AN EXPERIMENTAL-STUDY OF THE EFFECT OF SURFACTANTS ON THE FREE RISE VELOCITY OF GAS-BUBBLES

This study deals with the effect of impurities on the free rise veloci ty of gas bubbles in three Newtonian and eight non-Newtonian polymeric liquids. Experimentally, the rise velocities of air bubbles in liquid s which contain concentrations of a surfactant (sodium dodecyl sulphat e) ranging from 0-500 ppm were measured. It is shown that the surfacta nt lowers the surface tension of the system and has an effect on the v elocity of the bubbles, whose volume ranges from 1-1000 mu l. The expe rimental data were used to verify a recent theoretical approximation o f the force on a bubble moving in a contaminated fluid described by th e three-parameter Carreau model. An hypothesis is proposed to explain the experimental observation of a jump discontinuity in the log-log pl ot of bubble velocity versus bubble volume in the case of viscoelastic fluids. An equation for calculating for critical radius at which disc ontinuity occurs is given and is found to be in agreement with experim ental data.