The drag coefficient prediction of a rising bubble through a non-Newtonian fluid

The drag coefficient is one of the important parameters in studying the characteristics of bubble motion. In the present research, the drag coefficient of single bubble rising in non-Newtonian fluid has been investigated. Polyacrylamide solutions were selected with different concentrations as a Non-Newtonian fluid. As known, these solutions have viscoelastic properties which strongly influence the drag coefficient. This experiment has been done with different nozzle diameters, for three type of gas (Air, and ) at different injection flow rates. Hence, the results are more comprehensive than previous studies. A comparison between the obtained results and the equations in other studies showed that none of these relationships can predict the drag coefficient of a bubble rising in a non-Newtonian fluid with a viscoelastic properties. Therefore, two new correlations have been presented to predict the Drag coefficient based on Reynolds, Archimedes and Eötvös dimensionless number by dimensional analysis. The predicted drag coefficient by the equations is in very good agreement with experimental data. The first equation which obtained directly from the dimensional analysis was simpler than the second equation. The average error of first equation was 3.26%, while, the average prediction error of the second equation was about 1.7%, which is more complex in terms of formulation. In addition, new equations for predicting terminal velocities and the behavior of bubble rising in a non-Newtonian viscoelastic fluid are presented.