Abstract
The penetration of a long gas bubble through a viscoelastic fluid in a tube was studied. Experiments were carried out for two Newtonian and five polymeric solutions to investigate the relation between the coating film thickness and rheological properties of the test fluids. The polymeric solutions are viscoelastic fluids having shear-thinning viscosity. A bubble of air was injected into a tube filled with a test fluid to form hydrodynamic coating on a tube wall. The film thickness was evaluated by hydrodynamic fractional coverage m. The fractional coverage was characterized using the capillary number Ca and the Weissenberg number Wi. For viscoelastic fluids, Ca and Wi were evaluated considering the shear-thinning viscosity. Two kinds of representative shear rate were used for the evaluation of Ca and Wi. The dependence of m on Ca in viscoelastic fluids was different from that of the Newtonian case. The film was thinner than that of the Newtonian case at the same Ca when Wi was small, i.e. the viscous property was dominant. The shear-thinning viscosity had a role to make the film thin. On the other hand, the film tended to be thicker than the corresponding Newtonian results at large Wi because of normal stress effect.
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