The dynamics and dissolution of gas bubbles in a viscoelastic fluid

This paper reports an experimental study of the motion of dissolving and non-dissolving gas bubbles in a quiescent viscoelastic fluid. The objective of the investigation was to determine the influence of the abrupt transition in bubble velocity, which had been observed at a critical radius of approx. on the rate of mass transfer. Thus, a range of bubble sizes from an equivalent (spherical) radius of 0.2–0.4 cm was employed using CO₂ gas, and five different fluids, including one Newtonion glycerine/water solution and four viscoelastic solutions of Separan AP30 in water (0.1, 0.5, 1% by weight) and in a water/glycerine mixture.The experimental data on bubble velocity shows that the discontinuous increase with bubble volume observed previously for air bubbles in viscoelastic fluids, does not occur for dissolving CO₂ bubbles—presumably due to the continuous decrease in bubble volume. Instead, a very steep but definitely continuous transition is found. Mass transfer rates are found to be significantly enhanced by viscoelasticity, and comparison with available theoretical results shows that the increase is greater than expected for purely viscous, power-law fluids. We conclude that a fully viscoelastic constitutive model would be necessary for a successful analysis of the dissolution of a gas bubble which is translating through a (high molecular weight) polymer solution.