Canadian Journal of Chemical Engineering, Vol.80, No.5, 974-978, 2002
Wall effects for the free rise of solid spheres in moderately viscous liquids
For the first time ever, the influence of wall effects on the free rise of a buoyant solid sphere in a square column in a non-Newtonian (pseudoplastic) fluid was determined. It was found that in most cases, as the column width decreased, the terminal rise velocity of the sphere would decrease as well. It was also discovered that wall effects could change the rising sphere trajectory. Spheres that displayed a spiraling trajectory in larger columns would display a more linear trajectory in smaller columns. Occasionally, due to this change in tracjectory, the solid sphere terminal velocity would increase as the column width decreased. This phenomenon (the positive wall effect) has not been reported for falling spheres in Newtonian or non-Newtonian fluids.