Numerical Simulation of Interfacial Closures for 3D Bubble Column Flows Numerical investigation of flow hydrodynamics in a square cross-sectioned bub- ble column was conducted in a transient Euler-Euler environment by applying the simulation tool Ansys CFX 14.0. The influence of the drag coefficient (C D ) was investigated and the results were also compared with drag force models. Further- more, three different lift force models and a defined lift coefficient were studied. All results were compared with the available experimental data. All simulations were carried out for a single-hole sparger with given aspect ratio (H/D) and super- ficial gas velocity. Keywords: Bubble column, Computational fluid dynamics, Flow hydrodynamics, Interfacial closures, Numerical simulation Received: March 18, 2014; revised: November 08, 2014; accepted: February 16, 2015 DOI: 10.1002/ceat.201400182 1 Introduction Bubble columns are gas-liquid multiphase contactors where the gas that represents the dispersed phase, is sparged in the form of bubbles from the bottom of the column into the liquid which is the continuous phase. These reactors are intensively used in biochemical, chemical, metallurgical, and petrochemi- cal industries for oxidation, fermentation, coal liquefaction, and hydrogenation [7–9]. With significant increase in the com- putational power in recent years, more focus has been concen- trated on developing and improving computational fluid dynamics (CFD) tools for modeling of bubble column flows. Euler-Euler (E-E) [10–14] and Euler-Lagrange (E-L) [15–20] methods are the two most frequently used approaches to simu- late bubble columns. The E-L method provides direct physical interpretation of bubble-liquid interaction, but its application is restricted to smaller columns, since for larger systems more equations need to be solved. The E-E method gives ensemble averaged dynamics of gas phase similar to liquid phase in order to attain a set of Euler equations. Compared to the E-L approach, the lower computational cost and application to a wide range of void fractions are key advantages of the E-E approach. It is well known that a key challenge in bubbly flow simula- tions is to capture the physics involved. The interface forces, e.g., drag and lift forces, in bubble columns can be influenced by bubble-liquid interactions. Therefore, it is noteworthy to model interphase forces properly in order to capture the phys- ics accurately. Precise prediction of interface forces is still an exigent task in CFD of bubble columns, although ample litera- ture is available on this issue [3, 21–23]. Even though, numer- ous effects, such as lift force, virtual mass force, turbulent dis- persion force, and wall lubrication force, could be contributing factors in the interfacial momentum transport. Deen et al. [24] and Masood and Delgado [25] found that mainly drag and lift forces are prevailing. There are various empirical models sug- gested for the calculation of drag force in the literature, e.g., in [1, 2, 17, 18, 26, 27]. Also, several studies employed the afore- mentioned models [28–30] and the drag coefficient C D [31, 32] in their investigations. But to the best of our knowledge, no work reported on the study of the impact of C D in 3D square bubble column simulations. Therefore, the effect of C D on bubble col- umn flow simulations has been included in the current study. Mudde and Simonin [33] observed that the lift force is im- portant for the prediction of the wandering phenomena, which is a characteristic of bubble plume. There are plenty of models suggested for the calculation of lift force in the literature, e.g., in [3–6, 34–37]. Some previous studies, e.g., [19, 29, 38] in- cluded the lift force model like the model of Tomiyama [3] while others used lift coefficients [13, 24, 28, 30, 39] in the numerical investigations of bubbly flows. But as per our knowl- edge, no work comprised the lift force models of Saffman [4, 5] and Legendre and Magnaudet [6] in the numerical investiga- tions of 3D bubble column flows. This work studies the impact of lift force models in 3D square bubble column flows. The influence of the drag force coefficient was investigated and results were also compared with the drag force models of Ishii and Zuber [1] and Grace et al. [2]. Moreover, the lift force models of Tomiyama [3], Saffman [4, 5], Legendre and Mag- naudet [6] and lift coefficient with C L = 0.5 were analyzed. All results were compared with the experimental data of Deen [40]. The CFD investigations have been performed for square bubble columns in 3D transient E-E framework for a single- hole sparger with an aspect ratio (H/D) of 3 and superficial gas velocity of 0.0049 m s –1 . Chem. Eng. Technol. 2015, 38, No. 5, 777–786 ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Rao M. A. Masood Vojislav Jovicic Antonio Delgado FAU Erlangen, Institute of Fluid Mechanics, Erlangen, Germany. – Correspondence: Rao M. A. Masood (atif.rao.masood@fau.de), Insti- tute of Fluid Mechanics, FAU Erlangen, Cauerstraße 4, 91058 Erlangen, Germany. Research Article 777