exists if (11) 9

19 100 V SL (m/s) 10 1 BUBBLE SLUG TRANSITION MIST V SG (m/s) Bubble/Slug Slug/Transition Transition/Mist Figure 2 Air/Water vertical upward flow pattern map (Dons & Ros, 1963) The complex physical phenomena of multiphase flow cannot be simply addressed by the generalized empirical correlations. Mechanistic models have been developed to predict flow behavior more accurately under different flow conditions. The early mechanistic models include Orkiszewski (1967), Aziz et al. (1967), and Griffith & Wallis (1961). Ansari (1994) and Hasan and Kabir (1998) are two of the well-developed mechanistic models that have been applied widely on flow pattern based multiphase flow analysis. Taitel s (1980) mechanistic model graphically showed the effect of different variables on a simple map (Figure 3). 10

20 BUBBLE CHURN ANNULAR V SL (m/s) 0.1 SLUG V SG (m/s) bubble-slug slug-churn L/D=200 churn-annular slug-churn L/D=100 slug-churn L/D=50 Figure 3 Air/Water flow pattern map with different L/D (Taitel, 1980) The transition boundaries are represented by the following equations: Bubble/Slug transition: ( ( ) ) (12) Slug/Churn transition: (13) 11

21 Churn/Annular transition: ( ( )) (14) where the surface is tension and is the entrance length. There are more flow patterns maps based on different coordinate parameters, and these are shown in Figures 4, 5, and BUBBLE Bubble/Slug V SL (ft/sec) ANNULAR/MIST Slug/Transition 0.1 SLUG Transition/Annular -Mist 0.01 TRANSITION V SG (ft/sec) Figure 4 Air/ Water vertical upward flow pattern map (Aziz, 1967) 12

22 DISPERSED BUBBLE V SL (m/s) 1 BUBBLE 0.1 SLUG OR CHURN ANNULAR V SG (m/s) BUBBLE/DISPERSED BUBBLE DISPERSED BUBBLE/SLUG OR CHURN BUBBLE/SLUG OR CHURN SLUG OR CHURN/ANNULAR Figure 5 Ansari's Air/Water vertical flow pattern map (1994) 10 V SL (m/s) BUBBLE CHURN ANNULAR Bubble/Slug Slug/Churn SLUG Churn/Annular V SG (m/s) Figure 6 Hasan & Kabir's air/water flow pattern map (1998) 13

23 Drag reducing surfactants In two phase flow, the frictional resistance between the pipe wall and fluid can result in large pressure drop during the fluid transportation. Early studies showed that the unit pressure drop was significantly different for each flow pattern (Govier & Short, 1958). To decrease the friction, and reduce the pressure drop in the pipe, a drag reduction agent (DRA) was introduced to assist in lowering pressure loss. The first description of drag reducing additive was in 1931 by Forrest and Grierson. The first investigation of using polymer as DRA in single phase turbulence was reported by Toms in Since then, drag reducing polymers have been widely used in industrial applications, such as crude oil pipeline transportation. Polymer DRA is an excellent drag reducer due to the low dosage requirement. However, it is only good for once-through systems. In recirculation systems, polymer could degrade by mechanical and thermal effects and rapidly lose its efficiency. Surfactant DRA can be applied to overcome the degradation problem. If long micelles form, drag reduction can occur. Surfactant micelles are capable of self-repairing; so it has been applied on district heating or cooling system in Japan (Hellsten, 2001). Surfactant is a compound that can lower the surface tension of solution. It consists of a hydrophilic head group and a hydrophobic hydrocarbon tail. By adding surfactant in water, the interaction between water molecules on the surface can be disrupted by the hydrophobic tails, thus lowering the surface tension. And this phenomena could potentially change the flow pattern in multiphase flow, thus leading to a potential reduction in pressure drop which is separate from frictional reduction. 14

24 In water, the long chain hydrophobic groups of surfactant tend to form micelles. The critical packing parameter (CPP) is used to predict the geometry of micelles. Foam forms after surfactant is added. The foam stability closely corresponds to surface viscosity. Gas pressure difference between large bubbles and small bubbles could lead a decrease of foam stability. In Wilkens et.al (2006) study, they indicate that surface tension change is not the only factor on flow patterns, the tendency of foam formation also can influence the flow pattern. Impact of drag reducing surfactant on flow patterns Several works have indicated that the flow patterns can also be changed by adding DRA in horizontal multiphase flow (Al-Sarkhi & Soleimani, 2004). In one study, the liquid surface tension was reduced by 50% and the churn regime was significantly influenced by surfactant additive (Sawai, Kaji, & Urago, 2004). Lioumbas et al. indicated that the interfacial structure of two-phase flow in an inclined pipe was influenced by surfactant additive. The wave formation from the smooth to wavy stratified flow regime was delayed while the pressure drop was reduced (Lioumbas, Mouza, & Paras, 2006). Wilkens, et al. studied the influence of surfactant additive on flow patterns in horizontal air/water flow (Wilkens, et al, 2006). The surface tension was decreased by adding surfactant to the flow system. The slug occurrence was decreased, and the slug regime was replaced by a new flow pattern at high liquid superficial velocity. The surfactant used in their study was Sodium Dodecyl Sulfate (SDS). 15

25 The influence of surfactant on air/water inclined flow was studied by Xia and Chai in In this study, the stratified wavy to annular transition was significantly affected by surfactant addition. Stratified flow was found in air/ SDS solution for 10 degree pipe inclination while stratified flow could be observed in air/water without SDS mixture (Xia & Chai, 2012). In Duangprasert et al. s (2008) study, SDS surfactant has been added into airwater vertical upward flow. The air critical Reynolds number in slug regime has been decreased with an increase in the SDS concentration. For 2750 ppm SDS solution, the air critical Reynolds number has been reduced to 13.1 from 18 in slug flow regime, compared with pure water under the same condition. Therefore, the slug pattern transition also has been further influenced (Duangprasert, et al, 2008). 16

26 CHAPTER III EXPERIMENTAL SET UP AND RESEARCH METHOD The Multiphase Flow loop The experiment was carried out by using air/water two phase flow in the pipe apparatus diagram shown in Figure 7. This apparatus is capable of generating gas superficial velocity from 0.3 m/s to 10.3 m/s and liquid superficial velocity from 0.15 m/s to 0.91 m/s. The visual observations and video recording were made directly through the 2 schedule 40 clear PVC pipe at the test section. In this multiphase apparatus, water was pumped from a 226 gallon capacity storage tank by using a 2.2kW Bell & Gossett Series 3530 centrifugal pump. Air was supplied by a house compressor at approximately 100 psi. Air and water were then mixed and entered the meter tall vertical pipe. The two phase flow travelled along the vertical pipe for approximately 9 meters to allow for the full development of the flow pattern. The video camera was placed at 10 meters height to record different flow patterns. Then the gas/liquid mixture entered into separator where the gas is vented to the surroundings. In the separator tank, liquid was drained back to the storage tank through a recycle pipe. The storage tank was opened to the air, so the outlet pressure of the system remained at atmospheric pressure (around 14.7 psi). 17

27 The L/D (pipe length to diameter ratio) from the air/liquid mixture entrance location to the separator tank is 200. The recording camera was placed at the location L/D=173. Figure 7 Experimental apparatus (University of Dayton, Unit Operation Laboratory) 18

28 Methodology Initially, approximately 110 gallon of deionized water was added into the storage tank. The video camera was set up at the test section for flow pattern observation. Air-water two phase runs without surfactant were conducted to verify the proximity of the experimental flow pattern and the predicted models. Pressure, temperature, liquid density, surface tension and volumetric flow rate were recorded to calculate the superficial velocity. Liquid flow rate and gas flow rate were adjusted in order to generate the flow pattern map. After the flow pattern data collection of air/water without surfactant was complete, drag reducing surfactant was added into the storage tank at the desired concentration. The estimation of initial surfactant amount was based on the liquid level in storage tank. A sample titration was conducted from aliquot solution to calculate the accurate concentration (See Appendix). Then the concentration was adjusted to reach the desired value of 100 ppm by adding surfactant or deionized water into the tank. An aliquot was collected to measure the surface tension and liquid viscosity. Liquid flow rate and gas flow rate were both adjusted to develop the flow pattern map. The final concentration of SDS solution in the tank was 96 ppm. Under both conditions, with or without surfactant, data was collected by setting the liquid flow rate as constant, while the gas flow rates were adjusted from 0.4 to 14 m/s using m/s steps. The liquid flow rates were recorded at 0.1, 0.2, 0.35, 0.5, 0.6, and 0.9 m/s. At each flow rate, 1000 data points were recorded for superficial velocity calculation. Then these data points were averaged for further analysis. 19

29 After completion, the tank and pipe were rinsed by deionized water until there was no foam residual. The drag reducing agent used in this experiment was Sodium Dodecyl Sulfate (SDS) provided by Fisher (Lot ). 20

30 CHAPTER IV RESULTS AND DISCUSSION Physical and Chemical properties of SDS The surfactant used in this study is Sodium Dodecyl Sulfate (SDS). The equilibrium surface tension of 100 ppm SDS solution was measured at room temperature ( ). The physical and chemical properties of SDS are listed in Table 2. Table 2 Physical and chemical properties of SDS Molecular Formula Molecular Weight Ionic nature Anionic Appearance White Solid ( ) Water solubility CMC in soft water 180,000 ppm 1326 ppm 21

31 Physical properties of the liquid Table 3 lists the values of density, viscosity, surface tension at of deionized water and 100 ppm SDS solution. Table 3 Physical properties of the liquid in this study Liquid ( ) (kg/ms) (mn/m) Water ppm SDS where is liquid density, is liquid viscosity, and is liquid surface tension. Visual Observation of Flow Regimes by Video Camera Air/Water Mixture There were ten distinct flow patterns observed in air/water upward flow, which have been sketched in Figure 8 and Figure 9. The common flow patterns (bubble, slug, churn, annular) were observed during these experiments. The transitions between each of the flow regimes have been sketched, and are described as follows. Bubble-Slug. Small bubbles begin to coalesce to form larger sized bubble randomly distribute in a continuous liquid phase. The bubble sizes are not uniform. 22

32 Slug-Bubble. The bullet-shaped head starts appearing in the larger sized bubble. The slug region is still not very distinct. Small bubbles begin to form clusters after the large bubble. disappear. Slug-Churn. Taylor s bubbles start to twist and the bullet shape starts to Churn-Slug. Taylor s bubbles are almost destroyed. The downward falling film has totally disappeared. Twisted gas pockets are moving upward. Churn-Annular. The large gas pocket starts to form in the center of the pipe. The liquid slug pulses after one gas slug until the next gas slug passes through. Annular-Churn. The liquid film forms along the pipe wall. The large gas pocket become a gas core in the center of the pipe. Small liquid slugs occasionally appear. It still pulses in between two gas slugs. 23

33 Figure 8 Observed flow pattern in air/water vertical upward flow Figure 9 Observed flow patterns in air/water vertical upward flow (cont d) 24

34 The air/water system without surfactant flow pattern map is given in Figure 10. At the lowest gas flow rate, bubble flow was observed when the liquid superficial velocity was above 0.8 m/s. The transition zone from bubble to slug was broad at the low liquid flow rate. Slug flow formed when the gas superficial velocity was above 0.47 m/s. As the superficial gas velocity was increased, the churn flow was formed. Churn region was observed when the gas superficial velocity was above 1.4 m/s. The churn to annular transition was the broadest region on the flow pattern map in this study. Annular flow was formed when the gas superficial velocity was above 13.5m/s at low liquid flow rate, and 7 m/s at high liquid flow rate, respectively. The flow pattern map also has been plotted against several predictive models. The comparisons of each of the flow regime transition boundaries are displayed in the Figures 11, 12, and 13. Each of the observed flow pattern transitions has been compared with both empirical correlation models and mechanistic models that have been discussed in the literature review section. Figure 11 shows the boundaries for the bubble-slug transition for air/water flow. Taitel and Dukler s model has the best agreement with the experimental data. The bubble region appeared only at the high liquid velocity, and it had not been observed at the low liquid flow rate. The slug-churn transition was plotted in Figure 12. Slug/Churn and Churn/Slug flow patterns had been observed in this region. These new flow patterns provided the better understandings of the transition mechanism. The transition boundary was vertical on the plot. The transition region was broader at the lower liquid velocity. None of the 25

35 predictive models fit with the experimental data. Taitel and Dukler gives the best estimation of boundary location. The different definition and terminology of churn flow that given by the published correlation may cause the discrepancy of boundary location. For example, Duns and Ros defined the churn flow as the transition region (Duns, 1963), which results the location of a transition curve at a relatively high gas velocity. Therefore, it is reasonable that the prediction curves tend to depart from each other. The curve for churn to annular transition was compared with predictions in Figure 13. Churn/Annular and Annular/Churn two transition flow patterns were observed in this region. The annular data was not complete due to the limitation of the experimental instrument. The highest gas velocity that can be approached was 14.2 m/s. The transition was broader at higher liquid flow rate with the exception at 0.5 m/s of liquid. Aziz, Ansari and Taitel s models laid on top of each other. Moreover, in this flow pattern transition region, gas flow rate was more dominant over liquid flow rate. 26

36 1 BUBBLE slug slug/churn churn/slug Vsl (m/s) SLUG CHURN ANNULAR churn churn/mist mist/churn mist slug/bubble bubble Vsg (m/s) bubble/slug Figure 10 The air/water system without surfactant flow pattern map (the shaded area represent 4 general flow patterns, non-shaded area represent the transition regions) 1 slug slug/bubble bubble bubble/slug VSL (M/S) Duns and Ros Aziz Ansari Hasan and Kabir VSG (M/S) Taitel and Dukler Figure 11 Comparison of the bubble to slug transition for air/water flow 27

37 1 slug slug/churn churn/slug VSL (M/S) churn Duns and Ros Aziz Ansari Hasan and Kabir VSG (M/S) Taitel and Dukler Figure 12 Comparison of the slug to churn transition for air/water flow 1 churn churn/annular annular/churn annular VSL (M/S) Duns and Ros Aziz Ansari Hasan and Kabir VSG (M/S) Taitel and Dukler Figure 13 Comparison of the slug to annular transition for air/water flow 28

38 Surfactant Solution The surfactant used in this study is SDS. An additive of 100 ppm SDS did not result in a drastic change to the flow pattern map (see Figure 17). However, this flow pattern map was not complete due to the limit data of annular flow. In order to avoid too much foaming, and for laboratory safety, the highest gas and liquid velocities which could be reached were 7.26 m/s and 0.72 m/s, respectively. The equilibrium surface tension was decreased from 72 mn/m to 64.6 mn/m after 100 ppm SDS was added. A new flow pattern was observed with addition of 100 ppm SDS (Figure 14). At low gas/liquid flow rate (0.33 m/s and 0.14m/s respectively), the bullet shape of Taylor s bubble in slug region was instead by a relatively flat top. Also the bottom of this gas pocket remained in the shape of a slug bottom with a bubble cluster followed by a flat head liquid slug. The diameter of this large gas pocket was almost the same as the pipe diameter. The free falling thin film between gas slug and pipe wall still can be observed. 29

39 FLOW Figure 14 New flow pattern observed in 100 ppm SDS solution. (1. the flat top of the gas pocket; 2. the body of the gas pocket; 3. the bottom of the gas pocket) (Photos, courtesy of Steven Paul Photo,LLC) 30

40 Figure 15 Photo images of flow pattern structures in air/water two-phase upward flow Figure 16 Photo images of flow pattern structures in 100 ppm surfactant solution (Photos, courtesy of Steven Paul Photo,LLC) 31

41 The flow regimes of surfactant solutions were recorded by digital camera and also can be classified as four patterns. Figure 15 and 16 show the comparison of flow patterns in both cases of air/water mixture with surfactant. 1. Bubble flow. In surfactant solution, bubbles have smaller diameter but are more numerous at the same gas/liquid flow rate. The shape of bubbles is more close to sphere compared with clear air/water mixture. 2. Slug flow. The free falling thin film between Taylor s bubble and pipe wall was occupied by numerous small bubbles. The bottom of Taylor s bubble was a dense foam region followed by a large number of small bubbles. The shape of small bubbles was not uniform but still spherical in shape. 3. Churn flow. Churn flow is the broadest region in both air/water mixture and surfactant solution flow pattern maps. The pulse motion of the liquid slug can be observed in both flow. The turbulent motion resulted a lot of foaming. 4. Annular flow. Annular flow regime was not achieved in 100ppm SDS solution. As the gas velocity increased, more and more foam was generated and filled the separation tank. To avoid overflow, the superficial gas velocity was controlled below 7.26 m/s. In general, the characteristic sizes of bubbles were changed with 100 ppm surfactant solution in all flow regimes. 32

42 VsL (m/s) VsL (m/s) 1 SLUG CHURN bubble/slug slug slug/churn churn churn/annular Long gas pocket VsG (m/s) Figure 17 Flow pattern map of 100 ppm SDS solution (the shaded area represent 4 general flow patterns, non-shaded area represent the transition regions) 1 bubble/slug slug Duns and Ros Aziz Ansari Hasan and Kabir Taitel and Dukler VsG (m/s) Figure 18 Comparison of the bubble to slug transition for 100 ppm surfactant solution 33

43 VsL (m/s) 1 slug slug/churn churn Duns and Ros Aziz Ansari Hasan and Kabir Taitel and Dukler VsG (m/s) Figure 19 Comparison of the slug to churn transition for 100 ppm surfactant solution 1 Bubble/Slug VsL (m/s) Slug/Churn Churn/Annular SDS Bubble/Slug SDS Slug/Churn VsG (m/s) Figure 20 Comparison of flow pattern transition boundaries for water and 100 ppm surfactant solution 34

44 Five predictive models also have been plotted over the flow pattern maps. In bubble-slug transition (Figure 18), Taitel and Dukler gave the best fit. But bubble/slug transition flow only appeared at relatively high liquid velocities under this experimental condition while the gas flow rate was extremely low. Therefore, the downward edge of bubble region was difficult to determine. In slug-churn transition (Figure 19), the higher liquid velocity has slightly broader transition region. None of the predicted models fit the experimental transition boundary. Figure 20 showed the flow regime transitions comparison between air/water and air/sds solution. Only a few bubble flow conditions were observed in SDS solution. The bubble to slug transitions with or without surfactant have good agreement at higher liquid superficial velocity. The slug flow with large gas pocket was observed at lower liquid velocity and the transition of bubble/slug tend to shift towards lower gas velocity in SDS solution. The bubble flow has not been observed at low liquid velocity in air/surfactant solution under the same flow condition with air/water flow. The slug to churn transition in air/sds solution was significantly different from air/water mixture. The transition takes place at lower gas superficial velocity. The churn flow region in SDS solution was expanded toward the slug region at low gas velocity. The reduced surface tension of the working solution change the bubble sizes in all flow regimes, thus the transition boundary of slug to churn may be impacted and shifted to lower gas velocity. This result has good agreement with Rozenblit et al. s (2006) experiment. 35

45 CHAPTER V CONCLUSIONS The flow pattern map of two phase air/water upward flow through vertical pipe was recorded. The flow regime transition boundaries have good agreement with Taitel and Dukler s predictive model, especially at slug to churn transition. Taitel and Dukler s model depended on the entrance length to pipe diameter ratio, which considered different pipe conditions in vertical two phase flow. Air/ surfactant vertical upward flow was also plotted, however, annular flow was not observed due to the separator limitation. With SDS, the best models is still Taitel and Dukler s prediction. Aziz s prediction gives very poor agreement for both conditions. A new flow pattern has been observed at low gas and liquid velocity in SDS solution. The slug to churn transition boundary in SDS solution was significantly different from air/water mixture due to foam formation 36

46 CHAPTER VI RECOMMENDATIONS Further experimentation In order to complete the flow pattern map of air/surfactant solution and investigate the surfactant influence on flow regime transition, the following aspects were suggested for further study. Separator needs to be modified to measure the churn to annular transition of upward air/surfactant solution in vertical pipe to complete the flow pattern map for 100ppm surfactant solution. A comparison with air/water flow needs to be conducted. Measure the flow pattern transition of surfactant solution in various concentrations needs to be done for better understanding of surfactant influences on flow regime transition. 37

47 REFERENCES Al-Sarkhi, A.,.-N. (2006). Effect of drag reducing polymers on air-water annular flow in an inclined pipe. Int. J. Multiphase Flow, Al-Sarkhi, A., & Hanratty, T. (2001). Effect of drag-reducing polymer on annular gasliquid floe in a horizontal pipe. International Journal of Multiphase Flow, Al-Sarkhi, A., & Soleimani, A. (2004). Effect of drag reducing polymers on two-phase gas-liuqid flows in a horizontal pipe. Chemical Engineering Res. Des., Ansari, A., Sylvester, N., Sarica, C., Shoham, O., & Brill, J. (1994). A Comprehensive Mechanistic Model for Upward Two-Phase Flow in Wellbores. SPE Production & Facilities, Aziz, K., Govier, G., & Fogarasi, M. (1967). Pressure Drops in Vertical Pipes. AIME, 240. Daas, M. B. (2006). Computational and experimental investigation of the drag reduction and the components of pressure drop in horizontal slug flow using liquid of different viscosities. Experimental Thermal Fluid Science,

48 Duangprasert, T., Sirivat, A., Siemanond, K., & Wilkes, J. (2008). Vertical two-phase flow regimes and pressure gradients under the influence of SDS surfactant. Experimental Thermal and Fluid Science, Duns, H., & Ros, N. (1963). Vertical flow of gas and liquid mixtures in wells. Sixth World Petroleum Congress, Forrest, F., & Grierson, G. (1931). Friction loss in cast iron pipes. Paper Trade Journal, 92:298. Furakawa, T., & Fukano, T. (2001). Effect of liquid viscosity on flow patterns in vertical upward two-phase flow in a pipe. International Journal of Multiphase Flow, Govier, G., & Short, W. (1958). The Upward Vertical Flow of Air-Water Mixtures II. Effect of Tubing Diameter on Flow Pattern, Holdup and Pressure drop. The Canadian Journal of Chemical Engineering, Hasan, A., & Kabir, C. (1998). A study of multiphase flow behavior in vertical wells. SPE Production Engineering, Hellsten, M. (2001). Drag-reducing surfactants. Journal of Surfactants and Detergents, 70. Hewitt, G., & Roberts, D. (1969). Studies of Two-Phase Flow Patterns by Simulateous X-Ray and Flash Photography. Chemical Engineering Division, Hewitt, G., & Hall-Taylor, N. (1970). Annular Two phase flow. Pergamon Press. 39

49 Lioumbas, J., Mouza, A., & Paras, S. (2006). Effect of surfactant additives on co-current gas-liquid downflow. Chemical Engineering Science, McQuillan, K., & Whalley, P. (1985). Flow patterns in vertical two-phase flow. Int.J.Multiphase Flow, 11(2), Oliver, R.D. &Young Hoon, A.(1968). Two-phase Non-Newtonian Flow. Trans. Inst.Chem. Eng., T106 Rozenblit, R., Gurevich, M., Lengel, Y., & Hetsroni, G. (2006). Flow pattern and heat transfer in vertical upward air- water flow with surfactant. International Journal of Multiphase Flow, Sawai, T., Kaji, M., & Urago, T. (2004). Effect of surfactant additives on pressure drop reduction in vertical upward two-phase flow. In: Proceeding of 5th International Conference on Multiphase Flow, (p. paper No.323). Yokohama Japan. Taitel, Y., Bornea, D., & Dukler, A. (1980). Modelling flow pattern transitions for steady upward gas-liquid flow in vertical tubes. AlChE, Toms, B. (1949). Some observations on the flow of linear polymer solutions through straight tubes at large Reynolds numbers. In: Proceedings of the International Congress on Rheology, Holland, Amsterdam,, II135-II141. Wilkens, R. J., & Thomas, D. (2007). Multiphase drag reduction: Effect of eliminating slugs. International Journal of Multiphase Flow,

50 Wilkens, R., Thomas, D., & Glassmeyer, S. (2006). Surfactant use for slug flow pattern suppression and new flow pattern types in a horizontal pipe. Transactions of the ASME, Xia, G., & Chai, L. (2012). Influence of surfactant on two phase flow regime and pressure drop in upward inclined pipes. Journal of Hydrodynamics,

51 APPENDIX Flow Pattern Transition Boundaries Equations Aziz s Model (Figure 4) (Aziz, Govier, & Fogarasi, 1967) Govier and Aziz s flow pattern map coordinates ( ) (( ) ( )) (15) and (( ) ( )) (16) Bubble/Slug transition: ( ) (17) Slug/Transition: (18) 42

52 Transition/ Annular-Mist ( ) (19) where, Bubble flow exists if (20) Slug flow exists if (21) Mist flow exists if (22) Transition region exists when, transition region does not exist for (23) Ansari et al. Model (Figure 5) (Ansari, Sylvester, Sarica, Shoham, & Brill, 1994) Bubble/slug transition. Taitel gave the minimum diameter for which bubble flow occurs as ( ( ) ) (24) Bubble/dispersed bubble transition: ( ( ) ) (25) 43

53 Bubble/Slug or churn transition: ( ( ) ) ( ) ( ) ( ) (26) where f is obtained from the Moody diagram for a no-slip Reynolds number. Dispersed bubble/slug or Churn transition: (27) Slug or churn/annular transition: ( ( ) ) (28) Hasan and Kabir Model (Figure 6) (Hasan & Kabir, 1998) Bubble/Slug transition: (29) { } (30) Slug/Churn transition: ( ) ( ) ( ) (31) 44

54 Churn/Annular transition: ( ) (32) Surfactant Concentration Determination To find the surfactant concentration of working solution, a titration method was used in this experiment. The anionic surfactant SDS was titrated by using N cationic surfactant, Hyamine A mixed indicator, blue VN and dimidium bromide, were added to the sample. Methylene Chloride was added for titration. The titration endpoint was when the organic layer turned clear from pink (just before the blue complex formation). Sample Calculation: 6g (6mL) aqueous SDS solution (roughly 100ppm) was titrated to endpoint by using 5mL N Hyamine 1622 solution. The molecular weight of SDS is g/mol. (5mL)*(0.0004mol/L)*(0.001L/mL)*(288.38g/mol)/(6g)*(1000g/L)*(1000mg/g)=96ppm 45

55 Data for figure 10, 11, 12, 13 Observed Flow Vsg (m/s) VsL (m/s) Pattern bubble bubble-slug slug-bubble slug-bubble slug slug slug slug slug slug slug slug slug slug slug-churn slug-churn slug-churn slug-churn churn-slug churn-slug churn-slug churn-slug churn-slug churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular churn-annular annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular-churn annular annular annular annular 46

56 Data for figure 17, 18, 19 Vsg VsL Observed Flow (m/s) (m/s) Pattern slug slug slug/churn slug/churn churn churn churn churn churn churn churn churn churn churn churn churn slug slug slug slug slug slug slug-churn churn churn churn churn churn churn slug/bubble slug slug slug/churn churn/slug churn churn churn churn churn churn churn churn churn churn bubble/slug slug slug slug slug slug/churn churn/slug churn churn churn churn/annular churn/annular churn/annular slug/bubble Slug slug slug/churn churn/slug churn churn churn churn churn churn churn churn churn churn 47

57 Data for Figure 20 Water SDS solution Bubble/Slug Slug/Churn Churn/Annular VsG(m/s) VsL(m/s) VsG(m/s) VsL(m/s) VsG(m/s) VsL(m/s) Bubble/Slug Slug/Churn VsG(m/s) VsL(m/s) VsG(m/s) VsL(m/s)

58