Abstract
Bubble columns are widely used in the chemical industry because
of their simple design and high efficiency. The scale-up of these
kinds of columns is challenging and time-consuming. Since high
throughput is targeted, they are operated in the heterogeneous bub-
bling regime where the flow is complex and turbulent. Large-scale
bubble columns can in principle be simulated using continuum
models (TFM/MFM) with closures from more detailed models
such as Front Tracking (FT) or Volume of Fluid (VOF). Multi-fluid
models are capable of predicting the flow field, but to accurately
describe mass transfer rates, an accurate interfacial area of the
bubbles is required as well as mass transfer coefficients for dense
bubble swarms. This requires the MFM to be coupled with models
that can predict bubble size distributions. The Discrete Bubble
Model (DBM) can be scaled up but the bubble-bubble interactions
make it computationally very intensive.
Stochastic Direct Simulation Monte Carlo (DSMC) methods treat
the bubbles in a discrete manner while more efficiently handling
the collisions compared to the DBM. The DSMC model has earlier
been used for very small particles in the size range of Angstroms
to microns where the particles are purely inertial at high Stokes
numbers. In the work of Pawar et al. (2014) this was used for
micrometer sized particles/droplets where this method proved to be
60 to 70 times faster than more classical methods like the Discrete
Particle Model (DPM).
In this work the DSMC method has been extended to finite sized
bubbles/particles in the order of millimeters. A 4-way cou-
pling (liquid-bubble-bubble) is achieved using the volume-averaged
Navier Stokes equations. The model is verified first for mono-
disperse impinging particle streams without gas. Then the model
is verified with the DBM of a 3D periodic bubble driven system.
The collision frequencies are all within 10 percent accuracy and the
speed up achieved per DEM time step is nearly 10 times compared
to the DBM, which facilitates simulation of large systems.
of their simple design and high efficiency. The scale-up of these
kinds of columns is challenging and time-consuming. Since high
throughput is targeted, they are operated in the heterogeneous bub-
bling regime where the flow is complex and turbulent. Large-scale
bubble columns can in principle be simulated using continuum
models (TFM/MFM) with closures from more detailed models
such as Front Tracking (FT) or Volume of Fluid (VOF). Multi-fluid
models are capable of predicting the flow field, but to accurately
describe mass transfer rates, an accurate interfacial area of the
bubbles is required as well as mass transfer coefficients for dense
bubble swarms. This requires the MFM to be coupled with models
that can predict bubble size distributions. The Discrete Bubble
Model (DBM) can be scaled up but the bubble-bubble interactions
make it computationally very intensive.
Stochastic Direct Simulation Monte Carlo (DSMC) methods treat
the bubbles in a discrete manner while more efficiently handling
the collisions compared to the DBM. The DSMC model has earlier
been used for very small particles in the size range of Angstroms
to microns where the particles are purely inertial at high Stokes
numbers. In the work of Pawar et al. (2014) this was used for
micrometer sized particles/droplets where this method proved to be
60 to 70 times faster than more classical methods like the Discrete
Particle Model (DPM).
In this work the DSMC method has been extended to finite sized
bubbles/particles in the order of millimeters. A 4-way cou-
pling (liquid-bubble-bubble) is achieved using the volume-averaged
Navier Stokes equations. The model is verified first for mono-
disperse impinging particle streams without gas. Then the model
is verified with the DBM of a 3D periodic bubble driven system.
The collision frequencies are all within 10 percent accuracy and the
speed up achieved per DEM time step is nearly 10 times compared
to the DBM, which facilitates simulation of large systems.
| Original language | English |
|---|---|
| Title of host publication | Progress in Applied CFD – CFD2017 |
| Subtitle of host publication | Proceedings of the 12th International Conference on Computational Fluid Dynamics in the Oil & Gas, Metallurgical and Process Industries, 30 May -1 June 2017, Trondheim, Norway |
| Place of Publication | Blindern |
| Publisher | SINTEF Academic Press |
| ISBN (Electronic) | 978-82-536-1544-8 |
| Publication status | Published - 2017 |