Gas-assisted non-Newtonian fluid displacement in circular tubes and noncircular channels

The motion of long bubbles into Newtonian and non-Newtonian fluids confined in horizontal circular tubes, rectangular channels, and square cross-secti onal channels has been studied both theoretically and experimentally. Of pa rticular interest is the determination of residual liquid film thickness on the walls. Isothermal experiments have been conducted to measure the displ acement of the gas-liquid interface as a function of the applied pressure d ifferential. The velocity of the interface and residual liquid film thickne ss have been determined for both Newtonian and non-Newtonian (shear thinnin g and viscoelastic) fluids. These experimental results are in good agreemen t with similar experimental studies conducted by other investigators. The e xperimental results indicate that the liquid film thickness of constant vis cosity viscoelastic fluids (Boger fluids) deposited on the tube wall is thi cker than that of comparable Newtonian fluids. A simple mathematical analysis was developed using a power-law model. The m athematical model successfully captures the gas-liquid dynamics for Newtoni an and non-Newtonian fluid displacement in a tube and rectangular channel. The prediction of the liquid fraction deposited on the walls is in qualitat ive agreement with the experimental observations of previous investigators (Chem. Eng. Sci. 24 (1969) 471; A.I.Ch.E. 16 (1970) 925; Chem. Eng. Sci. 30 (1975) 379). The model gives similar results to a numerical solution (Polm . Eng. Sci. 35 (1995) 877) in which a constitutive equation containing a yi eld stress is used to model the non-Newtonian behavior. The model is used t o determine the location and velocity of the advancing bubble front for the case of a power-law fluid. The results indicate that the gas-liquid interf ace advances more rapidly with decreasing values of the power-law index abo ve a certain value of dimensionless time (t/t(b) approximate to 0.75). (C) 2001 Elsevier Science Ltd. All rights reserved.