Hydrodynamic study of an internal airlift reactor for microalgae culture

Rengel, Ana; Zoughaib, Assaad; Dron, Dominique; Clodic, Denis

doi:10.1007/s00253-011-3398-9

Cited by 24 publications

(13 citation statements)

References 29 publications

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“…This velocity can be considered as the transition from regimes I to regime II as the gas holdup in the downcomer was very low (∼1 %). In previous studies, the no‐bubble phase or very low gas holdup in the downcomer were found for V g well below 0.01 m/s . Similarly, for the same experimental setup, Klein et al observed the onset of bubble dispersion in the downcomer for 0.008 < V g < 0.02 m/s.…”

Section: Resultsmentioning

confidence: 59%

“…In previous studies, the no-bubble phase or very low gas holdup in the downcomer were found for V g well below 0.01 m/s. [26,30] Similarly, for the same experimental setup, Klein et al [21] observed the onset of bubble dispersion in the downcomer for 0.008 < V g < 0.02 m/s. This means the onset of regime II can be found around this superficial gas velocity range.…”

Section: Effect Of Gas Flow Rate On Flow Regimesmentioning

confidence: 76%

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CFD analysis of flow regimes in airlift reactor using Eulerian‐Lagrangian approach

Pawar

2016

Can J Chem Eng

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The hydrodynamic aspects of the concentric tube airlift reactor have been studied using two‐phase CFD simulations with a Eulerian‐Lagrangian approach. The three‐dimensional CFD simulations are carried out with the experimental geometry of airlift reactor (H/D = 12) reported in the published literature. The standard k‐ϵ turbulence model is used with additional consideration of production and dissipation of buoyancy‐induced turbulence. Two different bubble size distributions (BSDs) and their Sauter mean diameters have been considered to represent the gas distribution at sparger in the reactor. This study shows that the BSD1 (1–5–10 mm) containing a high fraction of small bubbles (≤ 5 mm) represents the hydrodynamics of flows appropriately as compared to the BSD2 (5–10–15 mm) containing a high fraction of large bubbles (≥ 10 mm) or the single size bubble diameters (5.25 mm and 10 mm). Further, three regimes of operation such as no gas bubbles in the downcomer (regime I), stationary gas bubbles in the downcomer (regime II), and gas bubble recirculation from the downcomer section to the riser section (regime III), are verified using CFD simulations with Lagrangian particle tracking. Satisfactory agreement (within 15 % deviation) with the experimental data was observed for parameters such as the gas holdups in the riser and downcomer and the liquid circulation velocity in the flow regimes I and II for BSD1.

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Section: Resultsmentioning

confidence: 59%

Section: Effect Of Gas Flow Rate On Flow Regimesmentioning

confidence: 76%

CFD analysis of flow regimes in airlift reactor using Eulerian‐Lagrangian approach

Pawar

2016

Can J Chem Eng

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“…For example, for a bubble diameter of 50 mm, the volume gas fraction of 0.075 is extremely high compared to other experimental work in similar airlift reactors using larger bubble sizes such as results reported by Rengel et al (2012). These authors give a maximum downcomer volume fraction of around 0.045 but to achieve this they require a superficial gas velocity of 0.047 m/s which is two orders of magnitude greater than that used in this work (0.00044 m/s).…”

Section: Results and Discussion Of Simulation Studymentioning

confidence: 64%

Airlift bioreactor for biological applications with microbubble mediated transport processes

Al-Mashhadani

Wilkinson

Zimmerman

2015

Chemical Engineering Science

102

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Microbubbles increase the mixing efficiency in airlift bioreactors. Dispersal of gas phase throughout the ALR occurs with decreasing the bubble size. Phase slip velocity decreases with smaller bubble size as gas rise rate decreases. a b s t r a c tAirlift bioreactors can provide an attractive alternative to stirred tanks, particularly for bioprocesses with gaseous reactants or products. Frequently, however, they are susceptible to being limited by gas-liquid mass transfer and by poor mixing of the liquid phase, particularly when they are operating at high cell densities. In this work we use CFD modelling to show that microbubbles generated by fluidic oscillation can provide an effective, low energy means of achieving high interfacial area for mass transfer and improved liquid circulation for mixing.The results show that when the diameter of the microbubbles exceeded 200 mm, the "downcomer" region, which is equivalent to about 60% of overall volume of the reactor, is free from gas bubbles. The results also demonstrate that the use of microbubbles not only increases surface area to volume ratio, but also increases mixing efficiency through increasing the liquid velocity circulation around the draft tube. In addition, the depth of downward penetration of the microbubbles into the downcomer increases with decreasing bubbles size due to a greater downward drag force compared to the buoyancy force. The simulated results indicate that the volume of dead zone increases as the height of diffuser location is increased. We therefore hypothesise that poor gas bubble distribution due to the improper location of the diffuser may have a markedly deleterious effect on the performance of the bioreactor used in this work.

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“…Our work uses a size‐adjustable riser and streamlined trumpet‐shaped hood in contrast to the three size‐fixed funnel internals . This streamlined hood changes the flow direction of the gas–fluid mixture gently before it enters the top half of the reactor, which causes most of the gas–liquid mixture to be circulated in the bottom half of the reactor . Meanwhile, the arch‐shaped holes in the bottom side of riser also create favourable hydraulic conditions for complete circulation of the gas–fluid mixture.…”

Section: Resultsmentioning

confidence: 99%

Oxygen mass transfer characteristics in an internal‐loop airlift reactor with preset trumpet‐shaped riser

Huang

et al. 2014

Asia-Pacific J Chem Eng

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A size-adjustable trumpet-shaped riser was installed into a conventional airlift reactor to form a modified internal-loop airlift reactor (ILAR). The volumetric oxygen mass transfer coefficient (k L a) and gas holdup of the ILAR were heavily influenced by the height ratio of riser to static fluid level above the spargers (h/H), the cross-sectional area ratio of riser to downcomer (A r /A d ) and the superficial gas velocity in the riser (U g ) when deoxidized distilled water was used as the oxygen absorbent. An oxygen transfer rate of (2.17 ± 0.11) × 10 À5 kg m À3 s À1 , k L a of (27.88 ± 1.12) × 10 À3 s À1 and gas holdup of 0.031 were obtained with the ILAR of A r /A d = 1.09 and h/H = 0.73 at U g = 18 mm s À1 . As the well-constructed preset trumpet-shaped riser provided ideal conditions for complete circulation and blending of the fluid, enhanced oxygen transfer efficiency was achieved. The gas holdup and k L a were increased by 16.2% and 10.2% at 19°C, as compared with those of the conventional airlift reactor without this preset riser. The fluid rising velocity in the riser (V R ) and falling velocity in the downcomer (V D ) may be expressed by power-law functions of U g and A r /A d , respectively. These metrics indicate that the ILAR has better performance, as compared with a conventional airlift reaction, for oxygen transfer and microorganism culture for chemical engineering, biological fermentation and environmental protection.

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Hydrodynamic study of an internal airlift reactor for microalgae culture

Cited by 24 publications

References 29 publications

CFD analysis of flow regimes in airlift reactor using Eulerian‐Lagrangian approach

CFD analysis of flow regimes in airlift reactor using Eulerian‐Lagrangian approach

Airlift bioreactor for biological applications with microbubble mediated transport processes

Oxygen mass transfer characteristics in an internal‐loop airlift reactor with preset trumpet‐shaped riser

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