Mixing Of Newtonian Fluids Research Articles

Reduced IMRs in a mixing tank via agitation improvement

Mixing of Newtonian fluids in a stirred tank at low Reynolds numbers was investigated experimentally by means of a visual decolourization technique and shaft power measurements. The research was focused on the Isolated Mixing Regions (IMRs), which are “doughnut-shaped” structures in a stirred tank exhibiting little mixing with bulk of the fluids. The effect of Reynolds number on the IMRs was determined. The critical Reynolds numbers beyond which IMRs are destroyed were presented. The study was focused on agitation design which consumes less power input to destroy the IMRs. A pitch-bladed impeller with an alternating pitch was found more energy efficient than other test impellers in eliminating IMRs in both baffled and unbaffled configurations. It was also found that dramatic reduction in the power consumption could be achieved with installation of baffles to eliminate IMRs at typically low Reynolds numbers. The improved energy efficiency was thought related to generation of more chaotic mixing from the disturbance generated by the baffles, or impeller blade asymmetry such as alternating pitch. An energy parameter was introduced to account for the mixing time scale and the power required in regimes above the critical Reynolds number, in order to evaluate the energy efficiency when IMRs are non-existent.

Three-Dimensional Chaotic Mixing of Fluids in a Cylindrical Cavity

Three-dimensional chaotic mixing of Newtonian fluids in a previously uninvestigated cylindrical cavity was studied both experimentally and numerically for creeping flow conditions. Such mixing processes have practical application to the blending of viscous fluids, biological suspensions, or can be used as test beds to study waterborne pollutant formation. A mixing chamber was fabricated which consisted of a cylindrical glass cavity with independently rotating upper and lower circular disks. Fluid motion was revealed by digitizing successive video images of a small neutrally buoyant sphere placed into the mixing cavity and also by photographing dyed blobs. Experimental particle tracking studies were supplemented by numerical simulations. Phase-space trajectories, return maps, and Lyapunov exponents were used to characterize the mixing process and to confirm chaotic behavior.