Contents lists available at ScienceDirect Experimental Thermal and Fluid Science journal homepage: www.elsevier.com/locate/etfs The efects of internals and low aspect ratio on the fully developed fow region and bubble properties in a pilot-plant bubble column Hayder Al-Naseri a,c , J.P. Schlegel b , Muthanna H. Al-Dahhan a,b, ⁎ a Chemical and Biochemical Engineering Department, Missouri University of Science and Technology, Rolla, MO 65409, USA b Mining and Nuclear Engineering Department, Missouri University of Science and Technology, Rolla, MO 65409, USA c Chemical Engineering Department, Tikrit University, Tikrit, Iraq ARTICLEINFO Keywords: Internals Bubble column Aspect ratio Bubble dynamic Fischer-Tropsch Multiphase fow ABSTRACT Thisworkinvestigates,forthe frsttime,theefectsofthepresenceofinternalsandlowdynamicliquidlevelson thebubbledynamicsinindustrial-sizepilotplantbubblecolumns.Experimentalworkthatconductedinabubble columnof0.6minnerdiameterand3.9mheightwithanair-watersystemwasutilizingouradvancedfour-point fberopticalprobetechniquetomeasuretheradialproflesofthebubbleproperties.Thesuperfcialgasvelocity varied from 0.2 to 0.45m/s to cover the churn turbulent fow regime. PVC pipe of 0.06m diameter used to represent the heat exchanging internals, occupying 24% of the column cross-section area, and three diferent aspectratios(H/D =3,4,and5)wereused.Dataobtainedshowthatthepresenceofinternalsslightlyincreases the overall gas holdup and signifcantly afects the radial profles and distribution of the bubble properties, particularlyinthefullydeveloped fowregion.However,thepresenceofinternalsincreasesthelocalgasholdup, the bubble pass frequency, and the interfacial bubble area, especially in the wall region, while decreases the bubble chord length and the bubble rise velocity. The variation in the aspect ratio (H/D) and the presence of internals exhibited a slight impact on the bubble dynamics in the sparger region, whereas the efect of internal on the local gas holdup was concentrated in the wall region. Meanwhile, the axial location (Z), where the fully developedfowregionoccurs,appearsahighsensitivitytowardtheinternalsexistenceandthevariationsinthe aspect ratio and the superfcial gas velocity. However, the presence of internals and the increase in aspect ratio both show that the fully developed fow region begins at lower axial locations, while an increase of the su- perfcial gas velocity delays the transition to fully developed fow to a higher axial location. 1. Introduction Bubble/slurry bubble column multiphase reactors are widely used in various felds of chemical and biochemical, petrochemical, and wastewater treatment processes [1–3]. Bubble/slurry bubble column reactors are characterized by high heat and mass transfer coefcients, excellent thermal control, few movable parts that contribute to a low cost, and high selectivity and conversion [4–8]. The disadvantages are the global liquid circulation and back mixing, which increase the pre- valence of undesirable products and difculty in the design due to the interaction among the phases [9]. Such reactors are used for processes such as Fischer-Tropsch synthesis (F-T), hydrogenation, oxidation, fer- mentation, coal liquefaction, liquid phase methanol synthesis, and many others. The bubble/slurry bubble column carries out exothermal reactions, and hence, using the heat exchanging internals is critical to maintain the reactions at desired temperature. Therefore, internals havebeenutilizedwithdiferentcoverageareaofthecross-sectionarea CSAofthebubblecolumn.Theexothermicprocessrequirestheremoval ofheatfromthereactor;thereforeheatexchangingtubes,whichoccupy about5–25%ofthecolumn’scross-sectionalareaCSAdependingonthe type of process that used [5,10–13],areanessentialpartofthereactor design. However, in this study heat exchanging internals, which covers 24%ofCSAofcolumn,hasbeenused,thesamethatusedintheFischer- Tropsch synthesis (F-T). Signifcant efort has gone into addressing the shortcomings in un- derstanding the interaction between the gas and liquid phases that complicate bubble/slurry bubble column reactors’ design. This is be- cause the bubble/slurry bubble columns are characterized with multi- scale phenomena that make the interaction among the phase complex. Therefore, multi-scale approach is needed in understanding such multi- scalephenomena,whichisthecaseforallmultiphase fows.Themixing intensity and gas-liquid interfacial area, which afect the transport https://doi.org/10.1016/j.expthermfusci.2019.02.011 Received 16 October 2018; Received in revised form 16 January 2019; Accepted 11 February 2019 ⁎ Corresponding author at: Chemical and Biochemical Engineering Department, Missouri University of Science and Technology, Rolla, MO 65409, USA. E-mail address: aldahhanm@mst.edu (M.H. Al-Dahhan). Experimental Thermal and Fluid Science 104 (2019) 284–301 Available online 12 February 2019 0894-1777/ © 2019 Published by Elsevier Inc. T