Flow of bubbles and foams in narrow microfluidic geometries

Solarski, Michal Marek (2020). Flow of bubbles and foams in narrow microfluidic geometries. University of Birmingham. Ph.D.

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Abstract

The movement of gas-liquid foams through narrow channels of various complex geometries is commercially challenging and technically important. This thesis investigates the dynamics of bubbles and foams in microfluidic channels with constrictions, expansions and obstacles.

The flow of single bubbles in a sudden contraction, followed by a sudden expansion was studied. Effect of the capillary number was investigated, showing that bubbles deformation increased with it. Larger bubbles were also investigated in different constrictions with the emphasis on the snap-off break-up. Effect of thin liquid films is shown experimentally to be the main contribution. Furthermore, inertial effects are found to be influential during the final neck collapse.

Foams in microfluidic channels with constrictions were investigated with regards to topological changes, including bubble re-arrangements and various break-ups caused by higher shear stresses. Effects of the geometry, including, constriction width and length, are highlighted. The neck collapse also gives different scalings for various break-ups, suggesting different dynamics and forces driving the break-ups. Furthermore, foams in suddenly and gradually expanding channels were analysed with regards to velocity, elasticity and plasticity.

Foams flowing in channels with spherical obstacles were studied. Dynamics of different foam regimes are presented as they flow around centrally located obstacle. The bamboo foam was found to generate two bubbles via lamella division mechanism. The sizes of the daughter bubbles are correlated with the capillary number, liquid fraction and initial bubble size. Additionally, shifting the location induced only size dependence. A more complicated structure consisting of four obstacles was studied experimentally and analysed with regards to the new number of bubbles generated. All the data is shown to collapse on a single line and to be in agreement with the numerical results.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):