Convective flow in methanogenic granules

Gas bubbles entrapped in biocatalyst particles subjected to hydrostatic pressure oscillations, e.g. during recirculation in loop reactors, will induce intraparticle liquid flows, and thereby enhance mass transfer in excess of diffusion. This ‘breathing particle’ mechanism was already demonstrated in methanogenic granules from an IC reactor, and led to an average macroscopic activity increase of 13%. The existence of the alternating convective liquid flow responsible for this higher activity has now been established independently with pulsed field gradient NMR, as the intraparticle water mobility during pressure oscillations was found 16.5% larger. Micro-electrode measurements of the internal pH of a granule revealed the occurrence of a fast liquid flow through a channel between a central cavity and the periphery during pressure cycling, and the subsequent diffusive relaxation under atmospheric conditions.

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Acceleration of mass transfer in loop reactors

Water Science & Technology ◽

10.2166/wst.1997.0069 ◽

1997 ◽

Vol 36 (1) ◽

pp. 311-319

Author(s):

J. C. Van den Heuvel ◽

P. G. Verschuren ◽

S. P. P. Ottengraf

Keyword(s):

Mass Transfer ◽

Hydrostatic Pressure ◽

Static Pressure ◽

Pressure Oscillations ◽

Activity Increase ◽

Model Predictions ◽

Carrier Materials ◽

Flow Through ◽

Liquid Flows ◽

Enhance Mass

Gas bubbles entrapped in biocatalyst particles subjected to hydrostatic pressure oscillations, e.g. during recirculation in loop reactors, will induce intraparticle liquid flows, and thereby enhance mass transfer in excess of diffusion. This ‘breathing particle’ mechanism was demonstrated in methanogenic granules, and led to a typical activity increase of 13% compared with static pressure conditions. From these experimental results and model predictions, it is concluded that convective acceleration of mass transfer in gas-producing systems offers interesting perspectives for the optimisation of biofilm processes in loop reactors. Development of special carrier materials with a central gas-filled cavity could lead to a novel type of bioreactor in which liquid flow through the biocatalyst is decisive.

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ESTIMATION OF PRESSURE DROP FOR NON-NEWTONIAN LIQUID FLOW THROUGH BENDS USING ADAPTIVE NON-PARAMETRIC MODEL

International Journal of Fluid Mechanics Research ◽

10.1615/interjfluidmechres.2019021943 ◽

2020 ◽

Vol 47 (1) ◽

pp. 59-69

Author(s):

Suman Debnath ◽

Anirban Banik ◽

Tarun Kanti Bandyopadhyay ◽

Mrinmoy Majumder ◽

Apu Kumar Saha

Keyword(s):

Pressure Drop ◽

Liquid Flow ◽

Parametric Model ◽

Newtonian Liquid ◽

Flow Through ◽

Non Parametric

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A Study on Liquid Leak Rates in Packing Seals

Applied Sciences ◽

10.3390/app11041936 ◽

2021 ◽

Vol 11 (4) ◽

pp. 1936

Author(s):

Abdel-Hakim Bouzid

Keyword(s):

Environmental Protection ◽

Liquid Flow ◽

Environmental Protection Agency ◽

Gas Flow ◽

Outer Boundary ◽

Health And Safety ◽

Toxic Substances ◽

Packing Materials ◽

Thickness Change ◽

Flow Through

The accurate prediction of liquid leak rates in packing seals is an important step in the design of stuffing boxes, in order to comply with environmental protection laws and health and safety regulations regarding the release of toxic substances or fugitive emissions, such as those implemented by the Environmental Protection Agency (EPA) and the Technische Anleitung zur Reinhaltung der Luft (TA Luft). Most recent studies conducted on seals have concentrated on the prediction of gas flow, with little to no effort put toward predicting liquid flow. As a result, there is a need to simulate liquid flow through sealing materials in order to predict leakage into the outer boundary. Modelling of liquid flow through porous packing materials was addressed in this work. Characterization of their porous structure was determined to be a key parameter in the prediction of liquid flow through packing materials; the relationship between gland stress and leak rate was also acknowledged. The proposed methodology started by conducting experimental leak measurements with helium gas to characterize the number and size of capillaries. Liquid leak tests with water and kerosene were then conducted in order to validate the predictions. This study showed that liquid leak rates in packed stuffing boxes could be predicted with reasonable accuracy for low gland stresses. It was found that internal pressure and compression stress had an effect on leakage, as did the thickness change and the type of fluid. The measured leak rates were in the range of 0.062 to 5.7 mg/s for gases and 0.0013 and 5.5 mg/s for liquids.

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Velocity bias in intrusive gas-liquid flow measurements

Nature Communications ◽

10.1038/s41467-021-24231-4 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

B. Hohermuth ◽

M. Kramer ◽

S. Felder ◽

D. Valero

Keyword(s):

Liquid Flow ◽

Breaking Waves ◽

Correction Method ◽

Force Balance ◽

Bubble Velocity ◽

Natural Environments ◽

Flow Measurements ◽

Gas Liquid Flow ◽

Liquid Flows ◽

Velocity Bias

AbstractGas–liquid flows occur in many natural environments such as breaking waves, river rapids and human-made systems, including nuclear reactors and water treatment or conveyance infrastructure. Such two-phase flows are commonly investigated using phase-detection intrusive probes, yielding velocities that are considered to be directly representative of bubble velocities. Using different state-of-the-art instruments and analysis algorithms, we show that bubble–probe interactions lead to an underestimation of the real bubble velocity due to surface tension. To overcome this velocity bias, a correction method is formulated based on a force balance on the bubble. The proposed methodology allows to assess the bubble–probe interaction bias for various types of gas-liquid flows and to recover the undisturbed real bubble velocity. We show that the velocity bias is strong in laboratory scale investigations and therefore may affect the extrapolation of results to full scale. The correction method increases the accuracy of bubble velocity estimations, thereby enabling a deeper understanding of fundamental gas-liquid flow processes.

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