Recirculation Zones and Its Implications in a Taylor Bubble Flow in a Square Mini/Microchannel at Low Capillary Number

A 3D numerical study is carried out for the formation of (i) isolated Taylor bubble and (ii) a train of Taylor bubbles, in a square channel of side 1.0 mm for the range of a capillary number 0.005 < Ca < 0.007. The fluid channel is carved in the rectangular solid substrate of dimensions 3 mm × 2 mm × 30 mm achieves a conjugate heat transfer condition. Constant heat flux is applied at the bottom wall of the substrate of area 3 × 30 mm2, while all the other surfaces were insulated. In the fluid channel, the bubble flows through the inlet section, the heating zone and the end section. We observed the recirculation zones all around the bubble body, the one at the back of the bubble is found to be strongest, which results in the maximum heat flux in the nearby region. Taylor bubble flow enhanced the heat transfer multifold times compared to the single-phase flow. To study the axial wall conduction in conjugate heating conditions, we carried out the simulations for the range of substrate wall to fluid thermal conductivity ratio 10 < ksf < 646 and the ratio of substrate thickness to channel depth 1 < δsf < 5.