Authors: Hadiyan Yusuf Kuntoro; Deendarlianto. Publication date: 29 April Conference: Seminar Nasional Thermofluid VI

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1 Conference paper: Experimental Study on the Holdup Characteristics of Air-water Horizontal Stratified Flow by Using an Image Processing Technique Authors: Hadiyan Yusuf Kuntoro; Deendarlianto Publication date: 29 April 24 Conference: Venue: Universitas Gadjah Mada, Yogyakarta, Indonesia Conference date: 29 April 24 Pages:

2 Yogyakarta, 29 April 24 Experimental Study on the Holdup Characteristics of Air-Water Horizontal Stratified Flow by Using an Image Processing Technique Hadiyan Yusuf Kuntoro, Deendarlianto 2 Fast Track Postgraduate Program of Mechanical Engineering, Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika 2 Yogyakarta 5528, Indonesia. hadiyan.y.kuntoro@mail.ugm.ac.id 2 Department of Mechanical and Industrial Engineering, Faculty of Engineering, Gadjah Mada University, Jalan Grafika 2 Yogyakarta 5528, Indonesia. deendarlianto@ugm.ac.id Abstract Understanding of the characteristics of stratified two-phase flow pattern in horizontal pipeline is a challenging problem relevant in many processes of chemical, nuclear, and petroleum industries. One of the most important parameter to study the flow characteristics of two-phase flow is the liquid holdup, defined as the cross sectional area occupied by the liquid phase divided by the cross sectional area of the inner pipe. Those complex behaviors had been studied by numerous researchers, a lot of mathematical models had been proposed to figure-out the phenomena. Meanwhile, there were some discrepancies among each other. Hence, the validation is needed to get a better understanding of it. From the fact, an experimental study of stratified two-phase flow pattern had been conducted in a 26 mm i.d. horizontal transparent acrylic pipe with emphasis on the study of liquid holdup. Air and water were used as the test fluids, flowing concurrently inside the pipe. The flow behavior was recorded by using a high speed-video camera and digital image processing technique was used to perform the quantitative analysis of the captured video data. The group of stratified smooth and wavy two-phase flow was successfully recorded and classified based on the visualization study from 24 couples of test condition of water and air superficial velocity. From these results, the behavior of stratified two-phase flow was discussed and used to evaluate the existing data and correlations. Keywords: Stratified Two-Phase Flow Pattern, Flow Characteristics, Holdup, Flow Behavior, Digital Image Processing.. Introduction Two-phase flow phenomena have been widely observed in various industries especially those that using pipeline system. Thus, comprehensive understanding regarding the phenomena is important key to improve the effectiveness of transport system of the fluid through the pipeline system, as well as the safety issues to the human and environment. Many researchers had been studied many flow patterns of two-phase flow phenomena in horizontal pipe cases. Many comprehensive explanations and correlations to predict the phenomena had been proposed by many researchers, but still, some discrepancies occurred between them. The researchers who carried out the study about it among others Mandhane et al [], Taitel et al [2], and Jayanti et al [3]. Stratified two-phase flow pattern is the one of the flow patterns in horizontal pipe. Researchers who had been focus investigated in stratified flow behavior among others Chen and Spedding [4], Kadambi [5], and Vlachos et al [6]. The important local parameter that widely used to study the two-phase flow phenomena is liquid holdup (η). holdup (η) is defined as the cross sectional area of the liquid phase divided by the cross sectional area of the inner pipe. Various methods and techniques had been used and developed to measure the liquid holdup. Deendarlianto et al [7] investigated the liquid film behavior at the onset of flooding in an inclined pipe by using the constant electric current method (CECM). Murai et al [8] studied three types of ultrasonic detection techniques and compared their application to five different configurations of gasliquid two-phase flows. Han et al [9] measured the liquid film thickness in a micro parallel channel by using interferometer and laser displacement meter. Another powerful technique that is recently developed to study the two-phase flow phenomena is digital image processing. This technique is broadly developed by researchers around the world to study on the basis of the visualization data from experiment of the two-phase flow phenomena. Their non-intrusive capability to process a lot of complex visualization Fakultas Teknik UGM 28

3 Yogyakarta, 29 April 24 Fig.. Schematic diagram of experimental apparatus. data become the excellence of this technique. Montoya et al [] performed the digital image processing technique for study of the interfacial behavior of the countercurrent gas-liquid two-phase flow in a hot leg of a PWR. Do Amaral et al [] investigated using image processing techniques in the case of horizontal two-phase slug flows. However, there were only a few researchers that develop this method to study the interfacial behavior on the focus of the stratified two-phase flow pattern. Thus, from this background, the research was carried out. The image processing technique algorithm was developed to study the stratified two-phase flow with emphasis on the liquid holdup study and the results were used to validate the previous work. 2. Experimental Apparatus A schematic diagram of the present experimental apparatus is shown in Fig.. As seen in Table, there were 24 matrix data ranging from.6 m/s to.92 m/s for the liquid superficial velocity (J L ) and from.2 m/s to 3.77 m/s for the gas superficial velocity (J G ). This matrix data was retrieved by refers to Mandhane et al [] flow pattern map to simulate the stratified two-phase flow pattern. A transparent acrylic horizontal pipe with inner diameter 26 mm was used in this experiment. Air and water were used as the test fluid flowing cocurrently inside it. The interfacial behavior of the stratified two-phase flow pattern was recorded by using a high speed video camera with shutter speed 2 fps and 64x48 pixel resolutions for 3s recording on each research matrix data. LED lamp was used as a light source. The visualization test section was 5 meter downstream from the mixer inlet of air and water to ensure the fully developed stratified flow recorded video data. To eliminate the refraction effect of the acrylic pipe, a correction box was used. Detail explanation regarding experimental apparatus and procedures had reported by Kuntoro et al [2]. Table. Matrix data. JL =.6 m/s JL =.3 m/s J G =.2 m/s J G =.88 m/s J G = 2.83 m/s J G = 3.77 m/s Local Holdup Measurement Using an Image Processing Technique Fig. 2 shows the recorded image samples of matrix data at 5, 7 and 6. The longitudinal section view of the pipe was used as the reference of the image recording; hence, the information that was obtained from the high speed video camera was in 2-D longitudinal view. The curvature of the gas-liquid interface was assumed to be plane. Taitel and Dukler [3] and Andritsos and Hanratty [4] also assumed plane curvature in their investigations. The local liquid holdup data was obtained by measure the local film thickness in the specific reference. The local film thickness data was used as the basis of the local liquid holdup data calculation. To measure the local film thickness data from the recorded image, the interface of the gas-liquid must be detected first. A sequence algorithm of image processing technique had been developed in the present study to detect the gas-liquid interface. The sequence algorithm of image processing technique and the equation to calculate the local liquid holdup data from the local film thickness data were reported by Kuntoro et al [2]. JL =.47 m/s JL =.63 m/s JL =.77 m/s JL =.92 m/s Fakultas Teknik UGM 29

4 Proceeding Yogyakarta, 29 April 24 gas and liquid phase due to the significant different in density (Fig. 4.a). Stratified smooth also can be recognized by the flat plot in the time series graph, and it indicates that there is no fluctuation of the liquid holdup against the change of the time (Fig. 4.b). The gathered dominant distribution of probability distribution function (PDF) plots in specific value is also the characteristics of it (Fig. 4.c). Fig. 4.c denotes that there is no spread variation of the liquid holdup in the range of certain time. a. Data 5 (JL =.77 m/s and JG =.2 m/s). -liquid interface Smooth interface b. Data 7 (JL =.6 m/s and JG =.88 m/s). Wave a. Data 2 (JL =.3 m/s and JG =.2 m/s). c. Data 6 (JL =.63 m/s and JG = 2.83 m/s). Fig. 2. Recorded image samples of stratified twophase flow pattern. ƞ(-),8 Fig. 3 shows the image detection results of the gas-liquid interface of the stratified two-phase flow pattern by using the present image processing technique algorithm. The interface of the gas liquid was clearly shown and was used to calculate the local film thickness in the specific references. The calculation results were plotted on the graph and were discussed to study the interfacial behavior of the stratified two-phase flow pattern.,6 flat plot,4, Time (s) b. Time series graph data 2.,8 gathered dominant distribution PDF,6 Reference,4,2,9,8,7,6,5,4,3,2 a. Data 5 (JL =.77 m/s and JG =.2 m/s). -liquid interface, ƞ(-) c. PDF data 2. Fig. 4. Stratified smooth characteristics. b. Data 7 (JL =.6 m/s and JG =.88 m/s). c. Data 6 (JL =.63 m/s and JG = 2.83 m/s). Fig. 3. The image detection results of the gas-liquid interface of the stratified two-phase flow pattern. 4. Results and Discussion Based on the experimental results, there were 2 distinguished liquid holdup distributions trend of the stratified two-phase flow. There were stratified smooth and stratified wavy characteristics. These characteristics were based on the flow visualization, time series graph of the liquid holdup, and the probability distribution function (PDF) of the liquid holdup. In the stratified wavy, the time series graph shows the fluctuated plot that indicates the fluctuation of the liquid holdup against the change of time (Fig. 5.b). The distribution value of the liquid holdup in the stratified wavy PDF (Fig. 5.c) looks to be widened spread over certain range of liquid holdup compared to the stratified smooth PDF (Fig. 4.c). Fig. 4.c informs that the widened dominant distribution of the liquid holdup occurs in the stratified wavy. The fluctuation of the liquid holdup also indicates the fluctuation of the pressure occurs inside the pipe. Fig. 6 to Fig. 8 shows the effects of the superficial velocity on the liquid holdup distribution. One of the superficial velocities is changed while the other is kept constant. Fig. 4 shows the stratified smooth flow characteristics, while Fig. 5 shows the stratified wavy flow characteristics. Stratified smooth is characterized by the smooth flat undisturbed interface separating the Fakultas Teknik UGM 22

5 Yogyakarta, 29 April 24 ƞ ( - ) PDF a. Data 6 (J L =.92 m/s and J G =.2 m/s).,8,6,4,2,8,6,4,2 fluctuative plot Time (s) b. Time series graph data 6. widened dominant distribution,,2,3,4,5 ƞ ( - ) Wavy interface c. PDF data 6. Fig. 5. Stratified wavy characteristics. As shown in Fig. 6, due to the increase of J L (liquid superficial velocity) at constant J G (gas superficial velocity), the liquid holdup distribution tend to increase and the value going to be widened dominant distribution from the gathered dominant distribution. It can be inferred from Fig. 6 that the flow pattern is going to change from the stratified smooth to be stratified wavy, as the result of increasing J L at constant J G. The increasing value of the liquid holdup distribution is related to the increasing of the inertia force of the liquid phase due to the increasing of the liquid supply (or liquid superficial velocity). The inertia force of the liquid phase pushes the gas phase resulting decrease in void fraction and increase in liquid holdup. In Fig. 7, under a constant J L of.6 m/s while the J G increases, the liquid holdup distribution is going to decrease, but the distribution trend still shows the same as the gathered dominant distribution. The distribution trend shows the stratified smooth pattern for all plots. It means that, as increasing the J G with constant J L, the liquid holdup distribution is going to decrease but no change from stratified smooth to stratified wavy. It also can be noticed from Fig. 7 that, at certain point, as increasing the J G, the distribution value still shows slightly the same as the previous distribution at lower J G (see J G = 2.83 m/s and J G = 3.77 m/s in Fig. 7). It can be said that the change of liquid holdup is saturated when the J G is going to keep-up with constant J L. This can be understood, as the J G increases, the inertia force of the gas is going to push,6,7,8,9 the liquid holdup, but, at certain point, the inertia force of the gas has no enough force to push down again the liquid holdup to more reduced, resulting the little change of liquid holdup distribution, as seen between J G = 2.83 m/s and J G = 3.77 in Fig. 7. In Fig. 8, as the J G increases at constant J L =.47 m/s, the liquid holdup distribution also shows the decreasing trend of distribution value, and same as the conclusion in Fig. 7, at variation of J G with constant J L, the distribution type remains the same from lower J G to higher J G. The distribution type still shows the widened dominant distribution type as identical as stratified wavy. From Fig. 7 and Fig. 8, it can be inferred as the J G increases at constant J L, the liquid holdup distribution value is going to decrease but there is no change in the distribution type which means no change from stratified smooth to stratified wavy, and vice versa. On the other hand, in Fig. 6, the liquid holdup distribution value is going to increase and the distribution type is going to change from the gathered dominant distribution type, at lower J L, to widened dominant distribution type, at higher J L, in case of constant J G =.2 m/s. From Fig. 6 to Fig. 8, it can be concluded, for the case of the present range of matrix data, the variation of J L at constant J G plays an important role in the change of the stratified sub-flow-pattern (from stratified smooth to stratified wavy, and vice versa). In Fig. 6, there is a change from stratified smooth to stratified wavy. The change of the sub-flow-pattern does not show when the J G is changed at constant J L. The change of the liquid holdup distribution is caused by the change of the inertia force of each phase due to the J L (or J G ) increases while the other is kept constant. Based on the Fig. 7, it can be concluded also that there is some point that the change of the liquid holdup distribution is very insignificant, and said to be saturated change in liquid holdup distribution. This is because the inertia force of the one of the phase has no enough force to insist another phase, and the force is going to at equilibrium state. Further investigations with wider range of matrix data is needed to study this phenomenon. Some researchers proposed the correlation to predict the mean liquid holdup based on the Martinelli Parameter X proposed by Lockhart and Martinelli [5]. Fig. 9 shows the comparison of the present data with several correlations proposed by Wallis [6], Kadambi [5], and Chen and Spedding [4]. The first reintroduced correlation based on the original paper of Lockhart and Martinelli [5] is proposed by Wallis [6]. The correlation is under predicted the present data. Chen and Spedding [4] and Kadambi [5], at the same year, proposed their own correlation. Both of them have slightly different trendline correlation, but the present data experiment tends to support the Chen and Spedding [4]. Fakultas Teknik UGM 22

6 Yogyakarta, 29 April 24 Fig. 6. The effect of J L on the liquid holdup distribution. Fig. 7. The effect of J G on the liquid holdup distribution. Fig. 8. The effect of J G on the liquid holdup distribution. Fig. 9. The mean liquid holdup prediction. Fakultas Teknik UGM 222

7 Yogyakarta, 29 April 24 The present data shows a tendency of mean liquid holdup to decrease along the increases of the parameter X, which is in good agreement with Chen and Spedding [4] correlation rather than Kadambi [5] that shows a tendency of mean liquid holdup to increases as does the parameter X. The parameter X used in this experiment is turbulent-turbulent type based on the Reynolds number calculation of each data which shows the turbulent category. In Chen and Spedding [4] correlation, they proposed the constant factor called k i, where the k i is the other factor including pipe diameter factor. Chen and Spedding [4] expected that the numerical value assigned to k i would be a function of pipe size because some factors which disturb the liquid film, such as the interfacial roughness and the velocity profile skewing effect are more pronounced in smaller diameter pipes. In this experiment, the value of k i is.5 which is determined by the trial and error method. Further investigations of k i value should be conducted to get factors that influence it and develop a method that find the value of k i precisely without trial-error method. 5. Conclusions An experiment of stratified two-phase cocurrent flow was performed in a 26 mm i.d. horizontal transparent acrylic pipe. A sequence algorithm of image processing technique was developed and used to study the interfacial phenomena on the basis of the liquid holdup distribution. The liquid holdup distribution has a tendency to increase as the J L increases at constant J G, while the liquid holdup distribution will decrease if the J G increases with constant J L. The liquid superficial velocity (J L ) plays more important role on the interfacial behavior rather than the gas superficial velocity (J G ), such as in change from stratified smooth to stratified wavy. Little change of J L has a significant change in the stratified subflow-pattern rather than J G. The present data support the correlation of Chen and Spedding [4] to predict the mean liquid holdup based on the parameter X proposed by Lockhart and Martinelli [5] rather than Kadambi [5] and Wallis [6]. Nomenclature J G : superficial velocity J L : superficial velocity k i : Constant factor PDF : Probability distribution function tt : Turbulent liquid, turbulent gas flow X : Martinelli parameter η : holdup Acknowledgments The authors would like to acknowledge Hibah Penelitian Unggulan Perguruan Tinggi (contract number LPPM-UGM/448/LIT/23) in fiscal year of 23 from Indonesia Directorate General for Higher Education (DIKTI), Ministry of Education and Culture, Republic of Indonesia for funding this work. The first author gratefully acknowledges the Fast Track Scholarship Program from Indonesia Directorate General for Higher Education (DIKTI), Ministry of Education and Culture, Republic of Indonesia. References [] J.M. Mandhane, G.A. Gregory, K. 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