Bioprocess and Biosystems Engineering

, Volume 41, Issue 1, pp 31–45 | Cite as

Computational fluid dynamics (CFD) analysis of airlift bioreactor: effect of draft tube configurations on hydrodynamics, cell suspension, and shear rate

  • Sanjay B. PawarEmail author
Research Paper


The biomass productivity of microalgae cells mainly depends on the hydrodynamics of airlift bioreactor (ABR). Thus, the hydrodynamics of concentric tube ABR was initially studied using two-phase three-dimensional CFD simulations with the Eulerian–Lagrangian approach. The performance of ABR (17 L) was examined for different configurations of the draft tube using various drag models such as Grace, Ishii–Zuber, and Schiller–Naumann. The gas holdups in the riser and the downcomer were well predicted using E–L approach. This work was further extended to study the dispersion of microalgae cells in the ABR using three-phase CFD simulations. In this model (combined E–E and E–L), the solid phase (microalgae cells) was dispersed into the continuous liquid phase (water), while the gas phase (air bubbles) was modeled as a particle transport fluid. The effect of non-drag forces such as virtual mass and lift forces was also considered. Flow regimes were explained on the basis of the relative gas holdup distribution in the riser and the downcomer. The microalgae cells were found in suspension for the superficial gas velocities of 0.02–0.04 m s−1 experiencing an average shear of 23.52–44.56 s−1 which is far below the critical limit of cell damage.


Microalgae cultivation CFD modeling Three-phase flow Airlift photobioreactor Discrete phase model 

List of symbols


Cross-sectional area of downcomer (m2)


Cross-sectional area of the riser (m2)


Interphase momentum transfer coefficient for the interphase drag force


Drag coefficient


Lift coefficient


Wall lubrication coefficient


Diameter of the reactor (m)


Bubble diameter (m)


Eotvos number


Buoyancy force acting on the particle (N)


Drag force acting on particle (N)


Pressure gradient force (N)


Virtual (or added) mass force (N)


Gravity vector (m s−2)


Turbulent energy (m2 s−2)


Interfacial momentum transfer term between gas–liquid phases


Morton number


Mass of single bubble (kg)


Pressure (Pa)


Turbulence production due to viscous forces (kg m−1s−3)


Turbulence production due to buoyancy effect (kg m−1s−3)


Turbulence dissipation due to buoyancy effect (kg m−1s−3)


Reynold’s Number


Vorticity Reynolds’s Number


Time (s)


Averaged liquid-phase velocity (m s−1)


Bubble velocity (m s−1)


Continuous phase velocity (m s−1)


Particle velocity (m s−1)


Bubble terminal velocity (m s−1)


Velocity (m s−1)


Superficial gas velocity (m s−1)


Liquid circulation velocity (m s−1)



Bubble phase


Continuous phase


Particle (solid) phase




Gas phase


Liquid phase







r, R


d, D


Greek letters


Viscosity of liquid phase (kg m−1s−1)


Density of phase (kg m−3)


Turbulent energy dissipation (m2 s−3)


Surface tension (N m−1)


Turbulent Schmidt number


Gas holdup


Rotation vector



The author is very grateful to the Department of Science and Technology, New Delhi for their financial support for this research work under the scheme of DST Inspire Faculty Award (IFA13-ENG63). The author is also very thankful to the Director, CSIR–NEERI Nagpur for providing enough infrastructure facilities to carry out this research.

Compliance with ethical standards

Conflict of interest

The author declares that there is no conflict of interest.

Supplementary material

449_2017_1841_MOESM1_ESM.tif (1.3 mb)
Fig. 1 s. Meshing of the geometry (for example: ALC3 and ALC5). (TIFF 1335 kb)
449_2017_1841_MOESM2_ESM.tif (587 kb)
Fig. 2 s. Mesh independency results for ALC3 geometry, A) V g = 0.01 m s−1, B) V g = 0.03 m s−1. (TIFF 587 kb)
449_2017_1841_MOESM3_ESM.tif (356 kb)
Fig. 3 s. Effect of different virtual mass force coefficients on overall gas holdup, riser gas holdup, and liquid velocity in ALC2 geometry at V g = 0.02 and 0.04 m s−1. (TIFF 356 kb)
449_2017_1841_MOESM4_ESM.tif (276 kb)
Fig. 4 s. Effect of consideration of lift force (LF) and wall lubrication (WL) force on overall gas holdup, riser gas holdup and liquid velocity in ALC2 and ALC3 geometries at V g = 0.02 and 0.04 m s−1, respectively. (TIFF 275 kb)
449_2017_1841_MOESM5_ESM.tif (4.7 mb)
Fig. 5 s. Prediction of hydrodynamics parameters under three-phase simulations of ABR (ALC3 geometry) for superficial gas velocity of 0.04 m s−1 a) microalgae velocity profile; b) volumetric distribution of microalgae cells; c) path followed by algae cells shown by streamlines; d) microalgae shear rate profile; and e) air bubble velocity profile and distribution of air bubbles. (TIFF 4860 kb)


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Copyright information

© Springer-Verlag GmbH Germany 2017

Authors and Affiliations

  1. 1.Environmental Biotechnology and Genomics Division, DST Inspire FacultyCSIR-National Environmental Engineering Research Institute (NEERI)NagpurIndia

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