Modares Mechanical Engineering

Modares Mechanical Engineering

Numerical Investigation of the Effect of Pipe Inclination on Annular Flow of Water and Non-Newtonian Crude oil

Document Type : Original Research

Authors
MohammadReza Karimi
Ali Jahangiri
Mohammad Ameri
Faculty of Mechanical and Energy Engineering, Shahid Beheshti University
10.48311/mme.2025.27865
Abstract
Transporting heavy crude oil through pipelines is a major challenge due to its high viscosity and the resulting significant pressure drop. Core-annular flow, in which a thin water layer separates the crude oil from the inner pipe wall, has been recognized as an effective method for reducing pressure loss. This study numerically investigates the effect of pipe inclination on the flow pattern of annular two-phase flow of water and non-Newtonian crude oil. The computational domain includes a pipe with an inner diameter of 40 mm and a length of 1.5 meters, where two phases are analyzed for inclination angles ranging from +90° (upward) to −90° (downward). Computational Fluid Dynamics (CFD) simulations were performed using ANSYS Fluent, and the Volume of Fluid (VOF) model was employed to capture the oil–water interface. The results indicate that core-annular flow can reduce the pressure drop by up to 85.5% compared to single-phase oil flow. As the pipe approaches a vertical orientation, the flow pattern transitions from semi-annular to fully annular and symmetric, which significantly reduces the likelihood of crude oil deposition on the pipe wall. In upward flow, increasing the inclination angle reduces the frictional pressure drop while increasing the gravitational component. Beyond 75°, the reduction in frictional component outweighs the gravitational increase, and the combined pressure drop is reduced from 1245 Pa at 75° to 1201 Pa at 90°. In downward flow, increasing inclination leads to higher frictional losses and lower gravitational contribution. For validation, the numerical results were compared with experimental data, and a maximum error of 7% was obtained
Keywords
Numerical Study
Annular Flow
Pressure Drop
Heavy Crude Oil
Inclination Angle

Subjects

1- International Energy Agency, "World Energy Outlook 2013,"International Energy Agency, Paris, 2013. doi: 10.1787/20725302
2- A. Archibong-Eso, J. Shi, Y. D. Baba, A. M. Aliyu, Y. O. Raji, H. Yeung, "High viscous oil–water two–phase flow: experiments & numerical simulations," Heat and Mass Transfer, vol. 55, pp. 755-767, 2019. doi: 10.1007/s00231-018-2461-9
3- D. Gordon, "Understanding unconventional oil," The Carnegie papers, Energy and climate, 2012.
4- M. D. Garmroodi, A. Ahmadpour, "A numerical study on two-phase core-annular flows of waxy crude oil/water in inclined pipes," Chemical Engineering Research and Design, vol. 159, pp. 362-376, 2020. doi: 10.1016/j.cherd.2020.04.017
5- A. Hart, "A review of technologies for transporting heavy crude oil and bitumen via pipelines," Journal of Petroleum Exploration and Production Technology, vol. 4, pp. 327-336, 2014. doi: 10.1007/s13202-013-0086-6
6- N. M. D. A. Coelho, M. E. S. Taqueda, N. M. Q. Souza, J. L. de Paiva, A. R. Santos, L. R. B. Lia, M. S. de Moraes, D. de Moraes Júnior, "Energy savings on heavy oil transportation through core annular flow pattern: An experimental approach," International Journal of Multiphase Flow, vol. 122, pp. 103-127, 2020. doi: 10.1016/j.ijmultiphaseflow.2019.103127
7- J. D. Isaac, J. B. Speed, "U.S. Patent No. 759,374," U.S. Patent and Trademark Office, Washington, DC, 1904.
8- M. E. Charles, G. T. Govier, G. W. Hodgson, "The horizontal pipeline flow of equal density oil‐water mixtures," the Canadian Journal of Chemical engineering, vol. 39, no. 1, pp. 27-36, 1961. doi: 10.1002/cjce.5450390106
9- J. L. Lum, T. Al-Wahaibi, P. Angeli, "Upward and downward inclination oil–water flows," International journal of multiphase flow, vol. 32, no. 4, pp. 413-435, 2006. doi: 10.1016/j.ijmultiphaseflow.2006.01.001
10- L. P. M. Colombo, M. Guilizzoni, G. M. Sotgia, "Characterization of the critical transition from annular to wavy-stratified flow for oil–water mixtures in horizontal pipes," Experiments in fluids, vol. 53, no. 5, pp. 1617-1625, 2012. doi: 10.1007/s00348-012-1378-1
11- M. R. Ansari, B. Habibpour, E. Salimi, P. Adibi, "Experimental study of gas-liquid two-phase flow in the consecutive inclinations of alarge bend," Modares Mechanical Engineering, vol. 14, no. 12, pp. 52-60, 2014. (In Persian) dor: 20.1001.1.10275940.1393.14.12.17.8
12- T. Ganat, M. Hrairi, R. Gholami, T. Abouargub, E. Motaei, "Experimental investigation of oil-water two-phase flow in horizontal, inclined, and vertical large-diameter pipes: Determination of flow Patterns, holdup, and pressure drop," SPE Production & Operations, vol. 36, no. 04, pp. 946-961, 2021. doi: 10.2118/205516-PA
13- R. A. Franchi, I. M. Carraretto, G. Chiarenza, G. Sotgia, L. P. M. Colombo, "Effect of the down-slope on the structure and the pressure loss of an oil-water stream," International Journal of Multiphase Flow, vol. 165, p. 104483, 2023. doi: 10.1016/j.ijmultiphaseflow.2023.104483
14- A. Al-Sarkhi, E. Pereyra, I. Mantilla, C. Avila, "Exploring the correlation between inclination angle and flow pattern transition in oil-water flow," Chemical Engineering Research and Design, vol. 203, pp. 697-708, 2024. doi: 10.1016/j.cherd.2024.01.065
15- P. B. Dehkordi, L. P. M. Colombo, M. Guilizzoni, G. Sotgia, "CFD simulation with experimental validation of oil-water core-annular flows through Venturi and Nozzle flow meters," Journal of Petroleum science and Engineering, vol. 149, pp. 540-552, 2017. doi: 10.1016/j.petrol.2016.10.058
16- F. Jiang, K. Wang, M. Skote, T. N. Wong, F. Duan, "Simulation of non-Newtonian oil-water core annular flow through return bends," Heat and Mass Transfer, vol. 54, pp. 37-48, 2018. doi: 10.1007/s00231-017-2093-5
17- J. Wu, W. Jiang, Y. Liu, Y. He, J. Chen, L. Qiao, T. Wang, "Study on hydrodynamic characteristics of oil-water annular flow in 90 elbow," Chemical Engineering Research and Design, vol. 153, pp. 443-451, 2020. doi: 10.1016/j.cherd.2019.11.013
18- N. Ayuba, F. R. Machado, C. A. da Rosa, T. J. Lopes, A. da Silva, "3D interface analysis of velocity, volume ratio, and Reynolds number effects on core annular flow (CAF)," Experimental and Computational Multiphase Flow, vol. 4, pp. 133-141, 2022. doi: 10.1007/s42757-020-0076-3
19- M. Momin, F. Rahmani, E. Makki, M. Sharma, J. Giri, T. Sathish, "The impact of 180° return bend inclination on pressure drop characteristics and phase distribution during oil-water flow," Heliyon, vol. 10, no. 2, e24251, 2024. doi: 10.1016/j.heliyon.2024.e24251
20- Z. Alizadeh Kaklar, M. Ansari, "Numerical simulation of two-phase flow within an effervescent atomizer using volume of fluid model," Modares Mechanical Engineering, vol. 17, no. 7, pp. 59-67, 2017. (in Persian) dor: 20.1001.1.10275940.1396.17.7.44.6
21- C. W. Hirt, B. D. Nichols, "Volume of fluid (VOF) method for the dynamics of free boundaries," Journal of computational physics, vol. 39, no. 1, pp. 201-225, 1981. doi: 10.1016/0021-9991(81)90145-5
22- J. U. Brackbill, D. B. Kothe, C. Zemach, "A continuum method for modeling surface tension," Journal of computational physics, vol. 100, no. 2, pp.335-354, 1992. doi: 10.1016/0021-9991(92)90240-Y
Modares Mechanical Engineering
Volume 25, Issue 10
October 2025
Pages 613-623