Bubble growth in a viscous liquid in a simple shear flow

The nucleation and growth of a bubble in a Newtonian liquid in simple shear and creeping flow were studied experimentally in a Couette apparatus operating under vacuum. A low molecular weight polyisobutylene was chosen as a typical high-viscosity Newtonian liquid. The volatile solvent in our experiments was simulated by air, and the formed or growing bubbles were photographed under shear. The experimental foaming results indicate that vacuum (at a level of supersaturation conditions) is not sufficient to boil a viscous solution, even in the presence of bubbles (nucleation sites), as shear also has to be applied. Furthermore, there is probably a critical shear rate (or stress) at which boiling appears. Bubble growth experimental results indicate that the growth rate of a slender bubble increases as the shear rate increases and as the pressure decreases. The experimental results agree well with theoretical models developed by Lee and Biesenberger (for bubble nucleation) and by the authors (for bubble growth).