The interaction between two spheres falling in a viscoelastic fluid

Abstract

The time evolution of the distance between two identical spheres falling in a viscoelastic fluid has been analyzed exper- imentally. The working fluid was a dilute solution of polyacry- lamide in an aqueous solution of glycerin. Several concentra- tions of polyacrylamide and glycerin have been used in order to analyze fluids with different viscoelastic properties. Two experi- mental configuration allow analyzing the effect of the boundary conditions. A CCD camera was used to record the movement of the spheres allowing the computation of evolution of the space separation between them. It has been found that beyond cer- tain critical initial elapsed time (tdc) the distance between the spheres grows in time, while the distance decrease for elapsed times smaller than the tdc. Reduction of the shear-thinning ef- fect tends to eliminate the repulsion interaction.