The characterization of the extensional rheology of polymeric solutions is important in several applications and industrial processes. Filament stretching and capillary breakup rheometers have been developed to characterize the extensional properties of polymeric solutions, mostly for high-viscosity fluids. However, for low concentration polymer solutions, the measurements are difficult using available devices, in terms of the minimum viscosity and relaxation times that can be measured accurately. In addition, when the slow retraction method is used, solvent evaporation can affect the measurements for volatile solvents. In this work, a new setup was tested for filament breakup experiments using the slow retraction method, high-speed imaging techniques, and an immiscible oil bath to reduce solvent evaporation and facilitate particle tracking in the thinning filament. Extensional relaxation times above around 100 μs were measured with the device for dilute and semi-dilute polymer solutions. Particle tracking velocimetry was also used to measure the velocity in the filament and the corresponding elongation rate, and to compare with the values obtained from the measured exponential decay of the filament diameter.

A slug flow simulator was developed considering: (i) an overtaking mechanism based on air-water co-current continuous experimental data [1]; (ii) expansion of the gas phase and its consequences in bubble length and velocity and (iii) several types of slug length and gas flow rate distributions, at column inlet. The simulator allows the monitoring of various flow characteristics, namely (i) the evolution of the distributions of several variables along the column; (ii) the definition of column zones, with different coalescence and (iii) the evaluation of the flow stability height (flow developing length), for certain flow conditions.The simulator was used to study the influence of the inlet slug length distribution over the stabilized slug flow pattern. Four similar simulations were prepared with inlet slug lengths normally distributed around averages of 0.075, 0.1, 0.15 and 0.2 m, and equal initial number of bubbles, inlet gas flow rate, and liquid flow rate. The output results showed to be independent of the inlet distributions, indicating that the bubble overtaking mechanism has dominant influence over the overall slug flow pattern development.

The lid-driven cavity flow is a well-known benchmark problem for the validation of new numerical methods and techniques. In experimental and numerical studies with viscoelastic fluids in such lid-driven flows, purely-elastic instabilities have been shown to appear even at very low Reynolds numbers. A finite-volume viscoelastic code, using the log-conformation formulation, is used in this work to probe the effect of viscoelasticity on the appearance of such instabilities in two-dimensional lid-driven cavities for a wide range of aspect ratios (0.125 ≤ Λ=height/length ≤ 4.0), at different Deborah numbers under creeping-flow conditions and to understand the effects of regularization of the lid velocity. The effect of the viscoelasticity on the steady-state results and on the critical conditions for the onset of the elastic instabilities are described and compared to experimental results.

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