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Cutting Bubbles Using Direct Numerical Simulation

Cutting Bubbles Using Direct Numerical Simulation

Authors: 
Baltussen, M. W. - Presenter, Eindhoven, University of Technology
Kuipers, J. A. M. - Presenter, Eindhoven University of Technology
Deen, N. - Presenter, Eindhoven University of Technology


font-family:"Times New Roman","serif"'>Due to an increase in the oil price, Fischer-Tropsch
synthesis, methanol synthesis and other gas-to-liquid processes become
increasingly attractive. These gas-liquid-solid processes are mostly performed
in bubble slurry columns [Wang et al., 2007, Yang et al., 2007]. However,
the efficiency of these columns is restricted due to limited heat removal rates
or limited interfacial mass-transfer rates. To improve the efficiency of these
reactors, a new reactor concept is developed: a micro-structured bubble column
[Jain et al. 2013, Segers et al., 2013].

In a
micro-structured bubble column, a static wire mesh is introduced. This wire
mesh can be used as a catalyst carrier, eliminating a filtration unit to remove
the catalyst particles from the product stream. Furthermore, the wire mesh also
ensures cutting of the bubbles. This will reduce the bubble size and enable a
higher surface per volume ratio [Jain et al. 2013, Segers et al.,
2013].

To determine the
efficiency gain due to the introduction of the wire mesh, a multi-scale
modelling approach is used. In this approach there are three types of models.
The largest scale models, the Euler-Euler and the Euler-Lagrangian models, need
closures to accurately model the interactions between the bubbles, the liquid
and the mesh. These interactions can be determined using the smallest scale
model: the Direct Numerical Simulations (DNS). While these DNS models are able
to simulate these interactions without any a priori assumptions, they are only
capable of simulating a small part of the micro-structured bubble column
[Segers et al., 2013, Roghair et al., 2011].

In this work, a
DNS model was developed to study the effect of a wire mesh in a
micro-structured bubble column. The DNS model is a combination of the Volume Of
Fluid (VOF) model of Baltussen et al. (2014) and the second order
implicit Immersed Boundary (IB) method of Deen et al. (2012). The
advantage of the use of the VOF model is the relatively easy treatment of 
break-up of bubbles and the inherent mass conservation. The used IB method
enables an implicit fluid-solid coupling,

Using this
VOF-IB method, the effect of the simplest wire mesh, a single wire, on a single
bubble is determined. Several simulations have been performed to study the
effect of the alignment of the bubble with the wire and the relative size of
the bubble upon break-up. An example of such a simulation is shown in figure 1.

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Figure
1. The simulation of the break-up of a single bubble by a wire using the VOF-IB
method.

 

 

References

color:black'>Baltussen, M.W.,  J.A.M. Kuipers,  N.G. Deen, Chem. Eng.
Sci., 109,  65-74
(2014)

Deen N.G., S.
Kriebitzsch, M.A. van der Hoef, J.A.M. Kuipers,  Chem. Eng. Sci., 81,
329-344 (2012).

Jain,
D., Y.M. Lau, J.A.M. Kuipers, N.G. Deen, Chem. Eng. Sci., 100, 496-505
(2013).

color:black'>Roghair, I., Y.M. Lau, N.G. Deen, H.M. Slagter, M.W. Baltussen, M.
van Sint Annaland, J.A.M. Kuipers, Chem. Eng. Sci. 66, 3204-3211 (2011).

Segers,
Q.I.E., J.A.M. Kuipers, N.G Deen, Chem. Eng. Sci., 100, 33-38 (2013).

color:black'>Wang, T., J. Wang, and Y. Jin, Ind. Eng. Chem. Res. 47,
5824-5847 (2007).

color:black'>Yang, G.Q., B. Du and L.S. Fan, Chem. Eng. Sci. 62, 2-27
(2007).

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