Volume of Fluid Modeling of CO2-Water Slug Flow in Circular T-junction Microchannel Reactor

Carbon dioxide (CO₂) plays a central role in various chemical and environmental processes, and process intensification is often needed to improve efficiency. Microchannel reactors are well-suited for such applications because they provide enhanced mass transfer, particularly when slug flow is formed due to their high interfacial area. Computational Fluid Dynamics (CFD) is widely used to investigate slug flow formation and gas-liquid interface dynamics. However, despite extensive studies, few verified and validated models are available for accurately predicting slug flow, especially in horizontal circular T-junction microchannels. This study aims to develop, verify, and validate a reliable computational fluid dynamics model to simulate slug flow formation using the volume of fluid (VOF) method. The use of CO₂-water system provides realistic hydrodynamic behavior relevant for studying CO₂ hydrodynamics inside microchannel reactors. Mesh sensitivity analysis was conducted using seven meshes to ensure mesh independence and computational efficiency. Mesh sizes beyond 370,000 elements showed only minor improvements in prediction accuracy. The model was then validated against experimental data by comparing the bubble length under multiple flowrate conditions, revealing strong agreement with deviations of 3.04%–6.90%. The experimental data showed high reproducibility with an average coefficient of variation of 2.4%, further confirming the model’s reliability. This validated model can serve as a foundation for future CO₂ studies on hydrodynamic optimization, such as the generation of flow pattern maps in microchannel reactors.

CO2 utilization; Computational fluid dynamics; Microchannel reactor; Slug flow

Akkarawatkhoosith, N., Nopcharoenkul, W., Kaewchada, A., & Jaree, A. (2020). Mass transfer correlation and optimization of carbon dioxide capture in a microchannel contactor: A case of CO2-rich gas. Energies, 13, 5465. https://doi.org/10.3390/en13205465

Bargal, M. H. S., Ben-Mansour, R., Al-Sarkhi, A., & Alhems, L. M. (2025). CFD modeling of two-phase flow (oil/air) with and without rotary mixer inside a vertical pipe for upstream of multiphase pump. Arabian Journal for Science and Engineering, 50, 9611–9630. https://doi.org/10.1007/s13369-024-09789-7

Celik, I., Ghia, U., Roache, P. J., Freitas, C., Coleman, H., & Raad, P. (2008). Procedure for estimation and reporting of uncertainty due to discretization in CFD applications. Journal of Fluids Engineering, 130, 078001. https://doi.org/10.1115/1.2960953

Chen, Y., Zhu, C., Fu, T., & Ma, Y. (2021). Mass transfer enhancement of CO2 absorption into [Bmim][BF4] aqueous solution in microchannels by heart-shaped grooves. Chemical Engineering and Processing: Process Intensification, 167, 108536. https://doi.org/10.1016/j.cep.2021.108536

Cranmer, J. A., Sharaborin, E., Khodaparast, S., Giustini, G., & Magnini, M. (2024). Non-negligible buoyancy effect on bubbles travelling in horizontal microchannels of comparable size at small Bond numbers. International Journal of Multiphase Flow, 181, 105019. https://doi.org/10.1016/j.ijmultiphaseflow.2024.105019

Cui, P., Tang, Y., Guo, A., Wang, C., Liu, M., Peng, W., & Yu, F. (2025). Enhanced CO2 adsorption properties with bimetallic ZnCe-MOF prepared using a microchannel reactor. Frontiers of Chemical Science and Engineering, 19, 14. https://doi.org/10.1007/s11705-025-2518-5

Du, W., Duan, Y., Wang, L., & Liu, D. (2023). Liquid–liquid two-phase flow and size prediction of slug droplets in microchannels. Processes, 11, 2390. https://doi.org/10.3390/pr11082390

Etminan, A., Muzychka, Y. S., & Pope, K. (2021). A review on the hydrodynamics of Taylor flow in microchannels: Experimental and computational studies. Processes, 9, 870. https://doi.org/10.3390/pr9050870

Etminan, A., Muzychka, Y. S., & Pope, K. (2022). Liquid film thickness of two-phase slug flows in capillary microchannels: A review. Canadian Journal of Chemical Engineering, 100, 325–348. https://doi.org/10.1002/cjce.24068

Gao, J., Hu, Z., Yang, Q., Liang, X., & Wu, H. (2022). Fluid flow and heat transfer in microchannel heat sinks: Modelling review and recent progress. Thermal Science and Engineering Progress, 29, 101203. https://doi.org/10.1016/j.tsep.2022.101203

Garstecki, P., Fuerstman, M. J., Stone, H. A., & Whitesides, G. M. (2006). Formation of droplets and bubbles in a microfluidic T-junction: Scaling and mechanism of break-up. Lab on a Chip, 6, 437. https://doi.org/10.1039/b510841a

Guo, F., & Chen, B. (2009). Numerical study on Taylor bubble formation in a micro-channel T-junction using VOF method. Microgravity Science and Technology, 21, 51–58. https://doi.org/10.1007/s12217-009-9146-4

Gupta, R., & Deshpande, A. (2023). CFD modeling of two-phase flow in mini and microchannels. In Handbook of multiphase flow science and technology (pp. 1279–1304). Springer. https://doi.org/10.1007/978-981-287-092-6_35

Habibi Matin, M., & Moghaddam, S. (2021). Mechanism of transition from elongated bubbles to wavy-annular regime in flow boiling through microchannels. International Journal of Heat and Mass Transfer, 176, 121464. https://doi.org/10.1016/j.ijheatmasstransfer.2021.121464

Hauner, I. M., Deblais, A., Beattie, J. K., Kellay, H., & Bonn, D. (2017). The dynamic surface tension of water. Journal of Physical Chemistry Letters, 8, 1599–1603. https://doi.org/10.1021/acs.jpclett.7b00267

Heidari, S., Esmaeilzadeh, F., Rafati, R., & Haddad, A. S. (2024). Experimental and modeling of CO2 absorption in a bubble column using a water-based nanofluid containing co-doped SiO2 nanoparticles. Modeling Earth Systems and Environment, 10, 3229–3241. https://doi.org/10.1007/s40808-023-01869-1

Janati, S., Aghel, B., & Shadloo, M. S. (2021). Effect of alkanolamine mixtures on CO2 absorption efficiency in T-shaped microchannel. Environmental Technology and Innovation, 24, 102006. https://doi.org/10.1016/j.eti.2021.102006

Jiang, M., & Zhou, B. (2020). Numerical study of flow regimes in microchannel with dynamic contact angle. International Journal of Hydrogen Energy, 45, 29782–29790. https://doi.org/10.1016/j.ijhydene.2019.09.035

Jin, Z., Liu, Z., Li, Y., Wang, F., & Wang, C. (2025). Impact of contact angle on droplet breakup dynamics in a T-junction microchannel. Chemical Papers, 79, 6315–6332. https://doi.org/10.1007/s11696-025-04193-3

Joseph, M., Mathew, G., Krishnaraj, G., Dilip, D., & Ranjith, S. (2019). Numerical simulation of liquid–gas interface formation in long superhydrophobic microchannels with transverse ribs and grooves. Experimental and Computational Multiphase Flow, 2, 162–173. https://doi.org/10.1007/s42757-019-0043-9

Kaouachi, A., Daoudi, S., & Mahi, I. E. (2024). Effect of turbulence models on multiphase flow through porous media simulation. In Proceedings of engineering studies (pp. 227–237). https://doi.org/10.1007/978-3-031-62715-6_13

Khan, W., Chandra, A. K., Kishor, K., Sachan, S., & Alam, M. S. (2018). Slug formation mechanism for air–water system in T-junction microchannel: A numerical investigation. Chemical Papers, 72, 2921–2932. https://doi.org/10.1007/s11696-018-0522-7

Khatoon, B., Hasan, S. U., & Alam, M. S. (2023). CO2 capturing in cross T-junction microchannel using numerical and experimental approach. Chemical Papers, 77, 6319–6340. https://doi.org/10.1007/s11696-023-02941-x

Kim, S. H., Hong, M. S., & Braatz, R. D. (2024). Investigation of particle flow effects in slug flow crystallization using multiscale computational fluid dynamics simulation. Chemical Engineering Science, 297, 120238. https://doi.org/10.1016/j.ces.2024.120238

Kumar, S., Kumar, P., & Grewal, K. S. (2025). Machine learning-driven multi-objective optimization of microchannel reactors for CO2 conversion. Advanced Sustainable Systems, 9. https://doi.org/10.1002/adsu.202500064

Kurimoto, R., Hayashi, K., & Tomiyama, A. (2024). Pressure drop and bubble velocity in Taylor flow through square microchannel. Microfluidics and Nanofluidics, 28, 58. https://doi.org/10.1007/s10404-024-02750-y

Li, D., Xing, J., Zhang, Z., & Wang, H. (2025). Numerical investigation on dynamic behavior of bubbles under forced flow in a microchannel. RSC Advances, 15, 23414–23426. https://doi.org/10.1039/D5RA02116B

Li, Q., Qiao, J., Wang, G., & Chen, S. (2025). Taylor flow characteristics and mass transfer in curved T-microchannels. Physics of Fluids, 37. https://doi.org/10.1063/5.0252466

Li, W. L., Liang, H. W., Wang, J. H., Shao, L., Chu, G. W., & Xiang, Y. (2022). CFD modeling of CO2 chemical absorption in a microporous tube-in-tube microchannel reactor. Fuel, 327, 125064. https://doi.org/10.1016/j.fuel.2022.125064

Li, W. L., Wang, J. H., Lu, Y. C., Shao, L., Chu, G. W., & Xiang, Y. (2020). CFD analysis of CO2 absorption in a microporous tube-in-tube microchannel reactor with novel gas-liquid mass transfer model. International Journal of Heat and Mass Transfer, 150, 119389. https://doi.org/10.1016/j.ijheatmasstransfer.2020.119389

Ling, B., Bao, J., Oostrom, M., Battiato, I., & Tartakovsky, A. M. (2017). Modeling variability in pore-scale multiphase flow experiments. Advances in Water Resources, 105, 29–38. https://doi.org/10.1016/j.advwatres.2017.04.005

Liu, L., Jiang, S., Zhu, C., Ma, Y., & Fu, T. (2022). Distribution of liquid–liquid two-phase flow in branching T-junction microchannels. Chemical Engineering Journal, 431, 133939. https://doi.org/10.1016/j.cej.2021.133939

Makarem, M. A., Farsi, M., & Rahimpour, M. R. (2021). CFD simulation of CO2 removal from hydrogen-rich stream in a microchannel. International Journal of Hydrogen Energy, 46, 19749–19757. https://doi.org/10.1016/j.ijhydene.2020.07.221

Makarem, M. A., Kiani, M. R., Farsi, M., & Rahimpour, M. R. (2021). CFD simulation of CO2 capture in a microchannel using aqueous MEA and [Bmim]BF4 with TiO2 nanoparticles. International Journal of Thermophysics, 42, 1–16. https://doi.org/10.1007/s10765-021-02812-1

Miranda, E. P., Sempertegui-Tapia, D. F., & Chávez, C. A. (2025). Turbulence model performance for predicting fluid flow and heat transfer in micro-scale channels. Numerical Heat Transfer Part A, 86, 4353–4373. https://doi.org/10.1080/10407782.2024.2318001

Mohsin, M., Masood, H. M., Ali, N., Shahzad, K., & Hassan, M. (2025). Hydrodynamic and thermal analysis of water slugs in super-hydrophobic T-junction microchannel. Journal of the Pakistan Institute of Chemical Engineers, 52. https://doi.org/10.54693/piche.05227

Momen, A. M., Sherif, S. A., & Lear, W. E. (2024). Modeling of two-phase gas-liquid slug flows in microchannels. Computational Thermal Sciences, 16, 113–128. https://doi.org/10.1615/ComputThermalScien.2024049784

Moscato, S., Cutuli, E., Camarda, M., & Bucolo, M. (2025). Experimental and numerical study of slug-flow velocity inside microchannels through in situ optical monitoring. Micromachines, 16. https://doi.org/10.3390/mi16050586

Muljani, S., Setyawan, H., & Nugraha, R. E. (2023). Bubble formation in absorber column for CO2 absorption and precipitated silica production. RSC Advances, 13, 33471–33483. https://doi.org/10.1039/D3RA05860C

Mustafa, A., Lougou, B. G., Shuai, Y., Wang, Z., & Tan, H. (2020). Recent developments in CO2 utilization for solar fuels and chemicals: A review. Journal of Energy Chemistry, 49, 96–123. https://doi.org/10.1016/j.jechem.2020.01.023

Nickel, N., Fitschen, J., Haase, I., Kuschel, M., Schulz, T. W., Wucherpfennig, T., & Schlüter, M. (2024). Novel sparging strategies to enhance dissolved carbon dioxide stripping in industrial stirred tank reactors. Frontiers in Chemical Engineering, 6. https://doi.org/10.3389/fceng.2024.1470991

Nie, X., Zhu, C., Fu, T., & Ma, Y. (2022). Mass transfer intensification in gas–liquid flow within microchannels with triangular obstacles. Chinese Journal of Chemical Engineering, 51, 100–108. https://doi.org/10.1016/j.cjche.2021.09.016

Qian, D., & Lawal, A. (2006). Numerical study on gas and liquid slugs for Taylor flow in T-junction microchannel. Chemical Engineering Science, 61, 7609–7625. https://doi.org/10.1016/j.ces.2006.08.073

Rae, V. R. S., Laziz, A. M., & Shaari, K. Z. K. (2022). Hydrodynamic study of internal circulation inside microreactor for transesterification process. IOP Conference Series: Earth and Environmental Science, 963, 012018. https://doi.org/10.1088/1755-1315/963/1/012018

Ramadan, Z., & Park, C. W. (2021). Numerical investigation of gas–liquid slug formation in T-junction microchannel using OpenFOAM. Chemical Papers, 75, 4381–4390. https://doi.org/10.1007/s11696-021-01530-0

Roache, P. J. (1994). Perspective: A method for uniform reporting of grid refinement studies. Journal of Fluids Engineering, 116, 405–413. https://doi.org/10.1115/1.2910291

Sadrehaghighi, I. (2021). Mesh sensitivity and mesh independence study. https://doi.org/10.13140/RG.2.2.34847.51365

Santos, R. M., & Kawaji, M. (2012). Developments on wetting effects in microfluidic slug flow. Chemical Engineering Communications, 199, 1626–1641. https://doi.org/10.1080/00986445.2012.660712

Sattari-Najafabadi, M., Nasr Esfahany, M., Wu, Z., & Sundén, B. (2018). Mass transfer between phases in microchannels: A review. Chemical Engineering and Processing, 127, 213–237. https://doi.org/10.1016/j.cep.2018.03.012

Sharaborin, E. L., Rogozin, O. A., & Kasimov, A. R. (2021). Computational study of the dynamics of Taylor bubbles. Fluids, 6, 389. https://doi.org/10.3390/fluids6110389

Sobieszuk, P., Cyga?ski, P., & Pohorecki, R. (2010). Bubble lengths in gas–liquid Taylor flow in microchannels. Chemical Engineering Research and Design, 88, 263–269. https://doi.org/10.1016/j.cherd.2009.07.007

Syrakos, A., Oxtoby, O., de Villiers, E., Varchanis, S., Dimakopoulos, Y., & Tsamopoulos, J. (2023). A unification of least-squares and Green–Gauss gradients under a common projection-based gradient reconstruction framework. Mathematics and Computers in Simulation, 205, 108–141. https://doi.org/10.1016/j.matcom.2022.09.008

van Steijn, V., Kreutzer, M. T., & Kleijn, C. R. (2007). ?-piv study of the formation of segmented flow in microfluidic t-junctions. Chemical Engineering Science, 62, 7505–7514. https://doi.org/10.1016/j.ces.2007.08.068

Wang, L. L. (2023). Study on the effect of gas–liquid two-phase physical features on slug flow in microchannels. Frontiers in Physics, 11. https://doi.org/10.3389/fphy.2023.1125220

Wang, N., Li, M., Ma, R., & Zhang, L. (2019). Accuracy analysis of gradient reconstruction on isotropic unstructured meshes and its effects on inviscid flow simulation. Advances in Aerodynamics, 1. https://doi.org/10.1186/s42774-019-0020-9

Xu, W., Qi, Z., Wang, L., Yang, X., Gao, Q., Huang, L., & Tao, W. (2022). Study of two-phase flow distribution in microchannel heat exchanger header: A numerical simulation. SSRN Electronic Journal. https://doi.org/10.2139/ssrn.4054227

Yan, Q., Li, D., Wang, K., & Zheng, G. (2024). Hydrodynamic evolution mechanism and drift flow patterns of pipeline gas–liquid flow. Processes, 12, 695. https://doi.org/10.3390/pr12040695

Yang, G., & Zhang, H.-C. (2024). Investigation of bubble formation dynamics of gas–non-Newtonian liquid two-phase flow in a flow-focusing generator. Microfluidics and Nanofluidics, 28, 63. https://doi.org/10.1007/s10404-024-02757-5

Yin, Y., Chen, W., Wu, C., Zhang, X., Fu,T., Zhu, C., & Ma, Y. (2022). Bubble dynamics and mass transfer enhancement in split-and-recombine (SAR) microreactor with rapid chemical reaction. Separation and Purification Technology, 287, 120573. https://doi.org/10.1016/j.seppur.2022.120573

Zhou, Y. L., & Chang, H. (2019). Numerical simulation of hydrodynamic and heat transfer characteristics of slug flow in serpentine microchannel with various curvature ratio. Heat and Mass Transfer, 55, 3343–3358. https://doi.org/10.1007/s00231-019-02664-4

Zhu, L., Wang, T., Guo, Q., & Yuan, X. (2023). NN-augmented k–? shear stress transport turbulence model for high-speed flows with shock-wave/boundary layer interaction. Engineering Applications of Computational Fluid Mechanics, 17. https://doi.org/10.1080/19942060.2024.2374316

Zhu, L., & Zheng, L. (2025). Droplet breakup through triangular obstacle in T-junction microchannel. Physics of Fluids, 37. https://doi.org/10.1063/5.0260801